DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1128 AM CST MON NOV 17 2003
VALID 181200Z - 191200Z
THERE IS A MDT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 10 NE GPT 25 WSW LUL 55 ESE GWO 25 NNE CBM 20 NW GAD 10 N AHN 15 ESE AGS SAV 20 NNE SSI 25 W JAX 40 SE TLH.
THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 35 SE JAX PIE ...CONT... 20 S BPT 40 SSW MLU 30 N GLH 25 NE JBR 25 E CGI 15 SSW OWB 55 W LOZ 25 WNW HSS 35 N HKY 20 E SSU 20 SSW CHO 30 NNW RWI 10 NE ILM.
GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 15 N DAB 25 SSE SRQ. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 35 SW PSX 45 N POE 25 SE ELD 30 SW PBF 20 WSW HOT 10 SSW FSM 50 ENE TUL 30 E MKC 35 NNW IRK 20 SW DBQ 15 SSE CWA 130 NE CMX ...CONT... 60 NNW ROC IPT 30 SSW NHK 30 E ECG.
...THERE IS A MDT RISK OF SVR TSTMS FROM ERN MS...ACROSS AL...GA AND NRN FL...
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK TO THE WEST AND NORTH FROM LA TO WRN VA...
...SIGNIFICANT SEVERE EPISODE IS POSSIBLE ACROSS MUCH OF THE GULF COAST REGION TUESDAY. TORNADOES AND DAMAGING BOW ECHOES ARE EXPECTED...
...GULF COAST...
PHASING OF NRN AND SRN STREAM OVER THE GULF COAST REGION DURING THE LATTER HALF OF THE PERIOD WILL ENHANCE LARGE SCALE DYNAMIC PROCESSES AND CREATE AN ENVIRONMENT FAVORABLE FOR SEVERE THUNDERSTORMS...ESPECIALLY DURING THE LATTER HALF OF THE PERIOD.
EARLY MORNING MODEL GUIDANCE SUGGEST UPPER LEVEL FLOW WILL BEGIN TO INCREASE ON DOWNSTREAM SIDE OF INTENSIFYING TROUGH AXIS OVER THE WRN GULF COAST REGION EARLY IN THE PERIOD...WITH H5 FLOW EXPECTED TO EXCEED 90KT BY EVENING AS SPEED MAX SHIFTS EWD ACROSS MS INTO GA BY 12Z/19TH. THIS FEATURE WILL TAKE ON A NEGATIVE TILT BY THE END OF THE PERIOD AS 12HR HEIGHT FALLS INCREASE FROM 90-180M. MARITIME BOUNDARY LAYER AIRMASS HAS RETURNED ACROSS THE WRN GULF OF MEXICO ONTO THE TX/LA COAST...WITH NWD SURGE EXPECTED ACROSS THE REMAINDER OF THE GULF REGION AS WARM FRONT LIFTS INLAND...WELL AHEAD OF COLD FRONT. MODELS DO NOT SIGNIFICANTLY DESTABILIZE THIS REGION IN PART THROUGH CONVECTIVE PROCESSES AND THE QUICK EVOLUTION TO MOIST-ADIABATIC LAPSE RATES. HOWEVER...VERY MOIST LOW LEVEL AIRMASS AND THE STRENGTH OF UPPER SYSTEM SUGGEST SUPERCELL STRUCTURE IS LIKELY WITH MOST SUSTAINED UPDRAFTS...DESPITE THE LIKLIHOOD FOR DISCRETE ACTIVITY TO MERGE AND EVOLVE INTO LINE SEGMENTS AND BOW ECHOES...ESPECIALLY ALONG SURGING COLD FRONT LATE IN THE PERIOD.
SEVERE THUNDERSTORMS SHOULD BE ONGOING EARLY IN THE PERIOD ACROSS PORTIONS OF THE LOWER MS VALLEY INTO MS. SEVERE THREAT WILL SHIFT EWD DURING THE DAY AS UPPER SYSTEM INTENSIFIES. TORNADOES AND DAMAGING BOW ECHOES ARE EXPECTED ACROSS THE WARM SECTOR SPREADING INTO PORTIONS OF THE CAROLINAS AFTER MIDNIGHT.
..DARROW.. 11/17/2003
Late evening forecast model guidance continues to suggest although once again, CAPE values quite low, the energy of the storm system is more than enough to generate the potential of a significant outbreak as stated by the SPC ... strong shear values as the system goes NEG TILT as the system reaches the Carolinas/Georgia tomorrow afternoon ...
The ETA/GFS continue to show very impressive upper divergence at the 200mb and 300mb level and winds in excess of 130kts at the 200mb level.... and impressive wind values even down around the 850mb level with both the ETA/GFS showing 55kts winds ...
These maps from the ETA valid for 00z WED NOV 19th (7 PM EST)...notice from the 850mb map to the 200mb map the changing of wind direction with height ... quite a bit of directional wind shear, and upper divergence at the 200mb level ...
Notice the winds are SOUTHERLY to South-Southeasterly across the Southeastern States at 5000 mb...
Now notice how the winds at the 500mb level (15,000 ft.) are SOUTHWEST over the Southeast states which is an abrupt changing of direction with height (45º angle turn or about 4-5º/1K ft) ...
Now look at the 200mb level wind field with the winds from the WSW over the Southeast, even more turning, and if you'll notice, a tendency for the arrows to diverge away from each other (Southwest winds over TN, and West Winds over Central Florida) or divergent wind shear ...
Divergence gives the low level atmosphere the ability to converge at the surface and draw air in to a common point (low pressure) and with high UVV's (Upward Vertical Volacities) and strong shear, despite a relatively low CAPE value, the overall setup still lends support for a potential of a significant severe weather outbreak ...
As the storms continue tomorrow night, based on the progged helicities and other parameters for severe weather, the threat begins to come more from a squall line and the potential for damaging winds ... though, in SC, marginal FZ line does the support the risk for large hail. Discrete supercells in South Carolina Wed Morning could produce an isolated tornado or two, however, the timing of the system may reduce the risk for severe in South Carolina.
SF
