5. Case Study Analyses of Three Cutoff Cyclone Events
5.1 The 2–3 February 2009 Cutoff Cyclone Event
5.1.1 Event Overview
The 2–3 February 2009 cutoff cyclone event was associated with difficult-toforecast precipitation and was considered a precipitation forecast bust for the Northeast
US, since heavy precipitation greater than 25 mm was forecast to occur but most
locations in the region received less than 5 mm. Forecast errors were mainly due to large
disagreement between NWP models in the speed, track, and intensity of the surface
cyclone (e.g., Grumm et al. 2009; Stuart 2009). As an example, the Global Ensemble
Forecast System (GEFS) MSLP forecast valid 1200 UTC 3 February 2009 showed large
spread among ensemble members 108 h prior to the validation time, with the largest
variability (8–16 hPa) evident throughout eastern New York and western New England
(Fig. 5.1a). Uncertainty in the location of the surface cyclone decreased as 1200 UTC 3
February 2009 approached; however, considerable variability among ensemble members
was still apparent (Figs. 5.1c,e). In addition, the average of all ensemble members
indicates that the forecast surface cyclone was initially located along the East Coast (Fig.
5.1b), but as the forecast projection decreased the location of the surface cyclone was
forecasted farther east, over the Atlantic Ocean (Figs. 5.1d,f).
On 2 February 2009, a large-scale trough at 500 hPa moved eastward across the
northern US and stalled over the Great Lakes (not shown). Figure 5.2 shows the mean
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500-hPa geopotential height field for the 24-h period (0000 UTC 3 February–0000 UTC
4 February 2009) during which the cutoff cyclone was within the Northeast cutoff
cyclone domain. The track of the 500-hPa cutoff cyclone indicates that the cyclone
developed and became cut off upstream of the large-scale trough at 0000 UTC 3 February
2009 (Fig. 5.2). The cutoff cyclone slowly moved southeastward around the base of the
large-scale trough and then moved northeastward, remaining over the Great Lakes for the
duration of its lifetime in the Northeast cutoff cyclone domain. At 0600 UTC 4 February
2009, the cyclone became reabsorbed into the large-scale flow and no longer met the
criteria to be considered a cutoff cyclone.
The two-day NPVU QPE for 2–3 February 2009 indicates that the precipitation
associated with this cutoff cyclone event was confined to coastal regions (Fig. 5.3). Most
regions received 2–10 mm, while Cape Cod and Maine received 10–15 mm of
precipitation. Most of the precipitation associated with this cutoff cyclone event fell in
the 6-h periods following 1800 UTC 3 February 2009 and 0000 UTC 4 February 2009;
therefore, in the following section the focus will be on examining the upper-level,
midlevel, and low-level tropospheric conditions at these times to determine the synopticscale and mesoscale features that contributed to the observed precipitation.
5.1.2 Meteorological Conditions
During the 2–3 February 2009 cutoff cyclone event, a dual jet streak was evident
at upper levels, with wind speeds greater than 75 m s−1, or 146 kt (Figs. 5.4a,b). The
position of the dual jet streak at 1800 UTC 3 February 2009 was consistent with
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divergence over eastern Maine, in association with the poleward exit region of the
southern jet streak and the equatorward entrance region of the northern jet streak (Fig.
5.4a), which provided conditions favorable for ascent over the region of heavy
precipitation. The dual jet streak weakened and was located farther east by 0000 UTC 4
February 2009 and the associated region of divergence was no longer located over the
Northeast US at this time (Fig. 5.4b).
At midlevels, there was cyclonic absolute vorticity advection over Pennsylvania
and New Jersey at 1800 UTC 3 February 2009, downstream of a lobe of moderate
cyclonic absolute vorticity, on the order of 16–20
10−5 s−1 (Fig. 5.5a). At 0000 UTC 4
February 2009, the lobe of cyclonic absolute vorticity moved northeastward around the
cyclone center and there was cyclonic absolute vorticity advection over southern New
York and Connecticut (Fig. 5.5b). By application of the traditional form of the QG
omega equation (Eq. 4.1), differential cyclonic vorticity advection, inferred from the
cyclonic vorticity advection at 500 hPa, contributed to favorable QG forcing for ascent
throughout Pennsylvania, New Jersey, New York, and southern New England, and likely
acted to support precipitation in those regions. Further examination of Fig. 5.3 reveals
that the regions of 500-hPa cyclonic absolute vorticity advection were in fact collocated
with the band of light precipitation (2–10 mm) extending from eastern Pennsylvania and
New Jersey northeastward into western Massachusetts. However, there was little, if any,
contribution to QG forcing for ascent by the Laplacian of temperature advection, as
inferred from the 850-hPa temperature and wind fields at 1800 UTC 3 February 2010
(Fig. 5.6). For example, across Pennsylvania, New Jersey, New York, and southern New
England, the northeasterly flow at 850 hPa was weak (<20 kt or 10 m s−1), resulting in
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little or no temperature advection in those regions. The 700-hPa Q-vector analyses at
1800 UTC 3 February 2009 and 0000 UTC 4 February 2009 confirm there was QG
forcing for ascent, indicated by Q-vector convergence, across regions of Pennsylvania,
New Jersey, and New York (Figs. 5.7a,b).
