Central United States Winter Storm of February 2013

Transcription

1 Central United States Winter Storm of February 2013 By Richard H. Grumm National Weather Service State College, PA Abstract: A strong winter storm brought heavy snow, sleet, and freezing rain to the central plains and lower Missouri Valley. Heavy snow affected Kansas, Nebraska, and Missouri with sleet and freezing rain along the southern edge of the snow shield across southern Kansas, Missouri and northern Arkansas. Snowfall amount between 12 and 20 inches were observed in Kansas to Nebraska and a more east-west band of heavy snow fell across Missouri. The heavy snow fell in a region of strong easterly winds. The 850 hpa u-wind anomalies during the storm reached -4σ below normal. The strong low-level easterly winds implied a strong frontal circulation which kept the low-level cold air in place and enhanced the lift. The strong low-level winds were the result of the gradient between a strong anchoring anticyclone to the north and a modest surface cyclone to the south. Not all major winter storms require a strong surface cyclone and often strong anticyclones are key players in mixed precipitation and heavy snow events. The storm was relatively well predicted by the NCEP forecast systems to include both the Global Ensemble forecast system and the short-range ensemble forecast system. Both showed the potential for heavy snow, an anomalous anticyclone to the north, anomalous easterly flow on the cold side of the boundary and sufficient QPF to produce heavy snowfall. During this event model precipitation types and areas to be affected by heavy snow and mixed precipitation were relatively well forecast with 3-5 days lead-time.

2 1. Overview A powerful winter storm brought snow, sleet, and freezing rain across the southwestern United States, across the southern plains and into the Midwest February. Snow amounts in excess of 11 inches (Table 1) indicated that the southern Plains were particularly impacted by the snow. The mid-tropospheric wave that produced the storm brought snow to Arizona on 20 February which caused a delay in the Golf tournament in Arizona (Reuters 2013a&b). South of the region of heavy snowfall a significant ice storm developed and reports of over 0.50 inches of freezing rain (Table 2) and accumulations of over 2 inches of sleet were reported (Table 3). The mid-tropospheric wave which produced the heavy snow was over southern California at 0000 UTC 20 February (Fig. 1a) and moved over the southwestern United States and over the southern Plains (Fig. 1a-f). One of the key downstream features was the strong blocking anticyclone over central Canada (Fig. 1e) which created an W block over eastern North America (Rex 1950). East winters storm (ECWS: DeGaetano et al 2002) are often associated with a jet entrance region and a strong anticyclone to the north and east of the developing storm (Kocin and Uccellini 1990;Kocin and Uccellin 2004;Uccellini and Kocin 1987). Stuart and Grumm (2006 & 2007) showed in the idealized patterns for ECWS shown by Kocin and Uccellini (2004) strong lowlevel u-wind anomalies on the order of -3 to -5s are often associated with significant winter storms. No formal study has been conducted with respect to central Plains and Midwestern snow storms. However, cases studies of single significant Midwest storms has shown that many contain anomalous low-level easterly wind anomalies in storms which produce climatologically significant snowfall in the Mid-West. The Chicago snow storm of February 2011 (Grumm 2011) produced over 20.5 inches in the City. During this storm the 850 hpa u-wind anomalies were in the -3 to -5σ range. The easterly flow was associated with a massive anticyclone with a central pressure in excess of 1050 hpa. This paper will examine the large scale conditions associated with the winter storm of February The significant snow in the Plains fell on 21 February with several new record snows for the date set in Kansas. Therefore a point near Wichita Kansas is placed in many of the images. The focus here is on the value of standardized anomalies in identifying the potential for a significant winter storm. Forecasts from NCEPS ensemble forecast system are used to show that this storm to include the pattern and the threat for heavy snow was relatively well predicted. 2. Data and Methods

