581
FXUS61 KPBZ 211653
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1253 PM EDT SAT MAR 21 2026
WHAT HAS CHANGED
CONFIDENCE IN SEVERE WEATHER OCCURRENCE CONTINUES TO RISE FOR
SUNDAY. HOWEVER, SOME TIMING AND PLACEMENT UNCERTAINTY CONTINUES
AMONG THE VARIOUS MODEL GUIDANCE. THERE IS ALSO SOME SLOWLY
INCREASING COALESCENCE AROUND THE TIMING OF OUR NEXT GOOD RAIN
CHANCE ON THURSDAY.
KEY MESSAGES
1) SEVERE THUNDERSTORMS REMAIN A GOOD POSSIBILITY AHEAD OF A
CROSSING COLD FRONT SUNDAY, WITH HAIL, WIND, AND TORNADO THREATS
ALL IN PLAY.
2) MOSTLY QUIET WEATHER MONDAY THROUGH WEDNESDAY, WITH THE NEXT
SHOWER AND THUNDERSTORM CHANCE AROUND THURSDAY.
DISCUSSION
KEY MESSAGE 1...
WHILE SOME EXACT DETAILS REMAIN QUESTIONABLE, THERE REMAINS A
GOOD SIGNAL FOR SEVERE WEATHER SUNDAY AFTERNOON AND EVENING. ALL
SEVERE THREATS REMAIN IN PLAY, ALTHOUGH LARGE HAIL AND DAMAGING
WIND CHANCES WILL DOMINATE, WITH A LESSER BUT STILL PRESENT
TORNADO THREAT.
SURFACE LOW PRESSURE CROSSING THE GREAT LAKES PROVIDES A WARM
FRONTAL PASSAGE TONIGHT, INTRODUCING A WARMER AIRMASS TO THE
REGION. THIS WILL BE FOLLOWED BY A COLD FRONTAL PASSAGE DURING
THE LATE AFTERNOON AND EVENING HOURS THAT WILL SERVE AS A FOCUS
FOR THUNDERSTORMS. 850MB TEMPERATURES WILL LIKELY RISE INTO THE
13C TO 15C RANGE BY 12Z SOUTH OF THE APPROACHING COLD FRONT,
WHICH SUPPORT HIGH TEMPERATURES WELL INTO THE 70S SOUTH OF
US-422, AND EVEN IN THE 80S SOUTH OF THE MASON-DIXON LINE.
INCREASED MOISTURE (PRECIPITABLE WATER OF 1.0 TO 1.2 INCHES JUST
AHEAD OF THE FRONT) HELPS TO DRIVE DEWPOINTS INTO THE MID TO
UPPER 50S DURING THE AFTERNOON, HELPING TO PUSH SURFACE-BASED
CAPE INTO THE 750 TO 1500 J/KG RANGE. MUCH OF THIS INSTABILITY
LIES IN THE FAVORABLE -10C TO -30C LAYER FOR HAIL GROWTH, WITH
MID-LEVEL LAPSE RATES OF 7C TO 7.5C PRESENT AS WELL. 700MB WSW
WIND OF 50-60 KNOTS WILL CONTRIBUTE TO 0-6KM SHEAR OF 45 TO 55
KNOTS AHEAD OF THE FRONT, ALONG WITH A SLOWLY VEERING VERTICAL
PROFILE. THESE PARAMETERS WOULD BE SUPPORTIVE OF SUPERCELL
STRUCTURES.
MUCH OF THE UNCERTAINTY FOR THIS EVENT COMES FROM:
1) TIMING, AS THE VARIOUS CAMS STILL DISAGREE ON WHEN CONVECTIVE
INITIATION OCCURS. THIS TIMING GENERALLY RANGES FROM ABOUT 18Z
TO 22Z, AND THIS HAS IMPLICATIONS FOR THE PLACEMENT OF THE
HIGHEST THREAT CORRIDOR DEPENDING ON FRONTAL PROGRESSION. RIGHT
NOW, MOST OUTCOMES WOULD OVERLAP THE 4 PM TO 8 PM PERIOD, SO
THIS COULD CURRENTLY BE CONSIDERED THE MOST LIKELY TIMING OF
ANY SEVERE WEATHER. IN MOST CASES, THE AREAL PLACEMENT OF THE
GREATEST THREAT WOULD LIE FROM NEAR PITTSBURGH AND SOUTH.