In addition, there was also Q-vector
convergence over Cape Cod and Maine at 1800 UTC 3 February 2009 (Fig. 5.7a), where
the heaviest precipitation was observed with this event.
During the 2–3 February 2009 cutoff cyclone event, there was very little support
for precipitation at low levels. The observed surface cyclone was located over the
western North Atlantic Ocean, southeast of Cape Cod (Fig. 5.8), suggesting that surface
fronts did not play a role in enhancing precipitation across the Northeast US during this
event. PW values throughout the entire Northeast US were less than 12 mm, except in
Cape Cod where PW values were 12–16 mm (Fig. 5.8), which corresponded to +0.5 to
+1.0σ (not shown). In addition, the northeasterly flow across the Northeast US resulted
in little PW transport into the region. The lack of low-level forcing for ascent and low
PW values likely contributed to the low precipitation amounts that were observed with
this cutoff cyclone event.
5.1.3 Conceptual Summary
A schematic diagram of the key synoptic-scale features that contributed to the
precipitation associated with the 2–3 February 2009 cutoff cyclone event is presented in
Fig. 5.9. The precipitation observed in eastern Maine was supported by ascent associated
with a dual jet streak at 250 hPa.
Light precipitation extending from eastern
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Pennsylvania and New Jersey northeastward into western Massachusetts was located in a
region of inferred differential cyclonic vorticity advection ahead of a lobe of cyclonic
absolute vorticity southeast of the 500-hPa cutoff cyclone center, which likely
contributed to QG forcing for ascent. There was little or no low-level support for
precipitation, with little or no temperature advection at 850 hPa and low PW values
observed throughout the Northeast US.
The cutoff cyclone would have been placed into the “LP positive trough”
composite category throughout the duration of its lifetime in the Northeast cutoff cyclone
domain, since it involved a cutoff cyclone embedded within a large-scale trough and less
than 25 mm of precipitation was observed in the Northeast precipitation domain.
Comparing the event schematic diagram (Fig. 5.9) to the schematic for the “LP positive
trough” category (Fig. 4.5f), it is evident that there was a difference in the location of the
500-hPa cutoff cyclone. At 1800 UTC 3 February 2009, the cutoff cyclone was located
farther south and west than the composite cutoff cyclone. In addition, the surface cyclone
at 1800 UTC 3 February 2009 was located a greater distance to the east of the midlevel
cyclone than the “LP positive trough” composite surface cyclone.
5.2. The 1–4 January 2010 Cutoff Cyclone Event
5.2.1 Event Overview
The 1–4 January 2010 cutoff cyclone event was a long duration event with
varying daily precipitation distributions throughout its lifetime. This cutoff cyclone event
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was also associated with record-breaking snowfall observed in Burlington, VT, with total
of 37.6 in. (95.5 cm) observed for 1–3 January 2010 (e.g., Sisson 2010). Numerical
models showed considerable variability in forecasting the precipitation distribution
leading up to the event (e.g., Stuart 2010a).
The NAM apparently forecast the
precipitation best, capturing the terrain enhancement just prior to the event, but QPF
amounts were higher than observed precipitation amounts.
The 1–4 January 2010 cutoff cyclone originated from a preexisting trough over
central Canada and entered the Northeast cutoff cyclone domain at 0000 UTC 2 January
2010 (Fig. 5.10).
Throughout the cutoff cyclone event, a highly amplified ridge
associated with a large-scale blocking pattern and the negative phase of the North
Atlantic Oscillation (NAO) was in place over Greenland (e.g., Sisson 2010). Studies
have found that the negative phase of the NAO is typically associated with a meridional
flow regime across the Northeast US, associated with blocking over the North Atlantic
Ocean, which results in troughing and colder than normal temperatures along the East
Coast (e.g., Bradbury et al. 2002, Stuart and Grumm 2006). During the 1–4 January 2010
cutoff cyclone event, the highly amplified ridge likely contributed to the cutoff cyclone
stalling over the western Atlantic Ocean at 0000 UTC 3 January 2010 and retrograding
into the Gulf of Maine (Fig. 5.10). At 0000 UTC 4 January 2010 the cutoff cyclone
began moving northeastward before finally exiting the Northeast cutoff cyclone domain
at 1800 UTC on the same day.
