Friday's Severe Outlook
byon 04-13-2012 at 02:35 AM (935 Views)
Tomorrow's highest severe risk may center up over the adjoining border areas of NE/IA/MO/KS with the highest risk along the KS/MO border as a guess.
The lead shortwave as forecast by today's 18Z GFS 500mb vorticity (below) providing good mid level forcing and 70 knots of SW flow. Valid at 1PM CDT shown below.
Combine this with a sub-1000mb surface low over Nebraska and at least a short-term oppotunity for a strong, southerly low-level jet. Short-term-possibly because the LLJ may start to veer a bit as the lead-shortwave exits to the NE. If instability can creep a bit farther north than forecast, northern MO and IA might see the full benefit of this set-up. Probably will not be much issue with a cap either so things may get started early.
Side-by-side Surface-Based CAPE comparison GFS (left), NAM (right). Both valid 1PM CDT Friday.
HPC Surface Forecast-Valid 1PM CDT, Thursday
Elevated storms that form or move north of the warm front boundary will pose a large hail risk. Capping may still be an issue farther south over parts of southern OK and into TX as well as a slightly weaker wind shear more parallel to the dryline/front. Still a large hail threat all along the dryline.
700mb temps-Thursday's 18Z GFS valid 1PM CDT
Thursday afternoon's Day 2. Slight risk.
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT THU APR 12 2012
VALID 131200Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM FAR NWRN TX INTO THE MID
MO RIVER VALLEY...
A MEAN TROUGH WILL EXIST OVER THE WRN U.S. WITH A LEAD SHORTWAVE
EJECTING NEWD ACROSS THE NRN PLAINS AND INTO THE UPPER MS VALLEY
DURING THE DAY. THIS WILL LEAD TO BRIEFLY RISING HEIGHTS ALOFT OVER
THE CNTRL AND SRN PLAINS DURING THE DAY...IN ADVANCE OF THE MAIN
TROUGH WHICH WILL EMERGE INTO OK AND NM BY SAT MORNING.
AT THE SURFACE...A LOW WILL MOVE FROM CNTRL SD AT 12Z NWD ACROSS ND
WITH THE EJECTING WAVE...WITH FRONT TRAILING SWD FROM ERN NEB INTO
NRN KS AND DRY AIR BEHIND. THIS BOUNDARY WILL WASH OUT OVER CNTRL
KS...MERGING WITH A DRYLINE THAT WILL EXTEND SWWD INTO NWRN TX BY
A VERY UNSTABLE AIR MASS WILL EXIST S AND E OF THESE BOUNDARIES WITH
DAYTIME HEATING AND DEWPOINTS MAINLY IN THE 60-64 F RANGE.
OVERNIGHT...THE INFLUENCE OF THE UPPER TROUGH WILL BEGIN TO AFFECT
PORTIONS OF THE CNTRL PLAINS...WITH DEEPENING LOW PRESSURE OVER
CNTRL NEB AND KS...AND AN INCREASING SWLY LOW LEVEL JET.
...NW TX AND WRN OK INTO SRN KS...
A LARGE AREA OF LOW LEVEL WARM ADVECTION WILL EXTEND FROM MN INTO
ERN OK AND NRN AR FRI MORNING IN ASSOCIATION WITH THE NRN PLAINS
TROUGH. THIS DEEP ZONE OF FORCING WILL BE ACCOMPANIED BY RAIN AND
EMBEDDED THUNDERSTORMS. SOME OF THESE STORMS MAY BE CAPABLE OF
HAIL...ALTHOUGH MUCH OF IT SHOULD BE NON-SEVERE.
LATER IN THE DAY...THE THREAT FOR DIURNAL ACTIVITY ALONG THE DRYLINE
IS UNCLEAR. WITH SELY FLOW RETURNING ACROSS THE WARM SECTOR...AND
NEUTRAL FORCING ALOFT...LOW LEVEL CONVERGENCE WILL BE SUBTLE. AS
SUCH...MUCH OF THE WARM SECTOR IS EXPECTED TO HAVE A WEAK CAPPING
INVERSION DUE TO RELATIVELY COOL BOUNDARY LAYER TEMPERATURES AWAY
FROM THE DRYLINE ITSELF. EARLY ACTIVITY OVER ERN OK INTO SWRN MO MAY
LEAVE RESIDUAL BOUNDARIES THAT COULD ACT AS A FOCUS FOR DAYTIME
ACTIVITY. IF THIS OCCURS...THERE WOULD BE A THREAT OF ISOLATED
SUPERCELLS THERE WITH HAIL AND A TORNADO OR TWO.
ALONG THE DRYLINE...HEATING WILL ERODE CIN COMPLETELY...AND AT LEAST
ISOLATED STORMS ARE LIKELY AS A RESULT. WITH PLENTY OF INSTABILITY
AND A FAVORABLE HODOGRAPH...SUPERCELLS WOULD BE THE STORM MODE WITH
VERY LARGE HAIL AND A FEW TORNADOES PERSISTING FROM LATE AFTERNOON
INTO THE EARLY EVENING.
...NERN KS...SERN NEB...NWRN MO LATE EVENING AND OVERNIGHT...
WITH INCREASING SLY LOW LEVEL FLOW OVERNIGHT...MOISTURE AND
INSTABILITY SHOULD RETURN RAPIDLY NWD ACROSS KS AND INTO NEB BY SAT
MORNING. SOME MODELS INDICATE THAT CONVECTIVE INHIBITION MAY REMAIN
LIMITED OVER ERN KS...SERN NEB...NWRN MO AND SWRN IA. THUS...FORCING
FROM WARM ADVECTION SHOULD BE SUFFICIENT TO INITIATE NOCTURNAL
STORMS CAPABLE MAINLY OF LARGE HAIL. CONDITIONALLY...HAIL COULD BE
VERY LARGE WITH AMPLE SHEAR AND COOL PROFILES ALOFT.