2) THE AMOUNT OF WARM AIR/INHIBITION IN THE LOWER AND MID
LEVELS. SOME HREF MEMBERS SUGGEST A WARM LAYER AROUND THE 800MB
LEVEL THAT MAY ACT AS A HINDRANCE TO SURFACE-BASED CONVECTION
INITIALLY. ALSO, TEMPERATURE/DEWPOINT SPREADS AHEAD OF
CONVECTION MAY BE AS LARGE AS 20F. IN THIS CASE, LARGE HAIL
WOULD THE HIGHEST THREAT WITH ANY INITIAL DISCRETE STORM
DEVELOPMENT GIVEN THE SHEAR AND FAVORABLE CAPE PROFILE, WITH
POTENTIAL WIND AND TORNADO THREATS POSSIBLY RAMPING UP A BIT
LATER ONCE ANY CAPPING IS ERODED OR (IN THE CASE OF STRAIGHT-
LINE WIND) WHEN STORMS BEGIN ORGANIZING INTO LINE SEGMENTS. THIS
IS CONSIDERED TO BE THE MORE LIKELY SCENARIO AT THIS TIME. A
LESS-LIKELY SCENARIO INVOLVES LESS WARM AIR ALOFT, ALLOWING FOR
MORE SURFACE-BASED CONVECTION AT THE START. IN THAT CASE, WIND
AND TORNADO THREATS WOULD BE HIGHER AND MORE WIDESPREAD FROM THE
BEGINNING OF THE EVENT.
IN ANY CASE, THE OVERALL CONFIDENCE IN SEVERE WEATHER OCCURRENCE
CONTINUES TO INCREASE, AND AT LEAST ONE AREA SEVERE THUNDERSTORM
AND/OR TORNADO WATCH SEEMS LIKELY TOMORROW. WE WILL ALSO NEED
TO MONITOR THE POTENTIAL OF TRAINING THUNDERSTORMS, AS MEAN
STORM MOTION SHOULD BE FAIRLY PARALLEL TO THE CROSSING COLD
FRONT. THUS, ISOLATED HEAVY RAINFALL TOTALS (EXCEEDING 1.5 INCH)
AND LOCALIZED WATER ISSUES CANNOT BE RULED OUT.
STORM INTENSITY SHOULD BEGIN TO RAMP DOWN BY THE MID TO LATE
EVENING WITH DIURNAL STABILIZATION, ALTHOUGH CONVECTION IS
LIKELY TO CONTINUE ALONG AND AHEAD OF THE COLD FRONT UNTIL IT
EXITS THE REGION TO OUR SOUTH AFTER MIDNIGHT.
KEY MESSAGE 2...
LARGELY QUIET WEATHER FOLLOWS FOR THE MONDAY TO WEDNESDAY
PERIOD. ALTHOUGH LAKE-850MB DELTA T VALUES APPEAR MARGINAL, THE
PASSAGE OF A SHORTWAVE TO OUR NORTH MAY SUPPORT SOME ISOLATED
LAKE-ENHANCED SHOWERS NORTH OF PITTSBURGH ON MONDAY. POPS MAY
NEED TO BE ADDED IF CONFIDENCE IN THIS INCREASES. IN THE WAKE OF
THE SUNDAY NIGHT COLD FRONT, TEMPERATURES START OUT BELOW-
NORMAL ON MONDAY, THEN WILL LIKELY MODERATE TO AND JUST ABOVE
CLIMATOLOGY BY WEDNESDAY.
THE NEXT CHANCE OF SHOWERS AND THUNDERSTORMS MAY ARRIVE ON OR
AROUND THURSDAY, ALTHOUGH ENSEMBLES DIFFER ON TIMING CURRENTLY.
GIVEN A WARM SURGE FOLLOWED BY ANOTHER COLD FRONTAL PASSAGE
DURING THIS PERIOD, THIS MAY REPRESENT OUR NEXT CHANCE FOR AT
LEAST ISOLATED SEVERE THUNDERSTORMS. EXTENDED MACHINE-LEARNING
GUIDANCE FROM CSU AND NCAR SUPPORT THIS IDEA.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
VFR WILL PREVAIL FOR THE TAF PERIOD WITH ONLY HIGH CLOUDS AND
PERHAPS A BRIEF SCATTERED VFR DECK LATE MORNING AND EARLY
AFTERNOON.
THERE IS MEDIUM CONFIDENCE IN A RESTRICTIONS MAKING THEIR WAY
TO FKL/DUJ IN THE 12Z TO 18Z WINDOW TOMORROW AS THE NEXT SYSTEM
ENCROACHES, SO OPTED TO MESSAGE IN TAFS. RESTRICTION CHANCES
SEEM QUITE CONFINED TO THESE PORTS, WITH CHANCES LESS THAN 30%
ELSEWHERE (LESS LIKELY TO THE SOUTH).
THUNDERSTORM CHANCES INCREASE AREA-WIDE IN THE 18Z TO 00Z WINDOW
AS A COLD FRONT PASSES. STRONG GUSTS EXCEEDING 50KTS AND LARGE
HAIL ARE POSSIBLE IN THE MOST INTENSE STORMS. LIKELIHOOD OF
HAIL/WIND INCREASES FROM NORTH TO SOUTH. BRIEF RESTRICTIONS IN
VIS/CIG ARE ALSO LIKELY IN ANY MORE INTENSE RAIN.
OUTLOOK...
RESTRICTIONS WILL LIKELY LINGER INTO MONDAY MORNING BEFORE VFR
RETURNS MONDAY AFTERNOON.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
DISCUSSION...CL
AVIATION...MILCAREK
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