Area Forecast Discussion
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000
FXUS61 KPBZ 311555
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1055 AM EST SAT JAN 31 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD IN THROUGH THIS EVENING. LOW PRESSURE
WILL BRING WINTRY WEATHER SUNDAY INTO MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
LINGERING STRATOCU FM DUJ TO LBE SHOULD CLEAR BY ERLY AFTN AS HIGH
PRES CONTS TO BLD IN. OTRW...MAINLY CLEAR SKIES AND DRY WEA ARE
EXPD THRU THE DAY WITH BELOW AVG TEMPS CONTG.

PREVIOUS...
TONIGHT...FRONTAL BOUNDARY BRIDGING FROM WEAK LOW DROPPING ACROSS
EASTERN GREAT LAKES...TO THE MORE SIGNIFICANT SURFACE SYSTEM
MOVING INTO MISSOURI... DROPS TOWARD THE NORTHERN CWA. AS THIS
OCCURS...MOISTURE BEGINS TO STREAK IN FROM THE WEST ESPECIALLY
AFTER 06Z. BEGINNINGS OF DEEP LIFT DRIVEN VIA ISENTROPIC ASCENT
AND RRQ OF H250 JET TO THE NORTH WILL START TO SPREAD SNOW ACROSS
THE CWA. SLOWED POPS SLIGHTLY FROM PREVIOUS FORECAST BUT STILL
BRING LIKELY POPS TO PIT/HLG BY 12Z. SNOW COULD START EARLY ENOUGH
TO GET A FRESH INCH ON THE GROUND NEAR ZZV BY 12Z...WITH LESSER
AMOUNTS TO THE NORTH AND EAST.

TEMPERATURES MODIFIED SLIGHTLY FROM PREVIOUS FORECAST...MAINLY BY
BLENDING IN NAM/MET. CL

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
PRECIPITATION WILL START OVERSPREADING THE AREA WEST TO EAST ACROSS
THE SFC COLD FRONT SUNDAY AHEAD OF THE VIGOROUS LOW MOVING OUT OF
THE PLAINS. SNOW WILL BE THE PRIMARY PRECIPITATION TYPE AS THE EVENT
BEGINS EARLY SUN. LATER SUN AFTERNOON SNOW WILL REMAIN NORTH OF
I-70...BUT A MIX OR PLAIN RAIN CAN BE EXPECTED SOUTH OF I-70 AS
TEMPERATURES WARM.

THE LOW INTENSIFIES AS IT ENTERS THE OHIO RIVER VALLEY...BOLSTERED
ALOFT AS TWO JET STREAKS TEMPORARILY PHASE TO MAXIMIZE UPPER LEVEL
DIVERGENCE. INTENSIFICATION OF THE LOW WILL AMPLIFY THE LLVL WIND
FIELD RESULTING IN A STRONG 50+ KT H85 JET NOSING INTO SWPA.
NAM/SREF/GFS ALL SHOW THE TRACK OF THE H85 LOW A LITTLE FURTHER
NORTH THAN THAT OF THE ECMWF AND NORTH OF PREVIOUS RUNS. AS THE
CLOSED H85 LOW TRACKS THROUGH NCENTRAL OHIO...THIS MEANS THAT WAA
WILL BRING POSITIVE H85 ISOTHERMS INTO NRN WV AND SWPA THROUGH EARLY
MON MORNING. THIS KEEPS RAIN OR A RAIN/SNOW MIX SOUTH OF I-70 BEFORE
THE COLD AIR PUSHES IN ON THE BACKSIDE OF THE LOW MON MORNING. THIS
SLIGHTLY WARMER SOLN MARKS THE LARGEST CHANGE MADE TO THE PREVIOUS
FORECAST.

LARGELY KEPT THE QPF PLACEMENT AND NUMBERS THE SAME...BLENDING THE
LATEST WPC GUIDANCE WITH THE PREVIOUS NUMBERS. THE WARMER AIR
INVADING UP THE WRN SLOPES OF THE RIDGES WILL WORK TO KEEP OUR SERN
ZONES RAIN LONGER AND ULTIMATELY CUT INTO SNOW TOTALS FOR THE
DURATION OF THE EVENT. HOW FAR NORTH THAT WARM AIR IS ABLE TO INVADE
IS ANOTHER QUESTION. IF THE H85 LOW FOLLOWS THE CURRENT ECMWF
TRACK...THE PGH METRO WILL STAY NEARLY ALL SNOW. IF IT FOLLOWS THE
MORE NORTHERN TRACK...SEVERAL HOURS OF RAIN DURING THE TIME OF BEST
PRECIPITATION COULD CUT INTO THE PGH METRO TOTALS AS WELL.

