Area Forecast Discussion
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FXUS61 KPBZ 241728
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
128 PM EDT FRI APR 24 2015

.SYNOPSIS...
DRY AND COOL WEATHER CAN BE EXPECTED TODAY AS HIGH PRESSURE SLIDES
ACROSS THE REGION...BUT THE REPRIEVE WILL BE BRIEF AS LOW PRESSURE
IS FORECAST TO GENERATE RAIN ON SATURDAY.

&&

.NEAR TERM /THROUGH SATURDAY/...
A FEW PUFFS OF DIURNALLY-INDUCED FLAT CUMULUS HAVE BEEN NOTED
GENERALLY ALONG THE I-80 CORRIDOR...WITH CLEAR SKIES CONTINUING
SOUTH OF THERE. GIVEN THE COLDER MID-LEVEL TEMPERATURES RETREATING
A BIT TO THE NORTHEAST...FURTHER DEVELOPMENT OF CUMULUS IS NOT
REALLY ANTICIPATED...WITH CLEARING LIKELY RESUMING ACROSS THE
NORTHEASTERN REACHES OF THE AREA EVEN BEFORE THE NORMAL DIURNAL
CONVECTIVE MAXIMUM.

AN UNSTABLE BOUNDARY LAYER THIS AFTERNOON HAS BEEN ALLOWING FOR
FREQUENT NORTHWESTERLY WIND GUSTS OF AROUND 20 KTS. THESE SHOULD
TAPER INTO THE EVENING AS CLEARING ALLOWS FOR WEAK INVERSIONS TO
SET UP. HIGH CLOUDS WILL ALSO BEGIN TO ENCROACH FROM THE WEST
OVERNIGHT AS THE NEXT SYSTEM STARTS TO COME INTO VIEW.
HOWEVER...BEFORE THEIR ARRIVAL...TEMPERATURES SEEM POISED TO NOSE
DIVE FOR SEVERAL HOURS. THE DURATION OF THE CLEAR SKIES WILL BE
THE MOST IMPORTANT MODULATOR TO THE DEPTHS TO WHICH THE MERCURY
WILL PROBE TONIGHT. AS SUCH...A RATHER LOW CONFIDENCE FORECAST
EXISTS FOR TEMPERATURES OVERNIGHT. HOWEVER...THE COLDEST READINGS
ARE VERY LIKELY TO BE IN THE 20S IN THE VALLEYS OF THE
NORTHEASTERN CWA...WHILE THE WARMEST READINGS ARE LIKELY TO BE
MAINLY IN OHIO.

WHILE THE SURFACE REFLECTION OF THE NEXT SYSTEM THAT WILL PLAGUE
THE AREA WILL LIKELY REMAIN WELL BACK IN THE MID-MISSISSIPPI
VALLEY BY SATURDAY AFTERNOON...A WARM FRONT WILL LIKELY EXTEND
WELL TO ITS EAST INTO THE CENTRAL APPALACHIANS. DIFFERENTIAL
THETA-E ADVECTION AS WELL AS PVA WILL STREAM NORTH OF THIS FRONT
OVER GENERALLY THE SOUTHWESTERN HALF OF THE CWA BY SATURDAY
AFTERNOON. THIS WILL RESULT IN RAIN INCREASING FROM THE SOUTHWEST
TO NORTHEAST THROUGH THE AFTERNOON. HOWEVER...DUE TO ABUNDANT DRY
AIR IN PLACE UPON ITS ARRIVAL...SEVERAL HOURS OF VIRGA ARE LIKELY
BEFORE THE RAIN ACTUALLY HITS THE GROUND. BECAUSE OF
THIS...PRECIPITATION OUTBREAK IN THE FORECAST MORE CLOSELY ALIGNS
WITH THE SLOWER-DEVELOPING AND HIGHER LOW LEVEL RESOLVING NAM.
ASSUMING THIS VERFIES...RAIN MAY HOLD OFF IN PITTSBURGH ITSELF FOR
THE MAJORITY OF THE DAY ON SATURDAY. EVEN STILL...A CONTINUATION
OF BELOW NORMAL TEMPERATURES WILL BE LIKELY. FRIES

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
PRECIPITATION IS EXPECTED TO SPREAD NORTHEASTWARD SATURDAY AS
WARM...MOIST ADVECTION INCREASES AHEAD OF LOW PRESSURE ADVANCING
OUT OF THE MIDWEST.

MODELS ARE IN GENERAL AGREEMENT THAT THE CENTER OF THE APPROACHING
SHORTWAVE TROUGH WILL PASS JUST SOUTH OF THE FORECAST AREA
SATURDAY NIGHT. SUCH A TRACK WOULD KEEP THE FORECAST AREA ALONG
OR JUST NORTH OF THE ASSOCIATED WARM FRONT...AND IN PRIME
TERRITORY FOR A BAND OF LIGHT TO MODERATE RAIN OWING TO
DEFORMATION AND ISENTROPIC LIFT. AT ANY RATE...THE SYSTEM IS
PROGGED TO MOVE RAPIDLY OVER THE ATLANTIC ON SUNDAY...SPELLING AN
END TO PRECIPITATION.

