Area Forecast Discussion
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000 FXUS61 KPBZ 271857 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 257 PM EDT SAT JUN 27 2015 .SYNOPSIS... RAINY AND COOL AS AN UNSEASONABLY DEEP LOW PRESSURE SYSTEM MOVES THROUGH THE REGION. && .NEAR TERM /THROUGH SUNDAY/... CURRENT RADAR IMAGERY SHOWS THE SYSTEM PLAYING OUT AS EXPECTED THROUGH EARLY AFTERNOON AS THE STEADY LIGHT TO MODERATE RAIN IS BEGINNING TO PUSH NORTHEAST OF THE FORECAST AREA. RAINFALL AMOUNTS FROM THIS MORNING THROUGH ABOUT NOON HAVE BEEN AROUND AN INCH WITH SOME LOCALIZED AREAS NEARING 1.5 INCHES. AS A RESULT...STORM TOTALS THUS FAR HAVE BEEN SLIGHTLY LESS THAN EARLIER INDICATIONS...AND THE AREA CREEKS AND STREAMS HAVE LARGELY BEHAVED. SOME MINOR FLOODING OF LOW SPOTS AND BASEMENTS IN ALLEGHENY/LAWRENCE/WESTMORELAND COUNTIES EARLIER MEANT A FLOOD ADVISORY WAS PRUDENT. THE WARM FRONT IS NEARING THE MASON-DIXON LINE AND PUSHING NORTH AND TAKING THE STEADY RAIN WITH IT. THE FOCUS NOW SHIFTS WEST TO THE THIN LINE ON RADAR INDICATING THE COLD FRONT. TO THIS POINT...AN ABUNDANCE OF CLOUDS HAS KEPT THE AREA AHEAD OF THE COLD FRONT STABLE...BUT SOME BREAKS IN THE CLOUD COVER HAVE DEVELOPED OVER EASTERN OHIO. SHOWERS ALONG THE COLD FRONT ARE MORE CELLULAR IN NATURE AND IF THEY CAN TAP INTO ANY AVAILABLE BOUYANCY...HAVE MORE THAN ENOUGH UPPER SUPPORT TO DEVELOP INTO STRONG OR SEVERE THUNDERSTORMS. CURRENT RAP ANALYSIS DEPICTS 500-1000J/KG SB CAPE NOSING INTO THE SOUTHERN PERIPHERY OF THE FORECAST AREA. THIS IS COLLOCATED WITH A STRENGTHENING UPPER-LEVEL JET PUSHING THROUGH THE UPPER OHIO VALLEY. WILL CONTINUE TO MONITOR THE THREAT FOR SEVERE WEATHER IN THE FORM OF DAMAGING WINDS AND AN ISOLATED TORNADO THROUGH THE EVENING HOURS FROM THE NORTHERN PANHANDLE OF WV THROUGH SOUTHWEST PA...NORTHERN WV AND WESTERN MARYLAND. WATER VAPOR IMAGERY SHOWING THE DRY SLOT ADVANCING AHEAD OF THE LOW...RESULTING IN SOME DRYING OF THE COLUMN. THE MOST IMPRESSIVE 850MB MOISTURE TRANSPORT IS NOW NORTHEAST OF THE AREA AS THE MID- LEVEL FLOW TAPS INTO THE ATLANTIC OCEAN FOR MOISTURE. STILL...PW VALUES OF GREATER THAN 1.5" RESIDE ACROSS THE BULK OF THE FORECAST AREA. ANY RE-DEVELOPMENT ALONG THE COLD FRONT COULD TAP THE DEEPER MOISTURE RESULTING IN EFFICIENT RAIN PRODUCERS. WITH A BASE COAT OF AROUND AN INCH OF RAIN ALREADY IN THE AREAS SOILS...HAVE DECIDED TO KEEP THE FLOOD WATCH UP THIS AFTERNOON. THE SYSTEM BEGINS TO OCCLUDE TONIGHT AND MOVES TO THE NORTH OF THE FORECAST AREA BY DAYBREAK SUNDAY. WRAP-AROUND MOISTURE WILL KEEP THE THREAT OF LIGHT RAIN SHOWERS IN THE FORECAST THROUGH SUNDAY...BUT SHOULD RESULT IN LITTLE MORE THAN AN ADDITIONAL ONE TO TWO TENTHS OF AN INCH. TEMPERATURES WILL BE WELL BELOW AVERAGE THROUGH THE WEEKEND AS THE NORTHWEST UPPER-LEVEL FLOW BEHIND THE FRONT RE-ENFORCES THE COOL AIR. TAX && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
