Area Forecast Discussion
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000 FXUS61 KPBZ 300006 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 806 PM EDT SUN MAR 29 2015 .SYNOPSIS... A WEAK COLD FRONT WILL CROSS THE REGION TONIGHT. LOW PRESSURE IS EXPECTED TO TRACK ACROSS THE AREA TUESDAY. && .NEAR TERM /THROUGH MONDAY/... A WEAK SHORTWAVE AND SURFACE TROUGH IS PROGGED TO ADVANCE ACROSS THE REGION TONIGHT. LIMITED MOISTURE AND UPPER SUPPORT SHOULD LIMIT PRECIP TO A SHORT PERIOD OF LIGHT RAIN FOR MUCH OF THE AREA. CRITICAL THICKNESSES AND MODEL SOUNDINGS INDICATE THE PRECIP SHOULD BE MAINLY LIGHT SNOW NORTH OF I 80...THOUGH LITTLE OR NO ACCUMULATION IS EXPECTED WITH MARGINAL TEMPS. WITH VERY DRY AIR IN PLACE AT THE SURFACE...MOST OF THE PRECIP ON RADAR ACROSS OH IS VIRGA. THIS SHOULD HELP MOISTEN THE ATMOSPHERE SOMEWHAT AHEAD OF THE MAIN TROUGH. AFTER ANY REMAINING SHOWERS EXIT MONDAY MORNING...UPPER TROUGHING ACROSS THE GREAT LAKES COULD ALLOW FOR A RAIN OR SNOW SHOWER NORTH OF I 80...THOUGH LIMITED MOISTURE SHOULD CAP THESE CHANCES. CLOUD COVER SHOULD BEGIN TO DECREASE BY AFTERNOON AS WELL. TEMPS SHOULD BE NEAR SEASONAL LEVELS TONIGHT...AND SEVERAL DEGREES BELOW AVERAGE ON MONDAY. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... UNSTABLE NORTHWESTERLY FLOW WILL BRIEFLY TURN WEST-SOUTHWESTERLY BY LATE MONDAY EVENING TO ALLOW FOR THE CWA TO DRY OUT AND AT LEAST PARTIALLY CLEAR OUT. HOWEVER...AN ACTIVE PATTERN LOOKS TO CONTINUE THEREAFTER. RATHER DISTURBING MODEL TRENDS SEEM TO HAVE TAKEN HOLD ON THE 06Z AND 12Z CYCLES TODAY...WITH THE MODELS LARGELY FALLING INTO TWO CAMPS. THE NAM AND CANADIAN FAVOR A MORE NORTHERN TRACK OF A SYSTEM THROUGH THE AREA ON TUESDAY...WHILE THE GFS AND 00Z ECMWF FAVOR A MORE SOUTHERLY TRACK. UNSURPRISINGLY...THE SREF BASICALLY SPLIT THE DIFFERENCE AND ALLOWED FOR A MIDDLE GROUND FORECAST...WHICH WAS LARGELY IN LINE WITH CONTINUITY...SO FORECAST CHANGES REALLY WERE NOT ALL THAT LARGE AS A RESULT. IT DOES SEEM THAT THE GFS WAS SUFFERING FROM SOME GRID SCALE ISSUES...WHILE THE NAM WAS LIKELY SUFFERING FROM ITS HABITUAL OVER DEVELOPMENT ISSUES. THESE PROBLEMS FURTHER LEND CREDENCE TO FAVORING AN ENSEMBLE MEAN APPROACH SUCH AS THE SREF MEAN. A COMPROMISE APPROACH STILL FAVORS RELATIVELY RAPID ENCROACHMENT OF WARM ADVECTION ISENTROPIC ASCENT OVER THE FORECAST AREA LATE MONDAY NIGHT INTO TUESDAY. THIS OCCURS AS A SURFACE LOW CROSSES THE AREA WITH AT LEAST THE SOUTHERN HALF OF THE AREA LIKELY TO ENTER THE WARM SECTOR FOR A PORTION OF THAT TIME AND PROBABLY HALT RAINFALL THERE FOR A TIME. AT THE ONSET...SOME PRECIPITATION TYPE ISSUES MAY BE PRESENT IF THE SOUTHERN SOLUTIONS VERIFY...HOWEVER ANY FROZEN PRECIPITATION SHOULD QUICKLY CHANGE TO RAIN AS WARM ADVECTION QUICKLY LOOKS TO ERODE ANY COLD AIR. THIS IS ESPECIALLY TRUE GIVEN THE LACK OF ANTECEDENT DRY AIR AS THIS SYSTEM ROLLS INTO THE AREA...MINIMIZING THE POTENTIAL FOR WET BULB COOLING AS PRECIPITATION DEVELOPS. A RELATIVELY QUICK DEPARTURE OF THE SYSTEM LOOKS TO OCCUR TUESDAY NIGHT WITH MUCH DRIER AIR FLOODING INTO THE CWA ON WEDNESDAY. SOME TEMPORARY COLD ADVECTION ON WEDNESDAY WILL LIKELY STILL HOLD TEMPERATURES BACK. HOWEVER...DRASTIC PATTERN AMPLIFICATION OF THE PATTERN TO OUR WEST LOOKS TO DEVELOP A STRONG THERMAL RIDGE THAT WILL BE POISED TO PUSH INTO THE AREA LATER IN THE WEEK. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... WHILE THE GFS HAS SLOWED THE ARRIVAL OF A FRONT ON THURSDAY FROM PREVIOUS MODEL RUNS...00Z ECMWF IS EVEN SLOWER THAN THAT. GIVEN THAT THE GFS IS THE MOST OPEN WAVE SOLUTION RELATIVE TO THE CANADIAN...GEFS...AND ECMWF...TIMING SLOWER THAN THE GFS IS LIKELY MORE OPTIMAL FOR THE ARRIVAL OF SHOWERS INTO THE CWA. AS A RESULT...WARM ADVECTION WILL RULE THE ROOST ON THURSDAY...LIKELY ALLOWING FOR THE WARMEST DAY OF THE SEASON TO THIS JUNCTURE. HOWEVER ONCE PRECIPITATION ARRIVES...LOW PRESSURE FORMING ALONG THE COLD FRONT WILL KEEP PRECIPITATION IN THE FORECAST FRIDAY UNTIL IT MOVES INTO NEW ENGLAND SATURDAY. TEMPS WILL DROP AFTER THURSDAY...LEADING BACK TO YET ANOTHER PERIOD OF BELOW NORMAL VALUES. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... A WEAK UPPER LEVEL TROUGH WITH A SURFACE REFLECTION AND COLD FRONT WILL APPROACH THIS EVENING AND EXIT MONDAY MORNING. VFR EARLY EVENING WILL DETERIORATE TO MVFR IN RAIN SHOWERS KPIT SOUTH WITH MAINLY SNOW SHOWERS NORTH. WINDS WILL BE FROM THE SOUTH 10KTS OR SO WITH SOME GUSTS OVER 20KTS THROUGH 03Z. LOW MVFR BEFORE DAYBREAK SHOULD IMPROVE TO VFR CIGS EARLY MONDAY AS SYSTEM EXITS. STILL SOME SCT VFR SNOW SHOWERS EARLY MONDAY NORTHERN PORTS WILL DIMINISH BY MIDDAY. .OUTLOOK.../MONDAY NIGHT THROUGH FRIDAY/... RESTRICTIONS ARE POSSIBLE ONCE AGAIN WITH CROSSING LOW PRESSURE TUESDAY AND THURSDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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