FXUS61 KPBZ 232348
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
648 PM EST WED DEC 23 2009
.SYNOPSIS...
COLD SURFACE HIGH PRESSURE WILL KEEP DRY AND COLD CONDITIONS
ACROSS THE UPPER OHIO VALLEY INTO THURSDAY NIGHT CHRISTMAS EVE.
THEN A STRONG LOW PRESSURE SYSTEM MOVING NORTHEASTWARD THROUGH THE
MIDWEST CAN BRING A PERIOD OF FREEZING RAIN CHRISTMAS MORNING
FOLLOWED BY RAIN CHRISTMAS AFTERNOON AND EVENING AND SNOW SHOWERS
LATE CHRISTMAS NIGHT INTO THE WEEKEND.
&&
.NEAR TERM /THROUGH THURSDAY/...
JUDGING FROM RECENT SREF MODEL OUTPUT CONTINUE TO EXPECT DRY
CONDITIONS THIS PERIOD ACROSS THE UPPER OHIO VALLEY. ADJUSTED LOW
TEMPERATURES FOR TONIGHT DOWN A COUPLE DEGREES FOR LOCATIONS NEAR
THE APPALACHIAN MOUNTAINS BASED ON RECENT OBSERVED TEMPERATURES
AND EXPECTED STRONG RADIATIONAL COOLING UNDER CLEAR SKIES AND OVER
A SNOW PACK. THIS MAY KEEP DAYTIME HIGHS THURSDAY FROM FULLY
REACHING RECENT NAM AND GFS MOS FORECASTED VALUES.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
CLOUDS WILL BE ON THE INCREASE THURSDAY NIGHT AS RECENT SREF MODEL
OUTPUT SHOWS MOISTURE MOVING NORTHEAST AHEAD OF STRONG STORM SYSTEM
IN THE PLAINS. LOOKS TO BE COLD ENOUGH AT THE START FOR PRECIP TO
BE FREEZING RAIN FOR A TIME NORTH OF THE PA TURNPIKE BEFORE
DAYBREAK FRIDAY. AN EXTENDED PERIOD OF FREEZING RAIN LIKELY FOR
THE RIDGES SOUTHEAST OF PITTSBURGH WHERE COLD AIR WILL BE TRAPPED
FOR A LONGER DURATION SO WINTER STORM WATCH ISSUED.
WARM AIR WILL SURGE NORTHWARD DURING THE DAY WITH PLAIN RAIN MOST
AREAS BY MIDDAY FRIDAY CHRISTMAS DAY...EXCEPT A MIX IN THE MOUNTAINS.
THE COMBINATION OF A SECONDARY SURFACE LOW DEVELOPING NEAR THE
CAROLINAS LATER FRIDAY NIGHT AND SATURDAY PLUS A COLD UPPER LOW
CENTER MOVING INTO THE GREAT LAKES WILL INDUCE COLD AIR
INSTABILITY SNOW SHOWERS LATE FRIDAY NIGHT AND SATURDAY...AND POSSIBLY
INTO MONDAY.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
CLOSED COLD UPPER LOW COULD CONTINUE TO INDUCE COLD AIR
INSTABILITY AND LAKE ENHANCED SNOW SHOWERS ACROSS THE UPPER OHIO
VALLEY SUNDAY INTO MONDAY NIGHT UNTIL IT EXITS TO NEW ENGLAND.
SURFACE HIGH SHOULD ALLOW FOR SOME DRYING WEDNESDAY. CLOUD COVER
WILL HOLD DAYTIME TEMPERATURES DOWN TO FEW DEGREES BELOW NORMAL
THROUGH THE EXTENDED PERIOD.
&&
.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
VFR CONDITIONS SHOULD PREVAIL THROUGH THE TAF PERIOD UNDER A
SURFACE RIDGE. THE POSSIBLE EXCEPTION WOULD BE AT NORTHERN SITES
DURING THE OVERNIGHT PERIOD...WHERE A DECK OF MVFR STRATOCUMULUS
MAY MANAGE TO CREEP SOUTH INTO NORTHWESTERN PENNSYLVANIA AND
AFFECT FKL AND DUJ. WINDS WILL SLOWLY BE ON THE INCREASE FOR
THURSDAY. LOW LEVEL WIND SHEAR COULD BE OCCURRING BY THE END OF
THE 30 HOUR TAF PERIOD FOR PIT...BUT CONFIDENCE IS NOT HIGH ENOUGH
TO INCLUDE AT THIS TIME. LLWS APPEARS LIKELY LATE THURSDAY NIGHT
AT ALL TAF SITES.
A LOW PRESSURE SYSTEM DEVELOPING OVER THE PLAINS IS FORECAST TO
TRACK SLOWLY ACROSS THE MS VALLEY AND INTO THE GREAT LAKES BY THE
WEEKEND...WHILE A SECOND SURFACE LOW FORMS OVER THE DELMARVA
REGION.
PRECIPITATION ASSOCIATED WITH THIS SYSTEM WILL SPREAD ACROSS OUR
REGION FRIDAY MORNING WITH CONDITIONS LOWERING TO MVFR/IFR. SURFACE
TEMPERATURES SHOULD BE COLD ENOUGH FOR PRECIPITATION TO BEGIN AS
FREEZING RAIN EARLY FRIDAY MORNING...THEN CHANGE TO RAIN BY MIDDAY
AS TEMPERATURES WARM.
MVFR/IFR RESTRICTIONS ARE EXPECTED TO PERSIST THROUGH THE WEEKEND
AND INTO MONDAY. SCATTERED RAIN AND SNOW SHOWERS WILL CHANGE OVER TO
ALL SNOW BY SATURDAY NIGHT AS COLDER AIR MOVES IN BEHIND THE EXITING
SYSTEM.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH FRIDAY
AFTERNOON FOR MDZ001.
OH...NONE.
PA...NONE.
WV...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH FRIDAY
AFTERNOON FOR WVZ023-041.
&&
$$
