365
FXUS61 KPBZ 041700
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
100 PM EDT MON MAY 4 2026
WHAT HAS CHANGED
NO SIGNIFICANT CHANGES WERE MADE TO THE FORECAST.
KEY MESSAGES
1) SHOWER AND THUNDERSTORM CHANCES INCREASE THIS EVENING AND
TONIGHT
2) ACTIVE WEATHER PATTERN EXPECTED THROUGH THE WEEKEND
3) FROST POSSIBLE THURSDAY NIGHT
DISCUSSION
KEY MESSAGE 1...
THE LATEST MESOANALYSIS SHOWS DIURNAL INSTABILITY BEGINNING TO
INCREASE IN THE WARM SECTOR ACROSS THE MIDWEST AND LOWER OHIO
VALLEY REGIONS. LOW SURFACE DEW POINTS CONTINUE TO HINDER
DESTABILIZATION, THOUGH EXPECT SOME MOIST ADVECTION LATER THIS
AFTERNOON AND EVENING IN SW FLOW AND AN APPROACHING LOW LEVEL
JET. ML CAPE IS STILL EXPECTED TO BE LIMITED ACROSS THE UPPER
OHIO VALLEY REGION (GENERALLY LESS THAN 750 J/KG,) THOUGH JET
ASCENT AND A CROSSING SHORTWAVE SHOULD SPARK SCATTERED SHOWERS
AND THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT. THERE IS A
BRIEF WINDOW LATE THIS AFTERNOON AND EARLY EVENING FOR STRONG
STORMS WITH 30-35 KT OF SHEAR ON THE NOSE OF THE JET, THOUGH
THIS POTENTIAL SHOULD WANE THIS EVENING AS THE LIMITED
INSTABILITY DIMINISHES.
ELEVATED INSTABILITY AND THE CROSSING SHORTWAVE SHOULD STILL
MAINTAIN SOME SHOWERS/STORMS OVERNIGHT.
KEY MESSAGE 2...
THE FOCUS WILL SHIFT TO AN APPROACHING COLD FRONT ON TUESDAY,
AS IT SINKS SLOWLY SOUTH TOWARD THE REGION. THE FLOW ALOFT IS
NEARLY PARALLEL TO THE FRONT, SO EXPECT ONLY A SLOW
PROGRESSION. SHOWER/STORM CHANCES WILL INCREASE FROM THE NW
THROUGH THE DAY, BUT SHOULD MAINLY BE CONFINED NORTH OF PIT
MOST OF THE DAY. SHEAR AND INSTABILITY IS EXPECTED TO BE EVEN
MORE LIMITED THAN TODAY, WITH ML CAPE LESS THAN 500 J/KG AND
LIMITED SHEAR. WARM AIR ALOFT SHOULD ALSO LIMIT BUOYANCY,
LIMITING ANY SEVERE WEATHER POTENTIAL. MORE WIDESPREAD SHOWERS
AND EMBEDDED THUNDERSTORMS ARE EXPECTED TUESDAY EVENING INTO
WEDNESDAY AS THE FRONT SLOWLY DROPS SOUTH ACROSS THE REGION.
A WAVE OF LOW PRESSURE IS PROGGED TO TRACK ALONG THE FRONT ON
WEDNESDAY AS IT STALLS ACROSS THE OHIO VALLEY AND CENTRAL PA,
MAINTAINING MORE SHOWERS AND ISOLATED THUNDERSTORMS. IT SHOULD
TURN MUCH COOLER NORTH OF THE FRONT WEDNESDAY, WITH HIGHS
AROUND 10 DEGREES BELOW AVERAGE. THE FRONT SHOULD PROGRESSES
FURTHER OUT OF THE REGION THURSDAY AS THE FLOW TURNS MORE WNW,
THOUGH IT SHOULD STILL BE IN CLOSE ENOUGH PROXIMITY TO MAINTAIN
SHOWER CHANCES.
THE UPPER OHIO VALLEY REGION IS THEN PROGGED TO BE UNDER A
BROAD UPPER TROUGH THROUGH THE WEEKEND. A SERIES OF SHORTWAVES
ROTATING THROUGH THE TROUGH WILL THEN KEEP PERIODIC SHOWER
CHANCES IN THE FORECAST.
