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000
FXUS61 KPBZ 120621 AAC
AFDPBZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
121 AM EST THU DEC 12 2013

.SYNOPSIS...
A BLAST OF ARCTIC AIR TODAY WITH SNOW SHOWERS AND FLURRIES
POSSIBLE. THE NEXT SYSTEM WILL BRING A MIXED BAG OF PRECIPITATION
FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TODAY/...
UNORGANIZED LAKE EFFECT/ENHANCED SNOW SHOWERS CONTINUE TO MOVE
SOUTHEASTWARD ACROSS THE NORTHERN TWO-THIRDS OF THE AREA. LATEST
SAT PICS ARE SHOWING DRIER AIR UNDERCUTTING THE SNOW BANDS AS THEY
EXIT THE LAKE. WINDS ARE CURRENTLY LINED UP PRETTY WELL...WHICH IS
ALLOWING PARTS OF THESE BANDS TO HOLD TOGETHER AS THEY RUSH
SOUTHWARD. AFT 09Z...VERTICAL WIND SHEAR WILL INCREASE...MAKING IT
MUCH MORE DIFFICULT FOR THE SNOW SHOWERS TO HOLD TOGETHER.
ADDITIONALLY...AS THE WINDS SHIFT MORE TO THE WEST...ACTIVITY WILL
BE NUDGED NORTHWARD. THERE ARE SOME EMBEDDED HEAVIER SQUALLS WITH
THE ACTIVITY...WHICH WILL RAPIDLY REDUCE VISIBILITIES AND ALSO
PROVIDE A QUICK INCH OR SO OF NEW SNOW. HOWEVER...IF THE CURRENT
TRENDS CONTINUE THESE OCCURRENCES WILL BE VERY LOCALIZED.

COLD AIR ALOFT BEGINS A SLOW RETREAT TO THE NORTH AFTER 12Z. BY
THIS TIME...STEERING WINDS WILL HAVE SHIFTED TO THE
WEST...REQUIRING THE CONTINUATION OF POPS ACROSS THE NORTHERN HALF
OF THE AREA.

WEAK WAA WILL CONTINUE THROUGHOUT THE DAY...SHUNTING THE SNOW
SHOWER ACTIVITY EVEN FURTHER NORTH BY LATE MORNING...INVERSION
HEIGHTS WILL BE LOW SO THE SNOW SHOWERS WILL REALLY BE WINDING
DOWN BY AFTERNOON. CLOUDS WILL BE ON A SLOW DECREASE FROM THE
SOUTHWEST AS THE RELATIVELY WARMER AIR MOVES NORTHWARD.

A VERY COLD DAY WITH TEMPS GENERALLY 20 DEGREES BELOW NORMAL. ALSO
WIND CHILL INDICES WILL COME INTO PLAY AS THEY WILL BE AT OR
SLIGHTLY BELOW ZERO FOR MUCH OF THE DAY. THE COLDEST WIND CHILLS
WILL BE OVER THE RIDGES...SO WILL CONTINUE THE CURRENT ADVISORY.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
WAA WILL CONTINUE INTO FRIDAY...ALLOWING FOR A MODERATION IN TEMPS
AND SOME SUN.

