396
FXUS61 KPBZ 171843
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
143 PM EST TUE DEC 17 2024
SYNOPSIS
RAIN RETURNS ON WEDNESDAY, WITH COLDER TEMPERATURES AND LIGHT
SNOW SHOWERS POSSIBLE TO END THE WEEK AND THROUGH THE WEEKEND.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- DRY REST OF THE DAY WITH NEAR NORMAL TEMPERATURES.
- INCREASING CLOUDS OVERNIGHT AS RAIN APPROACHES FROM THE WEST.
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MOSTLY SUNNY SKIES AND PLEASANT AFTERNOON TEMPERATURES HAVE
SETTLED ACROSS THE REGION UNDER WEAK UPPER-LEVEL HEIGHT RISES.
CLOUDS SHOULD REMAIN MOSTLY TO OUR NORTH THROUGH THE REMAINDER
OF TODAY BEFORE SAGGING SOUTHWARD INTO THE REGION OVERNIGHT
TONIGHT AHEAD OF THE NEXT APPROACHING LOW PRESSURE SYSTEM.
TEMPERATURES MAY DROP QUICKLY TO AROUND FREEZING AFTER SUNSET,
BUT SHOULD MODERATE SOME LATER IN THE NIGHT AS THE CLOUDS MOVE
IN AND HELP MITIGATE RADIATIVE COOLING. AREAS SOUTH OF I-70 IN
EASTERN OHIO HAVE A ROUGHLY 20-30% CHANCE AT SEEING RAIN SHOWERS
STARTING BEFORE SUNRISE ON WEDNESDAY.
SHORT TERM /WEDNESDAY THROUGH THURSDAY/
KEY MESSAGES:
- ABOVE NORMAL TEMPERATURES LIKELY WEDNESDAY.
- RAIN RETURNS ON WEDNESDAY WITH A PASSING COLD FRONT.
- COLDER TEMPERATURES ON THURSDAY.
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THE NEXT WEATHER SYSTEM WILL ARRIVE WEDNESDAY AND FEATURE A
DEEPENING TROUGH TRAVERSING THE GREAT LAKES REGION WHILE A WEAK
SURFACE LOW LIFTS FROM THE TN RIVER VALLEY TOWARDS THE MID-
ATLANTIC. BROAD JET ASCENT IS EXPECTED TO DEVELOP A PLUME OF
PRECIPITATION THAT CROSSES THE UPPER OHIO RIVER VALLEY LATE
TONIGHT, REACHING OUR EASTERN OHIO COUNTIES AROUND DAYBREAK
WEDNESDAY AND SPREADING EASTWARD THROUGH THE AREA THROUGHOUT THE
DAY. THERE IS A LOW (<10%) CHANCE THAT FREEZING TEMPERATURES
WILL BE OBSERVED AT THE ONSET OF RAIN. HOWEVER, EVEN IF THAT
WERE TO OCCUR, IT WOULD BE BRIEF AS TEMPERATURES CONTINUE TO
WARM, LIMITING ANY OVERALL POTENTIAL IMPACT. PRECIPITATION IS
EXPECTED TO REMAIN PREDOMINANTLY RAIN THROUGH MOST OF THE DAY
WEDNESDAY AS ENSEMBLE GUIDANCE CONTINUES TO SUGGEST 850MB
TEMPERATURES HOVERING AROUND 2-4 DEGREES C AND SURFACE
TEMPERATURES ABOVE FREEZING, LIMITING THE POTENTIAL FOR ANY
WINTRY PRECIP TO MIX IN. HOWEVER, A COLD FRONT PUSHES THROUGH
DURING THE AFTERNOON AND, IF COLD AIR BEHIND IT IS QUICK ENOUGH
TO MOVE IN, SOME SNOW OR ICE PELLETS COULD MIX IN WITH RAIN
BEFORE PRECIPITATION TAPERS OFF IN THE EVENING. NORTHWEST WINDS
BEHIND THE FRONT WILL THEN SUPPORT SCATTERED LIGHT LAKE-EFFECT
SNOW SHOWERS OVERNIGHT INTO EARLY THURSDAY MORNING, PRIMARILY
NORTHEAST OF PITTSBURGH AND IN THE RIDGES. LITTLE OVERALL
ACCUMULATION IS EXPECTED, GENERALLY A DUSTING TO PERHAPS A HALF
INCH. ALL PRECIPITATION ENDS ON THURSDAY AS HIGH PRESSURE BUILDS
INTO THE AREA, THOUGH COLD ADVECTION BEHIND WEDNESDAY'S FRONT
WILL FAVOR MORE SEASONABLE TEMPERATURES AND CONTINUED CLOUD
COVER.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
KEY MESSAGES:
- HIGH PROBABILITY FOR TEMPERATURES AROUND 10 DEGREES BELOW
NORMAL FOR THE WEEKEND.
