771
FXUS61 KPBZ 212351
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
751 PM EDT MON APR 21 2025
SYNOPSIS
HIGH PRESSURE IS EXPECTED TO MOVE INTO THE REGION BEHIND THE
COLD FRONT. THE AREA DRIES OUT BEHIND THIS FRONT AND COOLS OFF
THROUGH THE MIDWEEK BEFORE TEMPERATURES AND RAIN CHANCES RISE
LATE WEEK.
NEAR TERM /UNTIL 7 AM TUESDAY MORNING/
KEY MESSAGES:
- SCATTERED SHOWERS/THUNDERSTORMS AHEAD OF THE SFC COLD FRONT
- COLD FRONT BRINGS ANOTHER ROUND OF SHOWERS/STORMS LATER TODAY
- MARGINAL RISK FOR SEVERE STORMS THIS AFTERNOON
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8PM UPDATE...A FEW CELLS STILL REMAIN ACROSS THE AREA THIS
EVENING. THE AMOUNT OF INSTABILITY WILL CONTINUE TO DECREASE
AND EVEN THE SB CAPE HAD DROPPED TO 500 J/KG OR BELOW. WHILE
SOME SHEAR REMAINS, STILL ONLY 30 TO 35 KNOTS OF SHEAR REMAIN
BUT WITH THE AMOUNT OF INSTABILITY WANING, EXPECT THE CELLS TO
WEAKEN AND MOVE OUT OF THE AREA.
THE SHOWER AND THUNDERSTORM THREAT WILL COME TO AN END BY 01Z
WITH JUST SOME WEAK SHOWERS REMAINING. THE COLD FRONT TO THE
WEST WILL SLOWLY MOVE EAST AND PASS THROUGH THE AREA OVERNIGHT
LEAVING SOME GUSTY WEST WINDS REMAINING OVERNIGHT. THIS WILL
KEEP LOW TEMPERATURES RIGHT AROUND NORMAL.
PREVIOUS DISCUSSION...PRE-FRONTAL SHOWERS HAVE REALLY MUDDIED
THE PICTURE OF OUR POSSIBLY UNFOLDING SEVERE EVENT. PORTIONS OF
THE TRI- STATE AREA THAT STARTED THE DAY NEAR 70 AND ROSE TO
ALMOST 80 DEGREES (79 AT HLG) HAVE SEEN MIDDAY SHOWERS BRING
TEMPERATURES BACK DOWN INTO THE MIDDLE 60S. THE POSSIBILITY OF
BACKING IN THE LOW- LEVELS TO CREATE MORE CURVED HODOGRAPHS HAS
NOT MATERIALIZED AND THE POTENTIAL STORM MODE MAY BE SHIFTING
FROM ISOLATED LOW- TOPPED SUPERCELLS TO QLCS DRIVEN BY LARGELY
UNIDIRECTIONAL FLOW OUT OF THE SOUTHWEST.
40-50 KNOTS OF SHEAR AND BROAD UPPER-LEVEL JET SUPPORT ARE IN
PLACE BUT THE LIMITING REAGENT MAY BE A LACK OF INSTABILITY. SPC
MESOANALYSIS CURRENTLY SHOWS TWO AREAS OF 500 J/KG OF CAPE, ONE
IN WESTERN PA AND ANOTHER IN CENTRAL AND EASTERN OH, THE PA
AREA IS ABOUT TO BE SQUASHED BY SHOWERS THAT HAVE SEEN THE
TEMPERATURE DROP AROUND 11 DEGREES AT THE OFFICE. THE QUESTION
HAS BECOME, CAN ENOUGH RECOVERY OCCUR IN THESE AREAS BEFORE THE
SFC FRONT MOVES THROUGH? A 40-50 MILE GAP IS EVIDENT IN
SATELLITE IMAGERY THAT SHOWS SOME CU DEVELOPMENT BUT LITTLE
DEVELOPMENT HAS OCCURRED IN THIS AREA THUS FAR. THIS GAP IS MORE
PRONOUNCED (WIDER) FARTHER SOUTH AND THESE AREAS MAY SEE A
LONGER TIME FRAME FOR RECOVERY BUT SEEM TO LACK BETTER DYNAMICS.
WITH THESE COMPETING FACTORS, WE WILL KNOW MUCH MORE IN THE
NEXT HOUR OR SO AS TO WHAT IF ANY RECOVERY AND DEVELOPMENT CAN
OCCUR BEHIND THE LEADING SHOWERS BUT STILL AHEAD OF THE FRONT.
AT THIS TIME ALL SEVERE WEATHER HAZARDS REMAIN IN PLAY. THE MAIN
HAZARD REMAINS DAMAGING WIND GUSTS WITH STRONG FLOW ALOFT, BUT
HAIL AND A TORNADO OR TWO CANNOT BE RULED OUT. SEVERAL FACTORS
ARE HINTING AT THE MOST FAVORABLE ENVIRONMENT FOR TORNADO
DEVELOPMENT BEING IN NW PA BUT THESE AREAS MAY LACK TIME AND
INSTABILITY TO DRIVE STORM DEVELOPMENT.
THE REGION IS EXPECTED TO QUICKLY DRY OUT BEHIND THE FRONT AS
WINDS SLOWLY SUBSIDE WITH A SLACKENING PRESSURE GRADIENT. LOW
TEMPERATURES ARE EXPECTED TO DROP BACK TOWARDS AROUND 5 DEGREES
ABOVE NORMAL AS OPPOSED TO THE 10-15 DEGREES ABOVE NOTED THESE
LAST TWO NIGHTS.