The four-day NPVU QPE for 1–4 January 2010 indicates that heavy precipitation
(>25 mm) occurred throughout most of Maine in addition to the western slopes of the
Green Mountains and the Berkshires (Fig. 5.11). Lake-effect snow off of Lakes Erie and
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Ontario and Lake Champlain contributed to the heavy precipitation observed in western
New York and the Champlain Valley, respectively. During this cutoff cyclone event, the
precipitation distributions varied considerably from one cutoff cyclone day to the next
(Figs. 5.12a–d). On 1 January 2010, light precipitation (5–10 mm) occurred throughout
New England, with 10–20 mm of precipitation observed in southern Maine (Fig. 5.12a).
The heaviest 24-h precipitation associated with this event occurred on 2 January 2010
(Fig. 5.12b). On this day, 15–30 mm of precipitation was observed throughout most of
Maine, while 10–15 mm of precipitation was observed in regions of northern New York,
Vermont, and New Hampshire. Precipitation throughout the Northeast US was once
again light on 3 January 2010, with 5–10 mm of precipitation observed across New
England, western New York, and the Champlain Valley (Fig. 5.12c). On 4 January 2010,
the persistent precipitation was nearing an end, with little or no precipitation associated
with the cutoff cyclone observed in the Northeast US (Fig. 5.12d). The focus of the
following sections will be on examining the synoptic-scale and mesoscale features that
contributed to the varying precipitation distributions on 2 and 3 January 2010, while 1
and 4 January 2010 will not be discussed.
5.2.2 Meteorological Conditions: 2 January 2010
The heaviest precipitation on 2 January 2010 occurred in the 6-h periods
following 0000 UTC and 0600 UTC 3 January 2009. Therefore, in order to identify
synoptic-scale and mesoscale features that contributed to the heavy precipitation (15–30
mm) in Maine and the moderate precipitation (10–15 mm) in northern New York,
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Vermont, and New Hampshire (Fig. 5.12b), the upper-level, midlevel, and low-level
tropospheric conditions at these times will be discussed.
At upper levels, the large-scale trough and embedded cutoff cyclone was
negatively tilted at 0000 UTC 3 January 2010 and a developing easterly jet was evident
poleward of the cutoff cyclone (Fig. 5.13a). At 0600 UTC 3 January 2010, the region of
heaviest precipitation in Maine was located in a region of divergence associated with the
equatorward exit region of the easterly jet streak (Fig. 5.13b), which likely contributed to
ascent over this region. In addition, the 250-hPa zonal wind poleward of the cutoff
cyclone exceeded −3σ at 0000 UTC 3 January 2010 (Fig. 5.14), therefore satisfying the
−2.5σ threshold determined by Stuart and Grumm (2004, 2006) to be representative of
cyclones that are purely cut off from the background westerly flow.
At midlevels, a weak lobe of cyclonic absolute vorticity (16–20
10−5 s−1)
extending along the Massachusetts coast, west of the 500-hPa cutoff cyclone center, was
evident at 0000 UTC 3 January 2010 (Fig. 5.15a). At 0600 UTC 3 January 2010, the
lobe of cyclonic absolute vorticity had strengthened considerably and had moved slightly
westward (Fig. 5.15b). The precipitation in New York, Vermont, and New Hampshire
occurred downstream of this lobe in a region of inferred differential cyclonic absolute
vorticity advection, which likely contributed to favorable QG forcing for ascent over the
region. At 0000 UTC 3 January 2010, the 850-hPa northeasterly and easterly flow
poleward of the cutoff cyclone advected warm air into regions of northern Maine,
Vermont, and New Hampshire (Fig. 5.16). It can be inferred that the Laplacian of warm
air was maximized in this region of warm air advection, which would have further
contributed to QG forcing for ascent in Vermont and New Hampshire. Q-vector analyses
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indicate that 700-hPa Q-vector convergence was maximized (2–4
10−12 Pa m−2 s−1)
over Maine and northern regions of New Hampshire and Vermont at 0000 UTC and 0600
UTC 3 January 2010, respectively (Figs. 5.17a,b), further confirming that precipitation in
these regions was supported by QG forcing for ascent.
At 0000 UTC 3 January 2010, a region of 925-hPa frontogenesis along a warm
front was evident in eastern Maine (Fig. 5.18a). At 0600 UTC 3 January 2010, the region
of frontogenesis had strengthened and moved southwestward across Maine (Fig. 5.18b).
A cross section at 0600 UTC 3 January 2010 shows two regions of frontogenesis located
between 500 and 600 hPa and near the surface (Fig. 5.18c), suggesting that there was
forcing for ascent associated with frontogenesis at both midlevels and low levels, which
likely enhanced the precipitation over Maine. Also at low levels, anomalous PW (+1 to
+2σ) was advected into northern Maine from the east by the low-level northeasterly flow
poleward of the cutoff cyclone (Fig. 5.19). The advection of anomalous PW from the
east likely further contributed to the larger precipitation amounts observed Maine, as
compared to other regions of the Northeast US.
