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The persistent eastern United States cold of March 2013 -Draft
By
Richard H. Grumm
National Weather Service State College, PA
Contributions by Elyse Colbert
Abstract:
A persistent high latitude blocking high over northeastern North America and Greenland lead to
a relatively cool period of weather over much of the eastern United States in March of 2013. A
series of short-wave troughs moving beneath this block produced a trough, in the mean, over the
eastern United States and the western Atlantic Ocean. Several of these short-waves produced late
season and even an early spring snow event to the Mid-west, Mid-Atlantic region, and the
northeastern United States.
The flow pattern and resulting cool weather was in stark contrast to the relatively mild pattern of
March 2012. A strong ridge dominated the weather over eastern North America with above
normal surface and 850 hPa temperatures which lead to early tree blossoming’s. In contrast, the
trough and cold weather of March 2013 delayed tree blossoming’s and delaying the Washington,
DC Cherry Festival by nearly 2 weeks.
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1. Overview
The large scale pattern and resulting weather over North America during March of 2013 was
strikingly different from the pattern and the weather over North America during March of 2012.
March of 2012 (Grumm and Arnott 2012). March 2012 featured a strong 500 hPa ridge over the
Great Lakes with above normal 850 hPa temperatures over much of eastern North America and
western Europe (Grumm and Arnott Fig. 1). March 2013 (Fig. 1) had persistent trough over
much of southeastern North America with a high latitude blocking ridge. The 500 hPa heights
were +1 to +2s above normal over much of northeastern North America and Greenland with
below normal heights from southeastern North America across the western Atlantic. At the
surface, high pressure was present over much of northern and northeastern North America. The
strong surface anticyclone pushed cold air southward and the 850 hPa temperatures were below
normal over southeastern North America.
The resulting pattern suppressed the storm track to the south, limiting the surges of warm moist
air into the United States. This limited the severe storm activity over the United States producing
one of the quietest early tornado seasons since 19691. In addition to the reduced severe
convection, the pattern impacted the precipitation pattern across the United States (Fig. 2). Much
of the United States was relatively dry. Pacific storms impacted the West Coast from northern
California into southwestern Canada. The 250 to 300 mm of precipitation in Washington State
was the wet spot for the month of March. An active southern stream storm track produced
several storms which brought rain and snow from the central Plains to the East Coast. Areas of
100mm or more precipitation were limited to the Mid-Mississippi Valley, Ohio Valley and Gulf
States. (Fig. 2).
The relatively cold pattern over North America (Fig. 1b) and the high latitude blocking (Rex
1950a) was associated with a period of negative Arctic Oscillation (AO: Wallace and Gutzler 1981;
Hurrell 1995) and the North Atlantic Oscillation (NAO:Wallace and Gutzler 1981). Figure 3 shows the
AO values for the winter and early spring of 2013. The AO was -3.176 for the month of March 2013
compared to a value of +1.037 during March of 2012. The AO had been less than zero since October
20122. High latitude blocking (Rex 1950a,b;Glickman 2000) can impact the value of the AO and NOA.
The Rex block (Rex 1950a) is often characterized by a cut-off low beneath high latitude anticyclone. The
omega block, so named due to its similarity to the Greek letter Ω is characterized by an anticyclone
1
Based on Storm Prediction Center summary of March 2013.
CPC monthly AO data tables at
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table
2
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anchored by to cut-off cyclones on either side. Episodes of blocking can persist for periods of days to
weeks. During March 2013 the pattern persisted for nearly a month.
This paper will document the relatively cold month of March 2013 as it an excellent contrast to the warm
month of March 2012. The focus is on the pattern and general impacts of this pattern on the weather in
the eastern United States.
2.
METHOD AND DATA
The large scale pattern was reconstructed using the Climate Forecasts System (CFS) as the first
guess at the verifying pattern. The standardized anomalies were computed in Hart and Grumm
(2001). All data were displayed using GrADS (Doty and Kinter 1995). Data were viewed in 6hour increments and using compositing to produce a mean monthly pattern and mean monthly
anomalies. The daily data facilitated obtaining key features which impacted the daily weather
and the overall contribution to the larger scale pattern which dominated the monthly pattern.