3 The large scale pattern was reconstructed using the 00-hour forecast of the NCEP Global Forecast System as 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). The NCEP global ensemble forecast system (GEFS) and short range ensemble forecast system (SREF) data were used to show the larger scale forecasts. The pattern and the probability of precipitation, to include heavy snow, sleet, and freezing rainfall were relatively well predicted in this event. 3. Pattern over the region The 500 hpa pattern showed the strong short-wave which moved across the southwestern United States from 0000 UTC 20 through 1200 UTC 22 February. The +2 to +3σ 500 hpa ridge over eastern Canada (Fig. 1e) was associated with a strong surface anticyclone over central Canada with a central pressure around 1040 hpa (not shown) which extended southward into the northern and central Plains and lower Missouri River Valley (LMRV: Fig. 2). Despite the deep 500 hpa trough, with -2 to -3σ height anomalies, the surface pressure associated with the surface cyclone was underwhelming. More significant was the strong pressure gradient between the surface low and the massive anticyclone to the north. The resulting low-level flow between the strong anticyclone and the weak surface cyclone created strong low-level easterly flow (Fig. 3). North of the 850 hpa low the 850 hpa u-wind anomalies were -3 to 5σ below normal. The total winds (not shown) had total +2 to +3s wind anomalies in the cold air and +5s above normal anomalies in the warm (Fig. 4) and plume of moisture (Fig. 5) over Louisiana and Arkansas. The point near Wichita (black dot Fig. 3) was located just south of the most anomalous 850 hpa easterly wind anomalies. In this case the Younkin rule for heavy snowfall (Younkin 1968) worked relatively well though the heavy snow in Kansas fell close to the 850 hpa cyclone track. The strong anticyclone associated with the 500 hpa blocking ridge likely provided the shallow cold air damming which produced the sleet and freezing across Oklahoma, northern Arkansas, and Missouri. The reports of 1 to 3 inches of sleet (Table 3) imply a relatively deep layer of cold are below the warm air aloft. The GFS 00-hour forecasts of 925 hpa temperatures (Fig. 6) showed below normal 925 hpa temperatures and that 0C contour well south of the 850 hpa 0C contour. A relatively good set up for an ice event as identified by Harlan (1952) over half a century ago. 4. Forecasts The NCEP GEFS predicted the pattern relatively well at least 6 days prior to the event. Additionally, the GEFS produced forecasts suggesting the potential for over 6 inches of snowfall in the approximate region where significantly heavier snowfall was observed. A series of 9

4 GEFS forecasts from 1200 UTC 16 February through 1200 UTC 20 February 2013 are presented. These GEFS forecast of 500 hpa heights and anomalies (Fig. 7) show the blocking ridge over Canada and the trough coming out of the southwestern United States. The well predicted 500 hpa pattern (Fig. 7) produced good 850 hpa wind and u-wind anomaly forecasts (Fig. 8) and good forecasts of the 850 hpa baroclinic zone over the southern Plains (Fig. 9). The strong forcing in the GEFS produced a high probability of 25mm or more of QPF in the cold air (Fig. 10) and a representative pattern in the ensemble mean QPF field (Fig. 11). Similar to the NCEP GEFS, the NCEP SREF (Fig. 12) predicted the QPF and the potential for a band of QPF in excess of 25mm in the generally correct location (Fig. 13). The strong low-level easterly jet (Fig. 14) likely implied banded precipitation and confidence in heavy precipitation in the cold air. The SREF precipitation types (Fig. 15) showed a complex winter storm with snow, sleet, freezing rain over Arkansas and Missouri and rain farther to the south and east. The dark blues and purples showed regions of heavy snow in Missouri and Kansas for the period ending at 1800 UTC 21 February Precipitation observations The total estimated precipitation (QPE: Fig. 17) shows some implied mesoscale bands of over 24 to 40 mm over portions of Missouri and Kansas. The higher QPE amounts were clearly in the warm air well south of the wintry precipitation where QPE values exceeded 48 mm. As the storm system moved east, it weakened and the total QPE over Illinois and Wisconsin was considerably lower, as was the total snowfall (Fig. 18). The higher QPE over Missouri (Fig. 17) and the intense mesoscale precipitation bands around 1800 UTC (Fig. 19) were contributing factors to the band of 10-3 inches of snow from near Kansas City across the State of Missouri (Fig. 18). Precipitation type issues severely limited snowfall amounts across southern Missouri and points south. The heaviest snow was in a more north-south band (purple colors) from south-central Kansas into Nebraska where inches was recorded. This heavy snow likely occurred in the enhanced bands of rainfall observed at 1200 and 1800 UTC (Fig. 19a-b). The total QPE in this region implies similar amounts as observed in Missouri implying higher snow to water ratios. 6. Summary A strong winter storm brought heavy snow, sleet, and freezing rain to the central plains and lower Missouri Valley (Fig.18). Heavy snow affected Kansas, Nebraska, and Missouri with sleet and freezing rain along the southern edge of the snow shield across southern Kansas, Missouri and northern Arkansas. Snowfall amount between 12 and 20 inches were observed in Kansas to Nebraska and a more east-west band of heavy snow fell across Missouri. Heavy rain affected areas to the south and the Gulf Coast (Figs. 17& 19). The more intense rainbands in the Gulf States produced severe weather in the Gulf States (not shown). Snowfall amount between 12 and 20 inches were observed in Kansas to Nebraska and a more east-west band of heavy snow fell across Missouri.

