DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 251632
SWODY1
SPC AC 251630

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT WED APR 25 2012

VALID 251630Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS EVENING THROUGH TONIGHT
FOR PARTS OF THE MID MS AND OH VALLEYS...

...MID MS/OH VALLEY REGION THROUGH TONIGHT...
A SUBTLE MID-UPPER SPEED MAX OVER SD/NEB/IA WILL TRANSLATE SEWD TO
THE LOWER OH VALLEY BY TONIGHT. THE WEAK WAVE ALOFT WILL BE
ACCOMPANIED BY A REMNANT LEE CYCLONE WHICH WILL LIKEWISE DEVELOP
ESEWD FROM NW IA/SW MN ALONG A SURFACE WARM FRONT TO NW IL THIS
EVENING AND OH BY 26/12Z. 12Z SOUNDINGS REVEAL THAT A VERY WARM
ELEVATED MIXED LAYER HAS SPREAD EWD TO THE ERN PLAINS...AND THIS
LAPSE RATE PLUME WILL EXTEND AS FAR EWD AS THE MID MS/LOWER OH
VALLEY REGION BY THIS EVENING. MEANWHILE...LOW-LEVEL MOISTURE
RETURN IS UNDERWAY BENEATH THE MIDLEVEL LAPSE RATE PLUME AND AN
ASSOCIATED CAP. RECENT SHORT-TERM MODEL FORECAST...ASIDE FROM THE
HRRR...HAVE ALL DISPLAYED SERIOUS OVER-FORECAST BIASES IN THE
BOUNDARY LAYER MOISTURE PROFILES...WITH FORECAST ERRORS OF 1.5-2
G/KG IN 100 MB MEAN MIXING RATIOS...OR 5-7 F TOO HIGH FOR MEAN
BOUNDARY LAYER DEWPOINTS. THESE MOISTURE FORECAST ERRORS RESULT IN
SUBSTANTIAL OVER-FORECASTS OF CAPE...AND UNDER-FORECASTS OF
CONVECTIVE INHIBITION. INSTEAD OF MODEL FORECASTS OF 64-70 F
DEWPOINTS FROM OK-IL BY 00Z...EXPECT VALUES TO RANGE FROM 59-64 F
ACROSS THE SAME AREA.

THE MOISTURE ERRORS ALSO APPEAR TO BE IMPACTING CONVECTIVE
PRECIPITATION FORECASTS...INCLUDING THE STRONG MCS SIGNALS NOTED IN
THE CONVECTION-ALLOWING NSSL ARW AND HIGH-RES EAST/WEST WINDOWS OF
THE NMM. CONVERSELY...MORNING HRRR FORECASTS ARE SUBSTANTIALLY
DRIER IN THE BOUNDARY LAYER /PERHAPS TOO DRY/...AND STORM INTENSITY
IS MUCH REDUCED FROM THE OTHER MODEL FORECASTS. GIVEN OBSERVATIONAL
TRENDS AND LIKELY MODEL FORECAST BIASES...THE SEVERE STORM RISK
APPEARS TO BE LOWER THAN PREVIOUSLY ANTICIPATED ACROSS THE OH VALLEY
THIS EVENING INTO TONIGHT.

...NRN ROCKIES THIS AFTERNOON/EVENING...
CLOUD COVER IS MORE EXTENSIVE THIS MORNING COMPARED TO PREVIOUS
MORNINGS...AND REGIONAL SOUNDINGS SUPPORT A GRADUAL TRANSITION TO A
SOMEWHAT COOLER/MORE MOIST ENVIRONMENT THROUGH TOMORROW.
STILL...POCKETS OF SURFACE HEATING SHOULD AGAIN SUPPORT THUNDERSTORM
DEVELOPMENT /ESPECIALLY OVER THE HIGH TERRAIN/. THE COMBINATION OF
AT LEAST WEAK INSTABILITY AND DEEP-LAYER SWLY FLOW WILL SUPPORT SOME
RISK OF ORGANIZED STORM CLUSTERS CAPABLE OF PRODUCING ISOLATED
STRONG/DAMAGING GUSTS AND MARGINALLY SEVERE HAIL.

..THOMPSON/ROGERS.. 04/25/2012

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