Finally, enhanced precipitation (10–15 mm) was also observed along the Green
Mountains and the Berkshires on 2 January 2010 (Fig. 5.12b). Surface observations at
1000 UTC 3 January 2010 show west–northwesterly surface winds throughout the
Hudson and Champlain Valleys (Fig. 5.20). The direction of the low-level flow resulted
in upslope flow and enhanced precipitation along the western slopes of the Green
Mountains and the Berkshires, as indicated by a local maximum in base reflectivity
values (15–30 dBZ) in Fig. 5.20.
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5.2.3 Meteorological Conditions: 3 January 2010
The heaviest precipitation on 3 January 2010 occurred in the 6-h periods
following 1200 and 1800 UTC 3 January 2010. Therefore, the focus of this section will
be on examining the upper-level, midlevel, and low-level tropospheric conditions at these
times to identify the synoptic-scale and mesoscale features that contributed to the light
precipitation in New England, western New York, and the Champlain Valley (Fig.
5.12c).
At 1200 UTC 3 January 2010 the lobe of cyclonic absolute vorticity at 500 hPa
that contributed to precipitation in northern New England on the previous day was nearly
out of the region (Fig. 5.21a). This lobe of cyclonic absolute vorticity had weakened over
the Atlantic Ocean at 1800 UTC 3 January 2010 and a second lobe of cyclonic absolute
vorticity extending westward from the 500-hPa cutoff cyclone center was present over
Massachusetts (Fig. 5.21b). Inferred differential cyclonic absolute vorticity advection
downstream of this lobe likely supported the precipitation observed throughout New
England on 3 January 2010 by contributing to favorable QG forcing for ascent over the
region. Persistent advection of warm air into the Northeast US from the north and east at
850 hPa (Fig. 5.22), and thus an inferred maximum in the Laplacian of warm air
advection, also contributed to QG forcing for ascent. The precipitation in New England
was likely further supported by a quasi-stationary region of 925-hPa frontogenesis
associated with the southwestward moving warm front that had stalled over southern
New Hampshire (not shown).
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At the surface, PW values throughout the Northeast US at 1200 UTC 3 January
2010 were less than 12 mm (Fig. 5.23), which likely contributed to the low precipitation
observed on this day as they likely did on 1 January 2010. The 850-hPa flow across the
Northeast US was north-northwesterly and cold air (below −12°C) was in place over New
York (Fig. 5.22), both of which provided favorable conditions for the development of
lake-effect snow bands. Radar and surface observations at 1300 UTC 3 January 2010
show a prominent lake-effect precipitation band in upstate New York collocated with
low-level northwesterly flow over Lake Ontario (Fig. 5.24). Surface winds at Burlington,
VT, were north–northwesterly as compared to light westerly or southwesterly winds in
surrounding areas, suggesting that the low-level flow was being channeled through the
Champlain Valley. The north–northwesterly winds across Lake Champlain provided
favorable conditions for the ongoing support of a lake-effect snow band and contributed
to the record-breaking snowfall observed at Burlington, VT. Therefore, the lakes acted as
a moisture source, despite low PW values throughout the Northeast US, contributing to
the light precipitation observed in western New York and the Champlain Valley on 3
January 2010.
5.2.4 Conceptual Summary
Schematic diagrams of the key synoptic-scale features that contributed to the
precipitation distributions on 2 and 3 January 2010 in association with the 1–4 January
2010 cutoff cyclone event are presented in Figs. 5.25a,b.
On 2 January 2010,
precipitation across regions of northern New York, Vermont, and New Hampshire, and
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throughout Maine, was enhanced by: (1) ascent associated with divergence within the
equatorward exit region of an easterly jet streak at upper levels; (2) QG forcing for ascent
associated with inferred differential cyclonic vorticity advection west of the 500-hPa
cutoff cyclone and an inferred maximum in the Laplacian of warm air advection at 850
hPa; (3) a region of frontogenesis along a southwestward moving warm front; and (4)
advection of anomalous PW from the east poleward of the cutoff cyclone (Fig. 5.25a).
On 3 January 2010, light precipitation in New England occurred in a region of persistent
QG forcing for ascent associated with inferred differential cyclonic vorticity advection
and warm air advection, while light precipitation in western New York and the
Champlain Valley was attributed to lake-effect precipitation (Fig. 5.25b).
On 2 January 2010, the cutoff cyclone would have been placed into the “HP
neutral cutoff” composite category. Comparing the schematic diagram for 2 January
2010 (Fig. 5.25a) to the schematic diagram for the “HP neutral cutoff” category (Fig.
