Area Forecast Discussion
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000
FXUS61 KPBZ 300159
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
859 PM EST THU JAN 29 2015

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA TONIGHT...FOLLOWED BY BUILDING
HIGH PRESSURE FRIDAY AND SATURDAY. LOW PRESSURE MAY BRING MORE
WINTRY WEATHER SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
THE KITCHEN SINK AND POTPOURRI OF GOODNESS THAT HAS BEEN FALLING
FROM THE SKY OVER THE PAST ROUGHLY 12 HOURS IS ALREADY SHOWING
SIGNS OF TRANSITIONING TOWARD ALL SNOW TO OUR IMMEDIATE NORTH AND
WEST. SURFACE OBSERVATIONS AND DUAL POL SIGNATURES SUGGEST THIS IS
OCCURRING...AND MODEL SOUNDINGS INDICATE RAPIDLY STEEPENING LAPSE
RATES THROUGH THE EVENING...EVEN THOUGH SURFACE TEMPERATURES MAY
TAKE A FEW HOURS TO FALL OFF PRECIPITOUSLY. WHILE ALL BUT THE
NORTHERN TIER OF THE CWA IS LIKELY RAINING AT THE MOMENT...THE
TREND TOWARD FROZEN PRECIPITATION WILL BE RAPID THROUGH THE
EVENING HOURS.

THAT SAID...FREEZING SURFACE TEMPERATURES ARE ONLY REALLY NOTED IN
SURFACE OBSERVATIONS FROM LAWRENCE TO COSHOCTON COUNTIES AND TO
THE NORTH AND WEST. AS SUCH...SEVERAL HOURS OF SNOW ARE LIKELY
DURING THE EVENING WITH MARGINAL TEMPERATURES FOR ACCUMULATION AT
BEST. AS SUCH...THE INITIAL ONSLAUGHT OF SNOW THAT WILL BE LIKELY
DURING THE LATE EVENING IS FAIRLY UNLIKELY TO BE AN EFFICIENT
ACCUMULATOR. HOWEVER...THINGS WILL DRASTICALLY CHANGE OVERNIGHT
AFTER A BRIEF INTERLUDE BETWEEN THIS EVENING`S ACTIVITY AND THE
OVERNIGHT ACTIVITY IN WHICH THE DENDRITIC LAYER DRIES OUT. THIS
WILL ALLOW FOR A BRIEF PERIOD OF DRIZZLE OF FREEZING DRIZZLE TO
MOVE ACROSS THE AREA ALONG WITH SOME FAIRLY MALFORMED SNOW GRAINS
BEING GENERATED AS WELL. HOWEVER...AS DEEPER SATURATION RETURNS
OVERNIGHT...THAT ACTIVITY SHOULD END WITH A TRANSITION BACK TO
SNOW.

A DEEPER AND MUCH MORE THERMODYNAMICALLY ABRUPT SHORT WAVE AND LOW
LEVEL FRONTAL BOUNDARY COMBO WILL MOVE THROUGH THE AREA BETWEEN 06
AND 12Z TONIGHT. AS THIS OCCURS...THE DENDRITIC GROWTH ZONE WILL
TANK DOWN INTO THE SATURATED LAYER AND GIVEN FRONTOGENETICAL
LIFTING...THIS WILL LIKELY LEAD TO A PERIOD OF FAIRLY EFFICIENT
SNOW SHOWERS FOR ALL LOCATIONS GIVEN STEEP LAPSE RATES AND LARGE
SCALE FORCING FOR ASCENT. IN THE RIDGES...THIS LARGE SCALE ASCENT
WILL BE OVERLAID WITH UNIDIRECTIONAL NORTHWESTERLY UPSLOPE FLOW
WORKING ON VERY UNSTABLE LOW LEVEL LAPSE RATES. WHILE MOISTURE
FLUX INTO THE UNSTABLE LAYER FROM LAKE ERIE WILL LIKELY BE MINIMAL
DUE TO ABUNDANT ICE COVER...SATURATION BELOW THE INVERSION LEVEL
WILL NOT BE DEPENDENT UPON THIS...AND WITH
INSTABILITY...UPSLOPE...AND LARGE SCALE ASCENT ALL OVERLAYING
EACH OTHER IN THE OVERNIGHT HOURS...SNOW SHOWERS WILL LIKELY BE
HEAVY EFFICIENT DENDRITE PRODUCERS. AS SUCH...WHILE MOST LOCATIONS
WILL ONLY SEE 1-3 INCHES OF SNOW OVERNIGHT OUTSIDE THE
RIDGES...LOCATIONS IN THE HIGHER ELEVATIONS SEEM MORE LIKELY TO
END UP WITH 4 TO 8 GIVEN RATIOS SURGING TOWARD 25 TO 1 OVERNIGHT.

