Area Forecast Discussion
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000
FXUS61 KPBZ 041242
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
842 AM EDT MON MAY 4 2015

.SYNOPSIS...
WARM TEMPERATURES WILL CONTINUE INTO THE AFTERNOON. A SLOW MOVING
FRONTAL BOUNDARY WILL BRING RAIN CHANCES TONIGHT THROUGH
WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
ONLY MINOR TWEAKS TO SKY COVER AS MAINLY CIRRUS THIS MORNING WILL
GIVE WAY TO INCREASING MID DECK THIS AFTERNOON. NO CHANGES TO
TEMPERATURES.

WESTERLIES TRY TO SETTLE SOUTH LATER THIS AFTERNOON AND TONIGHT
WITH A WEAK FRONT ATTEMPTING TO PUSH SOUTH. THERE IS UNCERTAINTY
IN HOW FAR AND HOW QUICKLY THE FRONT MAKES SOUTHERLY PROGRESS. FOR
NOW...NAM/GFS AND SREF POINT TO A 12Z TUESDAY POSITION IN THE CWA
BUT NORTH OF PIT...AND WILL TAKE THIS SUGGESTION. PLACED LIKELY
POPS NORTH OF A PHD/BTP/DUJ LINE DUE TO THIS THINKING...WITH
CHANCE POPS TO THE SOUTH. ALTHOUGH THE FIRST RAINDROPS COULD
ARRIVE PRIOR TO 00Z...MOST CONFIDENT IN SEEING ACTIVITY AFTER THAT
TIME AS WE SHOULD ONCE AGAIN SEE DEEP MIXING AND A DRY BOUNDARY
LAYER DURING THE AFTERNOON. MODELS HAVE REALLY STRUGGLED WITH
DEWPOINTS THE LAST COUPLE OF DAYS...UNDERESTIMATING THE DOWNWARD
MIXING OF DRY AIR. WENT LIGHT ON THE THUNDER CHANCES THIS
AFTERNOON/EVENING WITH UNIMPRESSIVE INSTABILITY NOTED ON MODEL
SOUNDINGS. STILL LOOKS TOO WARM ALOFT TO SUPPORT DEEP CONVECTION.

ONLY TWEAKED PREVIOUS HIGH TEMPERATURE FORECAST...AS IT WAS ALREADY
WELL-PLACED ON THE WARMER SIDE OF GUIDANCE. H850 TEMPS LOOK TO BE
1-2C WARMER THAN YESTERDAY...AND WITH GOOD MIXING...THAT WOULD
CORRESPOND TO HIGH TEMPERATURES 3-5 DEGREES WARMER THAN YESTERDAY
IN MANY CASES. STUCK CLOSER TO MODEL CONSENSUS WITH LOW TEMPS
TONIGHT WITH CONTINUED MIXING AND THICKENING CLOUDS.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
THE REGION WILL REMAIN ON THE NORTHERN PERIPHERY OF A FLAT H5
RIDGE OVER THE CAROLINAS THROUGH THE MID-WEEK PERIOD...WHICH WILL
LEAD TO MODEST MID-LEVEL FLOW AND LITTLE SOUTHWARD PROGRESS OF THE
FRONTAL BOUNDARY. ANY MOVEMENT OF THE BOUNDARY IS MORE LIKELY TO
BE DRIVEN BY CONVECTION THAN JET DYNAMICS.

UPSWINGS IN CONVECTIVE COVERAGE ON TUESDAY WILL HINGE UPON THE
TIMING OF LOW-AMPLITUDE SHORTWAVE TROUGHS THAT WILL MOVE THROUGH
THE WNWLY FLOW. CLOUD COVER WILL BE CONSIDERABLE AND WILL SERVE TO
LIMIT DESTABILIZATION...BUT MOISTURE AND AN UNUSUALLY WARM
BOUNDARY LAYER ARE LIKELY TO PROVIDE SUFFICIENT INSTABILITY TO
GENERATE SHOWERS AND STORMS ON TUESDAY AS THE FRONTAL BOUNDARY
SAGS SOUTHWARD. POPS WERE INCREASED SLIGHTLY FROM THE PREVIOUS
FORECAST.

