Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 030402 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 1202 AM EDT MON AUG 3 2015 .SYNOPSIS... PERSISTENT LOW PRESSURE ALOFT...SITUATED OVER QUEBEC...WILL BRING THE THREAT OF SHOWERS AND THUNDERSTORMS MONDAY AFTERNOON INTO TUESDAY. A FEW STORMS COULD BE STRONG MONDAY AFTERNOON AND EVENING. COOLER AIR MOVES IN FOR THE MID TO LATE WEEK...AND IT WILL BE MAINLY DRY...ALTHOUGH SCATTERED SHOWERS WILL BE POSSIBLE IN THE MOUNTAINS WEDNESDAY. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... MIDNIGHT...OTHER THAN USUAL ADJUSTMENT OF T/TD FOR CURRENT OBS...DECIDED TO SCALE BACK POPS SIGNIFICANTLY THROUGH EARLY AFTERNOON MONDAY /SEE BELOW/. PREVIOUSLY...WARM AIR ADVECTION CIRRUS WILL EXIT TO THE EAST AND DIURNALLY DRIVEN CU WILL DISSIPATE AFTER SUNSET...LEAVING MAINLY CLEAR SKIES OVERNIGHT. WITH RELATIVELY LIGHT WINDS...EXPECT PATCHY INLAND FOG TO DEVELOP LATE TONIGHT. MOST OF THIS FOG WILL NOT BE OVERLY DENSE WITH TEMPERATURES DROPPING CLOSE TO THEIR DEW POINTS...IN THE MID TO UPPER 50S. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... UPDATE...BASED ON LATEST NAM12 AND MESOSCALE MODELS...SCALED BACK POPS THRU A GOOD CHUNK OF MONDAY...KEEPING THE MORNING DRY...AND MOST OF THE AFTERNOON...EXCEPT FOR FAR NRN AND WRN ZONES WHERE CHC POPS MOVE IN MID AFTERNOON...GIVEN LOW-MID LVL SUBSIDENCE OUT AHEAD OF APPROACHING WAVE. PREVIOUS...ANOMOLOUS UPPER LOW FOR THIS TIME OF THE YEAR...WILL CONTINUE TO PROGRESS SOUTH AND EAST TOWARDS NEW ENGLAND MONDAY AFTERNOON. STRONG DYNAMICS AND MODERATE INSTABILITY WILL COMBINE TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS DURING THE MID/LATE AFTERNOON HOURS IN THE FAR NORTH AND WEST. 12Z GUIDANCE CONTINUES TO SLOW THE SURFACE FRONT TO THE EAST WITH EACH RUN - AND IN FACT WE HOLD THE HIGHEST POPS UNTIL ABOUT THE 00Z TIMEFRAME. THEREFORE...ANY CHANCE FOR SEVERE WEATHER SHOULD BE LIMITED TO THE LATE AFTERNOON HOURS OVER THE NORTHERN AND WESTERN HALF OF THE FORECAST AREA. IT IS IN THIS LOCATION THAT SPC CONTINUES TO HOLD THE POTENTIAL FOR A SLIGHT RISK OF SEVERE THUNDERSTORMS. IT WILL BE HOT ON MONDAY IN ALL LOCATIONS EXCEPT FOR THE MIDCOAST...WHERE AN ONSHORE FLOW WILL KEEP READINGS COOLER FROM WISCASETT TO ROCKLAND. READINGS WILL APPROACH 85-90 OVER SOUTHERN INTERIOR LOCATIONS WITH HUMID CONDITIONS AS DEW POINTS CREEP BACK INTO THE MID/UPPER 60S. MESOSCALE MODELS INDICATED THIS CONVECTION WILL CONTINUE TO MARCH EAST...DISSIPATING SOMEWHAT AS THE PRECIPITATION REACHES THE