Area Forecast Discussion
Issued by NWS

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000 FXUS61 KPBZ 291821 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 221 PM EDT FRI APR 29 2016 .SYNOPSIS...
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DRIER CONDITIONS WILL RETURN TONIGHT INTO EARLY SATURDAY BEFORE ANOTHER SYSTEM APPROACHES WITH WIDESPREAD RAIN LATE SATURDAY. SHOWERS AND THUNDERSTORMS WILL CONTINUE AT TIMES INTO SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/... STAGNANT COOL AND MOIST AIR MASS WILL CONTINUE TO PLAGUE THE AREA THROUGH TONIGHT. SOME EROSION OF LOW STRATUS IS DEVELOPING ON THE SOUTHERN FLANK...ALLOWING FOR SCATTERING AND WARMING SOUTH OF THE MASON-DIXON LINE. THIS WILL AGAIN SET UP A SHARP GRADIENT IN TEMPERATURES THIS AFTERNOON WITH NORTHERN WEST VIRGINIA GETTING INTO THE UPPER 60S...WHILE NORTH OF I-80 MAY TOUCH 50 DEGREES. SHORTWAVE TROUGH AXIS CURRENTLY CROSSING LAKE ERIE WILL SKIRT THE NORTHERN HALF OF THE FORECAST AREA THIS AFTERNOON. EXPECT CURRENT SHOWER ACTIVITY TO BLOSSOM NORTH OF PITTSBURGH IN RESPONSE TO THE QUICK PASSING WAVE. ADDITIONALLY...HI-RES CAMS SHOW SHOWERS DEVELOPING JUST SOUTH OF PITTSBURGH. GIVEN THE STEEPENING LOW- LEVEL LAPSE RATES...LIFT FROM THE WAVE AND COPIOUS MOISTURE...THINK THAT CHANCE POPS THROUGH AND SOUTH OF THE PITTSBURGH METRO AREA SEEM PRUDENT. WAVE PASSES TO THE EAST TONIGHT AND SOME DRYING WILL OCCUR. MOISTURE WILL BEGIN TO ERODE FROM THE WEST...SCATTERING OUT THE LOW CLOUDS...BUT TIMING IS DIFFICULT TO PIN DOWN AT THIS POINT. LOW TEMPERATURES WILL DEPEND LARGELY ON TIMING AND EXTENT OF CLEARING OVERNIGHT. WITH THIS IN MIND...HAVE WESTERN PORTIONS OF THE FORECAST AREA RELATIVELY LOW COMPARED TO EASTERN PORTIONS. TAX && .SHORT TERM /SATURDAY THROUGH MONDAY/...
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SOME CLEARING WILL BE LIKELY EARLY SATURDAY AS LOW LEVEL MOISTURE FINALLY MIXES OUT BEHIND THE SYSTEM FROM FRIDAY AND IN ADVANCE OF ANOTHER SYSTEM FOR THE LATTER HALF OF SATURDAY. IN THE INTERIM...DIURNAL MIXING COMBINED WITH A DECREASE IN LAYER MOISTURE SHOULD ALLOW FOR A PERIOD OF CLEARING IN THE INTERCESSION. HOWEVER...THIS DECREASE WILL BE FLEETING AS ISENTROPIC ASCENT AHEAD OF A NORTHEASTWARD TRANSLATING WARM FRONT WILL MEAN CLOUDS WILL AGAIN OVERSPREAD THE AREA BY LATER IN THE AFTERNOON. AFOREMENTIONED ISENTROPIC ASCENT WILL SPREAD DEEP MOISTURE AND LIFT OVER THE AREA BY SATURDAY EVENING WITH A COUPLED JET STRUCTURE LIKELY TO TRANSLATE DOWN I-70. THE COMBINATION OF THESE TWO ASSURES RAIN WILL OVERSPREAD THE AREA...AND POPS WERE THUS RAISED TO 100 PERCENT. THE WARM FRONT IS SET TO MOVE NORTHWARD AND THROUGH THE AREA BY SUNDAY MORNING...PLACING THE MAJORITY OF THE CWA INTO THE WARM SECTOR BY THAT JUNCTURE. POPS WERE WOUND DOWN A BIT IN THE WARM SECTOR...HOWEVER KEPT AT LEAST CHANCE AS THE MODE WILL EVOLVE FROM STRATIFORM TO CONVECTIVE. IN THE WARM