821  
FXUS61 KPBZ 241155  
AFDPBZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PITTSBURGH PA  
755 AM EDT MON SEP 24 2018  
   
SYNOPSIS
 
 
PERIODIC SHOWERS AND THUNDERSTORMS ARE EXPECTED WITH A SERIES  
OF CROSSING DISTURBANCES THROUGH MID WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
CLOUDS SHOULD CONTINUE TO INCREASE AHEAD OF A SERIES OF  
SHORTWAVE TROUGHS EMBEDDED IN SOUTHWEST FLOW. AT THE SURFACE,  
WARM, MOIST AIR CONTINUES TO ADVECT NORTHWARD AND ABOVE A  
DIFFUSE WARM FRONTAL BOUNDARY SOMEWHERE NEAR THE VICINITY OF THE  
MASON-DIXON LINE.  
 
BY MID-AFTERNOON, RAIN WILL BEGIN TO OVERSPREAD THE REGION  
SOUTH-TO-NORTH AS THE FIRST OF SEVERAL SHORTWAVES EMBEDDED IN  
SOUTHWEST FLOW MOVE THROUGH. FORCING FROM THE DPVA OF EACH  
SHORTWAVE WILL BE MAXIMIZED IN THE VICINITY OF THE OHIO RIVER ON  
THE WV/OH BORDER. OPERATIONAL AND ENSEMBLE CONSENSUS DEPICTS,  
THROUGH 12Z TUESDAY, A CORRIDOR OF 1-2" ALONG THE WV PORTION OF  
THE OHIO TO AROUND 1 INCH IN PITTSBURGH AND LESSER NORTHEAST.  
 
WHILE THAT IS A "DECENT" AMOUNT OF RAINFALL ON TOP OF AN  
ALREADY-WET SEPTEMBER, FLOOD GUIDANCE IS IN REASONABLE GOOD  
SHAPE FROM THE COUPLE OF RECENT DRY DAYS. FLOODING IS STILL  
POSSIBLE, BUT GIVEN THE ISOLATED NATURE OF WHICH IT WOULD  
HAPPEN, HAVE NOT ISSUED A FLOOD WATCH.  
 

 
   
SHORT TERM /TUESDAY THROUGH WEDNESDAY/
 
 
PRECIPITATION WILL LIKELY STILL BE ONGOING OVER THE AREA  
TUESDAY MORNING, BUT WILL LIKELY COME TO AN END AS DNVA AND  
COMPARATIVELY DRY MID-LEVEL AIR FOLLOWS THE LAST OF THE SERIES  
OF SHORTWAVES.  
 
WHILE SOME ISOLATED CONVECTION WILL BE POSSIBLE TUESDAY  
AFTERNOON, ESPECIALLY IN AREAS WEST OF PA, THE MAIN SHOW WILL BE  
TUESDAY NIGHT AND WEDNESDAY MORNING AS CONVECTION INITIATES AND  
ORGANIZES ALONG A COLD FRONT OR JUST AHEAD ALONG A PRE-FRONTAL  
TROUGH. LOW-LEVEL WARM AIR ADVECTION AND SOME DIURNAL HEATING  
(ESPECIALLY PITTSBURGH SOUTHWESTWARD WHERE BREAKS IN CLOUDS ARE  
POSSIBLE) WILL COMBINE THROUGH THE DAY TUESDAY TO DESTABILIZE  
THE LOW-LEVELS. MODELS DEPICT A CORRIDOR OF 1500+ J/KG MU CAPE  
ALONG OR WEST OF THE OHIO, DECREASING TOWARDS THE EAST.  
SUFFICIENT BULK SHEAR AND FAVORABLE LOW- LEVEL HODOGRAPHS  
SUPPORT A LIMITED TORNADO THREAT TUESDAY NIGHT FOR REGIONS WEST  
OF PA WITH DISCRETE CONVECTIVE CELLS. BY EARLY WEDNESDAY  
MORNING, CONVECTION SHOULD CONGEAL AND SEVERE-MODE WILL  
TRANSITION TOWARDS A WIND-EVENT. HOWEVER, NEAR-SURFACE  
INSTABILITY MAY HINDER FULL POTENTIAL OF DOWNWARD MOMENTUM, THUS  
LIMITING THE OVERALL SEVERE THREAT.  
 
PRECIP SHOULD CLEAR MUCH OF THE REGION BY MID-AFTERNOON  
WEDNESDAY. A LAGGING UPPER-LEVEL FRONT AND MOIST AIR WILL KEEP  
CLOUD COVER AROUND FOR ANOTHER DAY.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
 
 
TEMPERATURES WILL BE NEAR SEASONAL THROUGH MUCH OF THE LONG  
TERM PERIOD. WHILE GLOBAL MODEL SOLUTIONS BEGIN TO DIVERGE THIS  
WEEKEND, A GENERAL CONSENSUS DEPICTS ANOTHER COLD FRONT, THIS  
ONE MOISTURE-LIMITED, MOVING THROUGH THE REGION FRIDAY. HIGH  
PRESSURE BUILDING IN BEHIND THIS FRONT SHOULD KEEP TEMPERATURES  
NEAR SEASONAL AND LIMIT THE POSSIBILITY OF PRECIPITATION THROUGH  
AT LEAST THE WEEKEND.  
 

 
   
AVIATION /12Z MONDAY THROUGH FRIDAY/
 
 
MVFR TO IFR STRATUS SHOULD CONTINUE IN MOIST E FLOW N OF I 80  
THIS MORNING. OTHERWISE, SHOWERS AND CONDITION DETERIORATION TO  
MVFR, WITH PATCHY IFR, IS EXPECTED AS A SHORTWAVE TROUGH  
CROSSES THE AREA THIS AFTERNOON. ANOTHER SHORTWAVE SHOULD  
MAINTAIN THE DEGRADED CONDITIONS OVERNIGHT.  
 
A LOW LEVEL JET IS PROGGED ACROSS THE UPPER OH VALLEY REGION  
THIS EVENING/OVERNIGHT, RESULTING IN A LLWS POTENTIAL.  
 
OUTLOOK...  
RESTRICTION POTENTIAL WILL CONTINUE UNTIL THE PASSAGE OF A LATE  
WEDNESDAY COLD FRONT.  
 

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

 
 

 
 
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