131
FXUS61 KPBZ 180529
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1229 AM EST MON NOV 18 2024
SYNOPSIS
DRY CONDITIONS CONTINUE TODAY WITH HIGHS SEVERAL DEGREES ABOVE
NORMAL. A TREND TOWARDS A COLDER AND MORE ACTIVE WEATHER
PATTERN BEGINS MIDWEEK AND WILL CONTINUE INTO NEXT WEEKEND.
ABOVE NORMAL TEMPERATURES WILL TRANSITION TO BELOW NORMAL BY THE
END OF THE WEEK.
NEAR TERM /UNTIL 6 AM THIS MORNING/
KEY MESSAGES:
- MILD TEMPERATURES EXPECTED THROUGH 6AM.
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A WEAK FRONT APPROACHING FROM THE NORTHWEST COULD RESULT IN
ISOLATED INSTANCES OF A TRACE TO 0.01" OVERNIGHT, BUT OVERALL,
SHOULD RESULT IN NOTHING MORE THAN INCREASED CLOUD COVERAGE AND
VIRGA GIVEN THE THE SUBSTANTIAL DRY LAYER UP TO 500MB EVIDENT IN
00Z SOUNDINGS.
OVERNIGHT LOW TEMPERATURES WILL GENERALLY BE A BIT ABOVE NORMAL
DUE TO INCREASED CLOUD COVERAGE AND WARM SOUTHWEST FLOW.
SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/
KEY MESSAGES:
- LIGHT RAIN CHANCES RETURN TUESDAY WITH A WARM FRONT.
- UPWARD TREND IN TEMPERATURES DURING THE EARLY WEEK PERIOD.
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UPPER RIDGING WILL BUILD OVER THE REGION TODAY, MAINTAINING DRY
CONDITIONS. DESPITE COOLER 850MB TEMPERATURES ON MONDAY,
WEST/SOUTHWEST FLOW AND BETTER INSOLATION DUE TO THINNER CLOUD
COVER WILL RESULT IN HIGH TEMPERATURES SEVERAL DEGREES WARMER
THAN THOSE OBSERVED SUNDAY. ABOVE- NORMAL TEMPERATURES ARE ALSO
PROJECTED MONDAY NIGHT WITH INCREASED WARM ADVECTION.
LOW PRESSURE WILL DEEPEN OVER THE UPPER MIDWEST TUESDAY AS THE
JET CORE MOVES BEYOND THE BACKSIDE INFLECTION POINT AND BEGINS
TO ROUND THE BASE OF THE TROUGH. THE PREVIOUSLY MENTIONED FRONT
WILL THEN LIFT NORTH AS A WARM FRONT. THE RESULTING SHIFT TO
LOW- LEVEL SOUTHWEST FLOW BEHIND THE WARM FRONT WILL BRING
1-INCH PLUS PRECIPITABLE WATER VALUES AND INCREASING ISENTROPIC
LIFT INTO OUR REGION, WHICH SHOULD RESULT IN A PERIOD OF
GENERALLY LIGHT RAINFALL TUESDAY INTO TUESDAY NIGHT. THE
SOUTHWEST FLOW WILL ALSO REINFORCE ABOVE- NORMAL TEMPERATURES.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
KEY MESSAGES:
- STEADIER RAIN ON WEDNESDAY WITH A COLD FRONT.
- MUCH COLDER TEMPERATURE APPEARS LIKELY THURSDAY INTO THE WEEKEND,
ALONG WITH ADDITIONAL PRECIPITATION CHANCES AND A PERIOD OF GUSTY
WIND.
- MEASURABLE SNOW IS A POSSIBILITY IN MOST OF THE REGION AT SOME
POINT BETWEEN THURSDAY AND SATURDAY, WITH IMPACTFUL ACCUMULATION
POSSIBLE IN THE HIGHER ELEVATIONS.
