Area Forecast Discussion
Issued by NWS Portland, ME

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183 FXUS61 KGYX 301428 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 1028 AM EDT SAT APR 30 2016 .SYNOPSIS... HIGH PRESSURE MOVES EAST INTO THE ATLANTIC AND THE CANADIAN MARITIME PROVINCES TODAY. LOW PRESSURE WILL TRACK THROUGH THE EASTERN GREAT LAKES AND THEN OFFSHORE TO THE SOUTH OF NEW ENGLAND SUNDAY INTO MONDAY WITH A PERIOD OF RAIN EXPECTED. A LARGE TROUGH OF LOW PRESSURE WILL MOVE INTO NEW ENGLAND ON WEDNESDAY AND REMAIN NEAR THE AREA THROUGH THE WEEKEND...KEEPING COOL TEMPERATURES AND WET WEATHER IN THE FORECAST. && 14Z UPDATE... QUIET WEATHER CONTINUES ACROSS NORTHERN NEW ENGLAND LATE THIS MORNING. PATCH OF MID LEVEL CLOUDS ACROSS SOUTHWEST NEW HAMPSHIRE QUICKLY MIXING OUT AND EXPECT THE ENTIRE FORECAST AREA TO BE MOSTLY CLEAR BY EARLY AFTERNOON. LIGHT GRADIENT AND FULL SUN WILL PRODUCE A RATHER SHARP SEA BREEZE WHICH SHOULD COME ROARING IN DURING THE EARLY AFTERNOON CAPPING TEMPS IN COASTAL AND SOUTHERN INTERIOR SECTIONS IN THE LOWER TO MID 50S. AWAY FROM THE COAST HIGH TEMPS WILL TOP OUT IN THE MID 50S TO LOWER 60S. HAVE ADJUSTED TEMPS/TD`S/SKY GRIDS BASED ON CURRENT OBS AND NO OTHER CHANGES PLANNED ATTM. PREVIOUS DISCUSSION... .NEAR TERM /UNTIL 6 PM THIS EVENING/... 710 AM...THE FORECAST ISSUE THIS MORNING IS THE DECK OF OF MID- LVL CLOUDS IN SW NH. MODELS ARE NOT REALLY HANDLING IT WELL...BUT NAM12 SEEMS TO BE THE BEST OF THE BUNCH AND SHOWS THE CLOUDS BRIEFLY SPREAD EWD ALONG THE NH/MA BORDER FOR THE NEXT HOUR OR TWO AND THE SLOWLY DISSIPATING MID-LATE MORNING...AND WENT WITH THE NAM12 FOR SKY...AT LEAST IN THAT AREA. PREVIOUSLY...500 MB WAVE CROSSING NEW ENGLAND OVERNIGHT IS PRODUCING MAINLY A DECK OF CIRRUS...BUT HIS SHOULD SHIFT EAST OF THE CWA AROUND OR SHORTLY AFTER SUNRISE MAKING FOR A MOSTLY SUNNY DAY WITH JUST SOME PATCHY CIRRUS AND A FEW SCT STRATOCU THAT WILL FORM ALONG SEA BREEZE FRONT AS IT WORKS INLAND. THE LACK OF ANY PRE GRADIENT WILL ALLOW THE SEA BREEZE TO WORK FAIRLY FAIR INLAND AND THIS WILL KEEP TEMPS DOWN IN THE LOW TO MID 50S NEAR THE COAST...BUT REACH UP TO AROUND 60 INLAND AREAS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... TONIGHT WILL SEE THE SFC RIDGE BEGIN TO SHIFT SLOWLY OFFSHORE...A PROCESS THAT WILL TAKE INTO SUNDAY TO FINISH...AS 500 MB RIDGING BUILDS JUST TO OUR EAST. LOOK FOR CLOUDS TO INCREASE FROM THE WEST...BUT ANY RAIN SHOULD HOLD OFF UNTIL...AT LEAST...AFTER SUNRISE ON SUNDAY. MINS WILL LKLY OCCUR CLOSER