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Record Cold Episode of November 2014_Draft
By
Richard H. Grumm
National Weather Service State College, PA
1. Overview
A record mid-November cold episode affected much of North America during the middle of
November 2014. The cold episode was accompanied by record cold with many record low-high
temperature records set, early snows and near record lake effect snows. The event may have been
triggered by the intensification of Typhoon Nuri 1(Fig. 1) which deepened to near record levels
reaching 924 hPa in the Bering Sea. This storm, relative to previously known historic north
Pacific Storms, is listed in Table 1. The “Superstorm” as it moved into the Bering Sea (Fig. 2)
pushed extremely warm air into Alaska and produce strong downstream ridging (Fig. 3).
The 500 hPa ridge is shown (Fig. 3 & 4) from a North American perspective using standardized
anomalies (Grumm and Hart 2001). A weak ridge was present over northwestern North America
at 0000 UTC 8 November, this feature steadily intensified through the 11th (Fig. 3d) reaching +3s
above normal. As this feature developed a deep 500 hPa vortex, with below normal 500 hPa
heights developed downstream (Figs. 3b-d). The ridge continued to strengthen (Fig. 4). An
omega block developed over northwestern North America with a closed 5700 m contour forming
in the anchoring ridge with +3 to +4s 500 hPa height anomalies (Fig. 4b-d). The strong northerly
flow on the east side of the ridge allowed cold air to move equatorward across much of central
and eastern North America (Fig. 5). At the surface, a massive anticyclone (Fig. 6) pushed into
the plains with mean sea-level pressure peaking near 1050 hPa at 0000 UTC 13 November 2014
(Fig. 6b).
The overall pattern was highly amplified (Figs. 2-3) and the northerly flow on the east side of the
high latitude ridge allowed cold air form high latitudes to advect southward. This led to a period
where the Pacific-North American Index (PNA) was positive and the Arctic Oscillation (AO) as
strongly negative. These three features are all suggestive of cold conditions central and eastern
North America.
The impacts of this extreme weather event (EWE) included record low temperatures, record
early snow fall over large portions of the southern United States, and a multi-day record Lake
Effect snow (LES) event across most of the Great Lakes as the cold surges pushed eastward.
Historic November LES was observed in western New York where locations received of 5 to 6
1
There may have been development ahead of Nuri contributing to the rapid development north of the original
circulation center.
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feet of snow (AP 2014a) were reported. Then New York State Thruway (AP2014b) was closed
due to extreme snowfall2.
Forecasting and how well this potential EWE was forecast was a critical issue. It will be shown
that using the GEFS and NAEFS, this event was incredibly well predicted. Using Reanalysis
climate data (R-Climate) relative to the GEFS and NAEFS showed that this event was well
predicted by both systems. This results section of this paper will document how well this cold
typed EWE was predicted.
2. Methods
The NCEP 21-member 55km Global Ensemble Forecast System (GEFS) and the bias corrected
50 member, 55km NCEP-CMC North American Ensemble Forecast System (NAEFS)-BC; Cui
et al 2014) are used to illustrate how well these systems predicted this historic November cold
episode.
The data is presented from the traditional standardized anomaly perspective (Hart and Grumm
2001; Grumm and Hart 2001; Graham and Grumm 2008) 16km SREF were used to show the
evolution of the rainfall and precipitation. The HRRR had the added value of showing the
“evolution” of the radar and convection. The 0.5 degree CFSR was used to construct the larger
scale pattern.
The NAEFS (Alcott et. al 2013) situational awareness table and anomalies were retrieved from
the NWS Western Region site. These data put the event in context relative to the 30-year period
of record used to compute the anomalies.
3. GEFS and NEAFS standardized anomalies
The NCEP GEFS forecasts of 500 hPa heights and standardized anomalies from 6 0000 UTC
forecasts all valid at 1200 UTC 15 November (Fig.7) and 1200 UTC 18 November 2014 (Fig. 8)
show the deep trough forecast over eastern North America. These data also show the sharp ridge
over northwestern North America discussed in the overview. These data also show the deep 500
hPa trough forecast to move into eastern North America and affect much of the eastern United
States. Note that as the forecasts converged toward the deep trough in the eastern United States
on 18 November, the shorter range forecasts, as expected, had more negative height anomalies.