The precipitation was estimated using the Stage-IV precipitation data in 6-hour increments to
produce estimates of precipitation during the 6, and 24 hour periods and were used to estimate
the precipitation pattern over the United States for the month of March 2013 (Fig. 2).
The NCDC COOP data was used to examine the number of daily records set in the United States
During March 2013. The daily records tied or broken for both highs and lows were retrieved and
plotted using eXcel.
3. Pattern overview
The Monthly pattern (Fig. 1) showed the persistent trough over the eastern United States and the
above normal 500 hPa heights associated with the strong ridge (Fig. 1a) and surface anticyclone
(Fig. 1d) over much of northern and northeastern North America. This allowed low-level cold air
to penetrate deep into southeastern North America (Fig. 1b). This period of high latitude
blocking with a strong ridge over northern North America was associated with a period of low
AO (Fig. 2). The AO data show three successive surges of the AO toward more negative values
from mid-February into late March. The third surge was marked by the lowest AO values and
coincided closely with the period of cold air (Figs 1b & Fig. 4) in the eastern United States as
well as a late season snow event on 24-25 March 2013.
An examination of the daily high (Fig. 5) and low temperature (Fig. 4) records set during March
2013 suggests that the coldest air entered the eastern United States after 20 March (Fig. 4) after a
surge of relatively warm air entered the United States 12-20 March 2013. An analysis of these
data showed most of the high temperatures during the period when high temperature records
were being set were set in the west and southwestern United States. During the period of cold
weather, most of the minimum temperature records were set in Midwest and southeastern United
States.
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The large scale pattern during the warm period (Fig. 6) showed a strong ridge over the
southwestern United States with above normal 850 hPa temperatures. This supported NCDC data
with above normal high temperatures focused in the west and southwestern United States. The
pattern during the latter half of the month (Fig. 7) showed a retrogression of the 500 hPa ridge
over northern North America with a large surface anticyclone covering most of northeastern
North America. A broad 500 hPa trough was present beneath the 500 hPa ridge with negative
height anomalies from the Plains eastward over the western Atlantic. The closed low in the mean
was the result of several cyclogenetic events along the coast that led to the persistent trough and
cut-off low over the Canadian Maritimes. The 500 hPa ridge had +2 to +3 height anomalies
with a lower latitude trough which had -1 to -2 height anomalies.
4. Daily evolution
The month began with a strong ridge along the West Coast and a deep trough over the eastern
United States (Fig. 8). A surge of high PW air with a long trajectory over the eastern Pacific
impinged upon the West Coast of Washington State and southwestern Canada. The relatively
progressive pattern produced a significant ECWS on 5-6 March 2013 which then persisted for
several days over the western Atlantic. The ECWS was present along the East Coast at 06/1200
UTC. This storm moved and the associated 500 hPa low moved beneath a strong 500 hPa ridge
in eastern Canada (Fig. 9).
Warm up and surge high PW air into MMV around 10 March ahead of a cold surge. This
produced heavy rainfall in the MMV and snow on the cold side of the developing storm system
as viewed at 11/0000 UTC (Fig 10). To the west a ridge began to develop and surge of high PW
air impinged upon Washington State for a second time. This surge of high PW air in the
northwestern United States persisted for nearly 5 days. This surge and the surge earlier in the
month contributed to the high amounts of precipitation (Fig. 2) in the Pacific northwest.
The high latitude block peaked around 20 March with surface pressures over Greenland reaching
1058 to 1064 hPa in the CFRS data. The 20/0000 UTC data shows the strong 500 hPa ridge (Fig.
11a) and the massive surface anticyclone over Greenland (Fig. 11d). In addition to the strong
anticyclone, the PW values peaked over 6s above normal along the West Coast of Greenland
(Fig. 11c).
