Area Forecast Discussion
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000 FXUS61 KPBZ 241616 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1216 PM EDT FRI APR 24 2015 .SYNOPSIS... DRY AND COOL WEATHER CAN BE EXPECTED TODAY AS HIGH PRESSURE SLIDES ACROSS THE REGION...BUT THE REPRIEVE WILL BE BRIEF AS LOW PRESSURE IS FORECAST TO GENERATE RAIN ON SATURDAY. && .NEAR TERM /THROUGH SATURDAY/... A FEW PUFFS OF DIURNALLY-INDUCED FLAT CUMULUS HAVE BEEN NOTED GENERALLY ALONG THE I-80 CORRIDOR...WITH CLEAR SKIES CONTINUING SOUTH OF THERE. GIVEN THE COLDER MID-LEVEL TEMPERATURES RETREATING A BIT TO THE NORTHEAST...FURTHER DEVELOPMENT OF CUMULUS IS NOT REALLY ANTICIPATED...WITH FULL CLEARING LIKELY VIRTUALLY IMMEDIATELY AFTER SUNSET. AN UNSTABLE BOUNDARY LAYER THIS AFTERNOON HAS BEEN ALLOWING FOR FREQUENT NORTHWESTERLY WIND GUSTS OF AROUND 20 KTS. THESE SHOULD TAPER INTO THE EVENING AS CLEARING ALLOWS FOR WEAK INVERSIONS TO SET UP. HIGH CLOUDS WILL ALSO BEGIN TO ENCROACH FROM THE WEST OVERNIGHT AS THE NEXT SYSTEM STARTS TO COME INTO VIEW. HOWEVER...BEFORE THEIR ARRIVAL...TEMPERATURES SEEM POISED TO NOSE DIVE FOR SEVERAL HOURS. THE DURATION OF THE CLEAR SKIES WILL BE THE MOST IMPORTANT MODULATOR TO THE DEPTHS TO WHICH THE MERCURY WILL PROBE TONIGHT. AS SUCH...A RATHER LOW CONFIDENCE FORECAST EXISTS FOR TEMPERATURES OVERNIGHT. HOWEVER...THE COLDEST READINGS ARE VERY LIKELY TO BE IN THE 20S IN THE VALLEYS OF THE NORTHEASTERN CWA...WHILE THE WARMEST READINGS ARE LIKELY TO BE MAINLY IN OHIO. WHILE THE SURFACE REFLECTION OF THE NEXT SYSTEM THAT WILL PLAGUE THE AREA WILL LIKELY REMAIN WELL BACK IN THE MID-MISSISSIPPI VALLEY BY SATURDAY AFTERNOON...A WARM FRONT WILL LIKELY EXTEND WELL TO ITS EAST INTO THE CENTRAL APPALACHIANS. DIFFERENTIAL THETA-E ADVECTION AS WELL AS PVA WILL STREAM NORTH OF THIS FRONT OVER GENERALLY THE SOUTHWESTERN HALF OF THE CWA BY SATURDAY AFTERNOON. THIS WILL RESULT IN RAIN INCREASING FROM THE SOUTHWEST TO NORTHEAST THROUGH THE AFTERNOON. HOWEVER...DUE TO ABUNDANT DRY AIR IN PLACE UPON ITS ARRIVAL...SEVERAL HOURS OF VIRGA ARE LIKELY BEFORE THE RAIN ACTUALLY HITS THE GROUND. BECAUSE OF THIS...PRECIPITATION OUTBREAK IN THE FORECAST MORE CLOSELY ALIGNS WITH THE SLOWER-DEVELOPING AND HIGHER LOW LEVEL RESOLVING NAM. ASSUMING THIS VERFIES...RAIN MAY HOLD OFF IN PITTSBURGH ITSELF FOR THE MAJORITY OF THE DAY ON SATURDAY. EVEN STILL...A CONTINUATION OF BELOW NORMAL TEMPERATURES WILL BE LIKELY. FRIES && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... PRECIPITATION IS EXPECTED TO SPREAD NORTHEASTWARD SATURDAY AS WARM...MOIST ADVECTION INCREASES AHEAD OF LOW PRESSURE ADVANCING OUT OF THE MIDWEST. MODELS ARE IN GENERAL AGREEMENT THAT THE CENTER OF THE APPROACHING SHORTWAVE TROUGH WILL PASS JUST SOUTH OF THE FORECAST AREA SATURDAY NIGHT. SUCH A TRACK WOULD KEEP THE FORECAST AREA ALONG OR JUST NORTH OF THE ASSOCIATED WARM