Area Forecast Discussion
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000 FXUS61 KPBZ 251307 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 807 AM EST TUE NOV 25 2014 .SYNOPSIS... A STORM SYSTEM MAY BRING SNOW TO PORTIONS OF THE AREA ON WEDNESDAY WITH COLDER CONDITIONS HOLDING SWAY THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... QUICK EARLY MORNING UPDATE TO BRING STRATUS DECK INTO FAR NORTHERN I-80 CORRIDOR AS AREA OF CLOUDS UNDER GREAT LAKES LOW HAS SHIFTED EAST. NO OTHER CHANGES. COLDER AIR CONTINUES TO SLOWLY INFILTRATE THE REGION EARLY THIS MORNING BEHIND THE COLD FRONT THAT CROSSED THE AREA YESTERDAY. FAIRLY STRONG LOW LEVEL LAPSE RATES AND AMPLE MIXING HAVE ALSO MANAGED TO KEEP THE WINDS UP A BIT OVERNIGHT. THIS WILL CONTINUE INTO THE DAYTIME TODAY AS MIXED LAYER FLOW GENERALLY AVERAGES AROUND 20 KTS OR SO THROUGH THE DAY FROM THE WSW AT MOST LOCATIONS. AS A RESULT...A STILL BRISK DAY IS ON TAP...BUT NOWHERE NEAR TO THE DEGREE OF YESTERDAY. A COMBINATION OF AN UPPER LOW GENERALLY REMAINING RELEGATED TO THE NORTHERN GREAT LAKES AND THE FACT THAT WARM ADVECTION AND DEEP SOUTHERLY FLOW IS RESTRICTED TO THE FAR EAST COAST AREAS LEAVES THE AREA IN A RELATIVE DRY REGION OF AIR THROUGH THE AFTERNOON. AS A RESULT...ABUNDANT SUNSHINE WILL COMBINE WITH STRONG MIXING TO ALLOW FOR DECENT TEMPERATURE RISES AGAIN THIS AFTERNOON. HOWEVER...DUE TO THE FACT THAT 850 MB TEMPERATURES HAVE FALLEN BACK PRECIPITOUSLY FROM YESTERDAY...JUST WIDESPREAD 40S SEEM LIKELY. FRIES && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... AN UPPER LOW CURRENTLY EMERGING FROM THE LEE OF THE ROCKIES AND DIGGING INTO THE SOUTHERN HIGH PLAINS IS PROJECTED TO ROUND THE BASE OF THE UPPER TROUGH OVER THE GREAT LAKES AND RAPIDLY DEVELOP AS IT ENCOUNTERS THE SUBTROPICAL JET FEED UP THE EASTERN SEABOARD. MODEL SOLUTIONS CONTINUE TO VARY A BIT ON THE EXACT CORRIDOR OF NORTHEASTWARD EJECTION OF THIS SYSTEM UP THE APPALACHIAN CHAIN...WHICH HAS DRASTIC RAMIFICATIONS TO OUR FORECAST IN THE UPPER OHIO VALLEY...HOWEVER MOST MODEL SOLUTIONS NOW FAVOR AT LEAST SOME SNOWFALL IN ALL POINTS FROM PITTSBURGH EASTWARD ON WEDNESDAY AT SOME POINT. AS THIS UPPER WAVE ADVANCES NORTHEASTWARD...THE MOISTURE FEED UP THE ATLANTIC IS RAPIDLY WRAPPED BACK INTO THE DEVELOPING HIGHLY TILTED BAROCLINIC CYCLONE. THE PREPONDERANCE OF MODEL SOLUTIONS SUGGEST AN 850 MB LOW TRACK TO THE EAST OF THE APPALACHIANS ON WEDNESDAY...WHICH SHOULD LARGELY KEEP OUR AREA ENTRENCHED ON THE COLDER SIDE OF