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THE BOTTOM LINE FOR THE EXTENDED PERIOD IS THAT A STARK PATTERN
CHANGE REMAINS LIKELY: A TRANSITION TO A COLDER REGIME WITH MULTIPLE
CHANCES OF PRECIPITATION. EXACT DETAILS OF COURSE REMAIN IN
QUESTION.
VIRTUALLY ALL MODEL SOLUTIONS NOW AGREE THAT A CLOSED 500MB LOW WILL
DEVELOP IN THE VICINITY OF THE FAR WESTERN GREAT LAKES/UPPER
MISSISSIPPI VALLEY BY 12Z WEDNESDAY. THERE IS ALSO BROAD AGREEMENT
THAT THIS UPPER LOW WILL TRANSITION ACROSS THE UPPER OHIO VALLEY AND
NORTHEAST CONUS THROUGH THE THURSDAY/FRIDAY PERIOD, BEFORE LIFTING
TOWARDS THE CANADIAN MARITIMES NEXT WEEKEND. CONFIDENCE IN THIS
OVERALL SCENARIO IS NOW EDGING TOWARDS THE HIGH CATEGORY.
GIVEN THAT, DETAIL DIFFERENCES IN STRENGTH AND TIMING REMAIN. SOME
OF THIS DEPENDS ON THE STRENGTH OF THE RIDGING THAT WILL VERY LIKELY
REMAIN ALONG THE ATLANTIC SEABOARD ON WEDNESDAY. THERE REMAINS A
MINORITY OF SOLUTIONS THAT LEAN TOWARDS A STRONGER RIDGE. AS A
RESULT, THERE ARE MODEL CLUSTERS KEEPING THE UPPER LOW CENTER MORE
TOWARDS THE MIDDLE OHIO VALLEY INITIALLY INTO THURSDAY, OR PERHAPS
KEEPING THE OVERALL TROUGH FROM DIGGING AS STRONGLY, THUS KEEPING
THE CENTER MORE TOWARDS THE GREAT LAKES. THESE SCENARIOS COULD SLOW
THE ARRIVAL OF COLDER AIR A BIT. HOWEVER, THE MAJORITY OF MEMBERS
STILL ARE GOING WITH THE MORE AGGRESSIVE ARRIVAL OF THE LOW INTO OUR
VICINITY BY THURSDAY. THUS, A LEAN TOWARDS THE LOWER END OF THE
TEMPERATURE GUIDANCE ENVELOPE SEEMS PRUDENT FOR THE END OF THE WEEK.
BIMODAL SOLUTIONS OF EARLIER RUNS CONTINUE TO TREND TOWARDS A MORE
CONFIDENT DEPICTION OF COLDER TEMPERATURE. ALSO OF NOTE: A PROLONGED
PERIOD OF GUSTY WIND IS ALSO LIKELY IN THIS PATTERN. PROBABILITIES
OF GREATER THAN 45 MPH (ADVISORY-LEVEL) GUSTS REMAIN LOW OUTSIDE OF
EASTERN TUCKER COUNTY, BUT MAXIMUM GUSTS OF 30 TO 40 MPH HAVE 50% OR
BETTER PROBABILITY AREAWIDE WEDNESDAY THROUGH FRIDAY.
