DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 181941
SWODY1
SPC AC 181938

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0238 PM CDT SAT MAY 18 2013

VALID 182000Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS FROM NWRN OK INTO SWRN NEB...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
WEST TX INTO SERN ND/WRN MN...

EARLIER THOUGHTS REGARDING CONVECTIVE EVOLUTION REMAIN. AS A
RESULT...ONLY MINOR MODIFICATIONS HAVE BEEN MADE TO 1630Z SEVERE
THREAT ALONG THE DRYLINE.

STRONG HEATING ACROSS THE HIGH PLAINS FROM THE TX PANHANDLE INTO
SWRN KS HAVE FORCED SFC TEMPERATURES TO NEAR/ABOVE 100F. AS A
RESULT...CAP HAS BEEN REMOVED AND BOUNDARY LAYER CU ARE DEEPENING
MARKEDLY ALONG LEADING EDGE OF STEEP LAPSE RATE PLUME ACROSS SWRN
KS. IT APPEARS TSTMS WILL EVOLVE OVER THE NEXT FEW HOURS ACROSS
THIS REGION.

HAVE OPTED TO EXTEND THE MDT RISK A BIT NORTH ACROSS NEB TO ACCOUNT
FOR SCT-NUMEROUS TSTMS THAT SHOULD EVOLVE ALONG WRN FRINGE OF HIGHER
MOISTURE/INSTABILITY. WEAK CONVERGENCE AXIS EXTENDS FROM JUST EAST
OF GLD INTO CHERRY COUNTY NEB AND THIS SHOULD FOCUS SEVERE TSTMS BY
MID-LATE AFTERNOON.

HAVE MADE A SWD ADJUSTMENT TO CATEGORICAL SLGT RISK ALONG THE
DRYLINE OVER SWRN TX TO ACCOUNT FOR EXPECTED SEVERE DEVELOPMENT AT
THIS LATITUDE. ALTHOUGH ACTIVITY SHOULD BE ISOLATED...IT APPEARS
SUFFICIENT FLOW ALOFT WILL SUPPORT DEEP ROTATING UPDRAFTS.

..DARROW.. 05/18/2013

.PREV DISCUSSION... /ISSUED 1127 AM CDT SAT MAY 18 2013/

...SYNOPSIS...
IN ADVANCE OF THE UPPER TROUGH OVER THE INTERMOUNTAIN WEST...WARM
ELEVATED MIXED LAYER AIR HAS OVERSPREAD MOST OF THE PLAINS AND LOWER
MISSISSIPPI VALLEY. THIS IS WHERE THE BOUNDARY LAYER CONTINUES TO
MOISTEN DUE TO BOTH EVAPOTRANSPIRATION AND A RETURN FLOW OF MOISTURE
OFF GULF OF MEXICO. VEERED LOW-LEVEL FLOW /AT 850 MB/ TO A
SUBSTANTIAL WESTERLY COMPONENT APPEARS TO BE CUTTING OFF THE GULF
RETURN FLOW TO THE CENTRAL/NORTHERN PLAINS...THOUGH...AT LEAST
TEMPORARILY. BUT THIS MAY BEGIN TO CHANGE BY THIS EVENING...AS
LOW-LEVEL FLOW BACKS TO A MORE PROMINENT SOUTHERLY COMPONENT...AND
STRENGTHENS...IN ASSOCIATION WITH DEEPENING AND CONSOLIDATION OF A
SURFACE LOW OVER THE CENTRAL PLAINS...AS MID-LEVEL HEIGHT FALLS
INCREASE TO THE EAST OF THE ROCKIES.

