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Area Forecast Discussion
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000
FXUS61 KPBZ 272345
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
645 PM EST TUE JAN 27 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD AND DECREASE CLOUDS TONIGHT. A COLD
WEDNESDAY WILL FOLLOW.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
COVERAGE OF LIGHT SNOW HAS BEEN EXPANDING RAPIDLY OVER THE PAST
HOUR OR SO AS THE LAST DEFORMATION ZONE HAS BEEN SHIFTING WEST AND
SOUTHWESTWARD FROM CENTRAL PENNSYLVANIA BACK INTO WESTERN
PENNSYLVANIA. THIS HAS ALLOWED FOR EXTREMELY EFFICIENT SNOW TO
DEVELOP WITH RATIOS LIKELY IN EXCESS OF 25 TO 1. THIS COUPLED WITH
UNIDIRECTIONAL UPSLOPE FLOW FROM THE NORTHWEST IN THE BOUNDARY
LAYER INTO THE RIDGES HAS ALLOWED FOR AN INTENSIFYING TREND FOR
SNOW SHOWERS IN THE RIDGES AS WELL. MODEL SOUNDINGS SUGGEST A 3
KFT SATURATED LAYER ENTIRELY BISECTING THE DENDRITIC GROWTH LAYER
WITH AN UNSTABLE...OROGRAPHIC...AND NOW LARGE SCALE LIFTING
MECHANISM ALL OVERLAYING THE RIDGES FOR THE NEXT ROUGHLY 10 HOURS
OR SO. GIVEN GROUND TRUTH REPORTS FROM GARRETT COUNTY OF NEAR
ADVISORY LEVEL ACCUMULATIONS TODAY ALONG WITH AN INCREASINGLY
FAVORABLE ENVIRONMENT FOR SNOW SHOWER DEVELOPMENT THROUGH MUCH OF
THE EVENING...WINTER WEATHER ADVISORIES WERE HOISTED FOR THE
RIDGES THROUGH 1 AM.  

ELSEWHERE...LIGHT SNOW WILL LARGELY BE GENERATED BY THE
SOUTHWESTWARD DRIFTING DEFORMATION ZONE. ACCUMULATIONS OUTSIDE OF
THE OROGRAPHIC LIFTING AREAS WILL LIKELY BE MINIMAL...DUE LARGELY
TO MEAGER QPF...THOUGH THE SNOW TO LIQUID RATIOS THAT COME OUT OF
IT WILL LIKELY BE LARGE. THAT SAID...IT WOULD NOT BE SHOCKING TO
GET AN INCH ANYWHERE IN PARTICULAR GENERALLY FROM STEUBENVILLE
EASTWARD. 

OTHERWISE...DRIER ARCTIC AIR WILL START TO ENCROACH FROM THE
NORTHEAST OVERNIGHT...WHICH SHOULD WIND SNOW SHOWER ACTIVITY DOWN
BY MORNING...AND ALLOW FOR TEMPERATURE FREE FALL LATE TONIGHT. IT
SEEMS THE SNOW GLOBE WILL CONTINUE TO BE SHAKEN OUTSIDE UNTIL THAT
TIME. FRIES

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
WEDNESDAY HIGHS WERE LIMITED TO ROUGHLY 10 DEGREES UNDR THE AVGS
WITH SFC HIGH PRES SLIDING ACRS THE UPR OH REGION. SHRTWV RIDGING
WL MAINTAIN DRY CONDITIONS THROUGH WEDNESDAY NIGHT...BUT STRENGTHENING
WARM ADVCTN IN ADVN OF TROUGH DIGGING RAPIDLY TWD THE WRN LAKES WL
IMPROVE THE THURSDAY MRNG LOWS.

THE NAM...GFS...ECMWF FORECASTED CENTER TRACK OF THAT SYSTEM RMNS
N OF THE REGION...HENCE CONTD WARM ADVCTN ON THE ERN FLANK IS
EXPECTED TO LIMIT SNOW ACCUMULATION POTENTIAL. HOWEVER...THE
SCENARIO WL FAVOR A WINTRY MIX COMPLICATED BY COLD SURFACES
LEFTOVER OVR FM THE PREVIOUS TWO NGTS.

