Area Forecast Discussion
Issued by NWS

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000 FXUS61 KPBZ 012346 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 646 PM EST SUN MAR 1 2015 .SYNOPSIS...
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SNOW WILL WIND DOWN OVERNIGHT. A SECOND STORM...ACCOMPANIED BY MILDER TEMPERATURES...WILL BRING POTENTIALLY HEAVY RAINFALL TO THE REGION TUESDAY AND TUESDAY NIGHT...LIKELY BEGINNING AS A PERIOD OF SLEET AND FREEZING RAIN EARLIER IN THE DAY. ICE ACCUMULATIONS ARE POSSIBLE.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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BACK EDGE OF SNOW IS MOVING INTO OHIO. WITH THE SPEED THAT PRECIPITATION IS MOVING TO THE EAST...HAVE SPED UP THE TIMING THAT PRECIPITATION WILL DIMINISH...AND MAY STILL NOT HAVE BEEN AGGRESSIVE ENOUGH. AS FOR PRECIPITATION TYPE ITSELF...RAIN/SNOW LINE HAS MADE IT AS FAR NORTH AS PITTSBURGH AND LATROBE. HOWEVER...THE NWS OFFICE NEAR PITTSBURGH INTERNATIONAL AIRPORT HAS ONLY REPORTED SNOW...WHILE ALLEGHENY COUNTY AIRPORT NEAR DOWNTOWN HAS MANAGED TO SWITCH OVER TO SNOW. EVEN THE HIGHER ELEVATIONS IN GARRETT AND TUCKER COUNTIES HAVE SWITCHED OVER TO RAIN...WITH MORGANTOWN REPORTING 40 DEGREES. ALL PRECIPITATION WILL CHANGE BACK OVER TO SNOW BY MIDNIGHT...BUT WITH PRECIPITATION DECREASING BY THAT TIME...THAT SHOULD HELP LIMIT ANY LARGE ACCUMULATIONS OF SNOW AFTER MIDNIGHT. IN ADDITION...SNOW RATIOS HAVE BEEN VERY LOW CONSIDERING TEMPERATURES ARE SO CLOSE TO FREEZING...WITH A 6:1 RATIO BEING OBSERVED LOCALLY. THE VERY WET SNOW CONTINUES TO MELT ON CONTACT IN MANY LOCATIONS. WITH PRECIPITATION CONTINUING AT ALL LOCATIONS AT THIS TIME...NO CHANGES TO HEADLINES WILL BE MADE AT THIS TIME. WITH THE EXTENSIVE CLOUD COVER OVERNIGHT...TEMPERATURES WILL ONLY DROP INTO THE MID 20S. THESE VALUES WILL BE THE FIRST TIME MUCH OF THE REGION HAS SEEN NEAR NORMAL LOW TEMPERATURES IN AT LEAST A WEEK.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
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MONDAY AND MONDAY NIGHT: ------------------------ A BRIEF LULL IN THE ACTIVE PERIOD AS HIGH PRESSURE SLIDES ACROSS THE REGION. WITH A FRESH SNOW PACK...HIGHS WILL STRUGGLE TO REACH THE MELTING POINT TOMORROW EVEN WITH SOME SUNNY INTERVALS EXPECTED. AT FIRST GLANCE...WOULD EXPECT TEMPERATURES TO FREE FALL TOMORROW NIGHT UNDER THE INFLUENCE OF HIGH PRESSURE AND FRESH SNOW. HOWEVER... MODEL CROSS SECTIONS SHOW RAPID ADVANCEMENT OF MID-HIGH LEVEL OVERCAST DURING THE EVENING AHEAD OF THE NEXT SYSTEM. THUS THIS BECOMES A HUGE TIMING ISSUE OF HOW FAST READINGS PLUMMET DURING THE EVENING BEFORE THE LONGWAVE RADIATION OUTBURST CEASES. HAVE DROPPED LOW TEMPS CONSIDERABLY OVER THE NORTHEAST CWA WHERE CONDITIONS ARE OPTIMAL THE LONGEST. VERY LOW CONFIDENCE TEMPERATURE FORECAST...ESPECIALLY IN THE NORTHERN MOUNTAINS WHERE THERE IS AN EQUAL POTENTIAL OF SEEING LOWS -5 TO -10...OR +5 TO +10 DEPENDING ON THE TIMING OF CLOUD COVER. WILL GO LOW SINGLE DIGITS FOR NOW ON A HEDGE...AND TEENS TO LOWER 20S ELSEWHERE. TUESDAY AND TUESDAY NIGHT: -------------------------- HIGHLIGHTS: A MAJOR STORM SYSTEM AND WARMER AIR WILL BRING RAINFALL (POTENTIALLY HEAVY) TO THE REGION. IMPACTS: INCREASING CONCERNS FOR BOTH RUNOFF AND ICE JAM INDUCED FLOODING. ADDITIONAL CONCERNS ABOUT SIGNIFICANT FREEZING RAIN/SLEET POTENTIAL EARLY IN THE EVENT. NUMEROUS FORECAST CHALLENGES THIS PERIOD AS MODELS CONTINUE TO DEPICT A TWO PART STORM PHASING AND DEEPENING AS IT CROSSES THE GREAT LAKES BENCHMARK. THIS PUTS THE CWA WELL INTO THE WARM SECTOR ALOFT...WITH ANOMALOUSLY HIGH MOISTURE CONTENT ROOTED IN BOTH THE PACIFIC AND GULF. INFLUX OF DEEP MOISTURE...COUPLED WITH STRONG AND PROLONGED WARM