ALL ADVISORIES WILL REMAIN IN EFFECT FOR THE OVERNIGHT AND INTO
FRIDAY. HEAVY SNOW SHOWERS WILL LIKELY BE HANDLED INDIVIDUALLY
WITH SPS STATEMENTS THROUGH THE NIGHT. FRIES

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
EXTENDED THE WINTER WEA ADVY THRU THE DAY FRI FOR THE
RIDGES...THOUGH WITH A FROZEN LAKE ERIE WL ALLOW FOR THE NW PA
PORTION EXPIRE AT FRI MRNG. UPSLOPE SNW SHWRS SHOULD CONT THRU THE
DAY IN THE RIDGES BEFORE THINNING MSTR IN THE SNW GROWTH RGN AND
LWRG TEMP INVERSIONS END THE PCPN. A CROSSING UPR TROF SHOULD
ALLOW FOR SOME SCT SNW SHWRS OUTSIDE OF THIS AREA AS WELL.

BLDG HIGH PRES SHOULD BRING DRY WEA FRI NGT INTO SAT.

BELOW SEASONAL AVG TEMPS WERE FCST USING THE LATEST SREF NMBRS.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
MODELS CONT TO JOUST IN HANDLING OF LOW PRES PROJECTED TWD THE MID
ATLANTIC REGION FM SATURDAY NGT INTO MONDAY. PERSISTENCE RMNS
PRUDENT WITH LATEST GFS IN GENL LINE WITH CURRENT THINKING OUTSIDE
OF TIMING ISSUES. MEANWHILE...ECMWF IS FORECASTING A SOUTHWARD
TRACK TO SFC SLOW CENTER AND PCPN SHIELD. BOTH MDLS CONT TO DEPICT
AN OPEN MID LVL WAVE.

BOTTOM LINE IS THAT AN EXTENDED PERIOD OF LGT...TO MODERATE...BUT
ACCUMULATING SNOW IS LIKELY...WITH CONFIDENCE BUILDING FOR AREAS
ALNG THE INTERSTATE 70 CORRIDOR.

COLDER WEATHER WL FOLLOW AS A SERIES OF SHRTWVS AGAIN DIG AN ERN
CONUS UPR TROUGH...DETAILS FOR WHICH WL BE REFINED WITH TIME.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
CONDITION DETERIORATION IS UNDERWAY AND DEGRADATIONS CAN BE
EXPECTED INTO FRIDAY AS MIXED PCPN SPREADS OVR UPR OH TERMINALS
AND CHANGES TO SNOW WITH CDFNT PASSAGE THIS EVE. IFR CAN BE
EXPECTED IN SNOW SHWRS THIS EVE...AND IN WIDESPREAD STRATUS WHICH
WL ACCOMPANY THE COLD SURGE OVR THE REGION.

.OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/...
IMPROVEMENTS CAN BE EXPECTED AS HIGH PRES BLDS LTR ON
SATURDAY...HOWEVER...SNOW AND RESTRICTIONS ARE LIKELY WITH SUNDAY
LOW PRES.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR MDZ001.
OH...NONE.
PA...WINTER WEATHER ADVISORY UNTIL 10 AM EST FRIDAY FOR PAZ007>009-
     015-016-023.
     WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR PAZ074-076.
WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR WVZ023-041.

&&

$$





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