4.4c), the synoptic-scale features contributing to precipitation are comparable in that the
primary features include: (1) ascent favored within the exit region of an upper-level jet
streak; (2) inferred differential cyclonic absolute vorticity advection downstream of a
500-hPa absolute vorticity maxima; (3) enhancement of precipitation along a surface
warm front; and (4) advection of anomalous PW into the Northeast US by the low-level
flow poleward of the surface cyclone.
While the features remain similar, the two
schematic diagrams appear to differ by a rotation of approximately 90°. For instance,
rather than a southwesterly upper-level jet streak as depicted in the “HP neutral cutoff”
schematic, there was an easterly upper-level jet streak poleward of the cutoff cyclone on
2 January 2010. This difference is largely due to the presence of a highly amplified ridge
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associated with a large-scale blocking pattern and the negative phase of the NAO on 2
January 2010 that acted to increase the geopotential height gradient north and east of the
cutoff cyclone and contributed to the development of an easterly jet streak poleward of
the cutoff cyclone.
The cutoff cyclone on 3 January 2010 would have been placed into the “LP
neutral cutoff” composite category. The schematic diagrams for 3 January 2010 (Fig.
5.25b) and the “LP neutral cutoff” composite category (Fig. 4.5c) are similar, with
northwesterly low-level flow west of the cutoff cyclone contributing to light precipitation
observed in the southwest quadrant of the cutoff cyclone, in association with lake-effect
snow bands. The schematic diagrams differ in that there is an upper-level easterly jet and
a southwestward-moving warm front that contributed to light precipitation in New
England on 3 January 2010, whereas these features are not evident in the composite
schematic diagram.
5.3 The 12–16 March 2010 Cutoff Cyclone Event
5.3.1 Event Overview
The 12–16 March 2010 cutoff cyclone event was a long duration event, with the
cutoff cyclone remaining within the Northeast cutoff cyclone domain for approximately
84 h. The event was associated with widespread flooding throughout southern New
England and high winds across New Jersey and southern New York. For instance, at
0000 UTC 14 March 2010 a wind gust of 64 kt (33 m s−1) was recorded at Kennedy
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International Airport (Grumm 2010). Leading up to the event, NWP models did well
forecasting that precipitation would occur; however, the forecast precipitation amounts
were much lower than observed and they did not capture the terrain influences well (e.g.,
Grumm 2010; Stuart 2010b).
The 12–16 March 2010 cutoff cyclone developed from a broad trough in place
over the central US and entered the Northeast cutoff cyclone domain at 1200 UTC 13
March 2010 (Fig. 5.26). The track of the cutoff cyclone indicates that the cyclone
remained south of Pennsylvania as it traveled eastward toward the Atlantic coast. On 15
March 2010, the cutoff cyclone stalled over the Atlantic Ocean and retrograded southeast
of New Jersey becoming reabsorbed into the background westerly flow at 0000 UTC 17
March 2010.
Extremely heavy precipitation was observed with the 12–16 March 2010 cutoff
cyclone event, as indicated by the four-day NPUV QPE (Fig. 5.27). Locations in eastern
Massachusetts and coastal New Hampshire received 125–180 mm of precipitation, with a
second precipitation maximum (120–160 mm) observed in New Jersey. This cutoff
cyclone event was associated with precipitation distributions that varied considerably
from one cutoff cyclone day to the next (Figs. 5.28a–d). The heaviest precipitation
associated with this cutoff cyclone event occurred on 13 and 14 March 2010. The
precipitation distribution for 13 March 2010 indicates that over 25 mm of precipitation
was observed throughout coastal regions of the Northeast precipitation domain, while
lower precipitation amounts (5–20 mm) were observed throughout the Hudson Valley in
eastern New York (Fig. 5.28b). The heaviest precipitation on this day was observed in
southern New England and northern New Jersey, with over 100 mm of precipitation. On
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14 March, over 80 mm of precipitation was observed in northern Massachusetts and
coastal New Hampshire, while lighter precipitation (>25 mm) persisted across regions of
New Jersey (Fig. 5.28c). The focus of the following sections will be on examining 13
and 14 March 2010 to determine what features contributed to the observed precipitation
distributions on these respective days.
5.3.2 Meteorological Conditions: 13 March 2010
The heaviest precipitation on 13 March 2010 occurred in the 6-h periods
following 1800 UTC 13 March 2010 and 0000 UTC 14 March 2010. Upper-level,
midlevel, and low-level tropospheric conditions at these times will be discussed to
identify the synoptic-scale and mesoscale features that contributed to the heavy
precipitation in southern New England and northern New Jersey (Fig. 5.28b).
