Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 171921 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 321 PM EDT FRI APR 17 2015 .SYNOPSIS... A WEAK COLD FRONT WILL CROSS THE AREA THIS AFTERNOON. HIGH PRESSURE WILL THEN MOVE IN FOR TONIGHT. A SECONDAY...DRY COLD FRONT WILL PUSH SOUTHEAST THROUGH THE AREA SATURDAY FOLLOWED BY A GUSTY NORTHWEST WIND IN THE AFTERNOON. A COMPLEX FRONTAL SYSTEM WILL BRING RAIN UP FROM THE SOUTHWEST LATE SUNDAY INTO TUESDAY. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A WEAK SURFACE COLD FRONT EXTENDED FROM NEAR KBGM TO KJST AT 19Z. VERY LITTLE LLVL CONVERGENCE AND DEEPER LAYER SHEAR IS ACCOMPANYING THIS FEATURE...SO WE ARE SEEING VERY LITTLE IN THE WAY OF CONVECTION SO FAR. AS THIS FRONT MOVES INTO THE SLIGHTLY BETTER /MID-50/ DEWPOINT AIR ACROSS THE MID AND LOWER SUSQ VALLEY...ISOLATED TO SECONDARY SHOWERS AND TSRA SHOULD DEVELOP PER THE LAST FEW RUNS OF THE HRRR. A COMPACT AREA OF HIGH PRESSURE WILL BUILD ACROSS THE STATE TONIGHT WITH CLEARING SKIES AND LIGHT WIND. THE RESIDUAL LLVL MOISTURE AND DIMINISHING WIND COULD LEAD TO SOME PATCHY VALLEY FOG LATE TONIGHT/EARLY SATURDAY. LOWS TONIGHT WILL BE CHILLY AND IN THE UPPER 30S ACROSS THE NRN MTNS...AND LOWER TO MID 40S ELSEWHERE. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... AFTER A TRANQUIL MORNING UNDER SFC HIGH PRESSURE...A POTENT SHORT WAVE WILL MOVE QUICKLY SE THROUGH NEW ENGLAND AND DRAG A DRY...QUASI BACKDOOR CFRONT THROUGH THE FCST AREA DURING THE MIDDLE OF THE DAY. DEEP VERTICAL MIXING AND A TIGHTENING LLVL P-GRADIENT WILL KICK THE WINDS UP...ESPECIALLY OVER THE CENTRAL AND NE PART OF THE STATE. MAX TEMPS SATURDAY WILL BE IN THE 70S FOR MOST...BUT PERHAPS ONLY THE M-U60S IN THE HIGHER ELEVATIONS/NW. && .LONG TERM /SUNDAY THROUGH FRIDAY/... UPPER RIDGE STAYS JUST TO THE WEST SAT NIGHT...AND SHOULD KEEP IT MAINLY CLEAR. TEMPS MAY GET FROSTY IN THE NRN MTNS...WITH 40S ELSEWHERE. THE LIGHT N/E WIND MAY BE ENOUGH TO KEEP TEMPS FROM REALLY FALLING OFF. SUNDAY LOOKS MAINLY DRY AT THIS POINT...WITH MOST GUIDANCE NOT BRINING ANY RAIN INTO THE AREA UNTIL AFTER 21Z. WILL KEEP CHC POPS IN THE SW FOR LATE IN THE DAY. GOOD TO ABOVE AVERAGE CONFIDENCE NOW IN EXTENDED RANGE FORECAST WITH LATEST 16/12Z MODELS CONTINUING THEIR TREND OF MUCH BETTER AGREEMENT ON EVOLUTION OF OVERALL PATTERN AND TIMING. THE KEY ELEMENTS OF THE FCST ARE NOW BECOMING RATHER CLEAR: 1) THE WEEKEND SHOULD TURN OUT TO BE DRY! 2) A POTENTIALLY SIGNIFICANT RAINFALL EVENT IS BEING SIGNALED BY THE MODEL AND ENSEMBLE DATA FOR LATE SUNDAY NIGHT INTO MONDAY AND 3) BEYOND MONDAY THE PATTERN LOOKS BLOCKY WITH A CORE OF NEGATIVE HEIGHT ANOMALIES CENTERED OVER THE MIDWEST/GREAT LAKES/NORTHEAST. THE UPPER LOW EXITING THE FOUR CORNERS REGION INTO THE CENTRAL PLAINS WILL MERGE WITH NORTHERN STREAM ENERGY DROPPING SWD ACROSS SOUTHERN CANADA...EVENTUALLY CARVING OUT A BROAD LONG WAVE TROUGH OVER THE EASTERN U.S. AT THE SFC...A DEEPENING LOW WILL TRACK NEWD THROUGH THE GREAT LAKES WITH ABOVE NORMAL PWS BEING DRAWN NWD ALONG AND AHEAD OF ITS TRAILING COLD FRONT VIA STRONG SLY FLOW. AIDED BY THE MAGNITUDE OF THE MSLP...850MB WINDS AND PW ANOMALIES THE PATTERN RECOGNITION SUGGESTS THE POTENTIAL FOR A SYNOPTIC TYPE HEAVY