Area Forecast Discussion
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000 FXUS61 KPBZ 191848 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 248 PM EDT SUN APR 19 2015 .SYNOPSIS... SHOWERS WILL OVERSPREAD THE REGION THIS EVENING AND CONTINUE THROUGH MONDAY. UNSEASONABLY COOL TEMPERATURES ARE EXPECTED FOR THE REMAINDER OF THE WEEK. && .NEAR TERM /THROUGH MONDAY/...
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DRY AIR SAMPLED BY THE 12Z UPPER AIR SOUNDING REVEALS A SUBSTANTIAL LAYER OF DRY AIR. THIS HAS KEPT THE RAIN AND CLOUDS AT BAY FOR MUCH OF THE DAY...ALLOWING FOR TEMPERATURES TO RISE QUICKLY ABOVE NORMAL. TEMPERATURE RISES HAVE BEEN AIDED...AT LEAST IN PART...BY DOWNSLOPING EASTERLY FLOW SUSTAINED AT 10-15KTS WITH GUSTS CLOSE TO 25KTS. TEMPERATURES THIS EVENING WILL DECREASE ACROSS THE SOUTH FIRST AS THE THICKER CLOUD COVER AND EVENTUAL RAIN SHOWERS MOVE IN. TIMING THE ONSET OF PRECIPITATION HAS BEEN PUSHED BACK AN HOUR OR TWO FOR MOST LOCATIONS TO ACCOUNT FOR THE DRY AIR IN PLACE. KEEPING CATEGORICAL POPS IN FOR THIS EVENING/EARLY TONIGHT...DESPITE SEVERAL OF THE LATEST HRRR RUNS CONTINUING TO SHOW CONSIDERABLE MOISTURE EROSION UPON ARRIVAL...RESULTING IN TRIMMING OF QPF GENERATION. ALL OTHER GUIDANCE INCLUDING THE VARIOUS OTHER HI-RES MODELS SHOW THE CURRENT SWATH OF RAIN ALONG THE WARM FRONT HOLDING TOGETHER THROUGH OUR AREA. TONIGHT THE DRY SLOT IN THE WARM SECTOR WILL RESULT IN A LULL IN PRECIPITATION THAT IS EXPECTED TO LAST THROUGH DAYBREAK. CLOUDS MAY DIMINISH TO THE POINT WHERE POCKETS OF CLEARING COULD AID THE MONDAY MORNING WARM-UP AS STRONG SOUTHEASTERLY FLOW VEERS SOUTHERLY. COLDER AIR ADVANCING EASTWARD ALOFT WILL RESULT IN INSTABILITY AND DRIVE THUNDERSTORM ACTIVITY ALONG AND AHEAD OF THE COLD FRONT. A SLIGHT RISK OF SEVERE THUNDERSTORMS IS INCLUDED FOR OUR AREA...WITH THE MAIN THREAT BEING DAMAGING WINDS. TAX
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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FRONT WILL BE IN OR JUST EAST OF THE RIDGES AT 00Z TUESDAY...WITH A SECONDARY COLD FRONT LAGGING BEHIND WITH THE UPPER LEVEL COLD AIR. ENOUGH MOISTURE AND STEEP ENOUGH LAPSE RATES REMAIN BEHIND THE IMMEDIATE SURFACE BOUNDARY TO KEEP SHRA/TSRA CHANCES GOING THROUGH MUCH OF THE NIGHT. DRIER AIR SHOULD ALLOW PRECIPITATION TO CEASE AREAWIDE BY 12Z. MODELS ARE IN GENERAL AGREEMENT THAT DECAYING MISSISSIPPI VALLEY SHORTWAVE GETS ABSORBED BY DEEPENING UPPER LOW...WHICH DROPS INTO THE NORTHERN GREAT LAKES BY 12Z TUESDAY. THIS LEADS TO A TROUGHING PATTERN FOR THE NORTHEAST U.S. WHICH LOOKS TO PERSIST FOR SOME TIME. CONFIDENCE IS HIGH IN