5 The heavy snow fell in a region of strong easterly winds (Fig. 3). The 850 hpa u-wind anomalies during the storm reached -4σ below normal (Fig. 3). The strong low-level easterly winds implied a strong frontal circulation which kept the low-level cold air in place and enhanced the lift. The 850 hpa isotherms (Fig. 4) show the frontal boundary over the region. The 850 hpa zero line implied the strong low-level wind anomaly as on the cold side of the boundary and the 925 hpa isotherms (Fig. 6) show the inferred cold air damming effect with cold air and below 0C air south of the 850 hpa 0C contours. The surge of warm moist air in the PW fields was to the east (Fig. 5). The strong low-level winds were the result of the gradient between a strong anchoring anticyclone (Fig. 2) to the north and a modest surface cyclone to the south. Not all major winter storms require a strong surface cyclone and often strong anticyclones are key players in mixed precipitation and heavy snow events. The anticyclone was beneath a high latitude blocking ridge centered over Canada (Fig. 1). The weak cyclone and strong anticyclone suggest that the key to big storms is not a strong cyclone but a strong gradient between anticyclones and cyclones. In this event, the surface cyclone was not very strong and was in fact a bit underwhelming (Fig. 2). Many ECWS lack deep cyclones especially when a strong anticyclone is present to the north and east. The storm was relatively well predicted by the NCEP forecast systems to include both the Global Ensemble forecast system and the short-range ensemble forecast system. Both showed the potential for heavy snow, an anomalous anticyclone to the north, anomalous easterly flow on the cold side of the boundary and sufficient QPF to produce heavy snowfall. During this event model precipitation types and areas to be affected by heavy snow and mixed precipitation were relatively well forecast with 3-5 days lead-time. Confidence in forecasting winter storms is often enhanced when the pattern and QPF include significant anomalies. In winter storms this includes significant 850 hpa u-wind anomalies, a strong gradient between the anticyclone and surface cyclone; and temperature profiles sufficiently cold enough to support snow, all which this storm had. All which was forecast by the NCEP forecast systems to include the NCEP GEFS and SREF. The GEFS forecasts showed the potential for high QPF amounts in regions where it was sufficiently cold for snow (GEFS PTYPE not shown 1 ). The GEFS also produced a favorable pattern known to be associated with a) high QPF amounts and b) heavy snow when it sufficiently cold to support snow, and c) strong u-wind anomalies near the region where heavy snow was expected. Figures showed that the NCEP SREF correctly predicted a band of heavy precipitation with high confidence based on the probability of 25mm or more QPF in close proximity to the strong low-level easterly jet and u-wind anomaly. The QPF combined with the u-wind anomalies should provide confidence in the potential for higher end QPF amounts. The 1 though it showed snow/sleet and freezing rain issues and over 12 inches of snow as much as 5 days out.

