378  
FXUS61 KPBZ 220101  
AFDPBZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PITTSBURGH PA  
901 PM EDT MON AUG 21 2017  
   
SYNOPSIS
 
 
QUIESCENT CONDITIONS WILL CONTINUE THROUGH TUESDAY MORNING.  
WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED ON TUESDAY AS  
A COLD FRONT CROSSES THE REGION.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
A RATHER PERVASIVE CIRRUS SHIELD HAS ADVANCED EASTWARD OVER  
MUCH OF THE CWA THROUGH THE EVENING HOURS. FURTHER, THE EARLIER  
DIFFUSE DEWPOINT GRADIENT HAS REALLY BECOME A NON-FACTOR. THUS,  
WITH NIGHTTIME STABILIZATION OCCURRING, A LACK OF A  
FOCUSING/LIFTING MECHANISM, AND CONVECTIVE BLOW OFF  
OVERSPREADING THE AREA, FURTHER CONVECTION DEVELOPMENT IS  
UNLIKELY. POPS HAVE BEEN LIMITED TO THE NORTH OF I-80 REALM FOR  
THE NEXT FEW HOURS BEFORE THE BULK OF THE OVERNIGHT HOURS BECOME  
DRY.  
 
AS CONVECTIVE BLOW OFF SEEMS POISED TO REMAIN OVER THE AREA FOR  
MUCH OF THE NIGHT, LOWS WILL HAVE DIFFICULTY DROPPING ALL THAT  
FAR FROM THE CURRENT READINGS. THUS, AN ABOVE NORMAL NIGHT LOOKS  
TO BE IN STORE WITH SOUPY CONDITIONS. FRIES  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/
 
 
A STRONG UPPER LOW WILL DIG INTO THE GREAT LAKES ON TUE AND  
ACQUIRE A NEUTRAL TO NEGATIVE TILT THROUGH THE DAY IN CONCERT  
WITH THE MOVEMENT OF A MID-LEVEL JET MAXIMUM. THE SYSTEM'S  
ASSOCIATED COLD FRONT WILL APPROACH THE OHIO VALLEY DURING THE  
EARLY EVENING, BUT A PREFRONTAL TROUGH IS EXPECTED TO BE THE  
FOCUS FOR DAYTIME CONVECTION IN THE AREA.  
 
ABUNDANT LOW-LEVEL MOISTURE, STEEPENING LAPSE RATES AND STRONG  
EFFECTIVE BULK SHEAR WILL SUPPORT THE DEVELOPMENT OF STRONG TO  
SEVERE THUNDERSTORMS BY EARLY AFTERNOON ALONG THE SHARPENING SFC  
TROUGH. CAPE ON THE ORDER OF 2000 J/KG AND EFFECTIVE SHEAR OF  
40-50KT WILL PROMOTE ORGANIZED, SEVERE CONVECTION.  
 
GIVEN THE DEEP-LAYER SHEAR ORIENTATION ROUGHLY PARALLEL TO THE  
SFC FEATURE, STORMS SHOULD CONGEAL QUICKLY INTO AN INTENSE  
CONVECTIVE LINE THAT WILL MOVE SEWD INTO THE INSTABILITY AXIS.  
DAMAGING WIND GUSTS WILL BE THE PRIMARY THREAT, BUT HAIL ALSO IS  
POSSIBLE IN MORE INTENSE, CELLULAR UPDRAFTS AHEAD OF THE LINE.  
 
STORMS WILL EXIT SEWD BY EARLY EVENING WITH RAIN LINGERING INTO  
THE EVENING BEHIND THE STORMS AS THE COLD FRONT TRAVERSES THE  
REGION. HIGH PRESSURE WILL BUILD IN ON WED/WED EVE, WITH LITTLE  
CHANCE OF RAIN AS DRY AIR INVADES.  
 

 
   
LONG TERM /THURSDAY THROUGH MONDAY/
 
 
ALTHOUGH ENSEMBLES STILL SHOW SPREAD IN THEIR UPPER PATTERN  
SOLUTIONS, IT APPEARS THAT BROAD SURFACE HIGH PRESSURE UNDER AN  
ERN-CONUS TROUGH/MIDWESTERN RIDGE PATTERN IS PROGGED TO SUPPORT  
A GENERALLY-DRY AIR MASS THROUGH THE PERIOD. DAILY TEMPERATURES  
BELOW CLIMATOLOGICAL AVERAGE CAN BE EXPECTED THROUGH EARLY NEXT  
WEEK.  
 

 
   
AVIATION /01Z TUESDAY THROUGH SATURDAY/
 
 
A FEW SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH  
01Z OR SO NEAR/NORTH OF I-80, AND HAVE INCLUDED VCTS AT FKL/DUJ  
AS A RESULT. AFTER THESE DISSIPATE WITH THE LOSS OF DAYTIME  
HEATING, MAINLY HIGH CLOUDS ARE EXPECTED OVERNIGHT. FOG DOES NOT  
APPEAR TO BE MUCH OF A THREAT GIVEN THE WARM OVERNIGHT  
TEMPERATURES WHICH WILL NOT ALLOW CROSSOVER VALUES TO BE  
REACHED.  
 
AS A COLD FRONT APPROACHES ON TUESDAY, SHOWERS AND THUNDERSTORMS  
WILL BECOME MORE NUMEROUS FROM LATE MORNING ON. HINTED AT FLIGHT  
CONDITION DETERIORATION WITH VCTS AND A DROP TO MVFR  
VISIBILITIES AT SEVERAL TERMINALS DURING THE AFTERNOON. IFR  
CONDITIONS ARE CERTAINLY POSSIBLE, AS ARE STRONG WIND GUSTS, BUT  
TIMING WILL NEED TO BE REFINED. EXPECT PREVAILING WINDS OUTSIDE  
OF CONVECTION TO INCREASE TO GUST TO BETWEEN 15 AND 25 KNOTS  
OUT OF THE SOUTHWEST DURING THE AFTERNOON.  
   
OUTLOOK
 
 
WITH PASSAGE OF AN EARLY WED COLD FRONT, GENERAL VFR CAN BE  
EXPECTED FOR THE REMAINDER OF THE WEEK.  
 

 
   
PBZ WATCHES/WARNINGS/ADVISORIES
 
 
MD...NONE.  
OH...NONE.  
PA...NONE.  
WV...NONE.  
 

 
 

 
 
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