THE FRONTAL BOUNDARY WILL MOVE LITTLE DURING THE PERIOD...BUT WILL
BECOME MORE DIFFUSE WITH TIME. AS A SHORTWAVE TROUGH EJECTS FROM
THE SOUTHERN PLAINS TO THE NORTHERN PLAINS...A H5 RIDGE WILL
AMPLIFY OVER THE GREAT LAKES. THE NET RESULT WILL BE INCREASING
INFLUENCE OF HIGH PRESSURE AND A SUPPRESSION TO THE SOUTH AND WEST
OF CONVECTION. THUS...POPS BY LATE WEDNESDAY AFTERNOON WERE
SHIFTED TO THE RIDGES AND TO THE SOUTHWEST OF THE FORECAST AREA.

UNTIL THE RIDGE AXIS TRANSLATES EAST OF THE FORECAST AREA...
DIURNAL INCREASE IN CU CAN BE EXPECTED BUT CHANCES FOR RAIN WILL
BE MINIMAL DESPITE LINGERING MOISTURE AND QUITE-AMPLE HEATING. IN
FACT...OWING TO INCREASING H9-H8 TEMPERATURES AND QUALITY
MIXING...MAXIMA ARE EXPECTED TO ECLIPSE CLIMATOLOGICALLY-NORMAL
VALUES BY SEVERAL DEGREES F. LINGERING MOISTURE AND CLOUD COVER
ALSO WILL SUPPORT MINIMA SEVERAL DEGREES ABOVE NORMAL VALUES.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
A BROAD H5 RIDGE WILL DOMINATE THE NERN CONUS INTO THE WEEKEND.
AGGRESSIVE WARM AIR ADVECTION /WITH H9 TEMPS REACHING 20-22C/ IS
INDICATED IN BOTH ECMWF AND GFS DESPITE DIFFERENCES IN THE DETAILS
OF THE OVERALL PATTERN EVOLUTION. THESE PATTERN DIFFERENCES
NOTWITHSTANDING...THERE IS HIGH CONFIDENCE IN PERSISTENT WARMTH...
WITH MAXIMA IN THE 80S AND MINIMA IN THE UPPER 50S-LOWER 60S.

THIS WARM AIR AND INCREASING LOW-LEVEL MOISTURE WILL COMBINE TO
FUEL OCCASIONAL SHOWERS AND STORMS THROUGH THE EXTENDED PERIOD.
ANY SUCH STORMS WILL BE TIMED WITH SUBTLE WAVES THAT ARE NOT
RESOLVED PARTICULARLY WELL BY THE MODELS AT THIS TIME. THUS...POPS
IN THIS FORECAST FOLLOW A GENERAL DIURNAL TREND AND ARE FOCUSED
HIGHEST IN PROXIMITY TO LARGER-SCALE UPPER-LEVEL TROUGH POSITION.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
VFR TO START...WITH ONLY PATCHY HIGH CLOUDS EARLY ON. DEEP MIXING
WILL LEAD TO ANOTHER CU FIELD TODAY...WITH BETTER VERTICAL
DEVELOPMENT THAN LAST COUPLE OF DAYS. WINDS WILL ALSO PICK UP OUT
OF THE SOUTHWEST AND GUST TO AROUND 20 KNOTS DURING THE AFTERNOON.
MID AND UPPER CLOUDS THICKEN THIS EVENING. A FRONTAL BOUNDARY WILL
APPROACH FROM THE NORTH...AND TAKE UP RESIDENCE NORTH OF PIT BY
12Z TUESDAY. CANNOT RULE OUT TSRA AT FKL/DUJ PRIOR TO 02Z THIS
EVENING BUT CONFIDENCE IS NOT HIGH ENOUGH YET TO INCLUDE. MVFR
CIG/VIS IN SHRA POSSIBLE BY THAT TIME FROM PIT ON NORTH. THINK
SOUTHERN TERMINALS LIKE ZZV/HLG/MGW HOLD ON TO VFR THROUGH THE TAF
PERIOD.

.OUTLOOK.../TUESDAY THROUGH THURSDAY/...
OCCASIONAL CIG/VSBY RESTRICTIONS IN SHOWERS AND STORMS CAN BE
EXPECTED THROUGH TUESDAY NIGHT AS A FRONTAL BOUNDARY SAGS
SOUTHWARD INTO THE REGION. WITH LINGERING MOISTURE AND LIGHT
OVERNIGHT WIND...RADIATIONAL FOG WILL BE POSSIBLE WEDNESDAY NIGHT
AND THURSDAY NIGHT AND MAY LEAD TO OCCASIONAL VSBY RESTRICTIONS.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$


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