The NAEFS forecasts valid at 1200 UTC 18 November (Fig. 9) show the same basic pattern3.
The shorter range forecasts showed a larger region affected by -3 to 4s 500 hPa height anomalies
than longer range forecasts. As the uncertainty decreases, the anomalies attain larger magnitudes
in extreme events. Thus some uncertainty information is contained in the anomalies.
2
http://www.wcvb.com/weather/lakeeffect-snow-pummels-new-york-state-closes-thruway/29792850
3
Note image reversal new to old in NAEFS
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The GEFS 850 hPa temperatures (Fig. 10) and mean sea-level pressure anomalies (Fig. 11) show
the cold air as it moved across the eastern United States. Similar to the 500 hPa forecasts, the
more negative thermal anomalies were observed at shorter forecast lengths due to lower
uncertainty. The -3 to -4s thermal anomalies are put into context in the next section.
The surface forecasts (Fig. 11) showedlarge surface anityclone forecast to move into the southen
US and the strong gradient between the surface cyclone in Canada and the anticyclone. These
forecasts implied and spread indicated (not shown) that track and intensity of the anitcyclone was
relatively uncertain. Thus, in the mean forecast the stronger anticyclone and large anomalies, in
the +3s range and in Mexico +4s range were forecast at relatively shorter forecast lengths.
The NAEFS 850 hPa temperature forecasts (Fig. 12) are similar to the GEFS forecasts (Fig. 10).
These data show the value of the R-Climate data in gaging how extreme the event may be and to
some degree provide some measure of uncertainty.
4. NAEFS Situational Awareness
The summarized situational awareness (SA) tables, as percentiles in the climatological PDF,
from the 0000 UTC NAEFS from 11, 12 and 13 November are shown in Figure 13. Forecasts
from 11 November indicated the potential for record low heights (Z) on or about 17-18
November in the eastern United States. The height values were in the bottom 2.5 to 1 percentile
from 1800 UTC 16 November through 1200 UTC 19 November. The 11 November data also
showed temperatures anomalies in the 2.5th to 1st percentile during this time. These data also
show the successful forecast of the first cold surge of 13-15 November 2014. The second cold
surge was clearly deeper and accompanied by a deeper trough and colder air.
Forecasts from 12 November showed a similar pattern. However, these data had less uncertainty
and thus forecast several periods of the lowest percentile in the height and temperature fields.
This trend continued into 13 November showing a convergence of forecasts and more extreme
temperature and height anomalies. These data all pointed to a EWE based on temperature and
height anomalies.
Figure 14 shows the forecasts from 16 November 2014. The formats include the traditional
standardized anomalies, the percentile, and the return period in years. Note that the CFSR
climatology is 30 years. Any value of 30 years represents a forecast of an extreme event relative
to the climatology. The -4 to -4.5s temperature anomalies represented 30-year return periods and
all-time minimums verse the CFSR (Figure 14 use 1200 UTC 18 November).
To examine the thermal anomalies, the temperature anomalies in the NAEFS can be displayed in
an SA Table (Fig. 15). These data show deep cold air with -4s or lower anomalies at 850 and 700
hPa centered on 18-19 November in the eastern United States. During this period near or
minimum values were forecast in the NAEF and GEFS (not shown). The 850 hPa temperatures
and anomalies over the eastern United States are from 1200 UTC 18 November 2014 (Fig. 16).
The 850 hPa temperature anomaly was near -4.5s at this time. The color bar is essential in
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determining if an extreme is for the hour or for the entire 21-day centered day. In this case the
bright red in the return intervals (Fig. 16-left) and the light purple in the percentile data (Fig.16left) show all-time minimums for all hours of that 21-day centered day. These data show where,
relative to the CFSR PDF these NAEFS forecast were. The -4.5minimum on this day
represented a 30-year or span of the CFSR climatological event.