THESE DETAILS. HOWEVER...TIMING OF INDIVIDUAL SHORTWAVES ROTATING AROUND BECOMES MORE PROBLEMATIC WITH TIME. MAIN VORT LOBE RESIDES IN OR NEAR OUR NORTHERN COUNTIES TUESDAY. THIS PLUS BETTER INSTABILITY LEADS TO HIGHER POPS IN THIS AREA TUESDAY AFTERNOON/EVENING. HELD OFF ON THUNDER FOR NOW WITH EQUILIBRIUM LEVELS MOSTLY BELOW 15K FEET...BUT THIS MAY HAVE TO BE REEVALUATED WITH COLD TEMPS ALOFT EXPECTED. A WEAK IMPULSE MAINLY AFFECTS THE SOUTHERN COUNTIES WITH A FEW SHRA TUESDAY NIGHT. THE NEXT...MORE ORGANIZED...FRONTAL BOUNDARY ARRIVES WEDNESDAY WITH BETTER RAIN CHANCES AREAWIDE. BEHIND THE FRONT...BOUNDARY LAYER MAY BE ABLE TO COOL SUFFICIENTLY TO ALLOW SNOWFLAKES TO MIX IN NORTH OF PIT LATE WEDNESDAY NIGHT...BUT NO ACCUMULATION IS FORESEEN. A GENERAL COOLING TREND IN TEMPERATURE WILL BE SEEN WITH VALUES SINKING BELOW NORMAL BY THE END OF THE PERIOD. CL
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&& .LONG TERM /THURSDAY THROUGH SATURDAY/... BROAD UPPER TROUGHING WILL REMAIN OVER THE EASTERN CONUS THROUGH THE EXTENDED AND RESULT IN BELOW NORMAL TEMPERATURES EACH DAY ALONG WITH CLOUDY SKIES AND SLIGHT CHANCES FOR PRECIPITATION THROUGHOUT THE PERIOD AS SHORTWAVES TRANSITION THROUGH THE FLOW AND CAA ALOFT PERSISTS. CONFIDENCE IS HIGH IN THE GENERAL FORECAST AS MODELS HAVE BEEN FAIRLY CONSISTENT IN PROGGING THIS LONGWAVE PATTERN...REFLECTED IN LATEST RMOP AND MODTRENDS GUIDANCE. HOWEVER...CONFIDENCE IN TIMING OF ANY MORE SIGNIFICANT PERIODS OF PRECIPITATION IS RELATIVELY LOW. FORECAST MAX/MIN TEMPERATURES ARE NOT EXCEPTIONALLY COLD...BUT PERSISTENT AROUND 10 DEGREES BELOW NORMALS AS ENSEMBLE ANOMALIES ARE SHOWING TEMPS AND HEIGHTS ALOFT ONLY RANGING FROM 1-2 STANDARD DEVIATIONS BELOW NORMAL THROUGH THE PERIOD. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... HIGH CIRRUS CONTINUES TO MOVE SLOWLY ACROSS THE AREA...BUT NO RESTRICTIONS ARE ANTICIPATED UNTIL THE RAIN SHOWERS ASSOCIATED WITH THE WARM FRONT ARRIVE THIS EVENING. EXPECTING RAIN TO FALL OUT OF MOSTLY VFR CIGS INITIALLY...BUT HEADING INTO THE OVERNIGHT THE CIGS SHOULD CONTINUE THIER DESCENT TO MVFR. CEILINGS MAY BE BROKEN AS WE HEAD INTO MIDDAY MONDAY...WITH THUNDERSTORMS EXPECTED THROUGH AFTERNOON. GUSTY EAST-SOUTHEASTERLY FLOW WILL CONTINUE EVENING AND OVERNIGHT...GRADUALLY RELAXING THROUGH THE EARLY MORNING MONDAY. SURFACE FLOW WILL AGAIN INCREASE AS IT VEERS MORE SOUTHERLY MONDAY AFTERNOON. TAX .OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... RESTRICTIONS ARE POSSIBLE WITH A MID WEEK UPPER TROUGH. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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