Area Forecast Discussion
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000 FXUS61 KPBZ 202323 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 623 PM EST SAT DEC 20 2014 .SYNOPSIS... HIGH PRESSURE WILL BE IN CONTROL INTO MONDAY. EXPECT INCREASING PRECIPITATION CHANCES TUESDAY. STORM SYSTEM BRINGS RAIN AND WIND CHRISTMAS EVE...AND SNOW SHOWERS CHRISTMAS DAY. && .NEAR TERM /THROUGH SUNDAY/... WITH 615PM UPDATE...LOWER CLOUDS REMAIN SCATTERED OUT FROM PITTSBURGH TO LATROBE AND MORGANTOWN...BUT DO NOT EXPECT THIS TO PERSIST THROUGH THE EVENING. MINIMAL CHANGES WERE NEEDED TO HOURLY TEMPERATURE TRENDS. PREVIOUS DISCUSSION FOLLOWS. WEAKER INVERSION ACROSS PORTIONS OF SOUTHERN PA HAS ALLOWED LOWER CLOUDS TO BREAK UP SOMEWHAT...ALTHOUGH THEY ARE HANGING TOUGH SO FAR ACROSS THE NORTHERN COUNTIES NEAR FKL/DUJ AS WELL AS IN SOUTHEAST OHIO. EXPECT THESE TO REFORM TONIGHT AS INVERSION SHARPENS UP AGAIN IN VERY WEAK FLOW...THUS GOING MOSTLY CLOUDY MOST AREAS. GOING TO HANG ON TO SLIGHT CHANCE POPS IN THE SOUTHEAST WITH SHORTWAVE TROUGH MOVING ACROSS AND SLIGHTLY BETTER MOISTURE PROFILE...BUT SNOW ACCUMULATION IS NOT EXPECTED. THIS POSSIBILITY ENDS BY 09Z. ONLY MINOR MODIFICATION TO GENERALLY SEASONABLE TEMPERATURES. INVERSION IS MAINTAINED SUNDAY MORNING...BUT BY AFTERNOON EXPECT STRATUS TO MIX OUT INTO A CU FIELD AND THEN SCATTER OUT BY EVENING. A BIT MORE SUN SHOULD ALLOW FOR AFTERNOON HIGH TEMPS AROUND 5 DEGREES WARMER THAN TODAY. CL && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... BENIGN WEATHER INITIALLY WITH HIGH PRESSURE TO OUR EAST AND IN CONTROL. SOUTHEAST WINDS IN RESPONSE TO SURFACE ANTICYCLONE POSITION WILL FACILITATE DEVELOPMENT OF STRATUS OVER EASTERN PORTIONS OF TUCKER AND GARRETT COUNTIES MONDAY INTO MONDAY NIGHT. PCPN ONSET HAS SLOWED DOWN FROM PREVIOUS CYCLES...BUT THERE REMAINS A VERY LOW PROBABILITY OF FREEZING RAIN AND/OR SLEET OVER AFOREMENTIONED AREAS MONDAY. FOR NOW...TRENDED FORECAST WITH PCPN COMMENCING DURING THE AFTERNOON WHICH REFLECT LATEST NUMERICAL MODELS. WITH THIS SCENARIO...LOW LEVEL SUB-FREEZING AIR SHOULD SCOUR OUT YIELDING AN ALL RAIN PTYPE. RAIN SHADOW EFFECT TAKES PLACES TUESDAY WITH SOUTHEAST WINDS WIDESPREAD OVER THE REGION. AN ISOLATED SHOWER REACHING EASTERN OHIO AND FAR NWRN PA IS NOT OUT OF THE QUESTION...SO KEPT A SLIGHT CHANCE. WOULD NOT BE SURPRISED TO SEE BREAKS IN THE CLOUDS WHICH COULD ALLOW FOR A FEW LOCATIONS TO EXCEED 60 DEGREES. RECORD HIGHS FOR PITTSBURGH...MORGANTOWN...AND ZANESVILLE ALL RESIDE WELL INTO THE UPPER 60S...SO AT THIS JUNCTURE RECORD WARMTH IS NOT FORESEEN. PRECIP ASSOCIATED WITH THE SURFACE LOW PRESSURE SYSTEM EJECTING FROM THE GULF COAST REGION REACHES SERN AREAS OF THE FORECAST AREA THAT EVENING. A BLEND OF THE ONGOING FORECAST AND BIAS CORRECTED ECMWF WERE USED FOR TEMPERATURES. