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000
FXUS61 KPBZ 100833
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
333 AM EST TUE DEC 10 2013

.SYNOPSIS...
A FAST MOVING DISTURBANCE WILL SPREAD SNOW ACROSS THE REGION THIS
MORNING. MUCH COLDER TEMPERATURE WILL FOLLOW PASSAGE OF THIS
SYSTEM.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
SHRTWV WITH WELL DEFINED JET STREAK WL SPREAD SNOW ACRS THE AREA
THIS MRNG AND USHER MUCH COLDER AIR TO THE REGION. RAPID PROGRESS
OF THE SYSTEM IS EXPECTED TO LIMIT SNOW AMOUNTS...HENCE ADVISORY
TOTALS TO THE SOUTH AND EAST OF PITTSBURGH HAVE BEEN MAINTAINED OR
TWEAKED DOWNWARD BASED ON THE LATEST DETERMINISTIC GUIDANCE.

THE SYSTEMS MID LVL DRY SLOT IS FORECAST TO ENCROACH BY EARLY AFTN
THUS NECESSITATING A DOWNWARD POP ADJUSTEMENT...AND FURTHER SPPRTG
LIGHTER AMOUNTS...ESPECIALLY FM PIT NWD.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
CHC TO LIKELY SNOW SHWRS HAVE BEEN ADDED TO MUCH OF THE REGION N
OF I 70 FOR WEDNESDAY AS A SHRTWV TROF IS PROJECTED ACRS THE
REGION. OTHERWISE...INTENSIFIED COLD ADVCTN IS EXPECTED TO SPPRT
LAKE ENHANCED SNOW SHOWERS ALNG AND N OF I 80.

WIND AND COLD TEMPS WL DROP THE WIND CHILL INDICES...ESPECIALLY
ON THURSDAY MRNG. LTR SHIFTS WL HAVE TO MONITOR THAT PARAMETER...MAINLY
OVR THE RIDGE ZONES.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A FAIRLY TIGHTLY CLUSTERED GROUP OF GLOBAL MODELS AND ENSEMBLES
REVEALS GOOD AGREEMENT IN THE ADVANCE AND EVOLUTION OF AN
OCCLUDING CYCLONE OVER THE UPPER OHIO VALLEY SATURDAY INTO
SATURDAY NIGHT. SEVERAL FEATURES ASSOCIATED WITH THIS SYSTEM SHOW
COMMON CHARACTERISTIC ON THE MODELS FROM WARM ADVECTION ALLOWING
FOR A SNOW TO RAIN TRANSITION FOR MOST LOCATIONS ON SATURDAY...TO
DRY SLOTTING AND THE ERADICATION OF MOISTURE IN THE DENDRITIC
LAYER POST-FRONTAL ON SATURDAY NIGHT WHICH RESULTS IN
DRIZZLE/FREEZING DRIZZLE POSSIBILITIES...TO THE MOVEMENT OF MUCH
COLDER AIR INTO THE REGION BY SUNDAY. HOWEVER...WHILE THE MODELS
AGREE FAIRLY WELL...THIS IS YET ANOTHER SYSTEM WHERE MIXED PHASES
OF PRECIPITATION SEEM LIKELY...ALONG WITH A PERIOD OF FAIRLY WEAK
FORCING SATURDAY NIGHT.

TO ACCOUNT FOR WARM ADVECTION ALOFT BEING MORE EFFICIENT THAN AT
THE SURFACE ON SATURDAY...A BAND OF FREEZING RAIN/SLEET DOES SEEM
POSSIBLE ENOUGH TO ADD THE MENTION OF IT IN THE FORECAST. IN
GENERAL...MOST EVERYWHERE SOUTH OF FRANKLIN AND DUBOIS WILL LIKELY
RISE ABOVE FREEZING BY LATE SATURDAY. THIS SHOULD CUT OFF ANY ICE
ACCUMULATIONS...HOWEVER ALONG/NORTH OF I-80 SNOW/ICE MAY CONTINUE
TO PLAGUE THE AREA THROUGH SATURDAY NIGHT.

LIFT FROM THIS SYSTEM EXIST ALONG WITH MID-LEVEL MOISTURE AS HIGH
PV AIR SURGES DOWN INTO THE MID-LEVELS AROUND THE BASE OF THE
DECAYING UPPER LOW SATURDAY NIGHT. THIS CUTS OFF AND SIGNIFICANT
SNOW/RAIN...BUT LEAVES A VERY MOIST BOUNDARY LAYER WITH WEAK
ASCENT ON A TEMPERATURE THROUGHOUT THE MOIST LAYER WELL BELOW THAT
OF ICE NUCLEI ACTIVATION. AS SUCH...DEPENDENT UPON SURFACE
TEMPERATURES...DRIZZLE OR FREEZING DRIZZLE DOES SEEM POSSIBLE.

BY SUNDAY...COLDER AIR STARTS TO FLOOD INTO THE REGION AND THE
DENDRITIC LAYER PLUMMETS. THIS SHOULD ALLOW A TREND BACK TOWARD
SNOW SHOWERS ALONG WITH SOME LAKE COMPONENT LIKELY WORKING INTO
THE PICTURE. WITH NORTHWEST WINDS GUSTING TO 25 MPH ON MONDAY
MORNING...WIND CHILLS BELOW ZERO MAY BECOME PROBLEMATIC BY THAT
JUNCTURE.

SLOW MODIFICATION OF THE COLD AIR IN PLACE LOOKS TO TAKE PLACE
INTO EARLY NEXT WEEK. HOWEVER...DRY CONDITIONS AND DECREASING
WINDS SHOULD ALLOW FOR MINIMAL PROBLEMS BEYOND SUNDAY NIGHT EVEN
WITH THE COLD TEMPERATURES IN PLACE. FRIES

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
A FAST MOVING LOW PRESSURE SYSTEM WL BRING SNOW TO THE REGION
THIS MORNING. DETERIORATION TO IFR IS EXPECTED WITH THE MOST
PERSISTENT SNOW AROUND 12Z FOR MOST OF THE SITES SOUTH OF I-80.

FURTHER NORTH...HAVE MAINTAINED MVFR WITH THE PERIOD OF SNOW
REMAINING RELATIVELY BRIEF. CONFIDENCE IN IFR VISIBILITIES IS
HIGHER FARTHER TO THE SOUTH WHERE THE BULK OF THE PRECIPITATION
WILL OCCUR. CONDITIONS SHOULD GRADUALLY IMPROVE AFTER
MIDDAY...WITH SOME OF THE GUIDANCE TRENDING TOWARDS VFR BY THE
AFTERNOON.

.OUTLOOK.../TUESDAY NIGHT THROUGH SATURDAY/...
A BRIEF RETURN TO VFR MAY BE POSSIBLE WEDNESDAY BEFORE A CLIPPER
SYSTEM BRINGS LIGHT SNOW AND OCCASIONAL RESTRICTIONS. CIG
RESTRICTIONS IN COLD NORTHWEST FLOW WILL LIKELY CONTINUE THROUGH
THE REMAINDER OF THE WEEK. A SYSTEM DEVELOPING TOWARDS THE GULF
COAST COULD BRING FURTHER RESTRICTIONS SATURDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
     MDZ001.
OH...NONE.
PA...WINTER WEATHER ADVISORY UNTIL 2 PM EST THIS AFTERNOON FOR
     PAZ031-075.
     WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
     PAZ074-076.
WV...WINTER WEATHER ADVISORY UNTIL 2 PM EST THIS AFTERNOON FOR
     WVZ012-021-022.
     WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
     WVZ023-041.

&&

$$

15/31