5. Impacts and records (under development)
Record lows set during the month of November and record low-high temperatures set. NCDC
data is not complete through the heart of the event.
Lake Effect snow tables and summaries are still being collected and update. At this point the
largest known snowfall near Buffalo, NY is 65 inches with a second maximum of 63 inches.
6. Summary
An historic cold episode affected much of eastern North America from 11 through 20 November
2014. This EWE set many low temperature and low-high temperature records, produce early and
new record earliest first snow dates; and produced incredible LES across the Great Lakes to
include the historic western New York snow event of 18-19 November 2014.
Forecasts from the NCEP GEFS and NCEP-CMC NAEFS showed remarkable skill predicting
this extreme cold outbreak. The SA Table summarizing height and temperature anomaly forecast
provided at least 11 days of lead-time for this record event. For brevity forecast prior to 10
November were not shown, but forecasts from as early as 8 November showed the potential for
the cold surge for 16-19 November and though not shown the first cold surge of 11-16
November was comparably well forecast.
The full PDF of the climatology in the CFSR verse the NAEFS and GEFS forecasts provide
significant value in identifying a range of EWEs. In this case an extreme cold event with a deep
trough. The standardized anomalies provide quick insights to the potential for extreme events.
However, when combined with the full PDF, displayed as return periods and probabilities the
potential magnitude of a EWE can be attained. The displays and color codes quickly alert
forecasters to the potential for HIWE and in this case and EWE.
The data shown here compared R-Climate to the forecasts. Certain fields, such as QPF should
also be displayed verse the forecast systems internal climate (M-Climate). These data lend
themselves to extreme forecast indices base on both R-Climate and M-Climate output.
7. Acknowledgements
WR SA data provided by Trevor Alcott. NAEFS references were provided by Bo Cui of NCEP.
8. References
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AP 2014a: Snow blankets parts of New York; US feels chill. 18 November 2014 and similar stories.
AP 2014b: Massive lake-effect snowstorm pummels Buffalo area, close New York State Thruway.
18 & 19 November 2014 and similar stories.
Cui, B., Y. Zhu, Z. Toth and D. Hou, 2014: "Development of Statistical Post-processor for NAEFS"
Submitted to Weather and Forecasting (in process)
Cui, B., Z. Toth, Y. Zhu and D. Hou, 2012: "Bias Correction For Global Ensemble Forecast"
Weather and Forecasting, Vol. 27 396-410
Grumm, R.H., and R. Hart, 2001a: Anticipating Heavy Rainfall: Forecast Aspects.
Preprints, Symposium on Precipitation Extremes, Albuquerque, NM, Amer. Meteor. Soc.,
66-70.
Grumm, R.H., and R. Holmes, 2007: Patterns of heavy rainfall in the mid-Atlantic. Preprints, Conference on Weather Analysis and Forecasting, Park City, UT, Amer. Meteor.
Soc., 5A.2.
Junker, N. W., R. S. Schneider and S. L. Fauver, 1999: Study of heavy rainfall events
during the Great Midwest Flood of 1993. Wea. Forecasting, 14, 701-712.
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Figure 1. Climate Forecast System reanalysis of the mean sea-level pressure over the north Pacific Basin. Data are in 24 hour increments from a)
0000 UTC 7 November through d) 0000 UTC 10 November 2014. Hot colors show the deep cyclone for pressures below 968 hPa cold colors show
high pressure values greater than 1036 hPa. Contours every 4 hPa. Return to text.
