Anomalies and Ensembles as tools to anticipate ice storms Richard Grumm NOAA/NWS State College, PA

Overview Overview of the use of anomalies –Standardized anomalies 101 Patterns and anomalies for some memorable ice storms. Ensembles: –Patterns of ice storms in EPS data –Probabilities  Of value during a potential ice storm.

Global Anomalies 101 NCEP/NCAR Re-analysis data –2.5x2.5 degree data (coarse) –Most mandatory fields –6-hourly increments –Referred to as GR or NRP data Climatology is 21-day centered data –Mean and standard deviations –Use to make anomalies

Displaying Cases from past –Use GR data of field –Compute Standard anomaly SD = (value-mean)/sigma Climatology is 21-day centered data –Mean and standard deviations –Use to make anomalies

15 Feb 1990 Example Valentines Day ice storm Base fields from GR Shading shows standardized anomalies.

Key Anomaly Patterns with Ice Storms A strong surface anticyclone to the north with above normal mean-sea level pressure anomalies. A strong quasi-east west frontal boundary with -1 to -3 SD below normal cold air to the north and normal to above normal anomalies to the south. Above normal PW water values over or just south of the affected region. An upper level ridge with about 1SD above normal heights at 500 hPa over or east of the affected region. A strong easterly jet with -1 to -3 SD anomalies in the cold air at 925 to 850 hPa. A strong 850 hPa jet with +1 to +3 SD anomalies in the v-wind component. Strong easterly u-wind at low-levels in the cold air associated with the frontal circulation.

Ice Storm Cases from literature

1951 Ice Storm Southern Ice Storm

1960 Southern Ice Storm

1998 Northeastern US and Canadian Ice Storm

Forecast example Use model forecast data Compute anomalies as in cases except now we use the model value not the GR value for the “current state”

Ensemble Example  December 2007 Ice storm in the Midwest –Multi-day event Good SREF Precipitation type example –Planview and plumes Followed a known pattern associated with ice storms in history –Key fields were well aligned as in examples.

What Happned

Stage-IV QPE Shows Light precipitation 6-8 December Heavier Precipitaiton –09/1200 to 10/1800 UTC Event of long duration. Period where most of the Precipitation fell These data can show hourly amounts too!

Precipitation Accumulations end to beginning

6-hourly 08 December

6-hourly 09 December

6-hourly 10 December

SREF Forecast Plumes help with single locations –AWIPS does not have this but AWIPS-II will –Plumes are an AWIPS-II feature! Provide probabilities of precipitation and temperature probabilities SREF Anomalies from GR data like past events. Most images will focus on AWIPS like data –Use NCEP files that are processed by AWIPS for display in D2D.

Plumes Explained Accumulations over time are color coded –By precipitation type using traditional colors for snow (blue), ice pellets (sleet:cyan), freezing rain (red), and rain (Green) 3-hourly amounts are gray and very light as not to cloud the data Statistics and summaries are provided on the LHS of each image. This case was exceptionally well forecast in many regards  types and timing were pretty good.

SREF Plumes

Traditional Products Ensemble means and standardized anomalies –To show the pattern and –Where there are some significant features Probabilities –To show where the temperature issues could affect the precipitation type Precipitation Type  key in ice storms. –Use yellow for ice pellets in these images.

0900 UTC 7 December Pattern with spread and anomalies

Moisture anomalies

Short-range 250 hPa jet strong coupled jet  banana jet in u-anomalies

Warm Over cold problem persisted

PTYPE and 3-hourly QPF color coded by intensity

Some Images in sequence Experimental GUI Case times are in the GUI so the cycle button has no effect  made on the fly and can and will be improved. 4 Case times available

Review Overview of the use of anomalies –Standardized anomalies 101 Patterns and anomalies for some memorable ice storms. Ensembles: –Patterns of ice storms in EPS data Winds, PW, MSLP showed common pattern –Probabilities  Of value during a potential ice storm to include PTYPE forecasts and critical level temperatures.

Ice Storm References Baker,B.W.1960: The 1960 ice storm in northern Alabama. Weatherwise,13, Forbes G. S., R. A. Anthes, and D. W. Thompson, 1987: Synoptic and mesoscale aspects of an Appalachian ice storm associated with cold-air damming. Mon. Wea. Rev., 115, 564–591. Gyakum J. R., and P. J. Roebber, 2001: The 1998 ice storm—Analysis of a planetary- scale event. Mon. Wea. Rev., 129, 2983–2997. Find this article onlineFind this article online Harlin, B.W. 1952: The great southern glaze storm of Weatherwise,5, Hart, R.E, and R.H. Grumm 2001: Using Normalized Climatological Anomalies to Rank Synoptic-Scale Events Objectively. Mon. Wea. Rev.129, Irland L. C., 2000: Ice storm 1998 and the forests of the Northeast. J. For., 96, 32–40. Find this article online Find this article online Robbins, C.C and J.V. Cortinas 2002: Local and synoptic environments associated with freezing rain in the contiguous United States. Wea. Forecasting,17, Rauber R. M., M. K. Ramamurthy, and A. Tokay, 1994: Synoptic and mesoscale structure of a severe freezing rain event: The St. Valentine's Day ice storm. Wea. Forecasting, 9, 183–208. Find this article onlineFind this article online Stewart R. E., 1992: Precipitation types in the transition region of winter storms. Bull. Amer. Meteor. Soc., 73, 287–296. Find this article onlineFind this article online Stewart R. E., and P. King, 1987: Freezing precipitation in winter storms. Mon. Wea. Rev., 115, 1270–1279. Find this article onlineFind this article online