Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 271255 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 855 AM EDT SUN JUL 27 2014 .SYNOPSIS... A WARM FRONT WILL PUSH THROUGH THE REGION TODAY FOLLOWED BY A LOW PRESSURE SYSTEM ON MONDAY. THE LOW LIFTS OUT TO THE NORTHEAST MONDAY NIGHT. OVERALL...AFTER A WET START TO THE WEEK...FAIR AND DRIER WEATHER IS EXPECTED FOR THE BALANCE OF THE WEEK AS HIGHER PRESSURE MOVES INTO THE REGION. && .NEAR TERM /TONIGHT/... 9AM UPDATE... LINE OF SHOWERS AND THUNDERSTORMS IS MOVING STEADILY EASTWARD ACROSS THE HUDSON VALLEY AND INTO VERMONT THIS MORNING IN ASSOCIATION WITH THE SHORTWAVE TROUGH. THIS WILL MOVE INTO NEW HAMPSHIRE IN THE NEXT TWO HOURS AND THEN ACROSS THE REST OF THE AREA THROUGH THE DAY TODAY. HAVE ADJUSTED HOURLY POP FORECAST TO BETTER REFLECT TIMING OF PRECIPITATION ARRIVAL AND HAVE INCREASE POP OVERALL CLOSER TO 100 PERCENT SINCE CONFIDENCE IN RAIN IS VERY HIGH. REMOVED MENTION OF HEAVY RAIN AS FLOODING SHOULD NOT BE A SIGNIFICANT THREAT. 630 AM UPDATE...HAVE MADE VERY MINOR CHANGES TO THE FORECAST FOR THE NEXT FEW HOURS BASED ON LATEST TRENDS IN OBSERVATIONAL DATA. LINE OF SHOWERS AND THUNDERSTORMS ACROSS CENTRAL NY CONTINUES TO PUSH EASTWARD THIS MORNING. ASSUMING NO SIGNIFICANT CHANGES TO THE LINE...IT SHOULD REACH THE CONNECTICUT VALLEY BETWEEN 14-16Z AND MOVE EASTWARD FROM THERE AT A PRETTY GOOD CLIP. THE MAIN THREAT WILL BE FREQUENT LIGHTNING AND HEAVY RAINFALL. ORIGINAL DISCUSSION... MAIN FORECAST CONCERNS FOR TODAY REVOLVE AROUND THE COVERAGE OF SHOWERS AND THUNDERSTORMS AND ANY POTENTIAL FOR SEVERE WEATHER. A WELL-DEFINED SHORT WAVE TROUGH MOVING ACROSS THE EASTERN GREAT LAKES REGION AS OF 3 AM WILL MOVE ACROSS NORTHERN NEW ENGLAND TODAY. INCREASING MOISTURE IN THE COLUMN AHEAD OF THE SHORT WAVE TROUGH ALONG WITH SOME LOW LEVEL SPEED CONVERGENCE WILL CONTINUE TO ALLOW FOR SHOWER AND THUNDERSTORM DEVELOPMENT ACROSS WESTERN UPSTATE NY OVER THE NEXT FEW HOURS. IN ADDITION...SOME LIGHT WARM ADVECTION SHOWERS ACROSS VT WILL MOVE ACROSS AT LEAST OUR WESTERN ZONES EARLY ON AS WELL. AS THE SHORT WAVE TROUGH MOVES EAST THIS MORNING...THE SHOWER AND THUNDERSTORM ACTIVITY CURRENTLY DEVELOPING OVER UPSTATE NY WILL MOVE INTO OUR REGION. THE BULK OF THE BAND SHOULD ARRIVE IN THE CONNECTICUT RIVER VALLEY LATE THIS MORNING...THEN MOVE ACROSS THE REST OF THE FORECAST AREA THROUGH MID AFTERNOON. IT WILL PROBABLY REACH THE COASTAL PLAIN MIDDAY. SOME FREQUENT LIGHTNING WILL BE POSSIBLE ALONG WITH SOME LOCALLY HEAVY RAINFALL. AFTER THIS BAND CLEARS WESTERN ZONES THIS AFTERNOON...THE QUESTION THEN BECOMES COVERAGE OF ANY THUNDERSTORMS THAT MAY REDEVELOP. WHILE WE WILL BE IN BETWEEN TWO SHORT WAVES WHICH SHOULD SUPPRESS WIDESPREAD DEVELOPMENT...WEAK CYCLONIC FLOW ALOFT AND SOME DESTABILIZATION SHOULD FOSTER THE DEVELOPMENT OF WIDELY SCATTERED SHOWERS AND THUNDERSTORMS...ESPECIALLY ACROSS NH. IF THUNDERSTORMS DO DEVELOP...ONE OR TWO COULD BE SEVERE...WITH GUSTY WINDS AND HEAVY RAINFALL THE MAIN THREATS. IT IS WORTH NOTING THAT SOME MODEL DATA SHOW RELATIVELY LONG AND LOOPING LOW LEVEL HODOGRAPHS THIS AFTERNOON...ESPECIALLY ACROSS NH. IF A FEW PERSISTENT DISCRETE CELLS WERE TO DEVELOP...A TORNADO OR TWO COULD OCCUR. