Area Forecast Discussion
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943
FXUS61 KPBZ 291821
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
221 PM EDT FRI APR 29 2016

.SYNOPSIS...
DRIER CONDITIONS WILL RETURN TONIGHT INTO EARLY SATURDAY BEFORE
ANOTHER SYSTEM APPROACHES WITH WIDESPREAD RAIN LATE SATURDAY.
SHOWERS AND THUNDERSTORMS WILL CONTINUE AT TIMES INTO SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
STAGNANT COOL AND MOIST AIR MASS WILL CONTINUE TO PLAGUE THE AREA
THROUGH TONIGHT. SOME EROSION OF LOW STRATUS IS DEVELOPING ON THE
SOUTHERN FLANK...ALLOWING FOR SCATTERING AND WARMING SOUTH OF THE
MASON-DIXON LINE. THIS WILL AGAIN SET UP A SHARP GRADIENT IN
TEMPERATURES THIS AFTERNOON WITH NORTHERN WEST VIRGINIA GETTING
INTO THE UPPER 60S...WHILE NORTH OF I-80 MAY TOUCH 50 DEGREES.

SHORTWAVE TROUGH AXIS CURRENTLY CROSSING LAKE ERIE WILL SKIRT THE
NORTHERN HALF OF THE FORECAST AREA THIS AFTERNOON. EXPECT CURRENT
SHOWER ACTIVITY TO BLOSSOM NORTH OF PITTSBURGH IN RESPONSE TO THE
QUICK PASSING WAVE. ADDITIONALLY...HI-RES CAMS SHOW SHOWERS
DEVELOPING JUST SOUTH OF PITTSBURGH. GIVEN THE STEEPENING LOW-
LEVEL LAPSE RATES...LIFT FROM THE WAVE AND COPIOUS
MOISTURE...THINK THAT CHANCE POPS THROUGH AND SOUTH OF THE
PITTSBURGH METRO AREA SEEM PRUDENT.

WAVE PASSES TO THE EAST TONIGHT AND SOME DRYING WILL OCCUR.
MOISTURE WILL BEGIN TO ERODE FROM THE WEST...SCATTERING OUT THE
LOW CLOUDS...BUT TIMING IS DIFFICULT TO PIN DOWN AT THIS POINT.
LOW TEMPERATURES WILL DEPEND LARGELY ON TIMING AND EXTENT OF
CLEARING OVERNIGHT. WITH THIS IN MIND...HAVE WESTERN PORTIONS OF
THE FORECAST AREA RELATIVELY LOW COMPARED TO EASTERN PORTIONS.
TAX

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
SOME CLEARING WILL BE LIKELY EARLY SATURDAY AS LOW LEVEL MOISTURE
FINALLY MIXES OUT BEHIND THE SYSTEM FROM FRIDAY AND IN ADVANCE OF
ANOTHER SYSTEM FOR THE LATTER HALF OF SATURDAY. IN THE
INTERIM...DIURNAL MIXING COMBINED WITH A DECREASE IN LAYER
MOISTURE SHOULD ALLOW FOR A PERIOD OF CLEARING IN THE
INTERCESSION. HOWEVER...THIS DECREASE WILL BE FLEETING AS
ISENTROPIC ASCENT AHEAD OF A NORTHEASTWARD TRANSLATING WARM FRONT
WILL MEAN CLOUDS WILL AGAIN OVERSPREAD THE AREA BY LATER IN THE
AFTERNOON.

AFOREMENTIONED ISENTROPIC ASCENT WILL SPREAD DEEP MOISTURE AND
LIFT OVER THE AREA BY SATURDAY EVENING WITH A COUPLED JET
STRUCTURE LIKELY TO TRANSLATE DOWN I-70. THE COMBINATION OF THESE
TWO ASSURES RAIN WILL OVERSPREAD THE AREA...AND POPS WERE THUS
RAISED TO 100 PERCENT. THE WARM FRONT IS SET TO MOVE NORTHWARD AND
THROUGH THE AREA BY SUNDAY MORNING...PLACING THE MAJORITY OF THE
CWA INTO THE WARM SECTOR BY THAT JUNCTURE. POPS WERE WOUND DOWN A
BIT IN THE WARM SECTOR...HOWEVER KEPT AT LEAST CHANCE AS THE MODE
WILL EVOLVE FROM STRATIFORM TO CONVECTIVE.

