487
FXUS61 KPBZ 182348
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
648 PM EST WED DEC 18 2024
SYNOPSIS
PRECIPITATION EXITS THE REGION THIS EVENING, POCKETS OF
FREEZING RAIN POSSIBLE IN THE RIDGES OVERNIGHT. RAIN AND SNOW
CHANCES RETURN FRIDAY AHEAD OF COLDER TEMPERATURES AND SNOW
SHOWERS FOR THE WEEKEND. DRY WEATHER TO START NEXT WEEK WITH
MODERATING TEMPERATURES.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
KEY MESSAGES:
- PRECIP CHANCES WINDING DOWN THIS EVENING.
- LAKE EFFECT SNOW SHOWERS POSSIBLE NORTH OF I-80.
- PATCHES OF FREEZING DRIZZLE POSSIBLE IN THE RIDGES.
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THE PRECIPITATION SHIELD IS BEGINNING TO EXIT THE REGION OVER
THE RIDGES AS OF THIS WRITING. AS SUCH, MUCH OF THE REGION
OUTSIDE OF THE RIDGES IS EXPECTED TO REMAIN DRY OVERNIGHT. THERE
IS A SLIGHT, CHANCE MAINLY NORTH OF PITTSBURGH, TO SEE A
PASSING SNOW SHOWER OR TWO MOVE IN FROM THE NORTHWEST WITH WEAK
ONSHORE FLOW.
IN THE PA AND WV RIDGES, PROFILES SHOW SHALLOW MOISTURE
EXTENDING UP TO AROUND -8C IN A CONDITIONALLY UNSTABLE
ENVIRONMENT WITH SUB-FREEZING SURFACE TEMPERATURES OVERNIGHT
TONIGHT. THE LACK OF ICE PRODUCTION IN THE CLOUD BEARING LAYER
COULD POINT TOWARD A PERIOD OF FREEZING RAIN AS THE
PRECIPITATION TYPE LINGERING THROUGH THE OVERNIGHT HOURS
TONIGHT, AND THE HREF PRECIP TYPE PROBS ARE SUGGESTING THIS.
THINKING THAT IT WILL BE A BIT MORE LOCALIZED THAN HREF PAINTS,
WITH THE HIGHEST ELEVATIONS AT THE MOST RISK. IN COORDINATION
WITH NEIGHBORS, HAVE RUN AN SPS OUT THROUGH THE OVERNIGHT HOURS
TO COVER THE THREAT, THOUGH A SHORT-FUSED ADVISORY MAY BE
NEEDED IF THE THREAT BECOMES MORE WIDESPREAD.
SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/
KEY MESSAGES:
- SCATTERED LAKE ENHANCED SNOW SHOWERS EARLY THURSDAY.
- SNOW/RAIN CHANCES RAMP BACK UP ON FRIDAY.
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THURSDAY LOOKS TO BE A TRANSITION DAY IN THE PATTERN AS WE GET A
BRIEF SHOT OF ZONAL FLOW AHEAD OF THE NEXT UPPER TROUGH. LAKE
ENHANCED SNOW SHOWERS ARE FAVORED TO CONTINUE INTO THE MORNING
HOURS THURSDAY NORTH OF PITTSBURGH. LOSS OF UPPER FORCING AND
SHALLOWING OF MOISTURE WILL WORK TO SHUT OFF SNOW CHANCES BY THE
AFTERNOON HOURS. ADDITIONAL ACCUMULATION THROUGH THE MORNING
LOOKS MINIMAL WITH HREF PROBS OF >0.5" AT 10-20%. 850 MB TEMP
ADVECTION WILL BECOME MORE NEUTRAL AS FLOW BACKS SOUTHWESTERLY.
VALUES RANGING FROM -3 TO -7C, COLDER TO THE NORTH, WILL SUPPORT
HIGHS IN THE MID 30S. CLOUD COVERAGE SHOULD START TO ERODE IN
THE LATTER HALF OF THE DAY FROM THE SOUTH WITH UNCERTAINTY ON
HOW FAR NORTH SCATTERING CAN GET REPRESENTED BY A SHARP CUTOFF
IN HREF HIGH END/LOW END COVERAGE SPREAD ALONG A LINE FROM
INDIANA DOWN THROUGH GREENE COUNTY.
