SWODY1
SPC AC 261958
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT SUN JUN 26 2011
VALID 262000Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN PLAINS REGION SEWD
INTO THE SOUTHEAST CONUS...
...NRN PLAINS/MID MO VALLEY REGION AND VICINITY...
SCENARIO REMAINS HIGHLY UNCERTAIN ATTM ACROSS THE REGION...WITH MOST
SUBSTANTIAL CONVECTION REMAINING FOCUSED OVER N CENTRAL NEB WHERE A
COUPLE OF HP-TYPE SUPERCELL STORMS HAVE CONTINUED TO EVOLVE. THIS
REGION REMAINS N OF THE NRN KS WARM FRONT...WITH LOW CLOUDS
WIDESPREAD ACROSS NEB BENEATH SUBSTANTIAL CAP -- WHICH REMAINED
QUITE STOUT AND EVEN INCREASED PER AREA 18Z RAOBS. THE CAPPING IS A
CONCERN...AS MODELS -- AND THE GOING SPC FORECAST -- INDICATING
WIDESPREAD/SIGNIFICANT SEVERE POTENTIAL WITHIN THIS STILL-STABLE
LOW-LEVEL ENVIRONMENT.
GIVEN THESE ISSUES AND ASSOCIATED UNCERTAINTY...AND OVERALL
EXPECTATION OF A SOMEWHAT LESS SIGNIFICANT TORNADO THREAT THAN
EARLIER FORECAST...WILL REMOVE MODERATE RISK FORECAST ATTM. MOST
LIKELY SCENARIO ATTM APPEARS TO BE THAT STORMS OVER N CENTRAL NEB
EVENTUALLY EVOLVE INTO A MORE LINEAR/BOWING MCS...WHICH SHOULD
ATTEMPT TO MOVE SEWD INTO THE MORE CAPPED AIRMASS. THUS...THOUGH
UNCERTAIN -- WILL MAINTAIN HIGHER PROBABILITY SEVERE FORECAST -- TO
INCLUDE POTENTIAL FOR DAMAGING WINDS...LARGE HAIL...AND A FEW
TORNADOES -- FROM ERN SD/N CENTRAL NEB SEWD ACROSS THE MID MO VALLEY
REGION.
...MO INTO THE MID SOUTH/SOUTHEAST...
CLUSTER OF STORMS CONTINUES MOVING ACROSS MIDDLE TN/NRN AL...WITH
STORMS ALSO INCREASING ON THE PERIPHERY OF THIS CLUSTER.
WELL-ORGANIZED CIRCULATION EXISTS WITH THIS MCS...ALONG WITH A VERY
UNSTABLE AIRMASS NEAR AND S OF THE STORMS INTO MS/AL.
THEREFORE...WILL MAINTAIN SLIGHT RISK INTO THE CENTRAL GULF COAST
REGION AHEAD OF THIS CLUSTER.
FARTHER W/NW...STORMS ARE DEVELOPING IN A VERY UNSTABLE AIRMASS
ACROSS SERN MO...WHERE FAVORABLY-VEERING FLOW WITH HEIGHT IS ALSO
INDICATED. WITH AN INCREASE IN CONVECTIVE COVERAGE AN INTENSITY
EXPECTED...HAVE EXPANDED MORE SUBSTANTIAL SEVERE WEATHER PROBABILITY
INTO THIS REGION FOR THIS AFTERNOON/EARLY EVENING.
..GOSS.. 06/26/2011
.PREV DISCUSSION... /ISSUED 1125 AM CDT SUN JUN 26 2011/
...NRN/CNTRL PLAINS INTO UPPER MS VALLEY...
VORTICITY MAXIMUM AND ASSOCIATED 40-50 KT+ MIDLEVEL JET STREAK OVER
THE NRN INTERMOUNTAIN REGION WILL TRANSLATE EWD INTO THE DAKOTAS BY
27/12Z...RESULTING IN A CORRIDOR OF 30M/12-HR HEIGHT FALLS AT 500 MB
OVERSPREADING REGION DURING THE LATTER HALF OF THE PERIOD. IN THE
LOW LEVELS...COLD FRONT FROM CNTRL ND TO LOW PRESSURE AREA OVER NWRN
NEB WILL PROGRESS SEWD THROUGH THE DAKOTAS AND MOST OF NEB BY THE
END OF THE D1 PERIOD. AT THE SAME TIME...WARM FRONT ANALYZED FROM
THERMAL LOW OVER SWRN KS NEWD THROUGH E-CNTRL KS AND CNTRL MO WILL
LIFT NWD TOWARD THE MID MO VALLEY WITH THE HIGHEST CONCENTRATION OF
SEVERE WEATHER EXPECTED LATER TODAY INTO TONIGHT TO THE N OF THIS
BOUNDARY...AND S/SE OF ADVANCING COLD FRONT.
TSTMS ARE ONGOING ACROSS PORTIONS OF THE DAKOTAS INTO NWRN NEB ALONG
THE NRN EDGE OF THE STRONGER CAPPING AND IN ADVANCE OF LEAD
SHORTWAVE TROUGH LIFTING NEWD THROUGH ERN PARTS OF MT/WY. FORCING
FOR ASCENT ATTENDANT TO THIS IMPULSE SHOULD SUSTAIN TSTM ACTIVITY
TODAY INVOF THE COLD FRONT OVER THE DAKOTAS INTO NWRN/N-CNTRL NEB
WHERE THE CAP IS WEAKER. CURRENT VISIBLE SATELLITE SUGGESTS THAT
POCKETS OF STRONGER DIABATIC HEATING WILL OCCUR ACROSS N-CNTRL NEB
INTO SRN SD WHERE MLCAPE VALUES WILL INCREASE TO 1500-2500 J/KG.