IN THE WARM SECTOR...THE 12Z GUIDANCE HAS TRENDED DECIDEDLY TOWARD
SOME AMOUNT OF CLEARING BY THE LATE MORNING ON SUNDAY. THIS WOULD
WORK TO STRONGLY DESTABILIZE THE COLUMN...AND MEAN A SECONDARY
INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY ON SUNDAY
AFTERNOON...PARTICULARLY SOUTH OF I-80. NAM PROFILES SUGGEST UP TO
2000 J/KG OF CAPE WITH THE VAST MAJORITY OF IT ABOVE A FAIRLY LOW
FREEZING LEVEL. EVEN IN THE ABSENCE OF STRONG VERTICAL
SHEAR...THIS CLOUD LEAD TO SOME HAILERS. THIS WILL NEED TO BE
MONITORED GOING FORWARD TO SEE HOW THE MODELS HANDLE THE WARM
SECTOR IN SUBSEQUENT RUNS.

EVEN AFTER A WEAK WAVE ON SUNDAY MOVES DOWN THE FRONT AND FORCES
THE SHOWERS AND THUNDERSTORMS...THE UPPER JET AXIS LOOKS TO REMAIN
RELATIVELY PARKED OVER THE OHIO VALLEY. THIS MEANS MOISTURE WILL
BE SLOW TO DECREASE INTO EARLY NEXT WEEK WITH SHOWER CHANCES
CURTAILING PAINFULLY SLOWLY. HOWEVER...AS A DEEPER UPPER LOW DIVES
TOWARD THE TENNESSEE VALLEY BY TUESDAY...THE UPPER JET AXIS SHOULD
FINALLY EVOLVE SOUTHWARD ENOUGH TO DRY OUT OUR AREA. FRIES

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE EXTENDED PERIOD LOOKS TO FEATURE A VERY STRONGLY ANCHORED
PATTERN OVER THE WESTERN CONUS AS A RIDGE LOOKS TO EVOLVE OVER THE
INTERMOUNTAIN WEST. DOWNSTREAM TROUGHING WILL THUS EVENTUALLY
BECOME ESTABLISHED OVER THE GREAT LAKES AND NORTHEAST BY THE END
OF THE WEEK AFTER A DRY MID-WEEK. THIS WILL MEAN SHOWER CHANCES
WILL RETURN AND TEMPERATURES WILL GENERALLY TREND NEAR OR BELOW
NORMAL. FRIES

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
IFR RESTRICTIONS GRADUALLY IMPROVING TO LOW MVFR...PRIMARILY SOUTH
OF PITTSBURGH WHERE SOME SCATTERING IS NOTED ON SATELLITE. ANOTHER
SHORTWAVE TROUGH WILL PASS ACROSS THE NORTH THIS
EVENING...REINFORCING THE LOW CIGS ACROSS THE NORTH. THIS WAVE
WILL ALSO GENERATE ADDITIONAL LIGHT RAIN SHOWERS...MAINLY FOR
NORTHERN AND EASTERN PORTS.

HIGH CONFIDENCE IN IFR CONDITIONS REOCCURRING TONIGHT...BUT AFTER
THE PASSAGE OF THE WAVE...LOWER-LEVELS BEGIN TO DRY OUT FROM THE
WEST. THIS WILL RESULT IN SOME AMOUNT OF SCATTERING/CLEARING FROM
KZZV EASTWARD NEAR DAYBREAK SATURDAY. CONFIDENCE IS MUCH LOWER ON
THE AMOUNT AND EXACT TIMING OF THE IMPROVEMENT NEAR SUNRISE. VFR
CONDITIONS ARE THEN EXPECTED FROM SATURDAY MID-MORNING THROUGH
THE DURATION OF THE OPERATIONAL TAF PERIOD.

LIGHT WEST WINDS WILL VEER TO THE NORTHWEST TONIGHT IN THE WAKE OF
THE PASSING WAVE. LIGHT NORTH WINDS TONIGHT WILL THEN VEER TO
EASTERLY SATURDAY. WIND SHOULD GENERALLY STAY 10KTS OR LESS
THROUGH THE PERIOD.
TAX

.OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/...
RESTRICTIONS ARE LIKELY AGAIN LATE SATURDAY THROUGH SUNDAY NIGHT
AS LOW PRESSURE CROSSES THE REGION.

&&

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

&&

$$



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