Area Forecast Discussion
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000 FXUS61 KPBZ 281841 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 241 PM EDT SAT MAR 28 2015 .SYNOPSIS... DRY CONDITIONS AND WELL BELOW NORMAL TEMPERATURES WILL PERSIST THROUGH THE WEEKEND BEFORE THE NEXT WEATHER DISTURBANCE IMPACTS THE REGION SUNDAY NIGHT INTO MONDAY. && .NEAR TERM /THROUGH SUNDAY/... CURRENT RADAR IMAGERY SHOWING WEAK ECHOES ASSOCIATED WITH LIGHT SNOW SHOWERS DISSIPATING AS THE FOCUS OF THE UPPER LEVEL LOW SHIFTS EAST. SURFACE HIGH PRESSURE...CURRENTLY CENTERED NEAR LAKE MICHIGAN...IS BEGINNING TO BUILD INTO OUR WEST. PRESSURE GRADIENT WILL BEGIN TO RELAX AS WE TRANSITION TO HIGH PRESSURE BUT BEFORE IT DOES...BRISK NORTH WINDS WILL REINFORCE THE COLD AIR AND KEEP TEMPERATURES WELL BELOW AVERAGE. TONIGHT...HIGH PRESSURE WILL BE FIRMLY PLANTED OVER THE AREA AND SURFACE FLOW DIMINISHES TO CALM. WITH CLEAR SKIES AND WEAK BOUNDARY LAYER FLOW...THERE SHOULD BE LITTLE TROUBLE DE-COUPLING THE LOWER LEVELS TONIGHT. THIS MEANS THAT DESPITE WARM AIR ADVECTION TAKING PLACE ABOVE 925MB...TEMPERATURES TONIGHT WILL REMAIN SOME 15 TO 20 DEGREES BELOW THE AVERAGE. ANY REMAINING SNOW COVER THAT SURVIVES MELTING AND SUBLIMATION TODAY COULD LOCALLY DRIVE SOME TEMPERATURES DOWN EVEN FURTHER. AXIS OF THE SURFACE HIGH SIFTS EAST OF THE AREA SUNDAY...ALLOWING LOW-LEVEL FLOW TO SHIFT TO THE SOUTH-SOUTHWEST. SUNSHINE AND SOUTHWESTERLY FLOW WILL BRING WARMER AIR BACK TO THE AREA AS A SYSTEM APPROACHES FROM THE WEST. COPIOUS DRY AIR IN PLACE WILL KEEP PRECIPITATION AT BAY THROUGH MUCH OF SUNDAY...BUT RAIN CHANCES WILL INCREASE QUICKLY HEADING INTO THE SHORT-TERM. TAX && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... ISENTROPIC ASCENT AHEAD OF AN INCOMING WARM FRONTAL BOUNDARY INCREASES RAPIDLY DURING THE EVENING HOURS ON SUNDAY. WHILE THE BOUNDARY LAYER STARTS OUT RATHER DRY...FAIRLY POTENT WARM/MOIST ADVECTION LOOKS TO QUICKLY OVERCOME THIS DRY AIR WITH WIDESPREAD LIGHT PRECIPITATION. MODEL SPREAD ON PRECIPITATION COVERAGE BY LATE SUNDAY EVENING IS NOT VERY LARGE...NOR IS THE DIVERGENCE OF QPF SOLUTIONS. ALL MODELS INDICATE A RATHER HIGH POP/LOW QPF TYPE OF EVENT FOR SUNDAY EVENING AND OVERNIGHT. THE REAL TOUGH PART OF THE FORECAST IS MORE LIKELY TO BE PRECIPITATION TYPE. WHILE THERMAL PROFILES SUNDAY EVENING AND OVERNIGHT DO NOT VARY SIGNIFICANTLY FROM MODEL TO MODEL...SMALL BOUNDARY LAYER DIFFERENCES AS WELL AS THE HANDLING OF QUICKLY ERODING COLD AIR WITH STRONG ADVECTION AND A LACK OF AN INVERSION TO INHIBIT MIXING ALL WILL WORK TOWARD MAKING PRECIPITATION ALL RAIN. HOWEVER...VERY WIDE DEWPOINT DEPRESSIONS AS WELL AS FAIRLY COLD INITIAL 850 MB AND BOUNDARY LAYER TEMPERATURES WILL WORK TOWARD MORE FROZEN PRECIPITATION