Area Forecast Discussion
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000 FXUS61 KPBZ 260647 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 147 AM EST THU FEB 26 2015 .SYNOPSIS... LIGHT SNOW SHOWERS THURSDAY WILL GIVE WAY TO DRY AND FRIGID CONDITIONS FRIDAY. && .NEAR TERM /THROUGH TONIGHT/...
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CURRENT RADAR IMAGERY SHOWING ECHOES BEGINNING TO ENCROACH THE AREA...SEEMINGLY FROM ALL SIDES. HOWEVER...CURRENT DEWPOINT SPREADS OF 10 TO 15 DEGREES AND A SIGNIFICANT LAYER OF DRY AIR RECORDED ON THE 00Z UPPER AIR SOUNDING HAVE KEPT ACTUAL PRECIPITATION AT BAY. THIS WILL MORE THAN LIKELY CONTINUE FOR SEVERAL MORE HOURS BEFORE THE DRY AIR IS ERODED ENOUGH FOR THE SNOW TO REACH THE GROUND. THUS...HAVE PUSHED BACK TIMING OF POPS THIS MORNING BY A FEW HOURS. AS THE SOUTHERN STREAM LOW PRESSURE SYSTEM GETS EJECTED FROM THE REGION BY THE UPPER LEVEL TROF THIS MORNING...DEEPER MOISTURE WILL SKIRT THE SOUTHEAST RIDGE ZONES. THIS WILL RESULT IN ENHANCED CLOUD COVER AND LIGHT SNOW BANDS ENTERING THE SOUTHEASTERN PART OF THE FORECAST AREA. BEST CHANCE OF THIS HAPPENING WILL BE FROM ABOUT SUNRISE THROUGH MIDDAY. CLOUDS OVERSPREADING THE AREA WILL KEEP TODAYS HIGHS IN CHECK. AT THE SAME TIME...A RELATIVELY DRY UPPER LEVEL TROF WILL SWING THROUGH THE SOUTHERN GREAT LAKES AND DEEPEN THE MOISTURE OVER THE EASTERN OH AND NORTHWEST PA. ALTHOUGH THERE IS A GENERAL LACK OF FORCING WITH THIS SYSTEM...THE MODEST LIFT WITH THE APPROACHING 700MB TROF AND DEEPER MOISTURE SHOULD BE ENOUGH TO GENERATE LIGHT SNOW. BY EVENING THE 850MB TROF IS CLEARING THE AREA AND WIND WILL SHIFT TO THE NORTHWEST. THIS WILL BRING IN MUCH COLDER AIR AS THE NIGHT PROGRESSES. A COMBINATION OF THE STRONG COLD AIR ADVECTION AND THE PASSAGE OF THE MID-LEVEL TROF WILL GENERATE POSSIBLY THE BEST CHANCES OF SNOW AREA WIDE FROM LATE EVENING TO MIDNIGHT. MODEL SOUNDINGS SHOW LOW LEVEL LAPSE RATES STEEPENING AS 850MB TEMPERATURES DROP BELOW -15C. CONVECTIVELY DRIVEN SNOW SHOWERS WILL GENERALLY BE LIGHT...BUT SNOW RATIOS SHOULD INCREASE AS THE COLDER AIR INVADES THE MOISTURE SOURCE LAYER. ALL TOLD A QUICK COATING COULD FALL THROUGH THE NIGHT...MAINLY EAST OF THE OH/WV BORDER...1-2" COULD OCCUR IN THE MOUNTAINS OF WV/PA/MD AS RESIDENCE TIME WILL BE LONGER. INCREASED LOWS A DEGREE OR TWO THURS NIGHT...AS THE COLDER AIR IS A BIT SLOWER TO MOVE IN. A NORTHWEST TO SOUTHEAST GRADIENT WILL BE PRESENT IN LOW TEMPERATURES THROUGH FRI MORNING. LOWS SHOULD BE IN THE SINGLE DIGITS BELOW ZERO ACROSS OUR FAR NORTHWESTERN ZONES IN OH/PA. WINDS WILL BE DIMINISHING...BUT MARGINAL ADVISORY LEVEL WIND CHILL VALUES MAY OCCUR. CONFIDENCE IN KEEPING WIND ABOVE 5KTS IS NOT HIGH ENOUGH AT THIS TIME...PRECLUDING THE NEED FOR AN ADVISORY. TAX
