Area Forecast Discussion
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000
FXUS61 KPBZ 191848
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
248 PM EDT SUN APR 19 2015

.SYNOPSIS...
SHOWERS WILL OVERSPREAD THE REGION THIS EVENING AND CONTINUE
THROUGH MONDAY. UNSEASONABLY COOL TEMPERATURES ARE EXPECTED FOR
THE REMAINDER OF THE WEEK.

&&

.NEAR TERM /THROUGH MONDAY/...
DRY AIR SAMPLED BY THE 12Z UPPER AIR SOUNDING REVEALS A
SUBSTANTIAL LAYER OF DRY AIR. THIS HAS KEPT THE RAIN AND CLOUDS AT
BAY FOR MUCH OF THE DAY...ALLOWING FOR TEMPERATURES TO RISE
QUICKLY ABOVE NORMAL. TEMPERATURE RISES HAVE BEEN AIDED...AT LEAST
IN PART...BY DOWNSLOPING EASTERLY FLOW SUSTAINED AT 10-15KTS WITH
GUSTS CLOSE TO 25KTS.

TEMPERATURES THIS EVENING WILL DECREASE ACROSS THE SOUTH FIRST AS
THE THICKER CLOUD COVER AND EVENTUAL RAIN SHOWERS MOVE IN. TIMING
THE ONSET OF PRECIPITATION HAS BEEN PUSHED BACK AN HOUR OR TWO FOR
MOST LOCATIONS TO ACCOUNT FOR THE DRY AIR IN PLACE. KEEPING
CATEGORICAL POPS IN FOR THIS EVENING/EARLY TONIGHT...DESPITE
SEVERAL OF THE LATEST HRRR RUNS CONTINUING TO SHOW CONSIDERABLE
MOISTURE EROSION UPON ARRIVAL...RESULTING IN TRIMMING OF QPF
GENERATION. ALL OTHER GUIDANCE INCLUDING THE VARIOUS OTHER HI-RES
MODELS SHOW THE CURRENT SWATH OF RAIN ALONG THE WARM FRONT
HOLDING TOGETHER THROUGH OUR AREA.

TONIGHT THE DRY SLOT IN THE WARM SECTOR WILL RESULT IN A LULL IN PRECIPITATION
THAT IS EXPECTED TO LAST THROUGH DAYBREAK. CLOUDS MAY DIMINISH TO
THE POINT WHERE POCKETS OF CLEARING COULD AID THE MONDAY MORNING
WARM-UP AS STRONG SOUTHEASTERLY FLOW VEERS SOUTHERLY. COLDER AIR
ADVANCING EASTWARD ALOFT WILL RESULT IN INSTABILITY AND DRIVE
THUNDERSTORM ACTIVITY ALONG AND AHEAD OF THE COLD FRONT. A SLIGHT
RISK OF SEVERE THUNDERSTORMS IS INCLUDED FOR OUR AREA...WITH THE
MAIN THREAT BEING DAMAGING WINDS. TAX

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
FRONT WILL BE IN OR JUST EAST OF THE RIDGES AT 00Z TUESDAY...WITH
A SECONDARY COLD FRONT LAGGING BEHIND WITH THE UPPER LEVEL COLD
AIR. ENOUGH MOISTURE AND STEEP ENOUGH LAPSE RATES REMAIN BEHIND
THE IMMEDIATE SURFACE BOUNDARY TO KEEP SHRA/TSRA CHANCES GOING
THROUGH MUCH OF THE NIGHT. DRIER AIR SHOULD ALLOW PRECIPITATION TO
CEASE AREAWIDE BY 12Z.

MODELS ARE IN GENERAL AGREEMENT THAT DECAYING MISSISSIPPI VALLEY
SHORTWAVE GETS ABSORBED BY DEEPENING UPPER LOW...WHICH DROPS INTO
THE NORTHERN GREAT LAKES BY 12Z TUESDAY. THIS LEADS TO A TROUGHING
PATTERN FOR THE NORTHEAST U.S. WHICH LOOKS TO PERSIST FOR SOME
TIME. CONFIDENCE IS HIGH IN THESE DETAILS. HOWEVER...TIMING OF
INDIVIDUAL SHORTWAVES ROTATING AROUND BECOMES MORE PROBLEMATIC
WITH TIME.

