Area Forecast Discussion
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000 FXUS61 KPBZ 011009 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 509 AM EST SUN MAR 1 2015 .SYNOPSIS... SNOW AND RAIN SHOWERS CAN BE EXPECTED TODAY AND AGAIN ON TUESDAY. TEMPERATURES WILL TREND WARMER THROUGH WEDNESDAY...BEFORE COLD RETURNS LATE IN THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... PRECIPITATION SHOULD BE STEADY BUT RELATIVELY LIGHT THE MAJORITY OF THE DAY WITH PERSISTENT MOISTURE ADVECTION AND ISENTROPIC LIFT ON THE FRONT SIDE OF AN APPROACHING TROUGH. STRONG LOW LEVEL WARM AIR ADVECTION WILL RESULT IN A CHANGEOVER TO MIXED PRECIPITATION SOUTH OF INTERSTATE 80 AND RAIN PRIMARILY SOUTH OF PITTSBURGH. ALTHOUGH MODEL QPF AMOUNTS CONTINUE TO SHOW LARGE VALUES...SNOW ACCUMULATIONS WILL BE HAMPERED BY THE MIXED PRECIPITATION AND RAIN ACROSS THE AFOREMENTIONED AREAS. ADDITIONALLY...SOUNDINGS SHOW THE SATURATED LAYER UP TO APPROXIMATELY 10KFT NEARLY ISOTHERMAL WITH TEMPERATURES ABOVE -10C WHICH IS NOT QUITE COLD ENOUGH FRO LARGE DENDRITIC SNOW GROWTH. FURTHER...AVERAGE MIXING RATIO VALUES OF ALONG 295K (WHICH SEEMS TO BE SHOWING THE BEST ISENTROPIC LIFT BETWEEN 700-750MB)LOOK TO BE AROUND 2.5-3G/KG FROM THIS MORNING UNTIL MONDAY MORNING...WHICH SUGGESTS THE POTENTIAL SNOWFALL THROUGH THAT TIME ONLY TO BE AROUND 5-6 INCHES. LOOKING AT UPSTREAM OBSERVATIONS AND SNOWFALL RATES THUS FAR AND THE DURATION THE FORECAST AREA WILL BE UNDER THE MAIN LIFT AND MOISTURE ADVECTION...THESE AMOUNTS SEEM PRETTY REASONABLE FOR LOCATIONS EXPECTED TO SEE ALL SNOW. (ALONG AND NORTH OF THE I80 CORRIDOR). THE ASSOCIATED COLD FRONT WILL PASS THROUGH OVERNIGHT CHANGING ANY REMAINING PRECIPITATION BACK OVER TO SNOW...DIMINISHING QUICKLY AS HIGH PRESSURE BUILDS BACK IN ACROSS THE REGION. ALL THINGS CONSIDERED...THE WINTER WEATHER ADVISORY THUS REMAINS APPROPRIATE AND HAS BEEN MAINTAINED FOR PROLONGED SNOW ACCUMULATION...AND FOR SOUTHERN LOCATIONS IN THE ADVISORY...A BRIEF PERIOD OF ICE IN THE MORNING. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... BUILDING SURFACE HIGH PRESSURE WILL RESULT IN MAINLY DRY CONDITIONS ON MONDAY...HOWEVER...HOWEVER...A SOUTH-SOUTHWESTERLY 850MB JET ON THE EASTERN FLANK OF MIDWESTERN LOW PRESSURE IS PROJECTED TO STRENGTHEN ON MONDAY NIGHT AND FUEL ANOTHER ROUND OF WARM...MOIST ADVECTION WITH LIGHT PRECIPITATION AGAIN DEVELOPING OVER THE REGION. THAT PRECIPITATION LIKELY WILL BEGIN AS LIGHT SNOW...BUT WITH RAPID WARMING ALOFT...A PERIOD OF FREEZING RAIN IS LIKELY IN THE ENTRENCHED SURFACE COLD. THAT PERIOD IS EXPECTED TO BE RELATIVELY BRIEF WITH THE SURFACE LOW PROJECTED TO PASS NORTHWEST OF THE FORECAST AREA...LEAVING THE OHIO VALLEY WELL WITHIN THE WARM...HENCE THE RAIN SECTOR UNTIL COLD FRONTAL PASSAGE ON WEDNESDAY. AS MODELS TEND TO OVERDO QPF IN WARM AIR ADVECTION PATTERNS...AND GIVEN THAT THIS PROJECTED SYSTEM IS AN OPEN WAVE...QPF ON TUESDAY WAS TONED DOWN SLIGHTLY FROM THE MORE ASSERTIVE GFS VALUES. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... 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 PRECIPIATION 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 /10Z SUNDAY THROUGH THURSDAY/... A QUICK DETERIORATION IN CONDITIONS OVERNIGHT FROM WEST TO EAST. LARGE AREA OF SNOW WILL OVERSPREAD THE REGION TAKING VFR CONDITIONS QUICKLY TO MVFR. THE MAIN PROBLEM WILL BE THE LONG TERM REDUCTION IN VISIBILITY...GENERALLY IFR...FOR MUCH OF THE FORECAST PERIOD. STILL SOME UNCERTAINTY ON HOW FAR NORTH THE WARMER AIR WILL MAKE IT...BUT IT DOES APPEAR A GOOD BET TO SEE AN EVENTUAL CHANGE OVER TO RAIN AT MGW BY LATE MORNING. A MIX IS POSSIBLE AT ALL PORTS EXCEPT FKL AND DUJ. RIGHT NOW CONFIDENCE IS LOW...SO KEPT ALL SNOW FOR THE FORECAST. WINDS WILL REMAIN LIGHT THROUGH THE DAY. .OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... RESTRICTIONS LIKELY WILL PERSIST THROUGH MUCH OF MONDAY. LOW PRESSURE CROSSING THE GREAT LAKES IS LIKELY TO SPAWN WIDESPREAD RESTRICTIONS ONCE AGAIN BY LATE TUESDAY. && .HYDROLOGY... MANY OF THE AREA RIVERS AND STREAMS ARE ICE COVERED. 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. && .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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