Area Forecast Discussion
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641
FXUS61 KPBZ 121050
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
550 AM EST FRI FEB 12 2016

.SYNOPSIS...
A COLD FRONT WILL BRING MORE SNOW SNOW TO THE AREA LATER TODAY
THROUGH SATURDAY. MUCH COLDER TEMPERATURES AND DANGEROUS WIND
CHILLS WILL CONTINUE INTO THE WEEKEND BEHIND IT.

&&

.NEAR TERM /THROUGH SATURDAY/...
CLEAR SKIES CONTINUE TO DOMINATE THE AREA EARLY THIS MORNING WITH
OVERNIGHT DECOUPLING KEEPING WARM ADVECTION TO OUR WEST FROM
GENERALLY IMPACTING SURFACE TEMPERATURES. HIGH CLOUDS HAVE
GENERALLY BEEN RELEGATED TO OUR SOUTH THROUGH THE NIGHT...WHICH
MEANS A VERY COLD START TO THE DAY TODAY. THAT SAID...280-290K
LAYER ASCENT WILL INCREASE SLOWLY GOING INTO THE AFTERNOON WITH
GFS AND NAM CONDENSATION PRESSURE DEFICITS IN THE LAYER DROPPING
BELOW 10 MB SHORTLY AROUND 18Z OR SHORTLY THEREAFTER. AS
SUCH...WHILE A DRY BOUNDARY LAYER WILL LIKELY KEEP MUCH MORE THAN
VERY LIGHT SNOW FROM FALLING OUT...GENERALLY CHANCE POPS FOR LIGHT
SNOW WERE MAINTAINED EXCLUSIVELY IN THE AFTERNOON.

A COLD FRONT WILL FOLLOW THE WARM ADVECTION WITH GOOD HI-RES AND
NAM/GFS MODEL AGREEMENT ON TIMING IT INTO THE NORTHERN REACHES OF
THE CWA TOWARD 00Z...DOWN TOWARD PITTSBURGH AROUND 03Z OR SO. THE
SNOW SQUALL PARAMETER IS STILL KEYING ON THIS BOUNDARY...AND HI-
RES REFLECTIVITIES ARE RATHER IMPRESSIVE AS IT SLICES THROUGH THE
NORTHERN PORTIONS OF THE AREA. HOWEVER...AS IT STRAY FARTHER SOUTH
AND AWAY FROM A BOUNDARY LAYER MOISTURE SOURCE..AKA LAKE ERIE...IT
GETS FAR LESS IMPRESSIVE. THUS...ACCUMULATIONS ABOVE AN INCH OR SO
WERE GENERALLY RELEGATED NORTH OF METRO PITTSBURGH.

BEHIND THE FRONT...VERY STEEP LAPSE RATES AND RISING INVERSION
HEIGHTS DUE TO RAPID COOLING AT 700 MB SHOULD ALLOW FOR LAKE
EFFECT BANDS TO PROPAGATE INLAND FAIRLY EFFICIENTLY. HI-RES
ARW/HRRR/NAM/GFS CONSENSUS DOES FAVOR A MULTI-LAKE FETCH
DEVELOPING ONE DOMINANT BAND DOWN THE LENGTH OF LAKE HURON AND
ACROSS LAKE ERIE INTO NORTHWESTERN PENNSYLVANIA OVERNIGHT TONIGHT
INTO SATURDAY MORNING. THE CONSENSUS OF THE POSITIONS FAVORS
VENANGO COUNTY IN OUR AREA...THUS A LAKE EFFECT SNOW WATCH WAS
ISSUED. THIS IS JUST A WATCH AND LATER MODEL RUNS MAY MEANDER THIS
BAND ONE WAY OR ANOTHER...SO FUTURE FORECASTS SHOULD BE MONITORED.