ALL TOLD...A GENERAL 8-10" NORTH ALONG THE I-80
CORRIDOR...BUT TIGHTENED THE ACCUMULATION GRADIENT NEAR THE PGH
METRO WITH NRN ALLEGHENY COUNTY IN THE 5-7" RANGE AND SRN PORTIONS
OF THE COUNTY IN THE 3-5" RANGE. TRIMMED BACK TOTALS ACROSS THE SRN
EXTENT OF THE CWA AS WELL WITH MANY LOCATIONS IN THE 1-3" RANGE. IF
THE WARMER SOLNS WIN OUT...NUMBERS ACROSS THE SOUTH COULD BE CLOSER
TO THE 1" SIDE OF THAT RANGE. WITH QUESTIONS SURROUNDING THE TRACK
AND EXTENT OF WARM AIR...A WELL COLLABORATED DECISION WAS MADE TO
HOLD WITH THE WINTER STORM WATCH IN PLACE.
TAX

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
LLVL MOISTURE WILL LINGER IN THE HIGH ACROSS THE HIGH TERRAIN
THROUGH THE PRE-DAWN HOURS TUES...BUT ANY CHC OF PRECIPITATION WILL
BE FLEETING AS SFC HIGH PRESSURE WILL BUILD IN FROM THE WEST. NRN
AXIS OF THE SFC RIDGE WILL QUICKLY SHIFT EAST OF THE AREA TUES UNDER
ZONAL FLOW ALOFT. SERN EXTENT OF THE HIGH WILL HOLD BACK TO THE
WEST...AND WILL TRY TO HOLD THE NEXT SYSTEM OFF TO OUR NORTH. A WEAK
SFC LOW PASSES NORTH WEDS...BUT WILL WORK TO AMPLIFY THE UPPER TROF.
THE TRAILING COLD FRONT SWINGS THROUGH WEDS NIGHT/THURS
MORNING...BRINGING THE BEST CHANCE OF POPS IN THE EXTENDED PERIOD.
MUCH COLDER AIR POURS IN BEHIND THE FRONT AS A STOUT HIGH PRESSURE
CENTERS OVERHEAD. TEMPERATURES EXPECTED TO BE WELL BELOW AVERAGE
FROM MID-WEEK THROUGH THE END OF THE 7 DAY PERIOD.
TAX

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
FINGERS OF STRATOCU ARE STARTING TO STREAM IN FROM ACROSS LAKE
ERIE. EXPECT THIS VARIABLE AND BORDERLINE MVFR CIG TO IMPACT
SEVERAL TERMINALS DURING THE MORNING AND EARLY AFTERNOON AS A WEAK
WARM FRONT LIFTS THROUGH. VFR CONDITIONS SHOULD RETURN BY MID TO
LATE AFTERNOON...BUT MID/HI CLOUDS WILL BE ON THE INCREASE AHEAD
OF OUR SIGNIFICANT SUNDAY STORM. SNOW WILL START ARRIVING FROM THE
WEST AFTER MIDNIGHT AND SPREAD EASTWARD WITH TIME...WITH MVFR
CIG/VIS DROPPING TO IFR WITHIN AN HOUR OR TWO AFTER SNOW
COMMENCES. AREAS EAST OF PIT/MGW MAY AVOID IFR UNTIL AFTER 12Z.
WINDS WILL GENERALLY BE 10 KNOTS OR LESS FROM THE SOUTHWEST
THROUGH MUCH OF THE TAF PERIOD. CL


.OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/...
WIDESPREAD RESTRICTIONS CAN BE EXPECTED INTO MONDAY AS A LOW
PRESSURE SYSTEM CROSSES THE REGION.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING
     FOR MDZ001.
OH...WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING
     FOR OHZ039>041-048>050-057>059.
PA...WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING
     FOR PAZ007>009-013>016-020>023-029-073>076.
WV...WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING
     FOR WVZ001>003-023-041.

&&

$$





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