RAINFALL EVENT LATE SUNDAY NIGHT INTO MONDAY. AS THE PARENT UPPER TROUGH TAKES ON A SLIGHT NEGATIVE TILT...IT ALSO APPEARS THAT A TRIPLE POINT LOW WILL FORM ALONG THE FRONT OVER THE SRN MID ATLC STATES...WHICH USUALLY SLOWS THE PROGRESSION AND ENHANCES RAINFALL. CURRENT FORECAST GRIDS ARE IN VERY GOOD SHAPE...AND MAINTAINED THE TREND OF INCREASED POPS FOCUSED AROUND DAY 3.5-4/SUNDAY NIGHT-MONDAY WITH ADDED CHC FOR +RA FROM THE SOUTH CENTRAL MTNS INTO THE SUSQ VLY. BASED ON CAPE FORECASTS...ADDED A MENTION OF CHANCE TSTM TO THE WEST MONDAY AS WELL WITH MOISTURE STREAMING IN ON NOTABLE 850MB SOUTHERLY JET. TEMPS SHOULD TREND COOLER INTO MIDDLE/LATE WEEK WITH SHOWERY /YET LIGHT/ REGIME ASSOCIATED WITH BROAD CYCLONIC FLOW ALOFT WITH CLOSED UPPER LOW CENTERED INVOF THE UPPER GREAT LAKES. DETAILS ON PRECIP DO REMAIN SKETCHY FOR THIS PERIOD...WITH LACK OF GOOD CONSENSUS IN GUIDANCE AFTER WED WITH DIVERGING SOLUTIONS IN POSITION OF BROAD TROUGH OVER S CANADA/NORTHEAST U.S. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... A WEAK SFC TROUGH NEARLY BISECTING THE STATE FROM THE NE TO SW AT 19Z WILL SLIDE SE ACROSS THE SUSQ VALLEY LATE TODAY HELPING TO SPARK A FEW...GENERALLY BRIEF SHOWERS AT CENTRAL AND SERN PENN TAF SITES. A FEW BRIEF TSRA MAY IMPACT TAF SITES SE OF A LINE FROM KSEG TO KAOO. TSRA ARE EXPECTED TO HAVE QUITE ISOLATED COVERAGE AND SHOULDN`T POSE ANY SIGNIFICANT WIND THREAT AS BULK WIND SHEAR IN THE LOWEST 3 KM AGL IS FROM THE WEST AND MAINLY UNDER 20 KTS. GENERALLY IMPROVING CONDS EXPECTED LATE TODAY/EARLY THIS EVENING ACRS THE CENTRAL AND WEST...AS WESTERLY FLOW DRAWS DRIER AIR INTO THE REGION. A RIDGE OF HIGH PRES WILL BUILD INTO THE AREA TONIGHT...BRINGING WIDESPREAD VFR CONDS AND LGT WIND THIS EVENING. CAN/T RULE OUT PATCHY RADIATION FOG LATE AT NIGHT/EARLY SAT AM. GUSTY NW WINDS 20-25 KTS WILL OCCUR ACROSS MUCH OF CENTRAL AND NEPA SATURDAY AFTERNOON AS A SECONDARY...DRY COLD FRONT PUSHES SE ACROSS THE REGION. OUTLOOK... SAT-SUN...NO SIG WX EXPECTED. MON...SHOWERS/LOW CIGS EXPECTED. TUE...NO SIG WX EXPECTED. && .FIRE WEATHER... AFTER A WETTING RAINFALL...WILDLAND FIRE SPREAD DANGER WILL BE VERY LOW FOR THE REST OF TODAY. SCATTERED SHOWERS AND PERHAPS A FEW BRIEF THUNDERSTORMS WILL AFFECT THE SOUTH-CENTRAL AND SOUTHEASTERN PART OF THE STATE THROUGH DUSK. CLEARING SKIES WILL SPREAD SOUTHEAST ACROSS THE AREA TONIGHT AS HIGH PRESSURE MOVES IN FROM THE OHIO VALLEY. PATCHY FOG IS POSSIBLE. SATURDAY WILL BE MILD AND DRY...WITH NORTHWEST WINDS PICKING UP ACROSS THE CENTRAL AND NORTHEAST PART OF THE STATE IN THE AFTERNOON. THE AFTERNOON RELATIVE HUMIDITY WILL DIP INTO THE 25 TO 30 PERCENT RANGE OVER ALMOST ALL OF THE AREA. FINER FUELS SHOULD DRY OUT SUFFICIENTLY FROM THE RECENT RAIN...AND THE CURRENT FIRE WEATHER WATCH FOR SATURDAY AFTERNOON AND EARLY SATURDAY EVENING MAY BE UPGRADED TO A RED FLAG WARNING WITH LATER FORECAST ISSUANCES. && .CTP WATCHES/WARNINGS/ADVISORIES... FIRE WEATHER WATCH FROM SATURDAY AFTERNOON THROUGH SATURDAY EVENING FOR PAZ006-011-012-018-019-025>028-037-041-042-045-046- 049>053-056>059-063. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...RXR AVIATION...LAMBERT FIRE WEATHER...LAMBERT

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