CURRENT OBSERVATIONAL DATA AND MODEL FORECASTS INDICATE LOW-LEVEL
ELY/SELY FLOW WILL BE MAINTAINED BENEATH 40-50 KT WINDS IN THE
MIDLEVELS RESULTING IN PRONOUNCED VEERING WITH HEIGHT AND MORE THAN
SUFFICIENT VERTICAL SHEAR FOR ORGANIZED STORM STRUCTURES.
THE PRIMARY UNCERTAINTY LIES IN THE DOMINANT CONVECTIVE MODE /AND
ATTENDANT SEVERE WEATHER HAZARDS/ OWING TO THE EARLY STORM FORMATION
AND POTENTIAL FOR MORE WIDESPREAD COLD POOL DEVELOPMENT. GIVEN THE
CO-LOCATION OF RICH BOUNDARY LAYER MOISTURE...STEEP MIDLEVEL LAPSE
RATES AND RELATIVELY STRONG VERTICAL SHEAR...THE POTENTIAL WILL
EXIST FOR SUPERCELLS AND BOWING STRUCTURES CAPABLE OF
TORNADOES...DAMAGING WINDS AND HAIL. FOR ADDITIONAL NEAR-TERM
GUIDANCE ON THIS AREA SEE MCD 1398.
FARTHER E/SE ACROSS THE MODERATE RISK AREA...SCENARIO IS COMPLICATED
BY A POTENTIALLY STRENGTHENING CAP TODAY AND LINGERING CLOUDS N OF
WARM FRONT LIFTING NWD THROUGH KS/MO. IT DOES APPEAR THAT EVOLVING
TSTM REGIME MENTIONED ABOVE WILL BEGIN TO IMPACT PORTIONS OF THE MID
MO VALLEY AREA LATER THIS AFTERNOON BEFORE PROGRESSIVELY
OVERSPREADING REGION TONIGHT. ADDITIONAL IN SITU STORM DEVELOPMENT
WILL BE POSSIBLE ALONG THE WARM FRONT LIFTING NWD WHERE LOCAL
ENVIRONMENT WILL BE QUITE FAVORABLE FOR TORNADIC SUPERCELLS GIVEN
MLCAPE OF 2500-4000 J/KG...EFFECTIVE SRH OF 200-400 M2/S2 AND
EFFECTIVE BULK SHEAR OF 45-60+ KT. THOUGH CONDITIONAL ON STORM
FORMATION/SUSTENANCE...SETUP WILL BE QUITE SUPPORTIVE OF INTENSE
SUPERCELLS CAPABLE OF TORNADOES /SOME STRONG/...VERY LARGE HAIL AND
DAMAGING WINDS.
...LOWER MO VALLEY/OZARKS INTO MID SOUTH...
A CLUSTER OF ELEVATED TSTMS HAS DEVELOPED THIS MORNING ACROSS SERN
KS INTO SWRN MO WITHIN A ZONE OF LOW-LEVEL WAA/ISENTROPIC ASCENT
ALONG THE ERN EDGE OF THE STRONGER CAP /REF. 12Z LMN SOUNDING/.
GIVEN THE LARGE-SCALE AIRFLOW REGIME FORECAST...THE CAP SHOULD
CONTINUE TO STRENGTHEN FROM W-E ACROSS REGION TODAY. AS
SUCH...SEVERE WEATHER POTENTIAL REMAINS SOMEWHAT UNCERTAIN.
HOWEVER...SHOULD ONGOING STORMS PERSIST...THEY WILL BE CAPABLE OF
HAIL AND DAMAGING WINDS AS THEY MOVE/DEVELOP EWD INTO THE OZARKS.
...GULF COAST STATES/SRN APPALACHIANS...
RESIDUAL OUTFLOW BOUNDARY ARCING FROM WRN NC INTO NRN PARTS OF AL/GA
AS OF LATE MORNING IS EXPECTED TO SERVE AS THE FOCUS FOR STORM
REGENERATION AND/OR RE-INTENSIFICATION OF LINGERING NOCTURNAL TSTM
ACTIVITY. 12Z REGIONAL SOUNDINGS SHOW THAT INFLOW AIR MASS IS
CHARACTERIZED BY STEEP MIDLEVEL LAPSE RATES OF AROUND 7.5 C/KM AND A
MOIST BOUNDARY LAYER...RESULTING IN AN ALREADY MODERATELY TO
STRONGLY UNSTABLE ENVIRONMENT. INCREASED DIABATIC WARMING SHOULD
ACT TO FURTHER DESTABILIZE BOUNDARY LAYER WITH MLCAPE VALUES
APPROACHING 3000-3500 J/KG. THOUGH REGION WILL REMAIN DISPLACED
FROM STRONGER MID TO UPPER-LEVEL WIND FIELD...THE THERMODYNAMIC
ENVIRONMENT WILL BE QUITE CONDUCIVE FOR UPSCALE GROWTH OF STORMS
INTO ONE OR MULTIPLE FORWARD-PROPAGATING CONVECTIVE SYSTEMS WITH
ATTENDANT RISKS OF DAMAGING WINDS AND HAIL.
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