SHORT TERM /7 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/
KEY MESSAGES:
- DRY WEATHER THEN RETURNS THROUGH WEDNESDAY NIGHT
- COOLER TUESDAY BEHIND THE FRONT
- WARMING BACK UP WEDNESDAY
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HEIGHTS RISE SUBTLY ON TUESDAY AS THE PATTERN BECOMES MORE ZONAL
AND SURFACE HIGH PRESSURE SETTLES IN ACROSS THE UPPER OHIO
VALLEY. THIS HELPS TO PROMOTE DRY WEATHER THROUGH WEDNESDAY
NIGHT.
A BRIEF COOL DOWN BEHIND OUR FRONT SEES TUESDAY HIGH
TEMPERATURES RETURN LARGELY TO THE 60S. 500MB HEIGHTS RISE
AGAIN SUBTLY ACROSS OUR AREA AS A DISJOINTED UPPER RIDGE SLIDES
THROUGH SOUTHERN ONTARIO ON WEDNESDAY. THIS WILL KICK OUR
TEMPERATURES BACK UP TO AROUND 10 DEGREES ABOVE AVERAGE FOR THIS
TIME OF YEAR.
LONG TERM /THURSDAY THROUGH MONDAY/
KEY MESSAGES:
- INCREASING SHOWER CHANCES THROUGH LATE WEEK INTO SATURDAY
- DRY WEATHER AND ABOVE AVERAGE TEMPERATURES RETURN FOR THE END OF
THE WEEKEND
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THE SOUTHERN PORTION OF THIS NON-PHASED UPPER RIDGE LOOKS TO
SLIDE OVER THE REGION ON THURSDAY AHEAD OF A DEVELOPING TROUGH
ACROSS THE CENTRAL CONUS. NBM PROBABILITIES OF HIGH TEMPERATURE
>80 DEGREES ARE OVER 70% ON THURSDAY FOR I-70 ON SOUTH AND
BETWEEN 50-70% FOR MUCH OF PITTSBURGH.
INCREASING MOISTURE AND WARM ADVECTION AHEAD OF THIS TROUGH
RETURNS SHOWER CHANCES TO THE AREA THURSDAY NIGHT. THE TROUGH
AND ITS ASSOCIATED SURFACE COLD FRONT ARE EXPECTED TO TRACK
ACROSS THE UPPER OHIO VALLEY REGION FRIDAY AND FRIDAY NIGHT,
WITH THE HIGHEST CHANCES FOR SHOWERS AND POSSIBLE THUNDERSTORMS.
THE TROUGH IS EXPECTED TO LIFT OUT OF THE REGION BY SATURDAY
WITH SHOWERS WINDING DOWN FROM WEST TO EAST.
HEIGHTS RISE SUNDAY AHEAD OF A CENTRAL CONUS RIDGE THAT SHOULD
RETURN DRY WEATHER TO THE REGION FOR THE REMAINDER OF THE WEEKEND.
THIS BUILDING RIDGE IS ALSO SUPPOSED TO BRING THE RETURN OF ABOVE
AVERAGE TEMPERATURES.
AVIATION /00Z TUESDAY THROUGH SATURDAY/
BROAD ASCENT IN THE PRESENCE OF A 300MB JET WILL INDUCE
GENERALLY LIGHT RAIN A FEW HOURS AHEAD OF INCOMING SURFACE COLD
FRONT. LIMITED MOISTURE CONTENT FAVORS MAINTENANCE OF VFR
CONDITION, THOUGH A PERIOD OF MVFR CIGS JUST AHEAD OF THE FRONT
IS POSSIBLE DUE TO MOISTURE CONVERGENCE.
A BROKEN LINE OF LOW-TOPPED SHOWERS WITH EMBEDDED THUNDERSTORMS
WILL BETWEEN 3PM-8PM EDT AHEAD OF A SURFACE COLD FRONT.
UNCERTAINTY IN THE DEGREE OF INSTABILITY AHEAD OF THIS LINE
CONTINUES TO LIMIT FORECASTER CONFIDENCE IN DEVELOPMENT OF
30-45KT GUSTS, BUT LOCALIZED SPEEDS TO THAT OR APPROACHING 50KTS
CAN'T BE RULED OUT. STORM MOTION SHOULD BE FAST ENOUGH THAT
TERMINAL IMPACTS LAST NO MORE 1-2 HOURS BEFORE THE LINE EXITS
EAST.
PASSAGE OF THE UPPER SHORTWAVE AXIS AND SURFACE COLD FRONT WILL
SEE A QUICK END TO CONVECTIVE ACTIVITY IN THE REGION. A
SLIGHTLY DELAY BEFORE THE ONSET OF WEAK COLD ADVECTION MAY
CREATE INITIAL CIG COVERAGE VARIATION, BUT LOW VFR AND SPOTTY
MVFR SHOULD DEVELOP/PERSIST OVERNIGHT AND FAVOR FKL/DUJ/LBE/MGW.
DRY ADVECTION WITHIN COLUMN WESTERLY FLOW WILL ERODE STRATOCU
WEST TO EAST NEAR DAWN, WITH VFR AND NO MORE THAN SCATTERED CU
AT ALL TERMINALS BY 16Z.
OUTLOOK...
HIGH PRESSURE AND WEAK RIDGING ALOFT WILL FAVOR VFR THROUGH
MUCH OF THE DAYTIME HOURS THURSDAY.
WEAK SHORTWAVE MOVEMENT WITHING SOUTHWESTERLY FLOW IS EXPECTED
TO INCREASE SHOWER AND THUNDERSTORM CHANCES LATE THURSDAY INTO
THE EARLY WEEKEND WHERE CONVECTIVE ACTIVITY BECOMES THE MAIN
DRIVER FOR TERMINAL RESTRICTIONS.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...SHALLENBERGER
NEAR TERM...SHALLENBERGER/AK
SHORT TERM...AK
LONG TERM...AK
AVIATION...FRAZIER
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