At upper levels, an easterly jet greater than 35 m s−1 (68 kt) was forming poleward
of the cutoff cyclone at 1800 UTC 13 March 2010 and extended farther west across
Pennsylvania by 0000 UTC 14 March 2010 (Figs. 5.29a,b). Divergence was evident
within the poleward entrance region of the easterly jet streak over Pennsylvania, New
Jersey, and southern New England, which likely contributed to ascent in these regions of
observed heavy precipitation. The 250-hPa zonal wind anomaly at 0000 UTC 14 March
2010 exceeded −3σ poleward of the cutoff cyclone (Fig. 5.30), indicating that the cyclone
was purely separated from the background westerly flow (e.g., Stuart and Grumm 2004,
2006).
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At 700 hPa, Q-vector convergence was evident east of the cutoff cyclone (Fig.
5.31), indicative of favorable QG forcing for ascent that likely contributed to the heavy
precipitation observed in New Jersey on 13 March 2010. At low levels, a strong (>60 kt)
southeasterly jet was in place across the Northeast US (Fig. 5.32), corresponding to zonal
wind between −3 and −5σ (not shown). The onshore low-level flow was favorable for
advection of moist air from the east, resulting in +1 to +3σ PW values across the
Northeast US (Fig. 5.33). The anomalous PW advection into the Northeast US likely
further contributed to the heavy precipitation observed in southern New England and
New Jersey on 13 March 2010.
Despite the widespread heavy precipitation observed on 13 March 2010, there
were also regions of suppressed precipitation associated with downslope flow.
For
example, the Hudson Valley in eastern New York received only 5–15 mm of
precipitation, while surrounding areas received greater than 25 mm (Fig. 5.28b). Surface
observations at 1800 UTC 13 March 2010 indicate that there were easterly surface winds
throughout the Northeast US (Fig. 5.34). The direction of the low-level flow resulted in
downslope flow and suppression of precipitation throughout the Hudson Valley in eastern
New York, as indicated by a local minimum in base reflectivity values.
5.3.3 Meteorological Conditions: 14 March 2010
The heaviest precipitation on 14 March 2010 occurred in the 6-h periods
following 1200 and 1800 UTC 14 March 2010. Hence, the focus of this section will be on
examining upper-level, midlevel, and low-level tropospheric conditions at these time
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periods in order to identify the synoptic-scale and mesoscale features contributing to the
heavy precipitation across northern Massachusetts, coastal New Hampshire, and New
Jersey (Fig. 5.28c).
At upper levels, the easterly jet streak poleward of the cutoff cyclone persisted
and divergence within the entrance and exit regions of this jet streak continued to provide
favorable conditions for ascent over the region of heaviest precipitation in northern
Massachusetts (not shown). At 500 hPa, a lobe of cyclonic absolute vorticity northeast of
the cutoff cyclone center was evident at 1200 UTC 14 March 2010 (Fig. 5.35a) and at
1800 UTC this lobe of cyclonic absolute vorticity had moved westward across southern
New England and over New Jersey (Fig. 5.35b). In addition, at low levels, southeasterly
flow east of the cutoff cyclone resulted in advection of warm air into New England (Fig.
5.36). By application of Eq. 4.1, favorable QG forcing for ascent, associated with
inferred differential cyclonic vorticity advection downstream the lobe of 500-hPa
cyclonic absolute vorticity and an inferred maximum in the Laplacian of warm air
advection at 850 hPa over New England, likely contributed to the precipitation observed.
The orientation of the southeasterly low-level jet continued to favor advection of
anomalous warm, moist air into the coastal regions, as indicated by the 850-hPa
equivalent potential temperature field at 1200 UTC 14 March 2010 (Fig. 5.37). At this
time, advection of warm, moist air was maximized [>20 K (3 h)−1] along coastal
Massachusetts. The strong equivalent potential temperature advection was collocated
with the region of heaviest precipitation observed across northern Massachusetts and
coastal New Hampshire on this day. In addition, a region of 925-hPa frontogenesis
developed in southern New England at 1200 UTC 14 March 2010 (Fig. 5.38), in
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association with the equivalent potential temperature advection.
This region of
frontogenesis remained quasi-stationary over the following 24 h (not shown), likely
acting to further enhance precipitation in Massachusetts and coastal New Hampshire.
5.3.4 Conceptual Summary
Schematic diagrams of the key synoptic-scale features that contributed to the
precipitation distributions on 13 and 14 March 2010 are presented in Figs. 5.39a,b. On
13 March 2010, the heavy precipitation in southern New England was supported by
favorable conditions for ascent in association with divergence within the entrance region
of an easterly jet streak at upper levels (Fig. 5.39a). Advection of anomalous warm,
moist air by a strong southeasterly low-level jet also contributed to the heavy
precipitation amounts observed on this day in both southern New England and New
Jersey. On 14 March 2010, support for precipitation in northern Massachusetts and
coastal New Hampshire was provided by persistent upper-level and low-level jet streaks
in addition to a region of frontogenesis that had developed along the coast (Fig. 5.39b).
