5 March 2003National Weather Service State College PA Mid-Atlantic Severe Weather Climatological Aspects by Kevin S. Lipton Richard H. Grumm and John LaCorte

5 March 2003National Weather Service State College PA Introduction Creating a Severe Weather Database Climatic Issues –Location, type, and –Time if severe weather events –Local Pennsylvania problems/considerations Improving the forecasting of severe weather events An example

5 March 2003National Weather Service State College PA Methods and Data NCDC Storm Data – Has some use issues – Tornado gets counted by every county it impacts – Inflates some numbers SPC Severe Plot Data – Lowers tornado probabilities – A cleaner data set – Loaded into mySQL and MS-Access NCEP-NCDC Reanalysis Data – Plot anomalies and show how case looked – Apply to model forecasts for forecasting (GrADS)

5 March 2003National Weather Service State College PA Creating a Severe Weather Database Prototype with Storm data to get top 20 events in eastern US – Case examples to follow Severe Plot used for a parallel study – Timing of events – Location of events – Seasonality of events The Severe Plot data was found to be more reliable

5 March 2003National Weather Service State College PA Climatic Issues Pennsylvania problems/considerations – Terrain may enhance bow echo climatology Focus on Pennsylvania Severe Weather – Location, – type (Severe and tornadic) – Seasonality – Diurnal trends

5 March 2003National Weather Service State College PA Enhanced Bow echoes terrain influence

5 March 2003National Weather Service State College PA 13 August 1999 Tuscarora valley SLBE SRM saw this bow before REF

5 March 2003National Weather Service State College PA Seasonality

5 March 2003National Weather Service State College PA Monthly Occurrences

5 March 2003National Weather Service State College PA Diurnal Trend in Pennsylvania

5 March 2003National Weather Service State College PA 68% of all Severe Weather occurs between 1PM and 7PM 50% occurs between 2PM and 6PM

5 March 2003National Weather Service State College PA # of events in each category

5 March 2003National Weather Service State College PA

5 March 2003National Weather Service State College PA Climatic Examples Test Climatic Anomalies – Top severe events – Compare to severe weather occurrences Wind Anomalies – Appear to have some forecast potential – Relate to helicity Precipitable water Shear climatology – This was only recently developed (Sep 2002) – Has many potential forecast Applications – Relates to helicity

5 March 2003National Weather Service State College PA Events with most reports Eastern US 1/21/1999-1/22/1999: 129 Tornadoes, 14 other severe; MS, LA, AR 11/21/ /23/1992: 84 Tornadoes, unknown severe; GA, AL, MS, LA 11/23/ /24/2001: 76 Tornadoes, 31 Severe; AL, MS, LA, AR 5/31/1985: 60 Tornadoes, 30 Severe; OH, NY, PA 4/16/1998: 48 Tornadoes, 72 Severe; TN, KY, AR, AL 5/30/1998-5/31/1998: 43 Tornadoes, 300 Severe; NH, MA, NJ, NY, PA, VT, MI, MN 11/15/ /16/1989: 32 Tornadoes, 3 Severe; NY, NJ, PA, GA, AL 7/12/1992: 30 Tornadoes, Unknown Severe; OH 4/14/ /15/1999: 25 Tornadoes, 30 Severe; NC, SC, GA, AL, MS 5/18/2002: 22 Tornadoes, 80 Severe; IL 5/15/1998: 21 Tornadoes, 184 Severe; IA, MN 7/19/1996: 20 Tornadoes, Unknown Severe; MD, PA 4/28/2002: 22 Tornadoes, 137 Severe; KY, TN, MD 5/16/1999: 14 Tornadoes, 104 Severe; IA 5/10/2001: 13 Tornadoes, 104 Severe; IA 4/20/2000: 13 Tornadoes, 101 Severe; IL, KY, TN

5 March 2003National Weather Service State College PA Shear Values 10m to Value 850 hPa Average Shear hPa Average Shear hPa Average Positive-Anomaly hPa Average Positive-Anomaly +1.71

