Area Forecast Discussion
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000 FXUS61 KPBZ 050539 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 139 AM EDT WED AUG 5 2015 .SYNOPSIS... GENERALLY DRY AND SUNNY CONDITIONS ARE EXPECTED THROUGH WEDNESDAY NIGHT. RAIN CHANCES INCREASE ON THURSDAY AS AN UPPER LEVEL DISTURBANCE APPROACHES THE REGION. && .NEAR TERM /THROUGH TODAY/... GENERALLY WEAKLY CYCLONIC FLOW REMAINS OVER THE REGION THIS EVENING...ALL THE WHILE DIURNAL CUMULUS FADES. THE POOL OF SLIGHTLY HIGHER SURFACE DEWPOINTS ALONG THE RIDGES DID MANAGE TO INCREASE INSTABILITY ENOUGH THAT A SHOWER WAS GENERATED...HOWEVER THAT HAS LONG SINCE DIED. AS THE MID AND UPPER TROUGH THAT HAS RESIDED OVER THE CENTRAL GREAT LAKES THROUGH THE DAY TRANSLATES EASTWARD OVERNIGHT...THE COLDER MID-LEVEL TEMPERATURES SHOULD LIKEWISE MOVE EASTWARD AS WELL. IT IS IN THIS MID-LEVEL COLD POOL THAT SHOWER ACTIVITY HAS GENERALLY MANIFEST ITSELF THROUGH THE LATE AFTERNOON AND EVENING...AND GIVEN THE TRAJECTORY OF THIS AIR...IT WOULD SEEM THE BULK OF THIS ACTIVITY SHOULD REMAIN NORTH OF OUR AREA. MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT IN TERMS OF TRACKING A JET STREAK FROM THE WESTERN GREAT LAKES AND ACROSS THE UPPER OHIO VALLEY TONIGHT. HOWEVER...THE SIMPLE PRESENCE OF THE RIGHT ENTRANCE REGION OF AN UPPER JET STREAK IS NOT SUFFICIENT FOR SHOWER DEVELOPMENT. BECAUSE OF THE FACT THAT RADAR IS DEVOID OF PRECIPITATION IN THE RIGHT ENTRANCE REGION OF THE JET STREAK CURRENTLY IN WISCONSIN...AND MODEL MID-LEVEL RH VALUES AVERAGE AROUND 20 PERCENT OVERNIGHT...AND THAT INSTABILITY WILL BE WANING GREATLY BY ITS ARRIVAL IN OUR AREA...SHOWER CHANCES WERE REMOVED FROM THE FORECAST OVERNIGHT. IT WOULD SEEM THE BEST SHOT AT ANY CLOUDS OVERNIGHT WILL COME FROM TRANSIENT CIRRUS CURRENTLY OVER ILLINOIS...WHICH TRAJECTORIES INDICATE SHOULD SAG SOUTHEASTWARD GENERALLY SOUTH OF I-70 OVERNIGHT. FRIES PREVIOUS DISCUSSION FOR WEDNESDAY AND WEDNESDAY NIGHT...AMID CONTINUED HIGH PRESSURE...WEDNESDAY WILL FEATURE CONSIDERABLE SUN IN THE MORNING...GIVING WAY TO PARTLY CLOUDY CONDITIONS AS COLD AIR ADVECTION AND STRONG HEATING YIELD A BROAD STRATOCU FIELD. DRY AIR AND HIGH PRESSURE JUSTIFY ELIMINATING POPS ALMOST EVERYWHERE WEDNESDAY AND WEDNESDAY NIGHT. MAXIMA WILL BE SLIGHTLY BELOW NORMAL WITH THE PRESENCE OF THE UNSEASONABLY COOL UPPER TROUGH...AND MINIMA ALSO BELOW NORMAL OWING TO DRY AIR AND GENERALLY EFFICIENT RADIATIONAL COOLING. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... DEEP SHORTWAVE TROUGH WILL DIG INTO THE MIDWEST THURSDAY MORNING. A SURFACE LOW WILL ACCOMPANY THE UPPER-LEVEL SYSTEM AND MOVE ACROSS MISSOURI INTO ILLINOIS. STILL SOME SIGNIFICANT DIFFERENCES BETWEEN DIFFERENT MODEL DEPICTIONS. 12Z NAM IS THE FASTEST AND HAS THE HIGHEST PRECIPITATION AMOUNTS...BUT THIS IS LIKELY DUE TO UNREALISTIC VERTICAL LIFT. 12Z GFS SEEMED TO BE THE DRY OUTLIER WITH THE BULK OF THE SYSTEM REMAINING TO THE SOUTH...BUT THE 12Z ECMWF CAME IN FARTHER SOUTH THAN ITS PREVIOUS RUN. HAVE STILL BUMPED UP POPS TO CATEGORICAL ACROSS THE SOUTHEASTERN RIDGES...BUT HAVE MADE A WIDER GRADIENT OVERALL FOR POPS FROM NORTH TO SOUTH. NORTH OF INTERSTATE 80...ONLY SOME SLIGHT CHANCE POPS WERE INCLUDED. MODEL SOUNDINGS STILL SHOW NO INSTABILITY TO WORK WITH...SO HAVE KEPT THUNDER OUT OF THE FORECAST. BULK OF RAIN SHOULD BE EAST OF THE REGION BY FRIDAY MORNING...WITH CONDITIONS CLEARING OUT FRIDAY EVENING. WITH EXTENSIVE CLOUD COVER...TEMPERATURES WILL BE A FEW DEGREES COOLER. && .LONG TERM /SATURDAY THROUGH TUESDAY/... MODELS STILL TRYING TO DETERMINE A SOLUTION FOR A SURFACE WAVE WHICH WILL MOVE OUT OF THE MIDWEST AND CROSS THE MID-ATLANTIC LATE THIS WEEK AND INTO THE FIRST HALF OF THE WEEKEND. AFTER THIS POINT...A LOW CONFIDENCE FORECAST DUE TO MODEL DISCREPANCIES IN TIMING OF SHORTWAVES IN THE NORTHWEST FLOW ALOFT. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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EXPECT VFR CONDITIONS TO CONTINUE OVERNIGHT WITH MAINLY HIGH CLOUDS SOUTH OF PIT...AND SOME HIGH-BASED SC NEAR FKL/DUJ. ELECTED TO REMOVE FOG MENTION FROM TAFS WITH DECENT MIXING AT THE TOP OF THE BOUNDARY LAYER...BUT WILL MONITOR. CANNOT RULE OUT A SPRINKLE NORTH OF I-80 AS WELL BUT TOO INSIGNFICANT TO MENTION. SCT CU THIS AFTERNOON WITH W/NW WINDS OF 10-15 MPH ANTICIPATED. WINDS WILL LIGHTEN AFTER 00Z WITH SOME PATCHY HIGH CLOUDS REMAINING. OUTLOOK...WEDNESDAY NIGHT THROUGH SUNDAY... SOME RESTRICTIONS REMAIN POSSIBLE SOUTH OF PIT THURSDAY AND THURSDAY NIGHT...ALTHOUGH MODELS ARE TRENDING TOWARDS KEEPING PRECIPITATION TO THE SOUTH.
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&& .EQUIPMENT... GREGS KNOB NOAA WEATHER RADIO IS OFF THE AIR WITH A FAILED TRANSMITTER. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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