Precipitation in New Jersey on 14 March 2010 was lighter than on 13 March 2010;
however, because of the proximity to the midlevel cutoff cyclone center, precipitation
continued due to favorable QG forcing for ascent provided by inferred differential
cyclonic absolute vorticity advection in the lower troposphere and an inferred maximum
in the Laplacian of warm air advection at 850 hPa.
Both the 13 and 14 March 2010 cutoff cyclone days would have been placed into
the “HP neutral cutoff” composite category. The 13 and 14 March 2010 schematic
86
diagrams (Figs. 5.39a,b) compare well with the “HP neutral cutoff” composite schematic
diagram (Fig. 4.4c). Several contributing features to heavy precipitation depicted in the
composite schematic diagram were confirmed by the examination of 13 and 14 March
2010: (1) the location of the cutoff cyclone was to the southeast of the Northeast
precipitation domain; (2) the heaviest precipitation occurred in the northeast quadrant of
the cyclone; (3) forcing for ascent was supported by divergence associated with an upper
level jet streak; (4) southeasterly low-level flow advected Atlantic moisture into the
region; and (5) a surface warm front acted to locally enhance precipitation.
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Fig. 5.1. NCEP Global Ensemble Forecast System valid at 1200 UTC 3 February 2009
and initialized at (a,b) 0000 UTC 30 January, (c,d) 1200 UTC 30 January, and (e,f) 1800
UTC 30 January. Left panels show 1008 and 1020 hPa MSLP isobars of each member
(hPa, colored contours), the mean of all members (hPa, black contour), and the spread
about the mean (hPa, shaded). Right panels show the average MSLP isobars of all
members (hPa, green contours) and the standardized anomalies computed from the mean
(σ, shaded). (Figure modified from Grumm et al. 2009, Fig. 13.)
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Fig. 5.2. Mean 500-hPa geopotential height (dam, black contours) for 0000 UTC 3
February–0000 UTC 4 February 2009 and the track of the 500-hPa cutoff cyclone center
every 6 h (red contours). The brown bold lines depict the Northeast cutoff cyclone
domain.
Fig. 5.3. Two-day NPVU QPE (mm, shaded) ending 1200 UTC 4 February 2009. The
black bold line depicts the Northeast precipitation domain.
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Fig. 5.4. 250-hPa geopotential height (dam, black solid contours), wind speed (m s−1,
shaded), and divergence (10−5 s−1, red dashed contours) at (a) 1800 UTC 3 February 2009
and (b) 0000 UTC 4 February 2009.
Fig. 5.5. 500-hPa geopotential height (dam, black solid contours), absolute vorticity (10−5
s−1, shaded), cyclonic absolute vorticity advection [10−5 s−1 (3 h)−1, blue dashed contours]
and wind (kt, barbs) at (a) 1800 UTC 3 February 2009 and (b) 0000 UTC 4 February
2009.
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Fig. 5.6. 850-hPa geopotential height (dam, black solid contours), temperature (°C,
shaded), and wind (>30 kt, barbs) at 1800 UTC 3 February 2009.
Fig. 5.7. 700-hPa geopotential height (dam, black solid contours), temperature (°C, green
dashed contours), Q vectors (>5 x 10−7 Pa m−1 s−1, arrows), and Q-vector convergence
(10−12 Pa m−2 s−1, shaded) at (a) 1800 UTC 3 February 2009 and (b) 0000 UTC 4
February 2009.
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Fig. 5.8. MSLP (hPa, black solid contours), 1000–500 hPa thickness (m, red dashed
contours), and PW (mm, shaded) at 1800 UTC 3 February 2009.
Fig. 5.9. Schematic depicting the 500-hPa geopotential height (dam, black contours) at
1800 UTC 3 February 2009 and key synoptic-scale features that contribute to
precipitation for the 2–3 February 2009 cutoff cyclone event. The brown bold line depicts
the Northeast precipitation domain.
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Fig. 5.10. Mean 500-hPa geopotential height (dam, black contours) for 0000 UTC 2
January–1200 UTC 4 January 2010 and the track of the 500-hPa cutoff cyclone center
every 6 h (red contours). The brown bold lines depict the Northeast cutoff cyclone
domain.
Fig. 5.11. Four-day NPVU QPE (mm, shaded) ending 1200 UTC 5 January 2010. The
black bold line depicts the Northeast precipitation domain.
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Fig. 5.12. 24-h NPVU QPE (mm, shaded) ending (a) 1200 UTC 2 January 2010, (b) 1200
UTC 3 January 2010, (c) 1200 UTC 4 January 2010, and (d) 1200 UTC 5 January 2010.