MODEST STRENGTHENING OF CYCLONIC MID/UPPER FLOW IS EXPECTED ACROSS
THE PLAINS TODAY...AS SEVERAL SMALLER SCALE IMPULSES BEGIN TO EMERGE
FROM THE INTERMOUNTAIN WEST. STRONGEST FLOW ALOFT...HOWEVER...WILL
PERSIST IN A BELT ACROSS THE NORTH CENTRAL PACIFIC COAST INTO THE
SOUTHERN ROCKIES...BUT COULD BEGIN TO NOSE EASTWARD ACROSS THE TEXAS
PANHANDLE REGION TOWARD THE END OF THE FORECAST PERIOD.
STILL...GIVEN THE THERMODYNAMIC PROFILES EVOLVING ACROSS MUCH OF THE
PLAINS...WHICH WILL INCLUDE AREAS OF STRONG TO EXTREME CAPE...A RISK
FOR SEVERE THUNDERSTORMS WILL EXIST ACROSS A FAIRLY BROAD AREA.
ORGANIZED CLUSTERS OF STORMS APPEAR POSSIBLE...IN ADDITION TO THE
RISK FOR DISCRETE SUPERCELLS ...THE STRONGEST OF WHICH MAY BECOME
CAPABLE OF PRODUCING VERY LARGE HAIL AND A COUPLE OF TORNADOES.

ALTHOUGH SEVERE PROBABILITIES STILL SEEM A BIT LOWER THAN THE
PLAINS...OTHER STRONG/ISOLATED SEVERE STORM DEVELOPMENT MAY ALSO
OCCUR TODAY EAST OF THE LOWER MISSISSIPPI VALLEY INTO PARTS OF THE
EASTERN GULF STATES. THIS IS WHERE LOWER/MID TROPOSPHERIC WARM
ADVECTION ON THE EASTWARD ADVANCING EDGE OF WARMER ELEVATED MIXED
LAYER AIR...IN THE WAKE OF A WEAKENING UPPER IMPULSE ADVANCING
TOWARD THE SOUTH ATLANTIC COAST...MAY CONTRIBUTE TO INCREASING LIFT
AND STEEPENING MID-LEVEL LAPSE RATES.

...CENTRAL PLAINS...
AN INITIAL IMPULSE...NOW LIFTING NORTHEAST OF THE PANHANDLE REGION
INTO THE CENTRAL PLAINS...IS CONTRIBUTING TO SOME UNCERTAINTY
CONCERNING DRYLINE POSITION AND CONVECTIVE POTENTIAL LATER THIS
AFTERNOON...MAINLY SOUTH OF THE KANSAS/OKLAHOMA BORDER.
HOWEVER...THE DRYLINE IS STILL EXPECTED TO BE THE MAIN FOCUS FOR
STRONGEST DESTABILIZATION AND STORM DEVELOPMENT LATER THIS
AFTERNOON. AIDED BY FORCING ASSOCIATED WITH CONTINUING MID-LEVEL
HEIGHT FALLS...SUBSTANTIAL MID-LEVEL INHIBITION IS EXPECTED TO
WEAKEN SUFFICIENTLY FOR THE INITIATION OF DISCRETE SUPERCELLS ACROSS
SOUTHWESTERN NEBRASKA INTO WESTERN KANSAS DURING THE 21-00Z TIME
FRAME...PERHAPS SOUTHWARD ACROSS WESTERN OKLAHOMA INTO NORTHWEST
TEXAS AS WELL.

VERY LARGE HAIL MAY BE THE PRIMARY SEVERE THREAT...INITIALLY... BUT
LOW-LEVEL LAPSE RATES PROBABLY WILL BE SUFFICIENTLY STEEP TO SUPPORT
A RISK FOR TORNADOES BENEATH INCREASINGLY CYCLONIC AND DIFLUENT
HIGH-LEVEL FLOW. AS THE 850 MB JET BECOMES MORE SOUTHERLY AND
STRENGTHENS TO 40-50+ KT LATER THIS EVENING...A WINDOW OF
OPPORTUNITY WILL EXIST FOR INCREASING TORNADIC POTENTIAL...INCLUDING
THE RISK FOR ONE OR TWO STRONG TORNADOES. THIS POTENTIAL APPEARS TO
HINGE LARGELY ON HOW LONG IT TAKES FOR CONVECTION TO GROW UPSCALE
INTO ORGANIZING MESOSCALE CONVECTIVE SYSTEMS...WITH DAMAGING
STRAIGHT LINE WINDS BECOMING A MORE PROMINENT THREAT. THIS REMAINS
UNCERTAIN...BUT IT APPEARS THAT UPSCALE GROWTH COULD OCCUR FAIRLY
QUICKLY.

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