Area Forecast Discussion
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000 FXUS61 KPBZ 241959 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 259 PM EST WED DEC 24 2014 .SYNOPSIS...
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STRONG LOW PRESSURE AND ITS ASSOCIATED COLD FRONT WILL CROSS THE REGION TODAY INTO TONIGHT BRINGING SHOWERS...A FEW THUNDERSTORMS... AND STRONG WINDS THIS EVENING.
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&& .NEAR TERM /THROUGH TONIGHT/...
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EARLIER REMOVAL OF POPS DUE TO LACK OF FORCING WITHIN THE QUASI-WARM SECTOR (EXCEPT FOR THE PA/WV/MD RIDGES) HAS PLAYED OUT WELL WITH NOTHING MORE THAN A FEW SPITS. THIS TREND SHOULD CONTINUE FOR THE NEXT SEVERAL HOURS WITH JUST A FEW BRIEF SHOWERS ACROSS MOST OF THE CWA...AND STEADIER RAINS ACROSS THE LAUREL HIGHLANDS AND POINTS SOUTH. MEANWHILE...A DEEPENING AND INCREASINGLY NEGATIVE TILT MID LEVEL TROUGH WAS BEGINNING TO ACCELERATE NORTHEAST THROUGH ILLINOIS THIS AFTERNOON. LARGE SCALE ASCENT...ASSOCIATED WITH STRONG MID LEVEL HEIGHT FALLS...WAS BEGINNING TO OVERTAKE THE WARM SECTOR...AND CONFIRMED BY VISIBLE SATELLITE IMAGERY WITH A RECENT INCREASE IN SW-NE ORIENTED LOW-TOPPED CONVECTIVE BANDS. THIS FORCED ASCENT IS OCCURRING WEST OF THE PRONOUNCED MID-HIGH LEVEL MOIST PLUME WHICH HAS ENVELOPED THE REGION...AND THUS ITS EVOLUTION OVER THE NEXT SEVERAL HOURS IS AN INTERESTING FORECAST CHALLENGE. DYNAMICALLY FORCED CONVECTION...MOST OF WHICH WILL BE ALONG AND POST SFC FRONTAL...WILL REACH THE WESTERN CWA AROUND 22Z AND EXIT THE EASTERN RIDGES AROUND 05Z. AN AXIS OF MODEST INSTABILITY...ON THE ORDER OF 100-200 J/KG MUCAPE...WILL GRADUALLY SHIFT NORTHEAST ACROSS THE ENTIRE CWA THIS EVENING...EVEN WITH THE LOSS OF DAYLIGHT. IN FACT...AREAS OF NW PA AND THE LAUREL HIGHLANDS...WHICH HAVE BEEN EITHER NORTH OF THE WARM FRONT OR EAST OF THE DAMMING WEDGE FRONT...WILL LIKELY SEE A SPIKE IN TEMPERATURES/DEWPOINTS EARLY THIS EVENING AS A PRE-FRONTAL TROUGH EFFECTIVELY SCOURS THE AREA AND SHIFTS WINDS INTO THE SOUTHWEST. PRECIPITATION LOOKS TO BE NEARLY CERTAIN...SO THE QUESTION PRIMARILY FOCUSES ON THUNDER CHANCES. GIVEN THE MID LEVEL SUBSIDENCE WITHIN THE SYNOPTIC DRY SLOT...SURFACE BASED CONVECTIVE CLOUD TOPS WILL LIKELY BE LIMITED TO AROUND 16-18KFT PER SOUNDING ANALYSIS...MAKING LIGHTNING GENERATION DIFFICULT BUT CERTAINLY NOT IMPOSSIBLE. HAVE RETAINED "ISOLATED THUNDER" WORDING FOR EARLY THIS EVENING. REGARDING THE WIND ADVISORY...THE WINDOW FOR STRONG GUSTS IS MUCH SMALLER THAN THE EXISTING ADVISORY WOULD SUGGEST...OWING TO A NATURALLY POOR THERMAL CONTRAST ASSOCIATED WITH PROGRESSIVE NEGATIVE TILT TROUGHS. IN THE ABSENCE OF STRONG COLD ADVECTION AND A SIZABLE POST-FRONTAL SURFACE HIGH...THE STRONG LOW LEVEL PRESSURE GRADIENT WILL BE CO-LOCATED BENEATH THE MID LEVEL JET AXIS...WHICH ITSELF WILL MOVE SWIFTLY THROUGH THE AREA. THIS LIMITS THE WINDOW OF OPPORTUNITY FOR STRONG WIND GUSTS TO FRONTAL CONVECTION AND ONLY A FEW HOURS BEHIND THE FRONT. THE EXCEPTION WILL BE OVER THE SOUTHEAST RIDGES WHERE THE EFFECTS OF STRONGER WINDS ALOFT WILL LINGER OVERNIGHT. DOWNWARD MOMENTUM TRANSPORT FROM PRECIPITATION WILL LIKELY YIELD MOST OF THE STRONGER GUSTS...NORTHEAST CELL MOVEMENT (PARALLEL TO MID LEVEL FLOW VECTORS) WOULD SUGGEST THAT STRONGER CONVECTIVE CELLS COULD YIELD SOME RATHER IMPRESSIVE GUSTS. GIVEN THE STRONG LINEAR FORCING UNDERWAY...WOULD NOT BE SURPRISED TO SEE A NARROW COLD-FRONTAL SQUALL LINE DEVELOP OVER OHIO/KENTUCKY OVER THE NEXT SEVERAL HOURS. DESPITE THE SPARSE LIGHTNING YIELD EXPECTED... ANY SHORT-FUSE THREAT FOR DAMAGING WINDS WOULD BE HANDLED BY SEVERE THUNDERSTORM WARNINGS. WIND ADVISORY IS IN THE PROCESS OF BEING MODIFIED AS FOLLOWS: OH/WV PANHANDLE: 22-04Z PA/WV (EXCEPT THE RIDGES): 00Z-06Z PA/WV/MD RIDGES: 03Z-09Z OTHERWISE...LARGE SCALE ASCENT ENDS QUICKLY FROM WEST TO EAST AFTER 06Z...AND ALTHOUGH A CHANGE-OVER FROM RAIN TO SNOW IS DEPICTED...ONLY FLURRIES OR EVEN DRIZZLE ARE ANTICIPATED. BOOKBINDER
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&& .SHORT TERM /CHRISTMAS DAY INTO CHRISTMAS NIGHT/...
