Area Forecast Discussion
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000
FXUS61 KPBZ 010258
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
958 PM EST SAT FEB 28 2015

.SYNOPSIS...
LOW PRESSURE WILL SPREAD SNOW AND RAIN OVER THE UPPER OHIO REGION
ON SUNDAY. WARMER...MORE SEASONABLE...WEATHER CAN BE EXPECTED FOR
THE COMING WEEK.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
ANOTHER LATE EVE UPDATE WAS ISSUED TO ACCOUNT FOR AN EARLIER SNOW START
LATE TONIGHT...AS WELL AS AN EARLIER DIMINISHMENT ON SUNDAY EVE.
SNOW TOTALS WERE TWEAKED DOWNWARD SLIGHTLY...BUT NO CHANGE WAS
NEEDED FOR THE OVERALL SITUATION AND ADVISORY.

PREVIOUS APPLIES...
BROAD...PERSISTANT...WARM...MOIST ADVECTION WILL SPREAD
SNOW...AND SOME RAIN OVER THE REGION ON THE EASTERN FLANK OF A
SHORTWAVE TROUGH. PASSAGE OF THE SYSTEM WL DRAG A COLD FRONT
ACROSS THE REGION IN THE PREDAWN OF MONDAY AND CHANGE REMAINING
PRECIPITATION BACK TO SNOW BEFORE SUPPRESSING IT VIA STRENTHENING
SUBSIDENCE.

MODELS REMAIN IN GENERAL AGREEMENT WITH THE SCENARIO AND OVERALL
SNOW AMOUNTS ARE EXPECTED TO BE LIMITED BY DIMINISHING EFFICIENCY
WITH THE WARM ADVECTION...AS WELL AS A LACK OF STRONG DYNAMICS
IN THE QUASI ZONAL MID LEVEL FLOW. THE WINTER WEATHER ADVISORY
THUS REMAINS APPROPRIATE AND HAS BEEN MAINTAINED FOR PROLONGED
SNOW ACCUMULATION...AND A TOUCH OF POSSIBLE ICE OVER SOUTHERN
ZONES IN THE MORNING.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
SURFACE HIGH PRESSURE SNOW IS PROJECTED TO RAPIDLY BUILD AND
SQUASH AND REMAINING SNOW SHOWERS ON MONDAY.

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 /WEDNESDAY THROUGH SATURDAY/...
COLD AIR ADVECTION IN THE WAKE OF THE TUESDAY NIGHT COLD FRONTAL
PASSAGE WILL RETURN THE REGION TO NEAR- OR SUB-FREEZING
TEMPERATURES FOR THE REMAINDER OF THE WEEK. UPSLOPE SNOW SHOWERS
LIKELY WILL PERSIST THROUGH WEDNESDAY EVENING...BUT SHOULD SEE A
MARKED DECREASE IN COVERAGE BY LATE WEDNESDAY NIGHT.

A QUICK-MOVING SHORTWAVE TROUGH COULD AFFECT THE REGION LATE IN
THE WEEK WITH LITTLE FANFARE ANTICIPATED. THE DRY AIRMASS AT THE
SURFACE PRECLUDES SIGNIFICANT IMPACTS AT THE MOMENT SAVE MODEST
LAKE-ENHANCED SNOW.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
SNOW IS EXPECTED TO DEVELOP LATE TONIGHT...AROUND 6Z NEAR ZZV TO
AROUND 9Z NEAR LBE/DUJ. ONCE SNOW COMMENCES...CONDITIONS WILL
DETERIORATE TO IFR BY MORNING.

SNOW WILL MIX WITH AND CHANGE TO RAIN AT MOST TERMINALS /EXCEPT
FKL AND DUJ/ MID-DAY...WITH MGW SEEING MOSTLY RAIN THRU THE DAY. A
WIND SHIFT IS EXPECTED SUNDAY EVE ASSOCIATED WITH A COLD FRONTAL
PASSAGE. PRECIPITATION WILL CHANGE BACK TO SNOW IN THE WAKE OF
THE COLD FRONT.

.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 FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR MDZ001.
OH...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR OHZ039>041-048>050-057>059.
PA...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR PAZ007>009-013>016-020>023-029-073>076.
WV...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR WVZ001>003-023-041.

&&

$$





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