ANY PCPN THAT DOES TURN TO RAIN WL STILL HAVE THE POTENTIAL TO
FREEZE ON CONTACT. IN ADDITION...THE DRY LAYER WHICH IS PROGGED TO
LIMIT PCPN ONSET IN THE MRNG MAY OFFSET A WEAKER WARM ADVCTN
REGIME VIA WET BULBING. BOTTOM LINE IS THAT FORECAST WL FEATURE A
WINTRY MIX WITH A CHANGE TO SNOW WITH PASSAGE OF THE SYSTEMS COLD
FRONT ON THURSDAY EVENING. A HAZARDOUS WEATHER OUTLOOK WAS ALSO
INCLUDED FOR THE FREEZING RAIN POTENTIAL. QPF WAS COMPLETED USING
WPC GUIDANCE TRIMMED FOR LOCAL POP TRENDS WITH SNOW TOTALS
ADJUSTED FOR SFC TEMP EXPECTATIONS.

IN THE WAKE OF THE FRONT...COLD TEMPS WL AGAIN VISIT THE REGION.
DEPTH OF COLD AT MOMENT LKS SUFFICIENT TO SPPRT SNOW SHWRS...SO
LIKELY POPS WERE MAINTAINED OVR THE RIDGES PAST DAYBREAK DESPITE
DRY ADVCTN AND LACK OF ANY REINFORCING LAKE ERIE MSTR DUE TO ICE.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
COLD ARCTIC HIGH SHIFTS EAST INTO SATURDAY WITH SNOW SHOWERS IN
NORTHWEST FLOW FRIDAY ENDING FRIDAY NIGHT. WITH 850MB TEMPS
PROGGED NEAR -20C BY 00Z SATURDAY TEMPERATURES FRIDAY WILL BE
STEADY OR FALL. CLOUDS SHOULD BEGIN TO BREAK AS CENTER OF HIGH
MOVES INTO REGION FRIDAY NIGHT...WITH LOWS BELOW ZERO NORTH AND
SINGLE DIGITS SOUTH. IF CONDITIONS GO CLEAR AND CALM FRIDAY NIGHT
MAY GO BELOW ZERO ACROSS THE ENTIRE REGION. TEMPERATURES RECOVER
TO MAINLY THE 20S SATURDAY. A SIGNIFICANT STORM LOOKS POSSIBLE FOR
SUNDAY INTO EARLY MONDAY BEFORE ARCTIC AIR RETURNS TO START THE
WORK WEEK.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
ONGOING SNOW SHOWERS WILL BEGIN TO WANE FROM NORTH TO SOUTH AS
DRIER AIR ARRIVES TO CHOKE OFF THE MOISTURE. EXPECTING MVFR
CIGS/VSBY TO CONTINUE IN THE LIGHT SNOW BEFORE FINALLY TAPERING
OFF LAST NEAR KMGW/KLBE AFTER MIDNIGHT. CLOUDS WILL BEGIN TO
SCATTER OUT AS THE DRIER AIR ARRIVES FROM THE NORTH. ALREADY
BEGINNING TO SEE THIS IN DUJ WHERE THE LLVL MOISTURE EVACUATED
LEAVING A MID-DECK LINGERING. CLEARING IS EXPECTED FOR MOST
TERMINALS BY ABOUT DAYBREAK WEDS MORNING...ALTHOUGH SOME SCT LOW
CLOUDS COULD REMAIN NEAR KMGW. WINDS WILL BEGIN TO DISSIPATE
TONIGHT AND THROUGH THE DAY WEDS AS RIDGE OF HIGH PRESSURE BUILDS
IN FROM THE WEST.
TAX

.OUTLOOK.../WEDNESDAY THROUGH SUNDAY/...
WIDESPREAD RESTRICTIONS ARE EXPECTED ON THURSDAY WITH CROSSING LOW 
PRESSURE. FREEZING PRECIPITATION IS POSSIBLE AT ALL TERMINALS 
THURSDAY WITH PRECIPITATION CHANGING OVER TO SNOW BY MIDNIGHT 
FRIDAY. RESTRICTIONS WILL CONTINUE INTO FRIDAY. VFR CONDITIONS ARE 
EXPECTED SATURDAY...WITH ANOTHER SET OF RESTRICTIONS POSSIBLE SUNDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR MDZ001.
OH...NONE.
PA...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR PAZ074-
     076.
WV...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR WVZ023-
     041.

&&

$$






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