SECTOR...THE 12Z GUIDANCE HAS TRENDED DECIDEDLY TOWARD SOME AMOUNT OF CLEARING BY THE LATE MORNING ON SUNDAY. THIS WOULD WORK TO STRONGLY DESTABILIZE THE COLUMN...AND MEAN A SECONDARY INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY ON SUNDAY AFTERNOON...PARTICULARLY SOUTH OF I-80. NAM PROFILES SUGGEST UP TO 2000 J/KG OF CAPE WITH THE VAST MAJORITY OF IT ABOVE A FAIRLY LOW FREEZING LEVEL. EVEN IN THE ABSENCE OF STRONG VERTICAL SHEAR...THIS CLOUD LEAD TO SOME HAILERS. THIS WILL NEED TO BE MONITORED GOING FORWARD TO SEE HOW THE MODELS HANDLE THE WARM SECTOR IN SUBSEQUENT RUNS. EVEN AFTER A WEAK WAVE ON SUNDAY MOVES DOWN THE FRONT AND FORCES THE SHOWERS AND THUNDERSTORMS...THE UPPER JET AXIS LOOKS TO REMAIN RELATIVELY PARKED OVER THE OHIO VALLEY. THIS MEANS MOISTURE WILL BE SLOW TO DECREASE INTO EARLY NEXT WEEK WITH SHOWER CHANCES CURTAILING PAINFULLY SLOWLY. HOWEVER...AS A DEEPER UPPER LOW DIVES TOWARD THE TENNESSEE VALLEY BY TUESDAY...THE UPPER JET AXIS SHOULD FINALLY EVOLVE SOUTHWARD ENOUGH TO DRY OUT OUR AREA. FRIES
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&& .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
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THE EXTENDED PERIOD LOOKS TO FEATURE A VERY STRONGLY ANCHORED PATTERN OVER THE WESTERN CONUS AS A RIDGE LOOKS TO EVOLVE OVER THE INTERMOUNTAIN WEST. DOWNSTREAM TROUGHING WILL THUS EVENTUALLY BECOME ESTABLISHED OVER THE GREAT LAKES AND NORTHEAST BY THE END OF THE WEEK AFTER A DRY MID-WEEK. THIS WILL MEAN SHOWER CHANCES WILL RETURN AND TEMPERATURES WILL GENERALLY TREND NEAR OR BELOW NORMAL. FRIES
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... IFR RESTRICTIONS GRADUALLY IMPROVING TO LOW MVFR...PRIMARILY SOUTH OF PITTSBURGH WHERE SOME SCATTERING IS NOTED ON SATELLITE. ANOTHER SHORTWAVE TROUGH WILL PASS ACROSS THE NORTH THIS EVENING...REINFORCING THE LOW CIGS ACROSS THE NORTH. THIS WAVE WILL ALSO GENERATE ADDITIONAL LIGHT RAIN SHOWERS...MAINLY FOR NORTHERN AND EASTERN PORTS. HIGH CONFIDENCE IN IFR CONDITIONS REOCCURRING TONIGHT...BUT AFTER THE PASSAGE OF THE WAVE...LOWER-LEVELS BEGIN TO DRY OUT FROM THE WEST. THIS WILL RESULT IN SOME AMOUNT OF SCATTERING/CLEARING FROM KZZV EASTWARD NEAR DAYBREAK SATURDAY. CONFIDENCE IS MUCH LOWER ON THE AMOUNT AND EXACT TIMING OF THE IMPROVEMENT NEAR SUNRISE. VFR CONDITIONS ARE THEN EXPECTED FROM SATURDAY MID-MORNING THROUGH THE DURATION OF THE OPERATIONAL TAF PERIOD. LIGHT WEST WINDS WILL VEER TO THE NORTHWEST TONIGHT IN THE WAKE OF THE PASSING WAVE. LIGHT NORTH WINDS TONIGHT WILL THEN VEER TO EASTERLY SATURDAY. WIND SHOULD GENERALLY STAY 10KTS OR LESS THROUGH THE PERIOD. TAX .OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/... RESTRICTIONS ARE LIKELY AGAIN LATE SATURDAY THROUGH SUNDAY NIGHT AS LOW PRESSURE CROSSES THE REGION. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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