THE SYSTEM. THIS SHOULD KEEP OUR PRECIPITATION TYPE AS ALL SNOW EVERYWHERE THAT PRECIPITATION DOES OCCUR...HOWEVER MARGINAL ONSET TEMPERATURES NEAR FREEZING MAY MAKE ACCUMULATIONS DIFFICULT TO MUSTER IN SOME OF THE LOWEST ELEVATIONS AROUND MORGANTOWN. THAT SAID...WHILE THE BULK OF THE LOW LEVEL FORCING FOR ASCENT AND STRONGEST OMEGAS ARE LIKELY TO REMAIN TO THE EAST OF THE AREA IN THE DEEPER MOISTURE FEED...SOME INTERESTING DYNAMICS SEEM LIKELY TO PLAY OUT IN THE MID-LEVELS. BOTH THE NAM AND GFS HAVE REALLY SEEMINGLY LATCHED ONTO A DEEP AND IMPRESSIVE LAYER OF FRONTOGENESIS FROM 700-400 MB...WITH THE UPWARD BRANCH OF THIS AGEOSTROPHIC CIRCULATION LIFTING INTO OUR SOUTHEASTERN THIRD OR QUARTER OF OUR CWA ROUGHLY 12-18Z ON WEDNESDAY. COINCIDENT WITH THIS LARGE OF LARGE SCALE LIFT IS THE DENDRITIC GROWTH ZONE...AND GIVEN THE AMOUNT OF ATLANTIC MOISTURE BEING THROWN BACK INTO IT...DENDRITE FORMATION SEEMS LIKELY TO BE FAIRLY ROBUST FOR A SHORT PERIOD ON WEDNESDAY CONCURRENT WITH THE RATHER SHORT WINDOW OF DEEP MOISTURE AND LIFT. MODEL SOLUTIONS HAVE LARGELY INCREASED THEIR QPF EXPECTATIONS ALONG THE SOUTHEASTERN FRINGE OF THE CWA WITH THIS...AND ALL SEEM RATHER REASONABLE EXCEPT THE NAM...WHICH HAS MASSIVELY UNREALISTIC NEGATIVE OMEGA VALUES NOTED IN THE UPWARD BRANCH OF THE FRONTOGENETICAL CIRCULATION. THE MITIGATING FACTORS FOR HIGH RATIO SNOWFALL WILL LIKELY COME VIA MARGINAL BOUNDARY LAYER AND GROUND TEMPERATURES. AS A RESULT...WHILE THE COBB NUMBERS WOULD FAVOR 15:1 SNOWS FOR MOST LOCATIONS...THE FORECAST FAVORS MORE ALONG THE LINES OF 7:1 IN THE LOWER ELEVATIONS AND 12:1 IN THE HIGHER ELEVATIONS FOR MELTING CONSIDERATIONS. THE END RESULT SEEMS MOST LIKELY TO BE VERY LIGHT ACCUMULATIONS EVERYWHERE EXCEPT MAYBE A AN INCH OR TWO INCHES IN MORGANTOWN...LATROBE...AND INDIANA...A GENERAL 3 TO 6 INCHES IN MOST THE RIDGES...EXCEPT AROUND 6 INCHES POSSIBLE IN THE SOUTHEASTERN RIDGES OF TUCKER/GARRETT COUNTY. THIS FORECAST FOLLOWS LARGELY ON PERSISTENCE WITH THE PREVIOUS FORECASTS...EXCEPT TO EXPAND VERY LIGHT ACCUMULATIONS A BIT DEEPER IN THE FORECAST AREA. DUE TO A BIT OF CONTINUED FLUX IN THESE NUMBERS AND A LACK OF CONFIDENCE IN WIDESPREAD WARNING CRITERIA NUMBERS...WINTER STORM WATCHES REMAIN IN EFFECT FOR WEDNESDAY. WITH COLDS AND LIGHT NORTHERLY WINDS ALONG WITH DYNAMICAL COOLING LIKELY TO PLAY A ROLE...HIGHS ON WEDNESDAY WERE ADJUSTED DOWNWARD. STATISTICAL GUIDANCE LIKELY IS COMPLETELY USELESS IN A PATTERN AS SUCH...SO TEMPERATURES WERE ADJUSTED HEAVILY