Area Forecast Discussion
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000 FXUS61 KPBZ 290404 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1204 AM EDT SUN MAR 29 2015 .SYNOPSIS... DRY AND COLD THROUGH SUNDAY. ANOTHER COLD FRONT WILL BRING LIGHT RAIN OR SNOW SUNDAY NIGHT. && .NEAR TERM /THROUGH TODAY/... NO CHANGES NEEDED AT THIS TIME WITH CLEAR SKIES AND LIGHT WINDS IN PLACE ACROSS THE REGION. PREV DISCUSSION FOLLOWS.. COLD SURFACE HIGH CENTERED OVER THE LOWER OHIO VALLEY WILL SHIFT EAST OVERNIGHT. VERY DRY AIR MASS WITH SINGLE DIGIT DEW POINTS OVERNIGHT INTO EARLY SUNDAY. WITH CLEAR SKIES AND WINDS BECOMING LIGHT...TEMPERATURES MAY GET CLOSE TO RECORDS FOR SUNDAY MORNING. THE RECORD IN PITTSBURGH FOR MARCH 29TH IS 13 SET IN 1923. SURFACE RIDGE AXIS WILL SHIFT EAST DURING THE DAY SUNDAY...WITH LOW LEVEL SOUTHWEST FLOW AND 850MB WARM ADVECTION PUSHING TEMPERATURES INTO THE 40S BY LATE AFTERNOON. && .SHORT TERM /TONIGHT 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 /04Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS ARE EXPECTED THROUGH SUNDAY UNDER HIGH PRESSURE. SW WINDS SHOULD INCREASE SUNDAY AFTERNOON AS THE HIGH SHIFTS EAST AND THE PRESSURE GRADIENT INCREASES. .OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... RESTRICTION POTENTIAL RETURNS SUNDAY NIGHT/EARLY MONDAY WITH AN OCCLUDED FRONT...AND AGAIN CROSSING LOW PRESSURE TUESDAY AND THURSDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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