NO CHANGES WERE MADE TO SATURDAY POPS WHICH CONTINUE TO FEATURE
CHANCE NUMBERS OVER THE I 80 CORRIDOR AND CATEGORICALS OVER I 70
GIVEN THE AFOREMENTIONED TRACK...ALTHOUGH ADJUSTMENTS WERE MADE
FOR FASTER EXITING AS PER THE LATEST TIMING TRENDS.

SUNDAY IS THUS EXPECTED TO BE A DAY OF IMPROVEMENT AS SURFACE HIGH
PRESSURE BUILDS UNDER NORTHERLY FLOW ALOFT. A FAIRLY STRONG...BUT
MOISTURE DEFICIENT SHORTWAVE IS FORECAST TO PASS THROUGH THE
WESTERN FLANK OF UPPER LOW PRESSURE EARLY ON MONDAY...SLIGHT TO
CHANCE POPS NUMBERS WERE MAINTAINED MAINLY OVER THE EASTERN HALF
OF THE COUNTY WARNING FOR PASSAGE OF THIS FEATURE...WHICH MAY
INCLUDE SOME SNOW SHOWERS OR FLURRIES.

TEMPERATURES PRIOR TO THE RAIN WILL BE TRICKY TONIGHT. INITIAL
CONDITIONS OF DRY AIR...LIGHT WIND AND CLEAR SKY WILL BE FAVORABLE
FOR RADIATIONAL COOLING...BUT CIRROSTRATUS IS EXPECTED TO BECOME
INCREASINGLY ABUNDANT AFTER MIDNIGHT AND WILL LIKELY LIMIT THE
IMMEDIATE PREDAWN DROP. THE COLD TEMP FORECAST WAS THUS
CONSTRUCTED FOR AN EARLY LOW READING...WITH STABILIZATION OR A
SLOW RISE WITH THE APPROACH OF DAWN.

THE REST OF THE PERIOD WILL FEATURE SUB AVERAGE READINGS GIVEN THE
PRESENCE OF THE NORTHEASTERN U.S. LOW. EXPECT TEMPERATURES ABOUT 5
TO 10 DEGREES BELOW NORMAL FOR THE START OF THE NEW WEEK.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
UPPER LEVEL LOW OVER NEW ENGLAND SHOULD BEGIN TO MOVE OFFSHORE
TUESDAY...WHICH SHOULD ALLOW FOR AT LEAST SOME PARTIAL CLEARING TO
OCCUR OVER THE REGION. THE CLEARING WOULD LIKELY BE SHORT LIVED...AS
MODELS PROJECT A SURFACE LOW WILL DEVELOP ALONG THE GULF COAST AND
MOVE TO THE NORTHEAST. STILL LOTS OF UNCERTAINTY WITH THE TRACK OF
THIS LOW...AND RECENT MODEL TRENDS HAVE SUGGESTED THE LOW MAY STAY
FARTHER TO THE SOUTHEAST. WILL TREND THE FORECAST IN THIS
DIRECTION...REDUCING BUT NOT ELIMINATING SHOWERS WEDNESDAY AND
THURSDAY.

ALTHOUGH TEMPERATURES ARE STILL EXPECTED TO BE A FEW DEGREES BELOW
NORMAL THROUGH THE EXTENDED FORECAST...THE MORE SOUTHERLY TREND OF
THE MID WEEK SURFACE LOW SHOULD ALLOW FOR MORE SUNSHINE
LOCALLY...AND HAVE BROUGHT TEMPS UP A FEW DEGREES TO COMPENSATE.
PRECIPITATION IN THE FORECAST.

&&

.AVIATION /17Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL CONTINUE THROUGH THE TAF PERIOD WITH GUSTY
WINDS SLACKENING QUICKLY AFTER SUNSET. HIGH CLOUDS WILL BE SLOW TO
LOWER INTO THE DAY SATURDAY...WITH RAIN LIKELY SLOW TO DEVELOP AS
WELL DUE TO DRY LOW LEVEL AIR. IT SEEMS MOST LIKELY TO DEVELOP
AROUND KZZV BY AROUND NOON...SPREADING EASTWARD THEREAFTER...WHICH
IS BEYOND THE TIME OF THE CURRENT TAF PERIOD. FRIES

.OUTLOOK.../TONIGHT THROUGH TUESDAY/...
CEILING RESTRICTIONS ARE EXPECTED SATURDAY AFTERNOON THROUGH
SUNDAY AFTERNOON AS LOW PRESSURE TRACKS ACROSS THE OHIO VALLEY.
ANOTHER ROUND OF RESTRICTIONS MAY BE POSSIBLE SUNDAY NIGHT INTO
MONDAY WITH SCATTERED SHOWERS.

&&

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

&&

$$



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