6 precipitation types issues implied a) issues as the where heavy freezing rain and heavy snow might fall and b) some timing issues when viewed in 1 or 3 hourly increments. This storm with its strong easterly wind anomalies and the Chicago storm of February 2011 (Grumm 2011) imply that a comprehensive study of Midwestern snow storms may help identify signatures and key anomalies to predict these storms. The generalized patterns identified by Kocin and Uccellini (2004) and standardized anomalies (Stuart and Grumm 2006) may be of significant value identifying storms which are potential high impact events. There were many issues related to model and EFS differences related to the rain snow line and where the heavy snow would fall. The high probability forecasts generally worked out. In reality, picking a model or ensemble forecast system is a fool s errand, the best forecast is based on an ensemble of all relatively comparable forecast systems. 7. Acknowledgements PSU for access to real-time data and research data. 8. References DeGaetano, A. T., M. E. Hirsch, and S. J. Colucci Statistical prediction of seasonal East Coast winter storm frequency. Journal of Climate 15: 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., Grumm,RH, 2011: Eastern United States Winter Storm of 31 January through 2 February Web document. Harlin, B.W. 1952: The great southern glaze storm of Weatherwise,5, Kocin, P. J., and L. W. Uccellini, 2004: Northeast Snowstorms, Volume I: Overview. Meteor. Monogr., Vol. 32, No. 54, Amer. Meteor. Soc., Kocin, P. J., and L. W. Uccellini, 1990: Snowstorms along the northeastern Coast of the United States: 1955 to Meteor. Monogr., No. 44, Amer. Meteor. Soc., 280p. Reuters, 2013a: Play called off for day a snowy Dove Mountain. And similar stories. 20 February Reuters, 2013b: Major snowstorm lashes Great Plains, heads East, and similar stories 22 February Rex, D. F., 1950a: Blocking action in the middle troposphere and its effect upon regional climate. I. An aerological study of blocking action. Tellus, 2,

7 , 1950b: Blocking action in the middle troposphere and its effect upon regional climate. II. The climatology of blocking action. Tellus, 2, Robbins, C.C and J.V. Cortinas 2002: Local and synoptic environments associated with freezing rain in the contiguous United States. Wea. Forecasting,17, Stuart,N.A and R.H. Grumm 2006: Using Wind Anomalies to Forecast East Coast Winter Storms. Wea. and Forecasting, 21, Stuart, N.A. and R.H. Grumm, 2007: Ensemble Predictions of the 2007 Valentines Day winter storm. 22 nd Weather and Analysis, and Forecasting Conference, Park City, Utah, Amer. Meteor. Boston, MA. [Link here] Younkin, R.J., 1968: Circulation Patterns Associated with Heavy Snowfall over the Western United States. Monthly Weather Review, 96, 12, Uccellini, L.W and PJ Kocin 1987: An examination of vertical circulations associated with heavy snow events along the East Coast of the United States. Wea. Forecasting, 2,

8 Location State Freezing rain CHANUTE KS 0.50 BATESVILLE AR 0.50 BERRYVILLE 5 NW AR 0.50 MELBOURNE AR 0.50 MOUNTAIN VIEW AR 0.50 OAK GROVE AR 0.50 BERNIE MO 0.40 LESTERVILLE MO 0.40 CHIMES AR 0.40 HEBER SPRINGS AR 0.30 ALTON MO 0.25 CLEVER MO 0.25 DONIPHAN MO 0.25 FAIR GROVE 3 NNE MO 0.25 MARSHFIELD MO 0.25 THAYER MO 0.25 WILLOW SPRINGS MO 0.25 OXFORD OH 0.25 BELLA VISTA AR 0.25 CALAMINE AR 0.25 DAHLGREN IL 0.20 WEST PADUCAH KY 0.20 PITTSBURG MO 0.20 CENTERVILLE OH 0.18 SALEM MO 0.10 NORTH LITTLE ROCK AR 0.10 Table 2. Listing of select reports of Freezing rain fall in inches Location State Snowfall RUSSELL 11.8 NNE KS NATOMA 6.7 NNE KS LA CROSSE 0.3 ESE KS NASHVILLE KS STOCKTON 10.4 WNW KS MONARCH PASS 1 NNW CO HAYS KS WOLF CREEK PASS 1 SSE CO PLAINVILLE KS RED RIVER 8 SSW NM JETMORE 8 N KS WICHITA MID CONTINENT KS HUTCHINSON 2 NW KS MACKSVILLE KS NORWICH KS ROSSVILLE 3 S KS ROZEL KS SPIVEY KS CLEARWATER 4 N KS HANSTON 1 W KS LEBO KS WARE 15 NE TX ALVA OK RAYMORE 1.2 SE MO RICHMOND SSW KS KINGMAN KS LONG ISLAND KS LYNDON KS OLATHE KS FREEMAN MO AYR NE TEXHOMA OK ELWOOD 8 S NE GOODLAND KS TOPEKA 5 SW KS HOLDREDGE NE Table 1. List of snowfall Feb for sites which reported 11 or more inches of snowfall. Return to text