ANOTHER TROUGH WILL APPROACH AND DEEPEN AS IT DOES SO THURSDAY
NIGHT INTO FRIDAY BRINGING WITH IT ANOTHER ROUND OF PRECIPITATION.
THE SURFACE LOW LOOKS TO TRACK JUST TO OUR SOUTH. PRECIPITATION
TYPE LOOKS TO START OFF AS SNOW AT ONSET AS IT MOVES INTO A
COLD AIRMASS, BUT A TRANSITION TO RAIN OR A RAIN/SNOW MIX SHOULD
OCCUR INTO THE AFTERNOON HOURS WITH DIURNAL HEATING AS
HIGH TEMPERATURES RISE ABOVE FREEZING WITH AN 80-100% CHANCE
DESPITE THE CLOUD COVERAGE. ACCUMULATION PROBABILITIES ARE LOW
AT LESS THAN 20% FOR >1", THOUGH SLIGHTLY HIGHER FOR THE RIDGES,
THROUGH FRIDAY NIGHT AS UPSLOPE ENHANCEMENT BEGINS.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
KEY MESSAGES:
- LAKE EFFECT AND UPSLOPE SNOW POSSIBLE ON SATURDAY.
- COLD BUT DRY END TO THE WEEKEND.
- MODERATING TEMPERATURES WITH MID-WEEK POSSIBLE MID-WEEK
PRECIPITATION CHANCES.
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UPPER TROUGHING LINGERS FOR THE WEEKEND AS SURFACE LOW PRESSURE
MOVES UP THE NEW ENGLAND COAST AND HIGH PRESSURE BUILDS IN FROM THE
GREAT LAKES. GRADIENT INDUCED NORTHWESTERLY FLOW BETWEEN THE HIGH
AND DEPARTING LOW PRESSURE IS FAVORING AN INVIGORATION OF LAKE
EFFECT SNOW. THERE IS A SURPRISINGLY DECENT SIGNAL FOR A LAKE HURON
TO LAKE ERIE PRECIPITATION BAND EXTENDING DOWN INTO THE WESTERN
PART OF OUR CWA ON SATURDAY. INCREASING SUBSIDENCE FROM THE
HIGH SUGGESTS THE DEPTH OF THE MOISTURE SHOULD BE SHALLOWING,
BUT CLUSTERS ALL SUPPORT ONE LAST WAVE AND SHOT OF COLDER AIR
ALOFT MOVING THROUGH THE DEPARTING UPPER TROUGH. EXACT PLACEMENT
OF ANY BANDING STILL REMAINS LOWER PREDICTABILITY, BUT NBM
PAINTS LOW END PROBS OF >2" OF SNOW ACROSS EASTERN OHIO, SO
SPATIAL INCONSISTENCIES ARE PRESENT, BUT THE OCCURRENCE OF IT IS
BECOMING HIGHER CONFIDENCE. THE OTHER LOCATION TO WATCH WILL BE
THE RIDGES OF BOTH PA AND WV WHERE DEEP LAYER NORTHWESTERLY
FLOW WILL RUN INTO THE HIGHER ELEVATION AND AID IN UPSLOPE
DRIVEN SNOWFALL. HERE, PROBABILITIES ARE HIGHER FOR ADVISORY
CRITERIA (3 INCHES) AT AROUND 45-55% WITH THE HIGH END OF THE
GOAL POSTS SITTING AT WARNING CRITERIA (6 INCHES). THE HIGH END
SOLUTION IS ONE THAT EMANATES FROM A DEEPER TROUGH WITH STRONGER
LOW- LEVEL FLOW/CONVERGENCE. WILL AWAIT BETTER AGREEMENT AMONG
THE GUIDANCE AS WE GET CLOSER AND CAN IRON OUT THE SMALL-SCALE
VARIATIONS THAT WILL BE OF HIGHER CONSEQUENCE.
