Area Forecast Discussion
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000 FXUS61 KPBZ 030203 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 903 PM EST MON MAR 2 2015 .SYNOPSIS... LOW PRESSURE CROSSING THE GREAT LAKES WILL SPREAD RAIN OVER THE UPPER OHIO VALLEY REGION ON TUESDAY. PRECIPITATION MAY BEGIN AS FREEZING RAIN OR A WINTRY MIX...AND WILL END BY TURNING BACK TO SNOW ON WEDNESDAY. && .NEAR TERM /THROUGH TUESDAY/...
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NO CHANGES WERE NEEDED FOR THE LATE EVE UPDATE. PREVIOUS... THE ONLY CHANGE TO THE NEAR TERM PROGNOSIS WAS AN UPWARD ADJUSTMENT TO OVERNIGHT LOWS AND HOURLY TRENDS BASED ON THE LATEST NAM GUIDANCE...WHICH SEEMED TO BETTER FEATURE THE EFFECTS OF RAPIDLY ENSUING WARM...MOIST ADVECTION ABOVE THE BOUNDARY LAYER TONIGHT AS PREVIOUSLY DEPICTED IN THE SKY FORECAST. PREVIOUS... TUESDAY WILL MARK THE START OF WHAT PROMISES TO BE A RATHER INTERESTING 48-60 HOUR PERIOD. DEVELOPING LOW PRESSURE OVER THE CENTRAL PLAINS WILL LIFT INTO THE GREAT LAKES BY 00Z WEDNESDAY. THIS WILL PUSH A WARM FRONT OUR WAY DURING THE AFTERNOON. A DEEP LAYER OF ISENTROPIC LIFT WILL PUMP MOISTURE NORTHWARD...WITH PWATS GETTING TO AROUND +2 STANDARD DEVIATIONS ABOVE NORMAL BY EVENING. EXPECT PRECIPITATION TO BREAK OUT FAIRLY RAPIDLY AFTER 12Z AND CONTINUE THROUGH THE AFTERNOON...WITH 100 POPS APPROPRIATE. WITH A DEEP WARM LAYER FORMING ALOFT AHEAD OF THE WARM FRONT...AND WITH COLD AIR STILL ENTRENCHED AT THE SURFACE...A VARIETY OF PRECIPITATION TYPES APPEAR LIKELY. BASED THE WEATHER GRIDS ON WARM LAYER ALOFT AS GIVEN BY THE NAM. PRECIPITATION WILL BEGIN AS SNOW...BUT A QUICK MIX WITH SLEET AND FREEZING RAIN WILL OCCUR. ALTHOUGH THIS INITITAL SHOT OF PRECIPITATION WILL BE FAIRLY LIGHT OVERALL...THERE IS ENOUGH OF A LIGHT ICING THREAT TO ISSUE A WINTER WEATHER ADVISORY FOR MOST COUNTIES. LEFT A FEW OF OUR SOUTH CENTRAL COUNTIES OUT...THINKING THAT ENOUGH SURFACE WARMING WILL OCCUR TO NEGATE THE ICING THREAT. A 4 TO 6 HOUR WINDOW OF MIXING APPEARS POSSIBLE AT MOST POINTS. THE CLIMATOLOGICALLY FAVORED FAR NORTHEAST CWA MAY SEE A SLIGHTLY LONGER PERIOD OF ICING INTO EARLY EVENING. MOST LOCATIONS WILL SEE A CHANGE TO RAIN BY 00Z WEDNESDAY AS STRONG LOW LEVEL SW FLOW SCOURS OUT THE COLD AIR.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... BUSY NEAR TERM GIVES WAY TO A BUSY SHORT TERM AS A TRAILING FRONT STALLS OVER THE AREA TUES NIGHT. TEMPERATURES WILL STAY WARM ENOUGH THROUGH THE OVERNIGHT INTO EARLY WEDNESDAY TO KEEP RAIN AS THE MAIN PRECIPITATION TYPE. A SOUTHWEST MOISTURE FEED ALONG A ZONE OF STRONG MID-LEVEL CONVERGENCE WILL KEEP RAIN PERSISTENT OVER OUR SOUTHERN ZONES. HOW FAR NORTH THE MODERATE TO HEAVY RAIN GETS IS A BIG QUESTION MARK AT THIS POINT. THE COARSE MODEL GUIDANCE OFFERS A BIT OF HOPE...KEEPING THE CONVERGENCE ZONE A LITTLE FURTHER SOUTH AND INTO CHARLESTON WFOS AREA. THE 12Z NAM KEEPS THAT ZONE A BIT FURTHER NORTH...HOLDING THE PRECIPITATION IN OUR AREA FOR MUCH LONGER. AT THIS POINT...WILL FOLLOW THE ECMWF/GFS IN KEEPING HIGHEST RAIN AMOUNTS TO OUR SOUTH. STILL...WITH STRONG MID-LEVEL MOISTURE TRANSPORT INTO THE AREA AND UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE RIGHT ENTRANCE REGION OF A +170KT JET...PORTIONS OF OUR FORECAST AREA COULD RECEIVE 1-1.5" OF LIQUID THROUGH LATE WEDNESDAY. THIS...COMBINED WITH THE POTENTIAL FOR SNOW MELT AND ICE ON LOCAL CREEKS AND STREAMS...COULD CAUSE HIGH WATER ISSUES FOR AREAS MAINLY SOUTH OF PITTSBURGH. AN AREAL FLOOD WATCH HAS BEEN ISSUED. COLDER AIR WILL BEGIN TO FILTER IN WEDS AS THE UPPER TROF APPROACHES FROM THE WEST. EXPECTING TEMPERATURES TO HOLD PRETTY STEADY THROUGH THE DAY...WHICH KEEPS THE RAIN/SNOW LINE NEAR PITTSBURGH THROUGH THE AFTERNOON. BY LATE EVENING TEMPERATURES WILL HAVE FALLEN ENOUGH TO TRANSITION RAIN TO SNOW FOR ALL LOCATIONS. AGAIN THERE ARE QUESTIONS SURROUNDING HOW MUCH MOISTURE STAYS IN OUR FORECAST AREA THROUGH THURS MORNING AS THE GULF OF MEXICO MOISTURE FEED KICKS IN AND THE UPPER LEVEL TROF BEGINS TO KICK THE BOUNDARY OFF TO OUR EAST. POTENTIAL FOR ACCUMULATING SNOW EXISTS...MAINLY SOUTH AND EAST OF PITTSBURGH WHERE THE DEEPEST MOISTURE HOLDS. CONFIDENCE IN SNOW TOTALS AT THIS POINT IS FAIRLY LOW...AND WILL LIKELY CHANGE AS WE MOVE CLOSER TO MID-WEEK. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... LARGE AREA OF HIGH PRESSURE WILL BUILD IN AND PROVIDE A QUIET BUT COLD END TO THE WEEK. TEMPS BEGIN TO MODERATE ON SATURDAY...BUT BY SUNDAY...FORECAST CONFIDENCE WANES AS MODEL SOLUTIONS SEPARATE. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... VFR CONDITIONS ARE EXPECTED THROUGH TUESDAY MORNING UNDER HIGH PRESSURE. AN ADVANCING WARM FRONT IS EXPECTED TO BRING A MIX OF SNOW AND FREEZING RAIN AT THE ONSET OF PRECIPITATION LATE TUESDAY MORNING INTO THE AFTERNOON...WITH AN EVENTUAL CHANGEOVER TO RAIN BY LATE TUESDAY WITH RAPID WARM ADVECTION. CONDITIONS SHOULD DETERIORATE TO MVFR WHEN PRECIP BEGINS...AND EVENTUALLY LOWER TO IFR BY LATE IN THE DAY. .OUTLOOK.../TUESDAY NIGHT THROUGH SATURDAY/... WIDESPREAD RESTRICTIONS ARE EXPECTED THROUGH WEDNESDAY NIGHT AS A COLD FRONT SLOWLY CROSSES THE REGION. A PERIOD OF LOW LEVEL WIND SHEAR IS POSSIBLE TUESDAY EVENING. && .HYDROLOGY... AN INCREASE IN FLOW AND STAGE IS EXPECTED TO CAUSE ICE MOVEMENT STARTING TUESDAY...BEGINNING ON THE SOUTHERNMOST RIVER BASINS. THE COMBINATION OF SNOW MELT AND DEVELOPING RAIN IS EXPECTED TO MOST AFFECT THE MONONGAHELA AND YOUGHIOGHENY BASINS. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER WEATHER ADVISORY FROM 10 AM TO 2 PM EST TUESDAY FOR MDZ001. FLOOD WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY EVENING FOR MDZ001. OH...WINTER WEATHER ADVISORY FROM 10 AM TO 2 PM EST TUESDAY FOR OHZ039>041-048>050-057>059-068. FLOOD WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY EVENING FOR OHZ049-050-057>059-068-069. PA...WINTER WEATHER ADVISORY FROM 10 AM TO 2 PM EST TUESDAY FOR PAZ029-075-076. FLOOD WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY EVENING FOR PAZ014-020>023-029-031-073>076. WINTER WEATHER ADVISORY FROM NOON TO 7 PM EST TUESDAY FOR PAZ007-013-014-020>023-073-074. WINTER WEATHER ADVISORY FROM 1 PM TO 9 PM EST TUESDAY FOR PAZ008-009-015-016. WV...WINTER WEATHER ADVISORY FROM 10 AM TO 2 PM EST TUESDAY FOR WVZ001>003-023-041. FLOOD WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY EVENING FOR WVZ001>004-012-021>023-041. && $$

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