TOWARD DIRECT MODEL OUTPUT FROM THE NAM...ECMWF...AND GFS...WHICH ALL FAVORED NOTHING MORE THAN LOWER TO MID 30S WHERE SNOW IS EXPECTED. FRIES && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... DEEPER MOISTURE FROM LARGE COASTAL LOW BEGINS PULLING AWAY TO THE EAST THANKSGIVING MORNING THANKS TO ANOTHER SW TROF MOVING QUICKLY IN FROM THE WEST. ENOUGH LLVL MOISTURE LINGERS WEDS NIGHT TO KEEP POPS WARRANTED AREAWIDE. THE SW TROF WILL STREAM WELL TO OUR SOUTH...ULTIMATELY KEEPING HIGHER POP CHANCES OVER WV...BUT DEEPER MOISTURE WILL POOL NORTHWARD ALONG THE WRN PERIPHERY OF THE HIGHER TERRAIN. WITH NW FLOW KICKING IN...SNOW CHANCES WILL INCREASE THROUGH THANKSGIVING DAY. MOST OF THE FORECAST AREA HAS A DECENT CHANCE OF SEEING AT LEAST SOME SNOW FLAKES ON THANKSGIVING...BUT DOWNSTREAM FLOW FROM THE LAKES AND UPSLOPING WILL FAVOR THE TYPICAL NW FLOW AREAS. BY THURS EVENING DRIER AIR BEGINS TO WORK IN FROM THE SW LIMITING THE POTENTIAL OVER ERN OHIO AND THE NRN PANHANDLE OF WV. AT THIS TIME THE CAA BRINGS H85 TEMPS NEAR -10C ENHANCING LAKE-INDUCED CAPE AND OVERALL SNOW CRYSTAL GROWTH. FORECASTING LIGHT ACCUMULATIONS FOR THE RIDGES AND DOWNSTREAM OF THE LAKE...PRIMARILY NORTH OF I-80. DRIER AIR UNDER SFC HIGH PRESSURE MOVES IN FOR FRI...BUT IT WONT STAY LONG. A STREAM OF MOISTURE FROM THE CANADIAN ROCKIES WILL KEEP CLOUDS AND PRECIPITATION CHANCES IN THROUGH THE WEEKEND AS NW FLOW HOLDS INTO EARLY SUN. HIGH PRESSURE WILL SLIDE SOUTH INTO THE NRN PLAINS OVER THE LATTER PART OF THE WEEKEND...DISLODGING A WEAK COLORADO LOW WITH RELATIVELY LOW MOISTURE INTO OUR AREA. WHILE THIS MEANS MORE LIGHT PRECIPITATION...THE GOOD NEWS IS A TRANSITION TO SWERLY FLOW AND OVERALL WARMING INTO NEXT WEEK. MODELS HAVE MADE REMARKABLE PROGRESS IN CONSISTENCY OVER THE LAST 24HRS LENDING TO HIGHER CONFIDENCE IN THE EXTENDED TRENDS. TAX && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... MVFR STRATUS AT TIMES AT KFKL WHIOCH MAY SPREAD TO KDUJ LATER THIS MORNING. OTHERWISE VFR CONDITIONS WILL CONTINUE WITH SCATTERED GUSTS TO 25KTS. OUTLOOK.../TONIGHT NIGHT THROUGH SATURDAY/... COASTAL LOW PRES COULD BRING PSBL RSTRNS EAST OF PITTSBURGH LATE TONIGHT INTO WEDNESDAY. PERIODIC RSTRNS ARE PSBL INTO THE WKEND WITH SVRL WK CROSSING DISTURBANCES. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY AFTERNOON FOR MDZ001. OH...NONE. PA...NONE. WV...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY AFTERNOON FOR WVZ041. && $$

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