SUNDAY SHOULD FEATURE THE DEPARTURE OF THE TROUGH AS HEIGHTS RISE
THROUGH THE DAY. SINKING SUBSIDENCE WILL SHUT OFF SNOW CHANCES AS
EACH FLAVOR OF ENSEMBLE CLUSTER RETURNS DRY CONDITIONS. TEMPS WON'T
REBOUND MUCH AT ALL, AND IN FACT, SUNDAY AND SUNDAY NIGHT ARE
FAVORED TO BE THE COLDEST OF THE PERIOD. HIGHS ECLIPSING 30 DEGREES
ARE LOW PROBABILITY AND SINGLE DIGIT OVERNIGHT LOWS ARE RANGING FROM
40-80% PROBABILITY NORTH AND EAST OF PITTSBURGH.
HIGH PRESSURE REMAINS DOMINANT WITH BUILDING HEIGHTS INTO NEXT WEEK.
A WEAK WAVE LOOKS TO MOVE THROUGH IN ZONAL FLOW RETURNING
PRECIPITATION CHANCES BY MID-WEEK, THOUGH THE SOURCE REGION FOR
MOISTURE BEING TO OUR NORTH AND WEST ISN'T SUGGESTING NOTABLE
PRECIPITATION ACCUMULATION. FOR THE WHITE CHRISTMAS DREAMERS OUT
THERE, LONG RANGE ENSEMBLES SUGGEST SUB-FREEZING TEMPERATURES
BEING MORE LIKELY CHRISTMAS EVE THAN CHRISTMAS DAY. IT'S STILL A
WEEK AWAY, SO PLENTY OF DETAILS TO IRON OUT AT THIS POINT.
AVIATION /00Z THURSDAY THROUGH MONDAY/
PRECIP CHANCES WILL CONTINUE TO DECREASE ACROSS THE REGION OVER
THE NEXT HOUR, MGW/LBE WILL LIKELY BE THE ONLY TERMINALS THEY
MAY SEE LIGHT MEASUREABLE PRECIP.
WITH THE COLD FRONT ADVANCING ACROSS THE LAUREL HIGHLANDS,
TERMINALS SHOULD BEGIN TO SEE SLIGHT IMPROVEMENT IN CEILINGS AND
VISIBILITIES. THERE IS STILL A CHANCE FOR A FEW SCATTERED LAKE-
EFFECT SNOW SHOWERS TO LINGER NORTH OF PIT. HOWEVER, THERE IS
LOW CONFIDENCE AND LIMITED SPATIAL COVERAGE TO INCLUDE IN
DUJ/FKL AT THE MOMENT. AMENDMENTS MAY BE NEEDED.
HI-RES ENSEMBLE GUIDANCE CONTINUES TO INDICATE AT LEAST 50-80%
PROBABILITIES (CLOSER TO 80-90% ALONG THE RIDGES) FOR MVFR/IFR
CEILINGS TO STICK AROUND AFTER PRECIPITATION ENDS THROUGH THE
REMAINDER OF THIS 24-HR TAF PERIOD.
OUTLOOK...
A BRIEF IMPROVEMENT TO VFR CEILINGS WILL BE POSSIBLE THURSDAY
EVENING, SAVE FOR FKL/DUJ WHERE PROBABILITIES FOR MVFR REMAIN
AROUND 30-50%. THE NEXT APPROACHING LOW PRESSURE SYSTEM BRINGS
RESTRICTIONS BACK TO THE REGION THURSDAY NIGHT AND PRECIPITATION
CHANCES ON FRIDAY. RESTRICTIONS MAY LINGER THROUGH AT LEAST
SATURDAY AS COLD ADVECTION UNDER NORTHWEST FLOW PROMOTES THE
CONTINUATION OF LAKE-EFFECT CLOUDS AND POSSIBLY A FEW SCATTERED
LIGHT SNOW SHOWERS. THE NEXT CHANCE FOR VFR DOESN'T LOOK TO
RETURN UNTIL SATURDAY NIGHT OR SUNDAY.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...MLB
NEAR TERM...MLB/AK
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...CERMAK/HEFFERAN
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