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SOUTHWEST WINDS WILL DIMINISH QUICKLY TOMORROW MORNING...AND A ONE-SHOT DAY OF COLD AIR WILL ARRIVE WITH TEMPERATURES STRUGGLING TO GET BACK TO 40 DEGREES UNDER CLOUD SKIES. ENOUGH RESIDUAL LIFT AROUND THE DEPARTING CYCLONE WILL PERSIST IN THE MORNING TO GENERATE SOME SCATTERED SNOW SHOWERS...ALTHOUGH THE MOISTURE DEPTH IS SO SHALLOW THAT IT MAY AGAIN BE MORE OF A DRIZZLE/SNIZZLE. DO NOT ANTICIPATE MORE THAN A LIGHT DUSTING UP TOWARD/NORTH OF I-80. ACROSS THE RIDGES...A STRONGER UPSLOPE WIND COMPONENT IS DEPICTED BY THE MODELS SO PERHAPS A SPARSE INCH COULD FALL ACROSS THE MD/WV RIDGES. BOOKBINDER
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/...
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AS IS TYPICAL WITH PROGRESSIVE NEGATIVE TILT TROUGHS...THE BRIEF SHOT OF COLD AIR WILL DEPART AS THE SYSTEM LIFTS INTO THE CANADIAN MARITIMES...ALLOWING FOR A TEMPORARY RETURN TO ZONAL AND/OR DAMPENED MID LEVEL RIDGING OVER THE EASTERN CONUS FRIDAY AND SATURDAY...FEATURING MUCH ABOVE NORMAL TEMPERATURES. A PROGRESSIVE WAVE WILL SETTLE ACROSS THE AREA SATURDAY NIGHT AND EARLY SUNDAY BRINGING A CHANCE FOR PRECIPITATION...AND BETTER ACCESS TO MORE SEASONABLY COLD AIR IN ITS WAKE. BOOKBINDER
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... WITH THE FORECAST AREA STILL MOSTLY IN THE WARM SECTOR...VFR CONDITIONS TO START FOR MOST TERMINALS. WITH THE EASTERN RIDGES ON THE FRINGE OF CONTINUED DAMMING...LOWER CLOUDS AND EVEN SOME FOG LINGER THERE. LLWS GROUPS INCLUDED AS SSW WINDS OF 40-50 LIE JUST A COUPLE THOUSAND FEET OFF THE SURFACE. WELL-ADVERTISED COLD FRONT WILL PUSH THROUGH DURING THE EVENING HOURS BETWEEN 22Z AND 04Z. BAND OF LOW-TOPPED CONVECTION STILL BEING FORECAST BY HRRR AND OTHER MODELS AND HAVE HANDLED THIS WITH TWO HOUR TEMPO GROUPS IN EACH TAF. CIGS WILL DROP BACK TO MVFR AS THE FRONT APPROACHES AND PASSES. MAIN ISSUE WILL BE THE WIND...WITH S/SW GUSTS TO 40-45 KNOTS POSSIBLE WITH CONVECTION..AND IMMEDIATELY FOLLOWING FROPA. WINDS WILL SLOWLY DIMINISH WITH TIME OVERNIGHT BUT STILL EXPECT AT LEAST 20-30 KNOT GUSTS THROUGH THE REMAINDER OF THE TAF PERIOD. MVFR CIGS WILL CONTINUE...PERHAPS LOWERING TO IFR BY 12Z CLOSER TO LAKE ERIE. LINGERING PRECIP WILL CHANGE OVER TO SNOW SHOWERS BY 12Z AREAWIDE...BUT SIGNIFICANT RESTRICTIONS FROM SNOW ARE NOT FORECAST. OUTLOOK.../WEDNESDAY NIGHT THROUGH MONDAY/... CIG/VIS RESTRICTIONS THROUGH THURSDAY WILL IMPROVE TO VFR FRIDAY AND CONTINUE UNTIL ANOTHER FRONTAL SYSTEM CROSSES THE REGION SATURDAY AFTERNOON. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...WIND ADVISORY FROM 9 PM THIS EVENING TO 4 AM EST THURSDAY FOR MDZ001. OH...WIND ADVISORY UNTIL 11 PM EST THIS EVENING FOR OHZ039>041- 048>050-057>059-068-069. PA...WIND ADVISORY FROM 7 PM THIS EVENING TO 1 AM EST THURSDAY FOR PAZ007>009-013>016-020>023-029-031-073-075. WIND ADVISORY FROM 9 PM THIS EVENING TO 4 AM EST THURSDAY FOR PAZ074-076. WV...WIND ADVISORY UNTIL 11 PM EST THIS EVENING FOR WVZ001>004-012. WIND ADVISORY FROM 7 PM THIS EVENING TO 1 AM EST THURSDAY FOR WVZ021-022. WIND ADVISORY FROM 9 PM THIS EVENING TO 4 AM EST THURSDAY FOR WVZ023-041.
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&& $$

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