SPC AC 211220
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0720 AM CDT SAT APR 21 2007
VALID 211300Z - 221200Z
...THERE IS A MDT RISK OF SVR TSTMS FROM SWRN NEB SWD THRU WRN KS
INTO TX PANHANDLE...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL AND SRN HIGH
PLAINS INTO ERN ND/NWRN MN...
...SYNOPSIS...
IMPRESSIVE... DYNAMIC SYSTEM SWRN U.S. ATTM WITH A CLOSED
CIRCULATION STILL EVIDENT TRACKING EWD ACROSS SRN AZ. MODELS IN
CLOSE AGREEMENT TAKING THE UPPER LOW/VORT MAX ENEWD ACROSS NM INTO
SRN/CENTRAL HIGH PLAINS BY THIS EVENING. JET MAX OF 80-100KT AT
500MB AND 50-60 KT AT 700MB CURRENTLY ALONG SRN AZ BORDER DRIVES
NEWD INTERACTING WITH THE N/S DRY LINE CENTRAL/SRN HIGH PLAINS BY
LATE THIS AFTERNOON.
AT THE SURFACE FRONTAL ZONE FROM ERN ND SWWD INTO WRN NEB WILL
REMAIN QUASISTATIONARY THRU THE AFTERNOON AS SURFACE LOW DEEPENS IN
ERN CO IN RESPONSE TO AZ TROUGH. SHARP DRY LINE WILL SET UP BY MID
AFTERNOON FROM NERN CO SSEWD ALONG KS/CO BORDER THEN SWD THRU WRN
PORTION OF TX PANHANDLE TO SWRN TX.
...CENTRAL/SRN HIGH PLAINS...
THE OPTIMAL TIMING OF THE INTERACTION OF THE STRONG ASCENT AND WIND
MAX ASSOCIATED WITH AZ TROUGH AND THE DRY LINE...SUPPORTS RAPID
DEVELOPMENT OF SUPERCELLS BY MID/LATE AFTERNOON. WITH LAPSE RATES
IN EXCESS OF 8C/KM AND 50-60KT OF DEEP LAYER SHEAR...THE ONLY CAVEAT
THAT PRECLUDES A HIGHER RISK IS THE LIMITATION OF LOW LEVEL
MOISTURE. HOWEVER MLCAPES AOA 2000 J/KG WILL BE COMMON ALONG AND E
OF DRY LINE WHICH WILL SUPPORT VERY LARGE HAIL AND TORNADO POTENTIAL
WITH ANY SUPERCELL THAT DEVELOPS PRIOR TO SUNSET.
WITH THE STRONG FORCING OF THE UPPER SYSTEM THE MODE SHOULD
TRANSITION FROM INITIALLY DISCRETE TO MORE OF A LINEAR MCS AFTER
DARK AS THE SEVERE THREAT SHIFTS FURTHER EWD INTO THE PLAINS. THIS
WOULD INCREASE POTENTIAL FOR DAMAGING WINDS AND GRADUALLY LESSEN
TORNADO CONCERN.
GIVEN THE INTENSITY OF THE UPPER SYSTEM AND JET MAX...EVEN WITH THE
EXPECTED RELATIVELY HIGH LCLS THERE IS STILL POTENTIAL FOR A FEW
STRONG TORNADOES PRIOR TO THE TRANSITION TO A MORE LINEAR MODE
DURING THE LATE EVENING.
......NRN PLAINS...
SEVERE THUNDERSTORMS ALSO EXPECTED TO DEVELOP VICINITY FRONTAL ZONE
BY MID AFTERNOON FROM ERN ND TO WRN NEB WHERE SHEAR AND STEEP LAPSE
RATES ALSO SUPPORT SUPERCELLS. AGAIN LARGE HAIL WILL BE THE
PREDOMINANT THREAT. HOWEVER GIVEN MLCAPES TO 2000 J/KG AND 40-50KT
OF DEEP LAYER SHEAR...ISOLATED TORNADOES WILL ALSO BE POSSIBLE WITH
ANY SUPERCELL THRU THE EVENING.
..HALES/DIAL.. 04/21/2007
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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