IN ADDITION TO PURE LAKE EFFECT...FAIRLY EFFICIENT UPSLOPE WILL
LIKELY COME INTO THE RIDGES TONIGHT INTO SATURDAY MORNING AS WELL.
SHALLOW MOISTURE WILL LIKELY BE OVERCOME BY EFFICIENT
MICROPHYSICS...HOWEVER EVEN WITH EFFICIENT RATIOS...A LACK OF QPF
SEEMS TO FAIL TO ALLOW MOST AREAS TO SURPASS ADVISORY CRITERIA ON
A WIDESPREAD BASIS. THUS...WHILE ACCUMULATING SNOW IS ALMOST
GUARANTEED...SIGNIFICANT SNOW SEEMS RATHER UNLIKELY.

ONE ADDITIONAL EVENTUALITY WITH THE COLD FRONTAL PASSAGE SEEMS TO
BE A FAIRLY DEEP MIXING PROFILE. JUST OFF THE SURFACE...ROUGHLY
25-35 KTS OF MOMENTUM LOOKS TO BE PRESENT. THIS COMBINED WITH
BOUNDARY LAYER TEMPERATURES PLUMMETING TOWARD 0F OVERNIGHT SHOULD
ALLOW FOR ALL AREAS TO SEE WIND CHILL TEMPERATURES DROP BELOW
-10F...WHICH NECESSITATED A WIND CHILL ADVISORY FOR MOST OF THE
AREA. IN THE HIGHEST TERRAIN...ADDITIONAL MOMENTUM AND COLDER
TEMPERATURES MAY ALLOW FOR SOME AREAS TO DROP BELOW -25F. BECAUSE
OF ONLY MODEST CONFIDENCE IN WIDESPREAD -25F NUMBERS IN THE HIGHER
TERRAIN...A WIND CHILL WATCH WAS ISSUED. FURTHER SHIFTS CAN REFINE
WHETHER THIS SHOULD BE UPGRADED TO A WARNING OR ADVISORY. EITHER
WAY...VERY COLD WIND CHILLS WILL LIKELY PERSIST IN THE RIDGES WELL
BEYOND THE NEAR TERM. FRIES

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
LAKE-EFFECT SNOW SHOWERS ACROSS THE NORTH WILL BE WANING LATE
SATURDAY NIGHT AS THE UPPER-LEVEL LOW MOVES EAST AND A SURFACE HIGH
APPROACHES FROM THE WEST. NORTHWEST FLOW BEHIND THE EXITING FRONT
WILL BRING TEMPERATURES NEAR THE ZERO DEGREE MARK FOR SUNDAY MORNING
LOWS. WITH HIGH PRESSURE STARTING TO BUILD IN...WINDS WILL BE
DECREASING ACROSS EASTERN OHIO. TO THE EAST AND NORTH
HOWEVER...SEVERAL MORE HOURS OF STRONG AND GUSTY WINDS WILL MEAN
WIND CHILL VALUES BELOW -10F. THE HIGHEST ELEVATIONS COULD SEE WIND
CHILLS AT OR BELOW -25F. WITH THIS IN MIND...THE WIND CHILL ADVISORY
WILL CONTINUE FOR MUCH OF THE CWA INTO SUNDAY MORNING...WITH A WIND
CHILL WATCH ACROSS GARRETT AND EASTERN TUCKER COUNTIES.

BRIEF RIDGING SUNDAY AFTERNOON WILL FINALLY DISRUPT THE MEAN
NORTHWEST FLOW PATTERN ALOFT. WARM AIR ADVECTION WILL GRADUALLY KICK
INTO GEAR...BUT WITH SUCH A LOW STARTING POINT...HIGHS WILL STAY
WELL BELOW AVERAGE SUNDAY. THE NEXT WEAK WAVE ARRIVES MONDAY MORNING
SPREADING CLOUDS AND LIGHT SNOW BACK ACROSS THE FORECAST AREA. AN
INCREASE OF CLOUD COVER AND RELATIVELY WARMER AIR SURGING NORTHWARD
WILL KEEP LOWS FROM BOTTOMING OUT MONDAY MORNING.
TAX