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THE UPPER LOW WILL CONTINUE TO TRUDGE OFF TO THE NORTH AND EAST SUNDAY NIGHT. THIS ALONG WITH DIURNAL STABILIZATION WILL ALLOW REMAINING SHRA TO END. TRANSIENT AND SMALL MIDLEVEL AND SURFACE RIDGING WILL KEEP THE CWA MOSTLY DRY LATER SUNDAY NIGHT AND MONDAY MORNING. YET ANOTHER SHORTWAVE WILL DIG INTO THE WESTERN GREAT LAKES BY MONDAY AFTERNOON...WITH A SURFACE LOW PASSING NEAR DETRIOT BY 12Z TUESDAY. THE NAM APPEARS TO BE A STRONG AND FAST OUTLIER AS COMPARED TO THE GFS AND ECMWF. WITH THE LESS DYNAMIC SYSTEM AND LOWER MOISTURE AVAILABILITY (PWATS BELOW 1.5 INCHES)...THE SYSTEM WILL NOT BE ABLE TO MANAGE RAINFALL AMOUNTS SIMILAR TO TODAY. SLOWED POPS A BIT MONDAY AFTERNOON...BUT WILL MAINTAIN LIKELY VALUES FOR MONDAY NIGHT. THINK QPF FROM THIS SYSTEM WILL REMAIN BELOW 0.5 INCH IN GENERAL. TIMING OF SYSTEM IS NOT FAVORABLE FOR SEVERE WEATHER...DESPITE THE STRONG FLOW PATTERN. THIS SYSTEM PULLS AWAY BY TUESDAY MORNING...BUT EXPECT THREAT OF SHRA AND A FEW TSRA TO CONTINUE THROUGH THE DAY...ESPECIALLY IN THE AFTERNOON AS LOW LEVEL LAPSE RATES STEEPEN. AFTER THE COOL TEMPERATURES SUNDAY...VALUES REBOUND TOWARDS SEASONABLE LEVELS MONDAY AFTERNOON. MORE ABUNDANT CLOUDS TUESDAY WILL COOL VALUES A FEW DEGREES FOR AFTERNOON HIGHS.
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&& .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... MODEL GUIDANCE FAVORS INCREASED RIDGING IN THE WEST WITH DOWNSTREAM DEEPENING TROUGHING ACROSS THE GREAT LAKES. THIS WILL LIKELY KEEP THINGS FAIRLY ACTIVE AND WET OVER THE CWA...WITH TEMPERATURES LIKELY TO REMAIN BELOW NORMAL. MONDAY NIGHT INTO TUESDAY SEES THE BEST SHOT AT WIDESPREAD RAIN SHOWERS ACROSS THE AREA. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... RAIN WILL TAPER OFF THROUGH THIS AFTERNOON WITH IFR CONDITIONS LIFTING TO MVFR CIG RESTRICTIONS. MOST TERMINALS SHOULD SEE A BREAK IN THE PRECIPITATION BY THIS LATE AFTERNOON AND IMPROVE TO VFR. A DRY SLOT IS MOVING IN WITH BREAKS IN THE CLOUDS THAT WILL ALLOW ADDITIONAL SURFACE HEATING FOR THE REMAINDER OF TODAY. THE HEATING OF RESIDUAL MOISTURE WILL AID IN DEVELOPMENT OF THUNDERSTORMS DURING THE LATE AFTERNOON INTO THIS EVENING. EXPECTING IFR CIGS CONDITIONS TO RETURN BY SUNDAY AM WITH -RA/DZ. .OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... RESTRICTIONS ARE LIKELY THROUGH THE REST OF THE WEEKEND WITH PASSAGE OF A STRONG LOW PRESSURE SYSTEM. AN APPROACHING COLD FRONT MAY CAUSE POSSIBLE RESTRICTIONS WITH RAIN MONDAY AND TUESDAY. && .HYDROLOGY... THE COLD FRONT IS JUST TO OUR WEST AND WILL SLOWLY TRACK RAIN SHOWERS AND ISOLATED THUNDERSTORMS INTO THE AREA THROUGH THE REMAINDER OF SATURDAY. AT THIS TIME... LOCALIZED URBAN AND SMALL STREAM FLOODING HAS BEEN REPORTED ACROSS THE REGION... HOWEVER WE ARE NOT EXPECTING SHARP RISES ON THE MAIN STEM RIVERS AT THIS TIME. THE TRACK OF THE SYSTEM HAS THE UPPER LOW PRESSURE CENTERED OVER DETROIT AND SLOWLY MOVING OFF TO THE NORTHEAST. OVER THE PAST 24 HOURS OUR CWA HAS RECEIVED FROM ONE-QUARTER /0.25/ TO JUST UNDER 2 /2.00/ INCHES OF RAINFALL WITH THE HIGHER AMOUNTS FALLING IN THE RIDGES OF WESTMORELAND AND TUCKER COUNTIES. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...FLOOD WATCH UNTIL 5 PM EDT THIS AFTERNOON FOR MDZ001. OH...FLOOD WATCH UNTIL 5 PM EDT THIS AFTERNOON FOR OHZ039>041- 048>050-057>059-068-069. PA...FLOOD WATCH UNTIL 5 PM EDT THIS AFTERNOON FOR PAZ014-020>023- 029-031-073>076. FLOOD WATCH UNTIL 2 AM EDT SUNDAY FOR PAZ007>009-013-015-016. WV...FLOOD WATCH UNTIL 5 PM EDT THIS AFTERNOON FOR WVZ001>004-012- 021>023-041.
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