KEY MESSAGE 3...
THERE IS SOME POTENTIAL FOR FROST THURSDAY NIGHT, THOUGH THIS
WILL BE HIGHLY DEPENDENT ON THE AMOUNT OF CLOUD COVER IN PLACE
AND THE RESULTING RADIATIONAL COOLING.
AVIATION /18Z MONDAY THROUGH SATURDAY/
VFR IS LIKELY TO PREVAIL THROUGH THE ENTIRE PERIOD. WIND WILL
PICK UP NOTABLY THIS MORNING AND AFTERNOON OUT OF THE SOUTHWEST
WITH A TIGHTENING GRADIENT AND MOMENTUM TRANSFER IN MODEL
SOUNDINGS SUGGESTING AT LEAST 20 KNOT GUSTS. THE STRONGEST LOW
LEVEL FLOW LIKELY DOESN'T ARRIVE UNTIL THE EVENING HOURS. CAN'T
RULE OUT A BRIEF PERIOD OF ENHANCED GUSTS IF THE ARRIVAL OF THE
STRONGER WINDS ALOFT ENDS UP BEING EARLIER, BUT WITH NOCTURNAL
DECOUPLING BEGINNING TO OCCUR AROUND THAT TIME ANY WINDOW FOR
HIGHER GUSTS WOULD BE BRIEF.
OVERNIGHT, 925 MB FLOW RAMPS UP TO AROUND 40 KNOTS AND 850 MB
FLOW TO 45-50 KNOTS. ENSEMBLE GUIDANCE CONTINUES TO SUGGEST
DECOUPLING DOES NOT OCCUR AND GUSTS CONTINUE INTO OVERNIGHT
HOURS, DESPITE WARM AIR ADVECTION REINFORCING A NOCTURNAL
INVERSION JUST OFF THE SURFACE. THE ALTERNATIVE SCENARIO IS THAT
WE DECOUPLE AND SURFACE GUSTS SUBSIDE, WHICH WOULD THEN LEAD TO
AN INCREASING LLWS THREAT AS SFC-2KFT SHEAR STRENGTHENS TO NEAR
OR JUST ABOVE 30 KNOTS. THERE IS STILL A BIT TOO MUCH
UNCERTAINTY WHICH SCENARIO WILL PLAY OUT, WHICH PRECLUDES THE
MENTION OF LLWS IN TAFS AT THIS TIME, BUT IT'S SOMETHING THAT
WILL WARRANT KEEPING AN EYE ON.
WITH INCREASING WARM ADVECTION, SOME SHOWERS MAY DEVELOP IN THE
EVENING AND EVEN POTENTIALLY LINGERING INTO OVERNIGHT HOURS
(THE LATTER MOST LIKELY OCCURRING NORTH OF PIT). THE SCATTERED
NATURE AND RUN TO RUN MODEL INCONSISTENCY WITH TIMING/OCCURRENCE
CONTINUES TO WARRANT -SHRA MENTION IN PROB30S RATHER THAN
PREVAILING GROUPS. IF CONFIDENCE IN OCCURRING/TIMING INCREASES
THROUGH THE DAY, A MORE TARGETED WINDOW FOR PREVAILING -SHRA MAY
BE INCLUDED. THUNDER IS POSSIBLE AS WELL, THOUGH WITH LIMITED
AVAILABLE INSTABILITY AND UNCERTAINTY REGARDING WHETHER UPDRAFTS
ARE ABLE TO GET TALL ENOUGH TO EXCEED -10C IN DRIER MID-LEVEL
AIR, THE PROBABILITIES FOR LIGHTNING ARE TOO LOW TO WARRANT
INCLUDING IN THE TAFS AT THIS TIME.
OUTLOOK...
A FEW THUNDERSTORMS ARE POSSIBLE ON TUESDAY. MORE WIDESPREAD
RESTRICTIONS IN SHOWERS AND THUNDERSTORMS ARE LIKELY TUESDAY
NIGHT INTO WEDNESDAY AS A WAVE OF LOW PRESSURE TRACKS ALONG AN
ADVANCING COLD FRONT.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
DISCUSSION...WM
AVIATION...CERMAK/MLB
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