May 18, 2013 1630 UTC Day 1 Convective Outlook
Updated: Sat May 18 16:30:37 UTC 2013
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20130518 1630 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20130518 1630 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
20130518 1630 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
20130518 1630 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MODERATE 55,416 444,330 North Platte, NE...Hays, KS...Woodward, OK...Lexington, NE...Pratt, KS...
SLIGHT 300,690 7,978,461 Oklahoma City, OK...Omaha, NE...Wichita, KS...Lincoln, NE...Sioux Falls, SD...
   SPC AC 181627
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1127 AM CDT SAT MAY 18 2013
   
   VALID 181630Z - 191200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS
   PARTS OF SOUTHWEST AND SOUTH CENTRAL NEBRASKA...WESTERN AND CENTRAL
   KANSAS...AND PARTS OF WESTERN OKLAHOMA...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK
   AREA ACROSS MUCH OF THE PLAINS...
   
   ...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.
   
   ..KERR/DEAN.. 05/18/2013
   
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