ADVECTION...AND A FAVORABLE JET STRUCTURE WILL COLLECTIVELY BRING PERIODS OF MODERATE TO HEAVY RAIN TO THE REGION TUESDAY AND TUESDAY NIGHT. KEY ISSUE NUMBER 1 IS AT THE ONSET. HAVING STARTED THE DAY OVERCAST WITH TEMPERATURES IN THE TEENS (IF NOT SINGLE DIGITS)...IT SEEMS TO REASON THAT A SIGNIFICANT ICING EVENT IS LIKELY TO OCCUR BETWEEN MID MORNING AND THE EARLY AFTERNOON BEFORE PRECIPITATION DRAG/WARM ADVECTION WARM THE BOUNDARY LAYER ABOVE FREEZING...PARTICULARLY OF CONCERN WOULD BE THOSE SAME NORTHEAST COUNTIES. SLEET/FREEZING RAIN ARE ACCOUNTED FOR IN THIS FORECAST UPDATE. KEY ISSUE NUMBER 2 IS WITH THE QPF. SEVERAL ENSEMBLE MEMBERS CONTINUE TO SHOW WIDESPREAD LIQUID QPF AMOUNTS ON THE ORDER 1-1.50" THROUGH TUESDAY NIGHT. THESE AMOUNTS ARE CERTAINLY JUSTIFIED...ALBEIT HIGHLY UNUSUAL FOR EARLY MARCH. A RAIN EVENT OF THIS MAGNITUDE...COUPLED WITH AN EXISTING HIGH-WATER CONTENT SNOW PACK...FROZEN GROUND AND ICED-OVER RIVERS/CREEKS...CERTAINLY HAS ME CONCERNED ABOUT FLOOD POTENTIAL -- BOTH FROM RUNOFF AND POTENTIAL ICE JAMS AS TEMPERATURES WARM INTO THE 40S TO THE SOUTH. KEY ISSUE NUMBER 3 IS WITH SURFACE TEMPERATURES. AS EXPECTED...A HUGE MODEL SPREAD EXISTS WITH RESPECT TO HIGH TEMPERATURES ON TUESDAY...NEVER MIND THE HOURLY TRANSITION. EXISTING SNOW PACK...PREVIOUS MORNING LOWS...PRECIPITATION INTENSITY AND THERMAL ADVECTION WILL ALL COMPETE TO WHAT LEADS TO A HIGH BUST POTENTIAL FORECAST ON TEMPERATURES -- THEREBY PLAYING INTO BOTH PRECIPITATION TYPE AND FLOODING POTENTIAL. THIS IS A HIGH CONFIDENCE...POTENTIALLY HIGH IMPACT EVENT WITH LOW CONFIDENCE DETAILS. HEADLINES FOR FREEZING RAIN AND/OR FLOODING MAY BE NECESSARY OVER THE NEXT 24 HOURS. PERSONS ARE URGED TO CLOSELY MONITOR FORECASTS OVER THE 24-36 HOURS. BOOKBINDER
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/... COLD FRONT CROSSES THE REGION TUESDAY NIGHT...REACHING THE MID- ATLANTIC REGION AROUND DAWN WEDNESDAY. RAIN WILL CONTINUE TO FALL AS THE FRONT PASSES THROUGH. WILL DECREASE POPS FROM NORTHWEST TO SOUTHEAST WEDNESDAY WITH COLDER AND DRIER AIR ADVECTING IN. ANY LINGERING PRECIPITATION WEDNESDAY AFTERNOON...WILL CHANGE TO SNOW SHOWERS AS COLDER AIR RUSHES IN FROM THE NORTHWEST. SURFACE HIGH MOVES IN THURSDAY...KEEPING THE REMAINDER OF THE LONG TERM DRY AND COLD. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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IFR/OCCASIONAL LIFR CONDITIONS WILL CONTINUE THIS EVENING AS A PASSING SHORTWAVE TROUGH CONTINUES TO SPREAD SNOW AND RAIN OVER THE REGION. GENERAL IFR CEILINGS ARE EXPECTED TO CONTINUE THROUGH THE NIGHT AS COLD ADVECTION ENSUES IN THE WAKE OF THE PASSING SYSTEM...BUT IMPROVEMENTS TO MVFR...AND FINALLY VFR CAN BE EXPECTED LATER ON MONDAY AS STRATOCU FINALLY GIVES WAY TO BUILDING HIGH PRESSURE. .OUTLOOK.../MONDAY NIGHT THROUGH FRIDAY/... LOW PRESSURE CROSSING THE GREAT LAKES IS LIKELY TO SPAWN WIDESPREAD RESTRICTIONS ONCE AGAIN BY TUESDAY AFTERNOON.
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&& .HYDROLOGY...
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AN INCREASE IN FLOW AND STAGE IS EXPECTED TO CAUSE ICE MOVEMENT STARTING TUESDAY...BEGINNING ON THE SOUTHERNMOST RIVER BASINS. THE CURRENT FORECAST CONTINUES TO HAVE A HIGH LEVEL OF UNCERTAINTY ABOUT PRECIPITATION PHASE AND AMOUNTS AS WELL AS THE DEGREE OF SNOW MELT.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR MDZ001. OH...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR OHZ039>041- 048>050-057>059. PA...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR PAZ007>009- 013>016-020>023-029-073>076. WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR WVZ001>003- 023-041. && $$

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