AT ONSET. IT DOES SEEM THAT AT LEAST INITIALLY MOISTURE AND LIFT WILL BE DEEP ENOUGH TO PARTIALLY BISECT THE DENDRITIC GROWTH REGION...HOWEVER DEEPER MOISTURE QUICKLY PEELS OFF AS AS SURFACE LOW MOVES THROUGH THE REGION. THIS LEAVES A BIT LEANER MOIST LAYER BELOW THE DENDRITIC GROWTH REGION WITH LIFT AND CONTINUED ENHANCED BAROCLINITY. THAT SAID...POPS WERE TOUGH TO RULE OUT INTO MONDAY AFTERNOON AND NIGHT ACROSS THE NORTHEASTERN ZONES AND P-TYPES DO LOOK TO TREND TOWARD LIQUID FOR A TIME. WHILE MOST OF THE AREA WILL TEMPORARILY DRY OUT WITH THE PASSAGE OF THE SURFACE LOW ON MONDAY...THIS WILL LIKELY ONLY BE TEMPORARY. ANOTHER SLUG OF MOISTURE AND WARM ADVECTION ASSOCIATED WITH THE NEXT LOW TO AFFECT THE REGION WILL SLIDE DOWN THE FRONTAL BOUNDARY THAT WILL REMAIN OVER THE AREA. DEJU VU LOOKS TO HAPPEN AS WELL WITH DEEPER MOISTURE AND LIFT AGAIN BISECTING THE DENDRITIC GROWTH REGION AND COLDER AIR TO THE NORTH FAVORING AT LEAST SOME MIX WITH SNOW...HOWEVER STRONG SOUTHWESTERLY FLOW WILL FAVOR ALL LIQUID ACROSS THE SOUTHERN HALF OF THE CWA. POPS WERE INCREASED FOR THIS SYSTEM ON TUESDAY AS MODEL SOLUTIONS REALLY SEEM TO HAVE FALLEN IN LINE FOR FAVORING THAT TIME FRAME FOR WET WEATHER. FRIES && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... HIGH PRESSURE WILL BRIEFLY BUILD INTO THE REGION TUESDAY NIGHT THROUGH WEDNESDAY NIGHT BEFORE NEXT SYSTEM APPROACHES FROM THE WEST. ALTHOUGH GFS/ECMWF BOTH SHOW A FRONT CROSSING THE REGION THURSDAY NIGHT...MODELS QUICKLY DIVERGE BY FRIDAY. HAVE THROWN OUT THE FAST GFS OUTLIER AND STUCK CLOSER TO ECMWF FORECAST WHICH HAS ENSEMBLE SUPPORT INDICATING THE FRONT WILL LIKELY HANG UP FOR ANOTHER DAY. THIS COULD ALLOW FOR A PROLONGED PERIOD OF RAIN ACROSS THE REGION. TEMPERATURES WILL BE NEAR NORMAL THROUGH THE PERIOD...WITH THURSDAYS VALUES RISING TO MORE THAN 10 DEGREES ABOVE NORMAL. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... DRIER AIR PUSHING IN FROM THE WEST HAS IMPROVED ALL TERMINALS TO VFR...BUT SPOTTY LIGHT SNOW SHOWERS REMAIN. TIGHT PRESSURE GRADIENT WILL HOLD IN THE EAST THROUGH THE DAYTIME HOURS...SO WINDS WILL REMAIN ELEVATED...BUT THEY WILL DECREASE RAPIDLY AFTER SUNSET AS HIGH PRESSURE BUILDS IN FROM THE WEST. CLEAR CONDITIONS CONTINUE INTO SUNDAY AS HIGH PRESSURE MOVES DIRECTLY OVERHEAD...EVENTUALLY SHIFTING THE FLOW TO LIGHT SOUTHWESTERLY. THIS IS AHEAD OF A RELATIVELY DRY SYSTEM THAT WILL ENTER SUNDAY NIGHT...JUST OUTSIDE OF THE CURRENT TAF PERIOD. TAX .OUTLOOK.../SUNDAY THROUGH WEDNESDAY/... THE NEXT CHANCE FOR WIDESPREAD RESTRICTIONS IS EXPECTED WITH A SUNDAY NIGHT FRONTAL SYSTEM. ANOTHER ROUND OF RESTRICTIONS WILL BE POSSIBLE ON TUESDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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