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
A DIGGING TROUGH WILL DEEPEN A SURFACE LOW NEAR THE LOWER MISSISSIPPI
VALLEY MONDAY. STRONG SUPPORT FROM THE UPPER-LEVEL JET WILL DEEPEN
THE LOW FURTHER AS IT ADVANCES THROUGH THE SOUTHEASTERN CONUS MONDAY
AFTERNOON. INCREASED SOUTHERLY FLOW WILL TAP INTO GULF AND ATLANTIC
MOISTURE...SPREADING IT NORTHWARD INTO OUR REGION AND EAST. STRONG
ISENTROPIC ASCENT WILL BRING PRECIPITATION THROUGH AT LEAST OUR
EASTERN ZONES BY LATE MONDAY INTO TUESDAY MORNING. STILL QUESTIONS
SURROUNDING THE EXACT TRACK OF THE LOW AND THE RESULTANT WESTWARD
EDGE OF PRECIPITATION...PRECIPITATION TYPE...AND INTENSITY. AS OF THE
00Z RUNS...GUIDANCE IS FAIRLY CONSISTENT ACROSS THE MODEL
SUITE...BUT ALL HAVE NUDGED THE SURFACE LOW WEST OF THEIR POSITION
24HRS AGO.

CURRENT FORECAST CALLS FOR LIKELY SNOW TUESDAY MORNING REACHING WEST
TO THE OHIO RIVER INCLUDING PITTSBURGH. SIGNIFICANT MODEL SPREAD
DOES EXIST FOR HIGH TEMPERATURE VALUES TUESDAY...AND WITH THE
WESTWARD TREND...HAVE BUMPED UP HIGHS A FEW DEGREES. THIS WOULD
FAVOR AT LEAST SOME MIX OF RAIN/SNOW TUESDAY AFTERNOON THAT COULD
ULTIMATELY CUT INTO THE POTENTIAL FOR ACCUMULATING SNOW. BEHIND THIS
SYSTEM...THE BROAD UPPER TROUGH WILL BRIEFLY RE-ESTABLISH OVER THE
NORTHEAST. TEMPERATURES WILL INITIALLY DROP BELOW AVERAGE
THURSDAY...BEFORE REBOUNDING WITH WARM AIR ADVECTION BY THE WEEKEND.
TAX

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL CONTINUE THROUGH THE MORNING BEFORE THE NEXT
SYSTEM BRINGS ANOTHER ROUND OF SNOW AND FLIGHT RESTRICTIONS THIS
AFTERNOON/EVENING. GUSTY NORTHWEST WINDS WILL COMMENCE BY EVENING
AS A COLD FRONT MOVES THROUGH THE AREA WITH A BURST OF SNOW
SHOWERS ALONG IT.

.OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/...
RESTRICTIONS WILL BE POSSIBLE IN SNOW SHOWERS LATER FRIDAY INTO
SATURDAY. THE NEXT CHANCE FOR WIDESPREAD IFR WILL BE WITH LOW
PRESSURE MONDAY AND TUESDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WIND CHILL WATCH FROM LATE TONIGHT THROUGH SUNDAY MORNING FOR
     MDZ001.
OH...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST
     SATURDAY FOR OHZ039-048-049-057>059-068-069.
     WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SUNDAY
     FOR OHZ040-041-050.
PA...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SUNDAY
     FOR PAZ007>009-013>016-020>023-029-031-073>076.
     LAKE EFFECT SNOW WATCH FROM THIS EVENING THROUGH SATURDAY
     AFTERNOON FOR PAZ008.
WV...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST
     SATURDAY FOR WVZ003-004-012.
     WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SUNDAY
     FOR WVZ001-002-021-509>513.
     WIND CHILL WATCH FROM LATE TONIGHT THROUGH SUNDAY MORNING FOR
     WVZ514.

&&

$$



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