-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 261135
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
635 AM EST THU FEB 26 2015

.SYNOPSIS...
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A DISTURBANCE WILL BRING CHANCES FOR SNOW TODAY. DRY AND FRIGID
CONDITIONS WILL END THE WEEK.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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UPDATE TO INCREASE POPS N OF I 80 WHERE SURFACE OBSERVATIONS AND
RADAR SHOWED SNOW REACHING THE GROUND. PREVIOUS...CURRENT RADAR
IMAGERY SHOWS WEAK ECHOES ASSOCIATED WITH VIRGA BEGINNING TO
ENCROACH THE AREA...SEEMINGLY FROM ALL SIDES. CURRENT DEWPOINT
SPREADS OF 10 TO 15 DEGREES AND A SIGNIFICANT LAYER OF DRY AIR
RECORDED ON THE 00Z UPPER AIR SOUNDING WILL CONTINUE TO HAMPER
FURTHER DEVELOPMENT OF SNOW THIS MORNING.

AS THE SOUTHERN STREAM LOW PRESSURE SYSTEM GETS EJECTED FROM THE
REGION BY THE UPPER LEVEL TROF THIS MORNING...DEEPER MOISTURE WILL
SKIRT THE SOUTHEAST RIDGE ZONES. THIS WILL RESULT IN ENHANCED
CLOUD COVER AND LIGHT SNOW BANDS ENTERING THE SOUTHEASTERN PART OF
THE FORECAST AREA. BEST CHANCE OF THIS HAPPENING WILL BE FROM
ABOUT SUNRISE THROUGH MIDDAY. CLOUDS OVERSPREADING THE AREA WILL
KEEP TODAYS HIGHS IN CHECK.

AT THE SAME TIME...A RELATIVELY DRY UPPER LEVEL TROF WILL SWING
THROUGH THE SOUTHERN GREAT LAKES AND DEEPEN THE MOISTURE OVER THE
EASTERN OH AND NORTHWEST PA. ALTHOUGH THERE IS A GENERAL LACK OF
FORCING WITH THIS SYSTEM...THE MODEST LIFT WITH THE APPROACHING
700MB TROF AND DEEPER MOISTURE SHOULD BE ENOUGH TO GENERATE LIGHT
SNOW. BY EVENING THE 850MB TROF IS CLEARING THE AREA AND WIND WILL
SHIFT TO THE NORTHWEST. THIS WILL BRING IN MUCH COLDER AIR AS THE
NIGHT PROGRESSES.

A COMBINATION OF THE STRONG COLD AIR ADVECTION AND THE PASSAGE OF
THE MID-LEVEL TROF WILL GENERATE POSSIBLY THE BEST CHANCES OF SNOW
AREA WIDE FROM LATE EVENING TO MIDNIGHT. MODEL SOUNDINGS SHOW LOW
LEVEL LAPSE RATES STEEPENING AS 850MB TEMPERATURES DROP BELOW
-15C. CONVECTIVELY DRIVEN SNOW SHOWERS WILL GENERALLY BE
LIGHT...BUT SNOW RATIOS SHOULD INCREASE AS THE COLDER AIR INVADES
THE MOISTURE SOURCE LAYER. ALL TOLD A QUICK COATING COULD FALL
THROUGH THE NIGHT...MAINLY EAST OF THE OH/WV BORDER...1-2" COULD
OCCUR IN THE MOUNTAINS OF WV/PA/MD AS RESIDENCE TIME WILL BE
LONGER.
TAX
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&&

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
INCREASED LOWS A DEGREE OR TWO THURS NIGHT...AS THE COLDER
AIR IS A BIT SLOWER TO MOVE IN. A NORTHWEST TO SOUTHEAST GRADIENT
WILL BE PRESENT IN LOW TEMPERATURES THROUGH FRI MORNING. LOWS
SHOULD BE IN THE SINGLE DIGITS BELOW ZERO ACROSS OUR FAR
NORTHWESTERN ZONES IN OH/PA. WINDS WILL BE DIMINISHING...BUT
MARGINAL ADVISORY LEVEL WIND CHILL VALUES MAY OCCUR. CONFIDENCE IN
KEEPING WIND ABOVE 5KTS IS NOT HIGH ENOUGH AT THIS
TIME...PRECLUDING THE NEED FOR AN ADVISORY.

FRIDAY WILL FEATURE CLEARING SKIES...BUT TEMPERATURES ARE EXPECTED
TO REMAIN WELL BELOW AVERAGE...TOPPING OUT IN THE TEENS. THIS IS DUE
TO THE MUCH COLDER AIR MASS IN PLACE IN THE WAKE OF THE LATEST
FRONT. SUNSHINE FRIDAY AFTERNOON WILL CHALLENGE THE COLD AIR AND MAY
BUMP HIGHS UP A FEW DEGREES...BUT OVERALL A COLD DAY IS ON TAP.