A southern stream wave came up the East Coast 24-25 March 2013 and producing a late season
snow storm in the Mid-Atlantic region. The system at 25/0000 UTC showed two cyclones over
the eastern United States (Fig. 12d) and a deep 500 hPa trough moving beneath the high latitude
ridge (Fig. 12a). A close 500 hPa low was present over the Canadian Maritimes, associated with
a deep oceanic cyclone which had developed 21-22 March and occluded.
The cold front with the cyclone of 24-25 March (Fig. 12) pushed the coldest air mass of the
month into the Gulf States on 26 March with 850 hPa temperature anomalies on the order of -3
to -4s below normal. At 27/0000 UTC the -3 to -4s 850 hPa temperature anomalies (Fig. 13b)
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were present along the Gulf Coast. The deep cyclone and 500 hPa low associated with the late
season Mid-Atlantic snowfall were still present over the western Atlantic.
.
5. Summary
A persistent high latitude block over northeastern North America produced relatively cold
conditions over much of the eastern United States during March 2013. A series of short-waves
moved beneath this block produced several late winter snow events in the eastern United States
and one significant early spring Mid-Atlantic snow event on 25-26 March 2013. In the west,
several large ridges developed keeping most of the southwestern United States relatively warm.
Several surge of Pacific moisture moving over the ridge brought moisture and heavy
precipitation to the Pacific Northwest (Fig. 2).
These daily data show contribution and the impact of the series of transient ridges in western
North America and short-waves moving beneath the high latitude ridge which contributed
significantly the monthly pattern. The only persistent feature though most of the month was the
persistent high latitude ridge over northeastern North America. The high latitude ridge was
associated with blocking and a period of strongly negative values of the AO.
The relatively warm conditions in March 2012 lead to early tree blossoming’s from the Great
Lakes to New England. A cold snap in April 2012 impacted fruit farmers in the eastern United
States. In contrast to March 2012, March 2013 was colder and snowier in the eastern United
States. This delayed the Cherry blossom blooming peak to 7-10 April (Washington Post April
2013). The peak blooming dates span 15 March 1990 through 18 April 1958, reflecting the
impact of cold temperatures on the blooming date (DC website). The cherry blossoms peaked
during the week of 19 March 2012.
6. Acknowledgements
7. References
Doty, B.E. and J.L. Kinter III, 1995: Geophysical Data Analysis and Visualization using GrADS.
Visualization Techniques in Space and Atmospheric Sciences, eds. E.P. Szuszczewicz and
J.H. Bredekamp, NASA, Washington, D.C., 209-219.
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Kalnay, Eugenia, Stephen J. Lord, Ronald D. McPherson, 1998: Maturity of Operational
Numerical Weather Prediction: Medium Range. Bull. Amer. Meteor. Soc., 79, 2753–
2769.
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Figure 1
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Figure 2. Monthly accumulated precipitation (mm) shaded in 25mm intervals and contours showing 25mm, 50 and every mm thereafter. Return to text.
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Figure 3. CPC daily observed Arctic Oscillation Values. Return to text.
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Figure 5. Daily high temperature records set showing the total number of records set and the number of new daily records set.
Return to text.
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Figure 4. As in Figure 4 except for minimum temperatures. Return to text.
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Figure 6. As in Figure 1 except for the valid time of 0000 UTC 13-17 March 2013. Return to text.
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Figure 7. As in Figure 1 except valid for the period of 0000 UTC 21 March through 0000 UTC 29 March 2013. Return to text.
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Figure 8. As in Figure 1 except for the conditions valid at 0000 UTC 1 March 2013. Return to text.
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Figure 9. As in Figure 8 except valid at 1200 UTC 6 March 2013. Return to text.
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Figure 10. As in Figure 9 except valid at 0000 UTC 11 March 2013. Return to text.
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Figure 11. As in Figure 10 except valid 0000 UTC 20 March 2013. Return to text.
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Figure 12. As in Figure 11 except valid at 0000 UTC 25 March 2013. Return to text.
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Figure 13. As in Figure 12 except valid at 0000 UTC 27 March 2013. Return to text.
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Not used images but relevant to the 8-9 day prediction issues:
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