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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/...
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.

&&

.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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