WITH HIGH PRESSURE OVERHEAD FRI NIGHT/SAT MORNING THE BOTTOM WILL
ONCE AGAIN FALL OUT ON THE TEMPERATURES AS IDEAL RADIATIONAL COOLING
WILL SET UP. DESPITE WARM AIR ADVECTION TAKING PLACE IN THE LOW- TO
MID-LEVELS...THE ATMOSPHERE SHOULD DECOUPLE AND WONT ALLOW THE
WARMER AIR TO MIX DOWN. WITH THE REMAINING SNOWPACK IN
PLACE...TEMPERATURES ARE EXPECTED TO ONCE AGAIN DIP BELOW
ZERO...POSSIBLY CHALLENGING SOME DAILY LOW RECORDS. ONCE
AGAIN...LACK OF SURFACE FLOW WILL PRECLUDE THE NEED FOR A WIND CHILL
ADVISORY...BUT IT WILL BE COLD NEVERTHELESS.

SATURDAY OFFERS A QUICK WARM UP WITH MIXING OF THE WARMER AIR ALOFT
AND ABUNDANT SUNSHINE. HIGH CLOUDS WILL BEGIN STREAMING IN FROM THE
SOUTHWEST LATER IN THE DAY...BUT THE DRY TREND WILL HOLD THROUGH
SATURDAY.
TAX

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
A SHORTWAVE AND ITS ASSOCIATED COLD FRONT IS PROGGED APPROACH AND
CROSS THE GREAT LAKES AND UPPER OHIO VALLEY REGION LATE SATURDAY
NIGHT THROUGH SUNDAY NIGHT. WARM ADVECTION AHEAD OF THE WAVE
SHOULD ALLOW FOR A MIX OF RAIN AND SNOW SOUTH OF I 80...WITH
MAINLY SNOW TO THE NORTH. A BRIEF PERIOD OF FREEZING RAIN IS
POSSIBLE BUT NOT ENOUGH CONFIDENCE IN THE DETAILS TO INCLUDE AT
THIS TIME.

A PATTERN CHANGE AND RELATIVE WARM UP THEN SETS UP THROUGH MUCH OF
NEXT WEEK AS WESTERN CONUS TROUGHING DEVELOPS. SHORTWAVES ARE
PROGGED TO EJECT OUT OF THE TROUGH AND MOVE ACROSS THE OHIO VALLEY
REGION IN SOUTHWEST FLOW...KEEPING PERIODIC RAIN AND SNOW CHANCES
THROUGH LATE WEEK. THE BEST CHANCE APPEARS TO BE WITH A
TUESDAY/TUESDAY NIGHT WAVE. MODEL QPF AMOUNTS APPEAR TO BE
OVERDONE IN THE WARM ADVECTION REGIME...BUT WILL MONITOR AS A
DECENT SNOWPACK REMAINS.

ENSEMBLE BASED WPC GUIDANCE OFFERED A REASONABLE START TO THE
FORECAST...THOUGH MADE ADJUSTMENTS TO THE LATEST GFS TO WARM SOME
TEMPS...WITH ADJUSTMENTS FOR PRECIP TYPE BASED ON GFS CRITICAL
THICKNESSES.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
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VFR CONDITIONS ARE EXPECTED FOR MOST PORTS INTO EARLY MORNING AS
CLOUDS INCREASE WITH A COUPLE OF APPROACHING SHORTWAVES. ANY SNOW
FROM A WAVE CROSSING THE MID ATLANTIC REGION SHOULD STAY TO OUR
SOUTH. THE SECOND SHORTWAVE PROGGED TO ADVANCE ACROSS THE GREAT
LAKES TODAY SHOULD SPREAD MVFR CONDITIONS WITH SCATTERED SNOW
SHOWERS ACROSS AREA PORTS...AND THIS WAS ALREADY AFFECTING FKL
THIS MORNING. PATCHY IFR CONDITIONS ARE EXPECTED ALSO THIS
AFTERNOON...ESPECIALLY FROM PIT NORTH. SNOW SHOWERS SHOULD
DECREASE AS SUPPORT EXITS TONIGHT...THOUGH MVFR CEILINGS SHOULD
REMAIN.

OUTLOOK.../FRIDAY THROUGH MONDAY/...
RESTRICTIONS ARE LIKELY WITH CROSSING LOW PRESSURE SUNDAY INTO
MONDAY.
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&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$