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY/... SNOW SHOWERS WILL BE DIMINISHING WEST TO EAST THURSDAY EVENING WITH 850MB TEMPS RANGING FROM -18 TO -20C BY 12Z FRIDAY BASED ON THE NAM. THIS WILL PUSH TEMPERATURES INTO THE SINGLE DIGITS WITH BELOW ZERO READING ACROSS THE NORTH. ARCTIC HIGH WILL BUILD OVER REGION FOR FRIDAY THROUGH SATURDAY KEEPING TEMPERATURE 25 TO 30 DEGREES BELOW AVERAGE. CLEAR SKIES FRIDAY NIGHT WITH CALM WINDS OVER SNOW WILL ALLOW FOR TEMPERATURES WELL BELOW ZERO FRIDAY NIGHT. SURFACE RIDGE AXIS BEGINS TO PUSH EAST SATURDAY AFTERNOON ALLOWING TEMPERATURES TO RECOVER INTO THE 20S WITH NEAR 30 FOR THE MASON DIXON LINE. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... MINIMAL CHANGES TO THE EXTENDED WERE MADE MAINLY FOR COORDINATION WITH SURROUNDING OFFICES. MARCH BEGINS WITH SFC HIGH PRESSURE BEING SHUNTED TO OUR EAST AS A LONGWAVE TROF DIGS IN ALONG THE PACIFIC COAST. THIS WILL AT LEAST TEMPORARILY BRING A CHANGE TO THE UPPER LEVEL FLOW TO A MORE ZONAL REGIME. A WEST TO EAST BOUNDARY WILL SERVE AS A LOOSE FOCUS FOR PRECIPITATION OVERSPREADING THE REGION BY LATE WEEKEND. TEMPERATURES SUNDAY SHOULD MOVE TOWARD THE SEASONAL AVERAGE...WHICH WILL PROVIDE A MIX OF PRECIPITATION TYPES. GIVEN THE RECENT COLD TEMPERATURES...SFC TEMPERATURES MAY RESULT IN FREEZING RAIN BEING INCLUDED IN FUTURE UPDATES. AT THE MOMENT...INCLUSION OF A FEW HOURS OF FREEZING RAIN IS A BIT TOO FINE SCALE AND THUS CONFIDENCE IS NOT HIGH ENOUGH. LONG RANGE GUIDANCE VARIES A BIT HEADING INTO NEXT WEEK...BUT SIGNS POINT TO ANOTHER STORM SYSTEM FROM THE SOUTHERN STREAM MOVING EAST MID WEEK WITH ANOTHER ROUND OF MIXED PRECIPITATION. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... VFR CONDITIONS ARE EXPECTED INTO EARLY MORNING AS CLOUDS INCREASE WITH A COUPLE OF APPROACHING SHORTWAVES. ANY SNOW FROM A WAVE CROSSING THE MID ATLANTIC REGION SHOULD STAY TO OUR SOUTH. THE SECOND SHORTWAVE PROGGED TO ADVANCE ACROSS THE GREAT LAKES THURSDAY AND THURSDAY EVENING SHOULD SPREAD MVFR CONDITIONS WITH SCATTERED SNOW SHOWERS...THOUGH FKL AND DUJ ARE PROGGED TO SEE BETTER MOISTURE AND STRONGER LIFT WHICH COULD PRODUCE IFR VISIBILITIES BY THIS AFTERNOON. SNOW SHOWERS SHOULD DECREASE AS SUPPORT EXITS OVERNIGHT...THOUGH MVFR CEILINGS SHOULD REMAIN. OUTLOOK.../FRIDAY THROUGH MONDAY/... RESTRICTIONS ARE LIKELY WITH CROSSING LOW PRESSURE SUNDAY INTO MONDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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