Area Forecast Discussion
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000 FXUS61 KPBZ 162241 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 541 PM EST TUE DEC 16 2014 .SYNOPSIS... SHOWERS WILL DIMINISH OVERNIGHT AS COLDER AIR MOVES INTO THE REGION. && .NEAR TERM /THROUGH WEDNESDAY/... SHOWERS IN PRE-FRONTAL SHOWERS CONTINUE TO COVER MUCH OF PENNSYLVANIA EARLY THIS EVENING...WHILE THE PATTERN IS ALREADY STARTING TO SHIFT TO OUR WEST. THE SURFACE COLD FRONT SEEMS TO BE SLICING THROUGH THE AREA...WITH THE 700 MB FRONT LAGGING A BIT. DEFORMATION ALONG THIS FRONTAL BAND SEEMS TO BE DRIVING A SECONDARY INCREASE IN SHOWER ACTIVITY AS THE 700-500 MB COLD POOL FRONT EDGE DRIVES SOUTHEASTWARD INTO OHIO. THIS SHOULD SECONDARILY INCREASE SHOWERS ACROSS THE AREA AGAIN AS THE EVENING WEARS ON. COLD ADVECTION GETS RAMPED UP OVER THE ENTIRE AREA OVERNIGHT...HOWEVER SIGNIFICANTLY COLDER AIR LAGS THE SURFACE FRONT FROM HUNDREDS OF MILES...AND IS LIKELY TRULY BOTTLED UP BEHIND A SECONDARY COLD BOUNDARY OVER THE LOWER OHIO VALLEY AND WESTERN GREAT LAKES. THIS WILL ALLOW FOR MUCH OF THE NIGHT TO CONTINUE WITH TEMPERATURES ONLY SLOWLY FALLING. IT WILL ALSO PRECLUDE MUCH OF ANYTHING BUT LIQUID PHASE HYDROMETEORS IN THE CWA. LOOKING AT BOTH THE NAM AND GFS OUTPUT...SURFACE TEMPERATURES EVEN IN THE RIDGES WILL TAKE UNTIL SUNRISE TO COME CLOSE TO FREEZING. THIS WILL SLOW ANY CHANGEOVER TO SNOW AS THE MOIST LAYER LEANS OUT...AND ICE MICROPHYSICS BECOME PROBLEMATIC TO SNOW CRYSTAL GROWTH. AS SUCH...IT WOULD SEEM IT SHOULD BE DAYTIME BEFORE ANY SNOW IS REALLY NOTED IN THE CWA...AND EVEN THEN...IT IS UNLIKELY TO BE PARTICULARLY EFFICIENT AT ACCUMULATING DUE TO POOR DENDRITIC GROWTH ZONE SATURATION. ADVECTION THROUGH THE NIGHT AND INTO THE DAY ON WEDNESDAY SHOULD ALLOW FOR A RELATIVELY NON-DIURNAL TEMPERATURE CURVE ON WEDNESDAY. TEMPERATURES WERE ADJUSTED TO ALLOW FOR LOWER AFTERNOON TEMPERATURES WITH MORNING HIGHS AS A RESULT. FRIES && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... AS STORM SYSTEM WINDS UP OFFSHORE NEW ENGLAND THURSDAY FLOW WILL TURN NORTHWEST FOR A TIME WITH SNOW SHOWER CHANCES INCREASING ACROSS THE NORTH INTO THE RIDGES. AGAIN INVERSION HEIGHTS LOOK LOW ON FORECAST SOUNDINGS SO ONLY CHANCE POPS WITH A LIGHT ACCUMULATION. THURSDAY NIGHT INTO FRIDAY A FAST MOVING SHORTWAVE WILL SLIDE EAST IN DEVELOPING ZONAL FLOW. ADDED SCATTERED FLURRIES WITH CONTINUED COLD TEMPERATURES. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... AN UPR TROF MOVG OUT OF THE CNTRL CONUS WL RTN PCPN CHCS FOR THE WEEKEND. CHC POPS WERE MAINTAINED WITH UNCERTAINTY IN NRN EXTENT OF ANY PCPN AND THE TRACK OF THE ATTENDANT SFC LOW. SEASONAL TEMPS WERE FORECAST CLOSE TO WPC GUIDANCE. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... CONDITION DETERIORATION TO LOW END MVFR AND EVENTUAL IFR WL CONT TDA WITH SHWRS AND RELATIVE SATURATION WITH PASSAGE OF THE ADVNG CDFNT. IN ADDITION...SFC WIND WL VEER TO THE WEST BY EVE WITH INITIAL GUSTS NR 20 KTS. IMPROVEMENT CAN BE EXPECTED WEDNESDAY...BUT THE SHRTWV CROSSING THE GREAT LAKES WL REINFORCE THE MIXING LYR VIA COLD ADVCTN...HENCE MVFR STRATOCU SHOULD QUICKLY RTN TO MOST PORTS AS EVE APCHS. OUTLOOK.../TUESDAY NIGHT THROUGH SUNDAY/... PERIODIC RSTRN POTENTIAL WL CONT FOR THE RMNDR OF THE WEEK WITH STRATOCU AND THE APCH OF MORE SUBSTANTIAL LOW PRES ON SATURDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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