THE NEXT SYSTEM BRINGS ITS AFFECTS LATE FRIDAY NIGHT...AS SNOW
WILL OVERSPREAD THE REGION. EVEN NOW THERE ARE BIG DIFFERENCES IN
MODEL SOLUTIONS ON SATURDAY. DIFFERENCES IN THE POSITION OF THE
WEAK SURFACE LOW...DIFFERENCES IN HOW FAR NORTH THE COLD AIR WILL
PUSH AND DIFFERENCES IN SNOWFALL/QPF DUE TO THE PLACEMENT OF THE
SURFACE LOW. OVERALL...IT DOES APPEAR THAT THE QPF WILL BE LIGHT
THROUGHOUT THE EVENT. ALTHOUGH...HERE THE NAM SEEMS TO BE
OVERDOING THIS ASPECT DUE TO ITS FURTHER NORTH PLACEMENT OF THE
SURFACE LOW. TOO EARLY TO ACCURATELY PLACE LOCATIONS OF HIGHER
SNOW ACCUMULATIONS...AS DIFFERENCES IN TEMPERATURE PROFILES ARE
DRASTIC ENOUGH TO PROVIDE A LARGE DIFFERENCE IN THE PLACEMENT OF
THE RAIN SNOW LINE. AT FIRST GLANCE...IT APPEARS THE NAM IS A BIT
TOO WARM AND TOO WET...WHILE THE GFS IS TOO COLD. THE 21Z SREF
SEEMS TO BE A DECENT COMPROMISE...MOVING TOWARD THE WARMER NAM
SOLUTION...BUT INCLUDING THE DRIER GFS. FOR CURRENT FORECAST WILL
LEAN ON 21Z SREF. A WARMER SOLUTION WILL PUSH THE RAIN SNOW LINE
FURTHER NORTH SATURDAY AFTERNOON. WITH THE PLACEMENT OF THE 85H
LOW TO OUR NORTHWEST...HISTORICALLY THIS MEANS THE WARMER AIR WILL
BE PULLED FURTHER NORTHWARD. STILL DON`T HAVE A GOOD FEEL FOR THE
ICE THREAT. IT DOES APPEAR THAT IT IS MINIMAL...BUT COLD AIR BEING
TRAPPED IN SHELTERED AREAS IS ALWAYS A RISK. MODELS ARE NOW
SHOWING A STRONGER HIGH MOVING ACROSS SOUTHERN CANADA...WHICH
POSITION ALSO VARIES BETWEEN SOLUTIONS...FURTHER COMPLICATING
THINGS.

IT IS LIKELY THAT ADVISORIES WILL BE NEEDED SATURDAY...JUST NOT
SURE WHERE AT THIS POINT.

ANOTHER COMPLICATION WILL BE THE LATE DAY DRY SLOT...WHICH WILL
ESSENTIALLY BRING AN END TO ACCUMULATING SNOWS.

LOTS YET TO BE DETERMINED.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
LOW PRES IS PROGGED OFF THE MID ATLANTIC COAST SUN...WITH LINGERING
SNW SHWR CHCS ACRS OUR RGN ON THE WRN SIDE OF THE SYSTEM. LK EFCT
AND UPSLOPE SHSN ARE PSBL INTO SUN NGT BUT THESE SHOULD BE ENDG BY
MON AS HIGH PRES BLDS IN. ANOTHER CDFNT IS PROGGED FOR TUE BEFORE
HIGH PRES BLDS IN AGAIN BY WED. BLO AVG TEMPS ARE EXPD TO CONT THRU
THE PD.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
SNOW SHOWERS ALONG PASSING COLD FRONT TONIGHT WILL BRING MVFR
CONDITIONS WITH BRIEF IFR FOR TERMINALS AROUND KPIT AND NORTH.
WINDS WILL GUST UP TO 20KT BRIEFLY FROM THE WNW AS THE FRONT
PASSES. BEHIND THE FRONT...EXPECT MVFR STRATOCU CEILINGS TO LINGER
THROUGH MID MORNING. CONDITIONS WILL GRADUALLY IMPROVE TO VFR BY
EARLY AFTERNOON WITH A BROKEN MID DECK EXCEPT FOR KFKL AND KDUJ
WHERE LOW END VFR STRATOCU CEILINGS WILL LIKELY REMAIN.

.OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
VFR CONDS UNDER HIGH PRES EXPD THRU FRI EVE BEFORE A LOW PRES SYSTEM
BRINGS RSTRNS OVRNGT FRI THRU ERLY SUN.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WIND CHILL ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR MDZ001.
OH...NONE.
PA...WIND CHILL ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR PAZ074-
     076.
WV...WIND CHILL ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR WVZ023-
     041.

&&

$$