FRONT...AND IN PRIME TERRITORY FOR A BAND OF LIGHT TO MODERATE RAIN OWING TO DEFORMATION AND ISENTROPIC LIFT. AT ANY RATE...THE SYSTEM IS PROGGED TO MOVE RAPIDLY OVER THE ATLANTIC ON SUNDAY...SPELLING AN END TO PRECIPITATION. NO CHANGES WERE MADE TO SATURDAY POPS WHICH CONTINUE TO FEATURE CHANCE NUMBERS OVER THE I 80 CORRIDOR AND CATEGORICALS OVER I 70 GIVEN THE AFOREMENTIONED TRACK...ALTHOUGH ADJUSTMENTS WERE MADE FOR FASTER EXITING AS PER THE LATEST TIMING TRENDS. SUNDAY IS THUS EXPECTED TO BE A DAY OF IMPROVEMENT AS SURFACE HIGH PRESSURE BUILDS UNDER NORTHERLY FLOW ALOFT. A FAIRLY STRONG...BUT MOISTURE DEFICIENT SHORTWAVE IS FORECAST TO PASS THROUGH THE WESTERN FLANK OF UPPER LOW PRESSURE EARLY ON MONDAY...SLIGHT TO CHANCE POPS NUMBERS WERE MAINTAINED MAINLY OVER THE EASTERN HALF OF THE COUNTY WARNING FOR PASSAGE OF THIS FEATURE...WHICH MAY INCLUDE SOME SNOW SHOWERS OR FLURRIES. TEMPERATURES PRIOR TO THE RAIN WILL BE TRICKY TONIGHT. INITIAL CONDITIONS OF DRY AIR...LIGHT WIND AND CLEAR SKY WILL BE FAVORABLE FOR RADIATIONAL COOLING...BUT CIRROSTRATUS IS EXPECTED TO BECOME INCREASINGLY ABUNDANT AFTER MIDNIGHT AND WILL LIKELY LIMIT THE IMMEDIATE PREDAWN DROP. THE COLD TEMP FORECAST WAS THUS CONSTRUCTED FOR AN EARLY LOW READING...WITH STABILIZATION OR A SLOW RISE WITH THE APPROACH OF DAWN. THE REST OF THE PERIOD WILL FEATURE SUB AVERAGE READINGS GIVEN THE PRESENCE OF THE NORTHEASTERN U.S. LOW. EXPECT TEMPERATURES ABOUT 5 TO 10 DEGREES BELOW NORMAL FOR THE START OF THE NEW WEEK. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... UPPER LEVEL LOW OVER NEW ENGLAND SHOULD BEGIN TO MOVE OFFSHORE TUESDAY...WHICH SHOULD ALLOW FOR AT LEAST SOME PARTIAL CLEARING TO OCCUR OVER THE REGION. THE CLEARING WOULD LIKELY BE SHORT LIVED...AS MODELS PROJECT A SURFACE LOW WILL DEVELOP ALONG THE GULF COAST AND MOVE TO THE NORTHEAST. STILL LOTS OF UNCERTAINTY WITH THE TRACK OF THIS LOW...AND RECENT MODEL TRENDS HAVE SUGGESTED THE LOW MAY STAY FARTHER TO THE SOUTHEAST. WILL TREND THE FORECAST IN THIS DIRECTION...REDUCING BUT NOT ELIMINATING SHOWERS WEDNESDAY AND THURSDAY. ALTHOUGH TEMPERATURES ARE STILL EXPECTED TO BE A FEW DEGREES BELOW NORMAL THROUGH THE EXTENDED FORECAST...THE MORE SOUTHERLY TREND OF THE MID WEEK SURFACE LOW SHOULD ALLOW FOR MORE SUNSHINE LOCALLY...AND HAVE BROUGHT TEMPS UP A FEW DEGREES TO COMPENSATE. PRECIPITATION IN THE FORECAST. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/... VFR CONDITIONS WILL CONTINUE THROUGH THE TAF PERIOD WITH WINDS BECOMING GUSTY AGAIN BY MID MORNING. .OUTLOOK.../TONIGHT THROUGH TUESDAY/... CEILING RESTRICTIONS ARE EXPECTED SATURDAY AFTERNOON THROUGH SUNDAY AFTERNOON AS LOW PRESSURE TRACKS ACROSS THE OHIO VALLEY. ANOTHER ROUND OF RESTRICTIONS MAY BE POSSIBLE SUNDAY NIGHT INTO MONDAY WITH SCATTERED SHOWERS. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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