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... HIGHLIGHTS: - A WET CHRISTMAS EVE - TEMPERATURES RETURN BACK TO NORMAL VALUES CHRISTMAS DAY - SLIGHTLY ABOVE NORMAL TEMPERATURES RETURN BY FRIDAY STRONG LOW PRESSURE SYSTEM THAT HAS BEEN MUCH ADVERTISED GIVEN THE TIME PERIOD WHICH IT AFFECTS OUR AREA IS STILL ON TRACK. LONG RANGE ENSEMBLE PREDICTION SYSTEMS AND OPERATIONAL MODELS ARE CONVERGING ON A TRACK THROUGH IND / ILL THEN NORTH INTO CANADA. THIS WILL MAKE FOR ALL LIQUID PRECIPITATION ON THE FRONT END. TEMPERATURES WILL SOAR TO NEARLY 20 DEGREES ABOVE NORMAL WEDNESDAY WITH 50S COMMON. COUPLED WITH INFLUX OF MOISTURE FROM THE GULF OF MEXICO...SOUNDINGS ILLUSTRATE ELEVATED INSTABILITY WHICH PUSHES TEMP DIFFERENTIAL BETWEEN H8 AND H5 TO NEARLY 0C. THIS COULD LEAD TO ISOLATED THUNDERSTORMS AHEAD OF THE BAROCLINIC ZONE. FOR THE TIME BEING...OPTED TO LEAVE THUNDER OUT OF THE FORECAST AND WAIT FOR BETTER CONTINUITY GIVEN THIS STILL IS FIVE DAYS OUT. DESPITE PWATS NEARLY TWO STANDARD DEVIATIONS ABOVE NORMAL...COMBINATION OF KATABATIC WINDS AND DRY CONVEYOR BELT WILL LIMIT QPF POTENTIAL TO NEGATE ANY FLOOD THREAT. LONG RANGE HYDROLOGIC MODELS SHOW VERY LITTLE RISE IN AREA RIVERS...WHICH CORRELATES WELL TO THE PROJECTED QPF OF 0.50 TO 1.00". WITH THE TRACK OF THE CYCLONE DUE N...COLD AIR INJECTED INTO THE AREA WILL BE OF MIDWEST ORIGIN...SO TEMPS WILL RETREAT BACK TO SEASONAL BENCHMARKS CHRISTMAS DAY. FOR THOSE WHO ARE LOOKING FOR SNOW ON CHRISTMAS...A CHANCE OF SNOW SHOWERS EXIST...BUT GIVEN TRAJECTORY FROM THE SOUTHWEST ANY ACCUMULATION ASSOCIATED WITH THE UPPER LEVEL SYSTEM WILL BE LIGHT AT BEST. HISTORICALLY...THERE IS ONLY A 17 PERCENT CHANCE OF AT LEAST ONE INCH OF SNOW ON THE GROUND AT PITTSBURGH CHRISTMAS MORNING. H8 WINDS PUSH 50KTS WEDNESDAY NIGHT INTO THURSDAY AND HIGHEST ANOMALIES RESIDE ALONG THE LAKE SHORE...SO EXPECT HIGHEST GUSTS WOULD DO SO AS WELL. NONETHELESS...PERIOD FROM WEDNESDAY NIGHT INTO THURSDAY STRONG ISALLOBARIC FLOW COULD YIELD GUSTS IN EXCESS OF 40 MPH ESPECIALLY IN THE MOUNTAINS OF WRN MD AND NRN WV. BALANCE OF THE EXTENDED IS CHARACTERIZED BY UNCERTAINTY AS ONE WOULD EXPECT IN THE DAY 6 -7 TIME FRAME. ECMWF HAS A STRONGER SYSTEM CROSSING FRIDAY NIGHT VERSUS GFS WHICH IS MUCH WEAKER. EITHER CASE PTYPE SHOULD BE RAIN WITH SNOW SHOWERS ON THE BACKSIDE. NO PLUNGES OF ARCTIC AIR ARE FORECAST IN THE NEXT 10 DAYS. MAX/MIN TEMPERATURES WERE A BLEND OF THE FORECAST AND ECMWF BIAS CORRECTED DATA SET. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/... WHILE FKL...DUJ...AND ZZV ARE EXPECTED TO REMAIN UNDER MVFR CIGS OVERNIGHT...REMAINING TERMINALS MAY CONTINUE TO HAVE LOWER CLOUDS SCATTER OUT LEAVING A MID DECK TEMPORARILY. BY MIDNIGHT ALL TERMINALS ARE EXPECTED TO RETURN TO UNIFORM MVFR CIGS. CANNOT RULE OUT SOME CIGS BELOW 2KFT BUT DID NOT HAVE CONFIDENCE TO INCLUDE THEM. UNCERTAINTY REMAINS AS TO WHEN SKIES SHOULD SCATTER OUT ON SUNDAY. THE SCATTERING TREND SHOULD MOVE FROM SOUTHWEST TO NORTHEAST...BUT CURRENT FORECAST DOES NOT ELIMINATE CIG FROM PITTSBURGH AND LOCATIONS NORTHEAST UNTIL 00Z MONDAY. OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... NEXT STORM SYSTEM WILL BEGIN TO IMPACT THE REGION ON TUESDAY AND RESULT IN WIDESPREAD RAIN...CIG/VIS RESTRICTIONS...AND PERIODS OF LLWS INTO THURSDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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