AT LEAST A FEW ROUNDS OF PRECIPITATION APPEAR LIKELY INTO THE
WEEKEND: AN INITIAL WAVE AHEAD OF THE MAIN COLD FRONTAL PASSAGE,
FOLLOWED BY ADDITIONAL PERIODS AS A RESULT OF WRAPAROUND MOISTURE
AND SHORTWAVES IN NORTHWEST FLOW. OF COURSE, GIVEN THE COLDER
SOLUTION, SNOW POSSIBILITIES MUST BE CONSIDERED STARTING AS EARLY AS
WEDNESDAY NIGHT. THE ENTIRE CWA HAS SOME POTENTIAL FOR MEASURABLE
SNOW. EVEN THE TYPICALLY WARMER METRO/VALLEY AREAS HAVE A 40-50%
CHANCE OF AT LEAST 0.1 INCH DURING THE 72-HOUR PERIOD ENDING AT 12Z
SUNDAY ACCORDING TO THE NBM. HOWEVER THE AREA TO WATCH WILL BE THE
LAUREL HIGHLANDS AND THE WEST VIRGINIA RIDGES. FOR THE SAME 72-HOUR
PERIOD, IMPRESSIVELY LARGE SPREADS IN MODELED SNOW ACCUMULATION
EXIST, PARTICULARLY FOR THE HIGHER ELEVATIONS OF PRESTON AND TUCKER
COUNTIES. TOTALS WILL OF COURSE DEPEND ON TEMPERATURE STRUCTURE AND
SUPPORT FOR VERTICAL MOTION FROM BOTH DYNAMIC AND UPSLOPE EFFECTS,
DETAILS WHICH NEED TO BE IRONED OUT IN FUTURE RUNS. HOWEVER, THERE
IS CERTAINLY THE POTENTIAL FOR IMPACTFUL SNOW ACCUMULATION IN THESE
FAVORED LOCATIONS. THIS FORECAST WILL OF COURSE BE REFINED AS WE
HEAD THROUGH THE UPCOMING WEEK.
MODEL CLUSTERS SHOW SOME POTENTIAL FOR QUIETER WEATHER BY SUNDAY AS
THE UPPER LOW AND ASSOCIATED TROUGH MOVE EAST, RESULTING IN LOWER
PRECIPITATION CHANCES. HOWEVER, THE MAJORITY OF SOLUTIONS CONTINUE
TO SHOW WELL BELOW-NORMAL TEMPERATURES ON THAT DAY.
AVIATION /05Z MONDAY THROUGH FRIDAY/
PASSAGE OF A WEAK SHORTWAVE TO THE NORTH WILL PUSH A MOSTLY DRY
SURFACE BOUNDARY SOUTHWARD INTO THE REGION THROUGH MONDAY
MORNING. MOISTURE CONVERGENCE ALONG THE BOUNDARY IS EXPECTED TO
SUPPORT BROKEN TO OVERCAST LOW VFR TO MVFR (50-80% PROBABILITY)
CEILINGS TO SITES AS FAR SOUTH AS KMGW AFTER 12Z. UNCERTAINTY
DURING THIS PERIOD DERIVES FROM THE STAUNCHLY DRY ATMOSPHERE
PRECEDING THE BOUNDARY THAT MAY MAKE DEVELOPMENT OF BKN/OVC
DECKS DIFFICULT IN THAT 1500-4000FT LAYER, THUS TRENDED TOWARD
TEMPORARY EXPERIENCE OF THOSE CONDITIONS.
IN RESPONSE TO RISING HEIGHTS ALOFT, THE BOUNDARY SHOULD LIFT
NORTHWARD THROUGH THE AFTERNOON AND ERODE ANY STRATOCU DECK THAT
DEVELOPS. WIDESPREAD VFR IS HIGHLY LIKELY (AT LEAST 80%
PROBABILITY) AT ALL TERMINALS BY 00Z. WIND IS EXPECTED TO BE
GENERALLY LIGHT THROUGH THE PERIOD, STARTING MAINLY OUT OF THE
WEST SOUTHWEST AND TURNING VARIABLE BY THE EVENING.
OUTLOOK....
A SERIES OF INCREASINGLY POTENT LOW PRESSURE SYSTEMS WILL BRING
BOUTS OF RESTRICTIONS, GUSTY WIND, AND RAIN TURNING INTO
POTENTIAL SNOW SHOWERS FOR THE SECOND HALF OF THE WEEK.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...88
NEAR TERM...88
SHORT TERM...CL
LONG TERM...CL
AVIATION...FRAZIER
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