COAST DURING THE LATE EVENING HOURS. IT IS AT THIS POINT THE FRONT WILL LIKELY BECOME STATIONARY FOR A PERIOD. THIS WILL CONTINUE THE THREAT OF SCATTERED SHOWERS AND STORMS AS WE HEAD INTO THE LONG TERM PORTION OF THE FORECAST. WITH THE OVERNIGHT PRECIP ON MONDAY...EXPECT MORE WIDESPREAD LATE NIGHT FOG TO DEVELOP. && .LONG TERM /TUESDAY THROUGH SUNDAY/... IN THE LONG TERM UPPER LEVEL LOW PRESSURE WILL BE THE DRIVING FORCE IN OUR WEATHER. A COLD FRONT WILL SLIDE OFF THE COAST TUESDAY WITH SHOWERS AND THUNDERSTORMS POSSIBLE. MODELS KEEP DELAYING THE PASSAGE OF THIS FRONT WITH EACH RUN. ONCE THE FRONT MAKES ITS WAY OFF SHORE WE WILL CONTINUE TO SEE CYCLONIC CIRCULATION ALOFT WHICH WILL TRANSLATE TO AFTERNOON SHOWERS AND MAYBE AN ISOLATED THUNDERSTORM IN THE MOUNTAINS WEDNESDAY. THE FORECAST GETS A BIT COMPLICATED FOR THURSDAY AND FRIDAY AS MODEL GUIDANCE IS SHOWING A SHORT WAVE MOVING JUST TO OUR SOUTH. THE 12Z GFS IS FASTER AND FARTHER NORTH WITH THIS FEATURE AND MOVES IT THROUGH SOUTHERN NEW ENGLAND THURSDAY AND OFF THE COAST BEFORE DAWN FRIDAY WHILE THE ECMWF MOVES THE FEATURE THROUGH SOUTHERN NEW ENGLAND FRIDAY AND OFF THE COAST FRIDAY NIGHT. A PERIOD OF RAIN IS POSSIBLE FOR SOUTHERN PORTIONS OF THE FORECAST AREA IN THIS TIME PERIOD. ONCE THIS SHORT WAVE MOVE THROUGH WILL STILL BE UNDER THE INFLUENCE OF 5H LOW WITH CHANCE OF AFTERNOON SHOWERS SATURDAY AND SUNDAY. && .AVIATION /04Z MONDAY THROUGH FRIDAY/... SHORT TERM...A LIGHT DEVELOPING SOUTHERLY GRADIENT IN ADDITION TO INCREASING MOISTURE ALOFT MAY DELAY ONSET OF INLAND VALLEY FOG TONIGHT. PATCHY FOG WAS MAINLY FORECAST FOR AFTER 09Z. FOG MAY BE MORE WIDESPREAD LATE MONDAY NIGHT WITH RAINFALL AND SCATTERED CONVECTION INCREASING THE LOW LEVEL MOISTURE. PATCHY IFR CONDITIONS ARE EXPECTED. LONG TERM...MVFR POSSIBLE IN SHOWERS AND POSSIBLE THUNDERSTORMS TUESDAY. EXPECT MOSTLY VFR WED EXPECT FOR BRIEFLY MVFR IN SHOWERS. MVFR POSSIBLE THURSDAY INTO FRIDAY DEPENDING ON HOW FAR NORTH SURFACE LOW TREKS. && .MARINE... SHORT TERM...A DEVELOPING SOUTHERLY GRADIENT ON MONDAY AND MONDAY NIGHT WILL INCREASE WINDS OVER THE COASTAL WATERS WITH WIND GUSTS TO 20 KT EXPECTED. SEAS WILL BE ON THE INCREASE AS WELL BEGINNING MONDAY AFTERNOON AND CONTINUING. SMALL CRAFT ADVISORY CONDITIONS MAY BE POSSIBLE BY MONDAY NIGHT. LONG TERM...SEAS OF 5 FEET POSSIBLE TUESDAY THROUGH THURSDAY. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...CEMPA SHORT TERM... LONG TERM... AVIATION... MARINE...

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