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hPa
inches
Date and notes
924
27.286
8 November 2014 Actual measured 929.8 hPa
925
27.32
Oct 26, 1977 @ 00z: 56N 169W Dutch Harbor
926
27.34
Dec 24, 1975 @ 12z: 49N 158W
928
27.40
Dec 21, 1981 @ 12z: 52N 174E
932
27.52
Jan 15, 2013 @ 06z: 41N 159E
934
27.58
Dec 14, 1984 @ 12z: 56.5N 169E
934
27.58
Dec 7, 1976 @ 12z: 47N 177.5E
936
27.64
Oct 3, 1981 @ 12z: 47.5N 154E
937
27.70
Dec 27, 1997 @ 06z: Gulf of Alaska
938
27.70
Nov 10, 1976 @ 12z: 46N 179W
938
27.70
Jan 20, 1988 @ 12z: 45N 180
938
27.70
Feb 22, 1998 @ 18z: 57N 176E
940
27.76
Jan 7, 1985 @ 12z: 52N 175W
940
27.76
Oct 26, 1998 @ 00z: Near Int'l Dateline
940
27.76
Mar 21, 1999 @ 18z: western Aleutians
940
27.76
Nov 18, 1999 @ 00z: central Bering sea
Table 1. List of deep cyclones by pressure in the north Pacific basin. Data courtesy
of David Roth via the Albany MAP. Return to Text.
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Figure 2. As in Figure 1 except for 24 hours from a) 1200 UTC 8 through d) 1200 UTC 11 November 2014. Return to text.
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Figure 3. As in Figure 1 except for 500 hPa heights (m) and 500 hPa height anomalies (standard deviations) from a) 0000 UTC 8 November
through d) 0000 UTC 11 November 2014. Return to text.
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Figure 4. As in Figure 3 except for 500 hPa heights (m) and 500 hPa height anomalies (standard deviations) from a) 0000 UTC 12 November
through d) 0000 UTC 15 November 2014. Return to text.
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Figure 5. As in Figure 4 except for 850 hPa temperatures ( C) and temperature anomalies in 24 hour increments from a) 0000 UTC 12 November
through d) 0000 UTC 15 November 2014. Isotherms are every 2C. Return to text.
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Figure 6. As in Figure 5 except for 850 hPa mean sea-level pressure and pressure anomalies. Return to text.
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Figure 7. NCEP GEFS forecasts of 500 hPa heights and standardized anomalies valid at 1200 UTC 15 November 2014 from GEFS initialized at 0000 UTC a) 10
November, b) 11 November, c) 12November, d) 13 November , e) 14 November and f) 15 November 2014. Return to text.
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Figure 8. As in Figure 7 except valid at 1200 UTC 18 November 2014. Return to text.
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Figure 9. As in Figure 8 except for the NCEP-CMC NAEFS. Note displays run newest to oldest as a) is 0000 UTC 15 November forecasts and f) is 0000 UTC 10
November forecasts. Return to text.
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Figure 10. As in Figure 8 except for GEFS 850 hPa temperatures (C) and 850 hPa temperature anomalies. Return to text.
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Figure 11. As in Figure 10 except for GEFS Mean sea level pressure forecasts (hPa) and pressure anomalies. Return to text.
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Figure 12. As in Figure 10 except for NCEP-CMC NAEFS from a) 0000 UTC 15 November through f) 0000 UTC 10 November. Return to text.
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Figure 13. SA Tables showing the percentiles of the anomaly for each variable from NAEFS runs initialized at 0000 UTC 11 November, 12 November, and 13
November 2014. Data include height (Z), temperature (T), u-wind (U), V-wind (V), wind speed (WSP), mean sea level pressure (SLP), specific humidity (Q),
precipitable water (PW), and integrated vertical moisture transport (IVT) . Return to text.
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Figure 14. As in Figure 13 except 16 November 2014 showing the traditional standardized anomalies, the percentiles, and the return period in years.
Return to text.
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Figure 15. As in Figure 13 except for a multi-level variable, temperature, showing the anomalies extremes for each level in the NAEFS. Data include the
traditional standardized anomalies, the percentiles and the return periods. Return to text.
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Figure 16. The NAEFS forecast of 850 hPa temperatures valid at 1200 UTC 18 November showing a) the return period and b) the percentile verse
the CFSR 30-year climatology. Return to text.
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