MAIN VORT LOBE RESIDES IN OR NEAR OUR NORTHERN COUNTIES
TUESDAY. THIS PLUS BETTER INSTABILITY LEADS TO HIGHER POPS IN THIS
AREA TUESDAY AFTERNOON/EVENING. HELD OFF ON THUNDER FOR NOW WITH
EQUILIBRIUM LEVELS MOSTLY BELOW 15K FEET...BUT THIS MAY HAVE TO BE
REEVALUATED WITH COLD TEMPS ALOFT EXPECTED.

A WEAK IMPULSE MAINLY AFFECTS THE SOUTHERN COUNTIES WITH A FEW
SHRA TUESDAY NIGHT. THE NEXT...MORE ORGANIZED...FRONTAL BOUNDARY
ARRIVES WEDNESDAY WITH BETTER RAIN CHANCES AREAWIDE. BEHIND THE
FRONT...BOUNDARY LAYER MAY BE ABLE TO COOL SUFFICIENTLY TO ALLOW
SNOWFLAKES TO MIX IN NORTH OF PIT LATE WEDNESDAY NIGHT...BUT NO
ACCUMULATION IS FORESEEN.

A GENERAL COOLING TREND IN TEMPERATURE WILL BE SEEN WITH VALUES
SINKING BELOW NORMAL BY THE END OF THE PERIOD.  CL

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
BROAD UPPER TROUGHING WILL REMAIN OVER THE EASTERN CONUS THROUGH
THE EXTENDED AND RESULT IN BELOW NORMAL TEMPERATURES EACH DAY
ALONG WITH CLOUDY SKIES AND SLIGHT CHANCES FOR PRECIPITATION
THROUGHOUT THE PERIOD AS SHORTWAVES TRANSITION THROUGH THE FLOW
AND CAA ALOFT PERSISTS. CONFIDENCE IS HIGH IN THE GENERAL FORECAST
AS MODELS HAVE BEEN FAIRLY CONSISTENT IN PROGGING THIS LONGWAVE
PATTERN...REFLECTED IN LATEST RMOP AND MODTRENDS GUIDANCE.
HOWEVER...CONFIDENCE IN TIMING OF ANY MORE SIGNIFICANT PERIODS OF
PRECIPITATION IS RELATIVELY LOW. FORECAST MAX/MIN TEMPERATURES ARE
NOT EXCEPTIONALLY COLD...BUT PERSISTENT AROUND 10 DEGREES BELOW
NORMALS AS ENSEMBLE ANOMALIES ARE SHOWING TEMPS AND HEIGHTS ALOFT
ONLY RANGING FROM 1-2 STANDARD DEVIATIONS BELOW NORMAL THROUGH THE
PERIOD.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
HIGH CIRRUS CONTINUES TO MOVE SLOWLY ACROSS THE AREA...BUT NO
RESTRICTIONS ARE ANTICIPATED UNTIL THE RAIN SHOWERS ASSOCIATED
WITH THE WARM FRONT ARRIVE THIS EVENING. EXPECTING RAIN TO FALL
OUT OF MOSTLY VFR CIGS INITIALLY...BUT HEADING INTO THE OVERNIGHT
THE CIGS SHOULD CONTINUE THIER DESCENT TO MVFR. CEILINGS MAY BE
BROKEN AS WE HEAD INTO MIDDAY MONDAY...WITH THUNDERSTORMS EXPECTED
THROUGH AFTERNOON.

GUSTY EAST-SOUTHEASTERLY FLOW WILL CONTINUE EVENING AND
OVERNIGHT...GRADUALLY RELAXING THROUGH THE EARLY MORNING MONDAY.
SURFACE FLOW WILL AGAIN INCREASE AS IT VEERS MORE SOUTHERLY MONDAY
AFTERNOON. TAX

.OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/...
RESTRICTIONS ARE POSSIBLE WITH A MID WEEK UPPER TROUGH.

&&

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

&&

$$


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