5 March 2003National Weather Service State College PA Strong Shear Events Event Date10m-850 hPa10m-700 hPa 31 May July April April May

5 March 2003National Weather Service State College PA Integrating Data sets GrADS-reanalysis-Severe plot (SPC)

5 March 2003National Weather Service State College PA Shear Examples Eastern US tornado Outbreak May 1985

5 March 2003National Weather Service State College PA Shear Examples PA-NY tornado Outbreak May 1998

5 March 2003National Weather Service State College PA Forecast Applications Use of ensembles Climatic anomalies Shear climatology verse model forecasts To anticipate a potentially large severe weather outbreak Example: November 2002 – Large shear anomalies – High CAPE for November – Largest severe weather outbreak of 2002

5 March 2003National Weather Service State College PA The two big events of April Eastern US Severe outbreak – LaPlata Tornado November 2002 Severe outbreak – F2 in Pennsylvania…rare in November

5 March 2003National Weather Service State College PA 28 April 2002 severe reports Figure 1. Storm Prediction Center (SPC) plots of severe weather over the eastern United States on a) 27 April and b) 28 April 2002.

5 March 2003National Weather Service State College PA Strong Shear Case LaPlata Tornado 28 April 2002

5 March 2003National Weather Service State College PA 28 April 2002 anomalous low and southwest winds Figure 2 Eta forecast initialized at 0000 UTC 28 April valid at 2100 UTC 28 April Upper panel shows 700 hPa heights (m) and anomalies (Standard deviations from normal) and lower panel MSLP (hPa). Figure 3. As in Figure 2 except forecasts of 850 hPa winds (U and V) and departures from normal.

5 March 2003National Weather Service State College PA 28 April 2002 SREF CAPE Probabilities and spaghetti Figure 5 NCEP SREF forecasts of CAPE (Jkg -1 ). Upper panel shows spaghetti plots and dispersion about the mean. Eta members are black and RSM members are red. Lower panel shows the probability of the CAPE greater than or equal to 1200 Jkg -1 and the position of the consensus 1200 and 2400 contours.

5 March 2003National Weather Service State College PA 28 April 2002 SREF CAPE Probabilities and spaghetti Figure 6. As in Figure 5 except valid at 2100 UTC.

5 March 2003National Weather Service State College PA LaPlata Supercell complete with hook and TV Figure 13. Reflectivity and SRM data from KLWX radar around 2357 UTC 28 April 2002.

5 March 2003National Weather Service State College PA Columbia County Tornado c Split in line depicts the F1 tornado location Figure 12. As in Fig 11 except at 2202 UTC.

5 March 2003National Weather Service State College PA Lebanon County Tornado c Oh no..its a tornado near RT-22 in Ono! Figure 1. Reflectivity and SRM valid at 2207 UTC showing the structure of the thunderstorm which produced a tornado in Lebanon County. The A denotes initial thunderstorm and the arrows refer to points noted in the text. A

5 March 2003National Weather Service State College PA November 2002 Severe outbreak Big in Mississippi Valley and east Strong southerly low-level flow High CAPE for November – Not uncommon as some big November events like 4 November 1950 Strong shear Rare strong tornado in western Pennsylvania in November

5 March 2003National Weather Service State College PA Figure Storm Prediction center storm reports. Color coded by type. Upper panel is 10 November and lowe r panel is 11 November 2002

5 March 2003National Weather Service State College PA Shear Forecasts with Anomalies Eta Model Figure. Eta shear forecasts initialzed at 1200 UTC 10 November valid from left to right a) 2100 and b) 0000 UTC 10 November and c) 0300 UTC 11 November Upper panels show the shear and anomalies from the surface to 850 hPa lower panels show the shear anomalies from the surface to 700 hPa. Eta surface based CAPE is plotted on the upper panels and layer CAPE on lower panels.

5 March 2003National Weather Service State College PA Conclusions Built a regional Severe Weather Database Addressed many Climatic Issues – Location, type, and – Time if severe weather events – Local Pennsylvania problems/considerations Climatic Anomalies show great forecast potential when applied to model and ensemble forecasts New tools to integrate Data sets