SPC AC 051259
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 AM CDT MON APR 05 2010
VALID 051300Z - 061200Z
...THERE IS A SLGT RISK OF SVR TSTMS THROUGH TONIGHT FROM CENTRAL
KS/NW OK TO THE MID MS VALLEY...
...SYNOPSIS...
DIFFICULT FORECAST TODAY ACROSS THE CENTRAL STATES...WITH THE
POTENTIAL FOR ISOLATED HIGH-END SEVERE EVENTS...AS WELL AS
SUBSTANTIAL UNCERTAINTY REGARDING WARM SECTOR THUNDERSTORM
INITIATION THIS AFTERNOON INTO EARLY TONIGHT ACROSS
IL/IA/MO/NEB/KS/OK. SHORT-TERM MODEL FORECASTS ARE IN AGREEMENT
MOVING A STRONG PAC COAST TROUGH INLAND ACROSS THE ROCKIES THROUGH
TONIGHT...WHILE EMBEDDED SPEED MAXIMA EJECT ENEWD OVER THE CENTRAL
PLAINS. AT THE SURFACE...A LEE CYCLONE INVOF SW KS/SE CO WILL
DEVELOP NEWD TO THE SE NEB/NE KS BORDER REGION BY 06/12Z...AS A
BROAD SWATH OF BOUNDARY LAYER DEWPOINTS IN THE 60S SURGES NWD. THIS
WILL CONTRIBUTE TO AN UNSTABLE WARM SECTOR...AND THE BOUNDARIES WILL
FOCUS THE SEVERE STORM THREAT THROUGH TONIGHT.
...ERN KS/SE NEB/MO/IA/IL THROUGH TONIGHT...
AS OF 12Z...A LOOSE AREA OF ELEVATED THUNDERSTORMS CONTINUES TO
DEVELOP SLOWLY NWD/NEWD ACROSS SE AND E CENTRAL KS. THIS CONVECTION
WILL DEVELOP NEWD THROUGH THE DAY IN THE ZONE OF ENHANCED WAA ON THE
NOSE OF A 40+ KT LLJ. THE DEGREE OF ELEVATED INSTABILITY /MUCAPE
AOA 1000-1500 J PER KG AND STEEP MIDLEVEL LAPSE RATES/...ALONG WITH
EFFECTIVE BULK SHEAR IN EXCESS OF 50-60 KT...WILL BE SUPPORTIVE OF
SUPERCELLS AND THE THREAT FOR AT LEAST ISOLATED LARGE HAIL THROUGH
THE DAY.
UNCERTAINTY BEGINS TO INCREASE BY LATER THIS AFTERNOON/EVENING ALONG
THE RETREATING WARM FRONT...ESPECIALLY ACROSS NRN MO AND SRN IA.
HERE...MODERATE INSTABILITY WILL BE PRESENT /MLCAPE VALUES OF
1500-2000 J PER KG/ AS A RESULT OF BOUNDARY LAYER DEWPOINTS IN THE
LOW-MID 60S BENEATH STEEP MID LEVEL LAPSE RATES. DEEP-LAYER
VERTICAL SHEAR WILL BE QUITE FAVORABLE FOR SUPERCELLS IN THIS SAME
CORRIDOR...WHERE LOW-LEVEL SHEAR IS MAXIMIZED INVOF THE RETREATING
WARM FRONT /EFFECTIVE SRH OF 250-500 M2 PER S2/. HOWEVER...A
RELATIVELY WARM EML AND RESULTANT CAP MAKES SURFACE-BASED
THUNDERSTORM INITIATION RATHER UNCERTAIN ALONG THE WARM FRONT DURING
THE AFTERNOON...AS REFLECTED BY A MULTITUDE OF SHORT-TERM AND
HIGH-RESOLUTION MODEL FORECASTS WITH LITTLE OR NO CONVECTIVE
PRECIPITATION IN THE WARM SECTOR. IF STORMS CAN FORM AND MOVE ALONG
THE WARM FRONT... EITHER DEVELOPING WITHIN THE WARM SECTOR OR
EVOLVING FROM THE SE FRINGE OF THE ELEVATED CONVECTION SPREADING
NEWD FROM ERN KS...THEN THERE WILL BE A DEFINITE THREAT FOR
TORNADOES...VERY LARGE HAIL...AND DAMAGING WINDS.
FARTHER E INTO IL...THE CAP WILL BE SOMEWHAT WEAKER AND THUNDERSTORM
DEVELOPMENT IS A LITTLE MORE PROBABLE DURING THE AFTERNOON. THE
ENVIRONMENT WILL NOT BE AS FAVORABLE AS NRN MO...BUT DEEP-LAYER
SHEAR AND INSTABILITY WILL STILL BE WELL WITHIN THE RANGE OF
SUPERCELLS. OTHERWISE...CLUSTERS OF THUNDERSTORMS ARE EXPECTED
OVERNIGHT IN THE ZONE OF FOCUSED WAA ACROSS IA...AND IN ADVANCE OF
THE SURFACE LOW IN SE NEB. THIS CONVECTION WILL SPREAD EWD
OVERNIGHT ACROSS IA AND NRN IL TOWARD THE SRN LAKE MI AREA...WITH AN
ATTENDANT THREAT FOR LARGE HAIL/DAMAGING WINDS...AS WELL AS A FEW
TORNADOES WITH STORMS CLOSE TO THE WARM FRONT.
...CENTRAL KS INTO W CENTRAL/NW OK THIS EVENING...
SUBSTANTIAL UNCERTAINTY EXISTS WITH REGARD TO CONVECTIVE INITIATION
ALONG THE CENTRAL KS AND W/NW OK DRYLINE THIS EVENING. MODEL
FORECAST SOUNDINGS SHOW THE POTENTIAL FOR A NARROW STRIP OF WEAKENED
CONVECTIVE INHIBITION ALONG THE DRYLINE...AND THE DEVELOPMENT OF A
STORM OR TWO CANNOT BE RULED OUT IN THE 22-01Z TIME FRAME. IF
CONVECTION BECOMES SUSTAINED IN THIS AREA...THE COMBINATION OF
INSTABILITY AND VERTICAL SHEAR WILL PROVE QUITE FAVORABLE FOR
SUPERCELLS CAPABLE OF PRODUCING VERY LARGE HAIL AND
TORNADOES...ESPECIALLY AS THE DRYLINE RETREATS SOME LATE THIS
EVENING AND LOW-LEVEL SHEAR INCREASES RAPIDLY WITH THE DEVELOPMENT
OF THE LLJ. STILL...CONVECTIVE INHIBITION WILL ALSO INCREASE
QUICKLY NEAR AND AFTER SUNSET...SO IT IS NOT CLEAR WHETHER OR NOT
ANY ISOLATED DIURNAL STORMS WILL EVEN SURVIVE INTO THE LATE EVENING.
GIVEN ALL OF THIS UNCERTAINTY...ALONG WITH THE POTENTIAL FOR
SIGNIFICANT SEVERE STORMS IF DEEP CONVECTION DEVELOPS...WILL
INTRODUCE A CONDITIONAL RISK OF LARGE HAIL AND TORNADOES.
..THOMPSON/ROGERS.. 04/05/2010
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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