9 Town State Sleet FORT SCOTT KS 3.00 STEELVILLE MO 3.00 VIENNA MO 3.00 MARSHFIELD MO 2.50 BOLIVAR MO 2.00 CAMDENTON MO 2.00 DIXON MO 2.00 GRAVOIS MILLS MO 2.00 NIXA MO 2.00 SALEM MO 2.00 PERRYTON TX 2.00 WALKER MO 1.75 CROSS TIMBERS MO 1.50 JOPLIN MO 1.50 MOUNT VERNON MO 1.50 OWENSVILLE MO 1.30 SULLIVAN MO 1.30 IBERIA MO 1.25 BRANSON MO 1.00 SPRINGFIELD 6 S MO 1.00 WAYNESVILLE MO 1.00 OSAGE 3 NW AR 1.00 ROCKHOUSE AR 1.00 SKIATOOK 5 SW OK 1.00 Table 3. As in Table 1 except for locations reporting 1 or more inches of sleet.

10 Figure 1. GFS 00-hour forecasts of 500 hpa heights (m) and 500 hpa height standardized anomalies (standard deviations from normal) in12 hour increments from a) 0000 UTC 20 February 2013 through f) 1200 UTC 12 February Black dot is near Wichita KS where around 14 inches of snow was reported. Return to text.

11 Figure 2. As in Figure 1 except for mean sea level pressure (hpa) and pressure anomalies in 6-hour increments from a) 0600 UTC 21 February through f) 1200 UTC 22 February Return to text.

12 Figure 3. As in Figure 2 except for 850 hpa winds (kts) and 850 hpa u-wind anomalies. Return to text.

13 Figure 4. As in Figure 2 except for 850 hpa temperatures and 850 hpa temperature anomalies. Return to text.

14 Figure 5. As in Figure 2 except for precipitable water and precipitable water anomalies. Return to text.

15 Figure 6. As in Figure 4 except for 925 hpa temperatures. Return to text.

16 Figure 7. GEFS forecasts of 500 hpa heights and height anomalies valid at 1800 UTC 21 February Return to text.

17 Figure 8. As in Figure 7 except for 850 hpa mean winds and mean u-wind anomalies. Return to text.

18 Figure 9. As in Figure 8 except 850 hpa temperatures. Return to text.

19 Figure 10. As in Figure 7 except GEFS probability of 25 mm or more QPF valid for the 24 hours from 0000 UTC 21 to 0000 UTC 22 February 2013.

20 Figure 11. As in Figure 10 except for the ensemble mean QPF and each members 25mm contour. Return to text.

21 Figure 12. As in Figure 11 except for NCEP SREF valid 0000 UTC 21 to 1200 UTC 22 February 2013 from forecasts initialized at a) 0300 UTC b) 0900 UTC, and c) 1500 UTC d) 2100 UTC 19 February 2013; and e) 0300 and f) 0900 UTC 20 February Return to text.

22 Figure 13. As in Figure 12 except for SREF probability of 25mm or more QPF in the same time period. Return to text.

23 Figure 14. As in Figure 14 except for SREF 850 hpa winds and u-wind anomalies valid at 1500 UTC 21 February Return to text.

24 Figure 15. As in Figure 14 except for SREF precipitation types color coded by types (Blue: Snow: Red;Rain;Yellow Freezing rain;red:sleet) shaded to show intensities. Return to text.

25 Figure 16. Total observed precipitation for the period of 1200 UTC 20 to 1200 UTC 22 February Units in mm as indicated to the right. Return to text.

26 Figure 18. Snowfall from NWS local storm reports and public information statements. Data in inches color coded with black for amounts under 5 inches, cyan for amounts 5-9 inches, blue for 10 to 15 inches and purple for amounts 15 inches and greater. Return to text.

27 Figure 17. As in Figure 16 except for QPE in 6-hour periods near the height of the storm in central Plains and Lower Missouri River Valley data valid for each 6 hour period ending at a) 1200 UTC and b) 1800 UTC 21 February, and c) 0000 and d) 0600 UTC 22 February Return to text.