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... MUCH OF THE NIGHT SHOULD BE FAIRLY QUIET AFTER ANY EVENING THUNDERSTORMS DIMINISH. HOWEVER...THE NEXT SHORT WAVE TROUGH APPROACHES...AND SHOULD BRING A W-E ORIENTED BAND OF SHOWERS AND THUNDERSTORMS TO OUR SOUTHERN ZONES LATE. HEAVY RAIN WOULD BE THE MAIN THREAT WITH THIS ACTIVITY...ALTHOUGH FREQUENT LIGHTNING WOULD NOT BE A SURPRISE. LOW PRESSURE...RELATIVELY STRONG FOR THIS TIME OF YEAR...LOOKS TO MOVE ACROSS THE FORECAST AREA ON MONDAY ALONG WITH ITS ATTENDANT STRONG SHORT WAVE TROUGH. DEPENDING ON THE TRACK OF THE LOW...A SEVERE WEATHER THREAT COULD EXIST GIVEN PLENTIFUL WIND SHEAR AND A MOIST AIR MASS CHARACTERIZED BY LOW LCL/S. THEREFORE...IF THE CENTER OF THE LOW MOVES ACROSS THE FORECAST AREA AND ALLOWS A PORTION OF THE AREA TO REMAIN IN THE WARM SECTOR FOR A WHILE...A WIND DAMAGE AND ISOLATED TORNADO THREAT COULD EXIST. HEAVY RAINFALL WILL BE A POSSIBILITY AS WELL. && .LONG TERM /TUESDAY THROUGH SATURDAY/... THE SURFACE/UPPER LOW MOVE ACROSS THE REGION MONDAY NIGHT WITH A TRAILING COLD FRONT THAT WILL MOVE OFF THE COAST BY TUESDAY MORNING. SHOWERS/THUNDERSTORMS WILL CONTINUE INTO MONDAY NIGHT WITH THIS SYSTEM AND COME TO AN END TUESDAY MORNING AS THE SYSTEM BEGINS TO EXIT INTO THE MARITIMES. TUESDAY WILL SEE A DRIER AND MORE STABLE WSW FLOW IN THE WAKE OF THE SYSTEM BUT STILL A FEW INSTABILITY SHOWERS CANNOT BE RULED OUT MAINLY IN THE MOUNTAINS. THE MEAN LONGWAVE TROUGH POSITION WILL REMAIN OVER THE GREAT LAKES THRU THE WEEK. A DISCREPANCY IN THE MODELS FOR THURSDAY WHETHER ANOTHER STRONG SHORTWAVE ROTATES OUT OF THE TROUGH THRU NORTHERN NEW ENGLAND PRODUCING ANOTHER ROUND OF SHOWERS. GFS SEEMS MOST PRONOUNCED WHILE EURO DAMPENS IT OUT. WILL KEEP THURSDAY WITH A CHANCE OF SHOWERS AS PER SUPERBLEND MODEL GUIDANCE SUGGESTS. THE END OF THE WEEK LOOKS MAINLY DRY AT THIS TIME BUT THERE IS STILL A RISK OF ANOTHER SHORTWAVE MOVING OUT OF THE TROUGH SO LOW CHANCE POPS WILL PREVAIL ALMOST DAILY AS A HEDGE. WITH THE TROUGH REMAINING TO THE W THRU THE WEEK...DAILY TEMPERATURES WILL VARY LITTLE AND REMAIN IN THE 70S TO AROUND 80 EACH DAY WITH LOWS IN THE 50S TO AROUND 60. USED A BLEND OF THE MODELS FOR POPS AND TEMPERATURES. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/... SHORT TERM...LOCAL IFR CONDITIONS IN FOG WILL IMPROVE EARLY THIS MORNING. HOWEVER...A BAND OF SHOWERS AND THUNDERSTORMS IS EXPECTED TO MOVE ACROSS THE FORECAST AREA FROM WEST TO EAST LATER THIS MORNING THROUGH MID AFTERNOON. LOCALLY LOWER CONDITIONS...POSSIBLY BRIEFLY IFR ARE EXPECTED. TONIGHT...WE EXPECT FOG AND STRATUS TO BE THE MAIN PROBLEM WITH LOWER CONDITIONS EXPECTED. WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED ON MONDAY WITH LOW CONDITIONS. LONG TERM...MVFR/IFR CONDITIONS EXPECTED IN SHOWERS AND THUNDERSTORMS MONDAY NIGHT. TUESDAY CONDITIONS IMPROVE TO VFR BEHIND THE FRONT AS DRIER AND MORE A MORE STABLE AIR MASS MOVES INTO THE REGION. A FEW WIDELY SCATTERED AFTERNOON SHOWERS STILL POSSIBLE TUESDAY AND AGAIN WEDNESDAY MAINLY IN THE MOUNTAINS BRIEFLY LOWERING CEILINGS TO MVFR. && .MARINE... SHORT TERM...SOUTHERLY WINDS WILL INCREASE ON SUNDAY AS THE PRESSURE GRADIENT STRENGTHENS BETWEEN HIGH PRESSURE TO THE EAST AND A TROUGH OF LOW PRESSURE TO THE WEST. WINDS WILL GUST TO AROUND 20 KT. WAVE HEIGHTS WILL BE BUILDING... BUT PROBABLY NOT TO THE HEIGHTS ADVERTISED BY THE MODELS. STILL COULD SEE SOME 5 FT WAVES BY LATE AFTERNOON OR TONIGHT...BUT WILL HOLD OFF ON A SCA AT THIS TIME. LONG TERM...DUE TO A PROLONGED SOUTHERLY FLOW A SCA WILL LIKELY BE NEEDED MONDAY NIGHT AND TUESDAY DUE TO SEAS REACHING OR EXCEEDING 5 FT OVER THE OUTER WATERS. BY TUESDAY NIGHT SEAS WILL SUBSIDE AS WINDS SHIFT TO THE W AND SW. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ NEAR TERM UPDATE... KIMBLE

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