- SNOWFALL POTENTIAL CONTINUES TO APPEAR LOW END, WITH THE
THREAT FOR ANY IMPACTS LIKELY LIMITED TO NEAR LAKE ERIE.
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ANOTHER UPPER LEVEL TROUGH IS LIKELY TO DEVELOP OVER THE EASTERN
CONUS FRIDAY INTO THE WEEKEND AS IT DROPS SOUTHEAST FROM CENTRAL
CANADA. THIS PATTERN SHIFT WILL SUPPORT ANOTHER PERIOD OF
PRECIPITATION (MAINLY SNOW) WITH THE INITIAL WAVE PASSAGE FRIDAY
INTO SATURDAY) AND BELOW AVERAGE TEMPERATURE INTO THE WEEKEND.
MODEL VARIATIONS REMAIN FAIRLY HIGH ON THE OVERALL DEPTH OF THE
TROUGH AS WELL AS THE SHORTWAVE MOVEMENT WITHIN IT; THESE
FACTORS WILL PLAY LARGER ROLES IN HOW ACTIVE LAKE EFFECT SNOW
DEVELOPS AND THE BOUNDARY LAYER FLOW ANGLE FOR THOSE BANDS.
DEEPER/COLDER LEADS TO MORE EFFECTIVE SNOW BANDS (MEANING
GREATER ACCUMULATION POTENTIAL FOR FAR NORTHWEST PA AND THE
HIGHER TERRAIN) WHILE LESS DEEP/SLIGHTLY WARMER KEEPS THE REGION
DRIER AND LEADS TO MORE INCONSEQUENTIAL SNOWFALL TOTALS. STAY
TUNED AS SMALL-SCALE VARIATIONS FOR THIS WEEKEND PERIOD WILL
DETERMINE IF IMPACTS MAY DEVELOP OR NOT.
AVIATION /18Z TUESDAY THROUGH SUNDAY/
FAIRLY HIGH CONFIDENCE FORECAST OF VFR THROUGH THE TAF PERIOD
WITH INCREASING INFLUENCE OF SURFACE HIGH PRESSURE IN A POST-
FRONTAL ENVIRONMENT. THE BIGGEST UNCERTAINTY LAYS IN THE CUT
OFF LINE OF A MORE ENTRENCHED MVFR STRATUS DECK ASSOCIATED WITH
COLDER AIR TO THE NORTH. FKL/DUJ MAY SEE PERIODS OF BKN 1.5-3KFT
DECKS BUT TIMING AND DURATION OF IMPACT IS HIGHLY UNCERTAIN.
THE MIXED BOUNDARY LAYER PLUS SURFACE PRESSURE GRADIENT WILL
CONTINUE TO FOSTER 15 TO 25KT GUSTS OUT OF THE WSW THROUGH THIS
AFTERNOON BEFORE WANING TONIGHT.
WARM, MOIST ADVECTION AHEAD OF THE NEXT UPPER LEVEL TROUGH WILL
SPREAD RAIN AND LOWERING CEILINGS WITH RESTRICTIONS GENERALLY
DEVELOPING A FEW HOURS AFTER RAIN ONSET. THE EARLIEST
PRECIPITATION ONSET TIME IS 12Z-14Z WEDNESDAY, WITH A MOST
LIKELY TIMEFRAME OF 14Z-18Z.
OUTLOOK...
WIDESPREAD RAIN AND MVFR/IFR RESTRICTIONS ARE LIKELY WEDNESDAY
AFTERNOON AND EVENING AMID WARM, MOIST ADVECTION AHEAD OF THE
NEXT UPPER LEVEL DISTURBANCE. PASSAGE OF THE SURFACE COLD FRONT
AFTER 00Z WILL SUPPORT A POTENTIAL RAIN-TO-SNOW TRANSITION, BUT
DURATION WILL BE LIMITED AS AVAILABLE MOISTURE SHIFTS EAST WITH
COLD/DRY ADVECTION DEVELOPING.
ENSEMBLE MODELS ARE BEARISH FOR A REPRIEVE OF MVFR CIGS (MOST
TERMINALS WITH 50-80% PROBABILITY OF PERSISTENCE) UNTIL THURSDAY
EVENING; THIS LIKELY MEANS ANY PERIOD OF VFR WILL BE SHORT-LIVED
BEFORE THE NEXT LOW PRESSURE SYSTEM ARRIVES FRIDAY.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...CERMAK
NEAR TERM...CERMAK
SHORT TERM...CERMAK
LONG TERM...CERMAK/FRAZIER
AVIATION...FRAZIER
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