The black bold line depicts the Northeast precipitation domain.
Fig. 5.13. As in Fig. 5.4 except at (a) 0000 UTC 3 January 2010 and (b) 0600 UTC 3
January 2010.
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Fig. 5.14. 250-hPa geopotential height (dam, black contours) and standardized anomalies
of 250-hPa zonal wind (σ, shaded) at 0000 UTC 3 January 2010.
Fig. 5.15. As in Fig. 5.5 except at (a) 0000 UTC 3 January 2010 and (b) 0600 UTC 3
January 2010.
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Fig. 5.16. As in Fig. 5.6 except at 0000 UTC 3 January 2010.
Fig. 5.17. 700-hPa geopotential height (dam, black solid contours), temperature (°C,
green dashed contours), Q vectors (>5 x 10−7 Pa m−1 s−1, arrows), and Q-vector
convergence (10−12 Pa m−2 s−1, shaded) at (a) 0000 UTC 3 January 2010 and (b) 0600
UTC 3 January 2010.
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Fig. 5.18. 925-hPa frontogenesis [K (100 km)−1 (3 h)−1, shaded], potential temperature (K,
black solid contours), and wind (kt, barbs) at (a) 0000 UTC 3 January 2010 and (b) 0600
UTC 3 January 2010; (c) cross section of 925-hPa frontogenesis [K (100 km)−1 (3 h)−1,
shaded], potential temperature (K, black solid contours), and omega (μb s−1, dashed
contours; upward is indicated in red, downward is indicated in blue) at 0600 UTC 3
January 2010. The blue dashed line in (b) indicates the approximate location of the cross
section in (c).
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Fig. 5.19. 850-hPa geopotential height (dam, black solid contours), wind (kt, barbs), PW
(mm, red dashed contours), and standardized anomalies of PW (σ, shaded) at 0000 UTC
3 January 2010.
Fig. 5.20. Base reflectivity (dBZ) and surface observations at 1000 UTC 3 January 2010.
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Fig. 5.21. As in Fig. 5.5 except at (a) 1200 UTC 3 January 2010 and (b) 1800 UTC 3
January 2010.
Fig. 5.22. As in Fig. 5.6 except at 1200 UTC 3 January 2010.
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Fig. 5.23. As in Fig. 5.7 except at 1200 UTC 3 January 2010.
Fig. 5.24. As in Fig. 5.19 except at 1300 UTC 3 January 2010.
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Fig. 5.25. As in Fig. 5.8 except for (a) 2 January 2010 and (b) 3 January 2010.
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Fig. 5.26. Mean 500-hPa geopotential height (dam, black contours) for 0600 UTC 13
March–1800 UTC 16 March 2010 and the track of the 500-hPa cutoff cyclone center
every 6 h (red contours). The brown bold lines depict the Northeast cutoff cyclone
domain.
Fig. 5.27. Four-day NPVU QPE (mm, shaded) ending 1200 UTC 16 March 2010. The
black bold line depicts the Northeast precipitation domain.
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Fig. 5.28. 24-h NPVU QPE (mm, shaded) ending (a) 1200 UTC 13 March 2010, (b) 1200
UTC 14 March 2010, (c) 1200 UTC 15 March 2010, and (d) 1200 UTC 16 March 2010.
The black bold line depicts the Northeast precipitation domain.
Fig. 5.29. As in Fig. 5.4 except at (a) 1800 UTC 13 March 2010 and (b) 0000 UTC 14
March 2010.
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Fig. 5.30. At in Fig. 5.13 except at 0000 UTC 14 March 2010.
Fig. 5.31. As in Fig. 5.16 except at 0000 UTC 14 March 2010.
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Fig. 5.32. 850-hPa geopotential height (dam, black contours), wind speed (m s–1,
shaded), and wind (kt, barbs) at 0000 UTC 14 March 2010.
Fig. 5.33. As in Fig. 5.18 except at 0000 UTC 14 March 2010.
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Fig. 5.34. As in Fig. 5.19 except at 1800 UTC 13 March 2010.
Fig. 5.35. As in Fig. 5.5 except at (a) 1200 UTC 14 March 2010 and (b) 1800 UTC 14
March 2010.
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Fig. 5.36. As in Fig. 5.6 except at 1200 UTC 14 March 2010.
Fig. 5.37. 850-hPa equivalent potential temperature (K, black contours), equivalent
potential temperature advection [K (3 h)−1, shaded], and wind (m s–1, barbs) at 1200 UTC
14 March 2010.
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Fig. 5.38. As in Fig. 5.17a except at 1200 UTC 14 March 2010.
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Fig. 5.39. As in Fig. 5.8 except for (a) 13 March 2010 and (b) 14 March 2010.
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