955  
ACUS01 KWNS 220548  
SWODY1  
SPC AC 220547  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1247 AM CDT TUE MAY 22 2018  
 
VALID 221200Z - 231200Z  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE  
MID-ATLANTIC STATES AND OHIO VALLEY...SOUTHERN HIGH PLAINS...PARTS  
OF THE CENTRAL ROCKIES AND EAST INTO SOUTH DAKOTA...  
   
..SUMMARY
 
 
ISOLATED STRONG TO SEVERE THUNDERSTORMS ARE FORECAST THIS AFTERNOON  
AND EVENING ACROSS PORTIONS OF THE HIGH PLAINS FROM WEST TEXAS INTO  
SOUTHEAST MONTANA. SEVERAL STRONG TO LOCALLY SEVERE THUNDERSTORMS  
MAY ALSO DEVELOP IN THE MID-ATLANTIC STATES AND OHIO VALLEY.  
   
..SYNOPSIS
 
 
A MID- TO UPPER-LEVEL TROUGH OVER THE INTERIOR WEST WILL VERY SLOWLY  
MOVE EAST FROM NV TO UT WHILE A RIDGE SLIDES EASTWARD INTO THE UPPER  
MIDWEST FROM THE GREAT PLAINS. IN THE LOW LEVELS, SURFACE LOW  
PRESSURE WILL ENCOMPASS THE CENTRAL ROCKIES/HIGH PLAINS WITH A WARM  
FRONT ARCING EAST INTO SD AND THE MIDDLE MO VALLEY. FARTHER EAST, A  
BELT OF MODERATE WESTERLY MID-LEVEL FLOW WILL OVERSPREAD THE OH  
VALLEY AND NORTHERN MID-ATLANTIC STATES. A COLD FRONT WILL MOVE  
SOUTHEAST ACROSS THE OH VALLEY WITH A WEDGE FRONT DRAPED FROM  
WESTERN NY SOUTHEAST THROUGH EASTERN PA.  
   
..MID-ATLANTIC STATES/OH VALLEY
 
 
A RELATIVELY WEAK MID-LEVEL LAPSE RATE REGIME WILL DESTABILIZE  
DURING THE DAY AS CLOUD DEBRIS DISSIPATES AND STRONG HEATING OCCURS,  
ESPECIALLY ACROSS THE EASTERN SLOPES OF THE CENTRAL APPALACHIANS AND  
LOWER ELEVATIONS TO THE EAST. MODELS SUGGEST TWO CORRIDORS OF  
CONVECTIVE ACTIVITY LATER THIS AFTERNOON.  
1) THUNDERSTORMS DEVELOPING OVER THE HIGHER TERRAIN IN WESTERN  
VA/EASTERN WV AND MOVING EAST TOWARDS THE I-95 CORRIDOR BY LATE  
AFTERNOON/EARLY EVENING. THE STEEPENING OF 0-2 KM LAPSE RATES DUE  
TO HEATING AND 60S DEGREE F DEWPOINTS WILL YIELD MODERATE BUOYANCY  
(1000-1500 J/KG MLCAPE). THE GREATEST STORM ORGANIZATION POTENTIAL  
WILL LIKELY FOCUS OVER NORTHERN VA/MD WHERE 25-30 KT EFFECTIVE SHEAR  
WILL AID IN COLD POOL ORGANIZATION IN 1 OR MORE SMALLER THUNDERSTORM  
BANDS. LOCALIZED STRONG GUSTS (45-55 MPH) MAY RESULT IN WIND DAMAGE  
AND A POCKET OR TWO OF SLIGHTLY STRONGER GUSTS CANNOT BE RULED OUT.  
2) IN THE OH VICINITY, LOW-LEVEL CONVERGENCE WILL INCREASE AS A  
COLD FRONT ACCELERATES SOUTHEAST DURING THE DAY. ISOLATED TO  
SCATTERED THUNDERSTORMS WILL LIKELY DEVELOP BY EARLY-MID AFTERNOON.  
FORECAST SOUNDINGS SHOW MODERATE DESTABILIZATION AND AROUND 30-40 KT  
DEEP-LAYER SHEAR. ISOLATED BOUTS OF HAIL/WIND MAY OCCUR WITH THE  
MORE INTENSE THUNDERSTORMS BEFORE WEAKENING DURING THE EVENING.  
   
..HIGH PLAINS
 
 
MODEST LOW-LEVEL MOISTURE ADVECTION IS ANTICIPATED ACROSS THE PLAINS  
AND HIGH PLAINS ON TUESDAY AS LEE TROUGHING SUPPORTS A TIGHTENING  
SURFACE PRESSURE GRADIENT AND SOUTHERLY 850MB FLOW PERSISTS.  
HOWEVER, DESPITE THIS FAVORABLE RETURN FLOW, STRONG BOUNDARY-LAYER  
MIXING IS ANTICIPATED, LIKELY RESULTING IN UPPER 40S-LOW 50S  
DEWPOINTS DURING THE AFTERNOON. STEEP MID-LEVEL LAPSE RATES ATOP  
THIS MODEST MOISTURE WILL MODERATE INSTABILITY WITH MLCAPE EXPECTED  
TO BE AROUND 1500-2000 J/KG ACROSS PORTIONS OF THE SOUTHERN AND  
NORTH-CENTRAL HIGH PLAINS. MODELS IMPLY SEVERAL STRONG UPDRAFTS  
CAPABLE OF HAIL AND DAMAGING WIND GUSTS ARE POSSIBLE.  
 
...MIDDLE MO VALLEY LATE TUESDAY NIGHT INTO EARLY WEDNESDAY  
MORNING...  
A STRENGTHENING LOW-LEVEL JET WILL CONTRIBUTE TO INCREASING  
ISENTROPIC ASCENT ACROSS THE WARM FRONTAL ZONE STRETCHING FROM THE  
LOW NEAR THE NE/WY/SD BORDER INTERSECTION EASTWARD INTO WESTERN IA.  
MODEST ELEVATED INSTABILITY AND VERTICAL SHEAR WILL SUPPORT A FEW  
STORMS CAPABLE OF LARGE HAIL.  
 
..SMITH/COOK.. 05/22/2018  
 

 
 
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