TO MIDNIGHT WITH TEMPS STEADY OR RISING AFTER THAT...AND WILL BE IN THE MID TO UPPER 30S. THE BIG QUESTION FOR SUNDAY IS HOW QUICKLY THE RAIN MOVES IN...AND HOW FAR EAST IT GETS. ANY PRECIP IS DRIVEN BY SOME MID LVL ISENTROPIC LIFT...MAINLY IN THE 600-800MB RANGE. THE NAM BRINGS A ROUND OF RAIN INTO NH SUNDAY AFTERNOON...WHILE THE EURO HOLDS IT BACK A LITTLE LONGER. THERE IS PROBABLY ENOUGH TO LIFT TO GENERATE A FEW SHOWERS OR SOME VERY LIGHT RAIN IN NH SOMETIME TUE AFTERNOON...BUT DYNAMIC FORCING IS FORCED BY 500MB WAVE CRASHING INTO RIDGE SO HOLDING OFF LKLY POPS UNTIL MID-LATE AFTERNOON IN NH AND JUST KEEPING CHC IN ME. MAX T WILL BE AFFECTED BY CLOUDS AND RAIN...AND WARMEST TEMPS WILL BE IN THE INLAND KENNEBEC AND PENOBSCOT VALLEY WHERE HIGHS COULD GET CLOSE TO 60. ELSEWHERE LOOK FOR LOW TO MID 50S AT BEST. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... POTENT SHORTWAVE TROUGH ALOFT TRACKS EAST THROUGH THE GREAT LAKES AND NEW ENGLAND SUNDAY NIGHT AND MONDAY. THIS WILL DRIVE SURFACE LOW PRESSURE THROUGH THE EASTERN GREAT LAKES... WITH A NEW AREA OF LOW PRESSURE FORMING NEAR THE SOUTHERN NEW ENGLAND COASTLINE. THE NEW LOW BECOMES DOMINANT BY MONDAY NIGHT AS IT CONTINUES EASTWARD INTO THE ATLANTIC TOWARD NOVA SCOTIA. SHOULD SEE AN INITIAL AREA OF RAIN SUNDAY EVENING WITH A LEADING SHORTWAVE TROUGH BEFORE ANOTHER ROUND OF RAIN BEGINS MONDAY MORNING LASTING INTO MONDAY EVENING AS THE OFFSHORE LOW BEGINS TO TAKE OVER. WITH THE COASTAL LOW FORMING IT WILL PULL IN COLDER AIR ON THE BACK SIDE OF IT JUST AS PRECIPITATION IS ENDING. THIS COULD ALLOW FOR A BRIEF CHANGE TO SNOW MAINLY IN THE HIGHER TERRAIN BUT POSSIBLY EXTENDING INTO THE VALLEYS OF NORTHWEST MAINE AND NORTHERN NEW HAMPSHIRE MONDAY EVENING. THE ECMWF IS MORE AGGRESSIVE WITH THE HAND OFF BETWEEN THE FIRST SURFACE LOW AND THE DEVELOPING COASTAL LOW... AND AS A RESULT THE ECMWF SCENARIO WOULD GIVE THE BEST CHANCE OF A CHANGE OVER TO SNOW AS PRECIPITATION ENDS. SHOULD SEE A BREAK ON TUESDAY AS WEAK HIGH PRESSURE BUILDS INTO THE AREA. TEMPERATURES REMAIN COOL WITH HIGHS REACHING THE UPPER 50S TO LOW 60S. ON WEDNESDAY A LARGE TROUGH BEGINS TO DIG INTO THE GREAT LAKES AND CUTS ITSELF OFF OVER THE CENTRAL APPALACHIANS. CUT OFF LOWS AND THE ASSOCIATED MINOR WAVES ROTATING AROUND THEM ARE NOTORIOUSLY DIFFICULT FOR MODELS TO FORECAST... SO THE SPECIFIC DETAILS OF THE FORECAST FROM WEDNESDAY ONWARD ARE VERY MURKY. BUT WITH THE LOW JUST TO OUR WEST EXPECT OUR AREA TO SEE AT LEAST A FEW ROUNDS OF WET WEATHER WITH TEMPERATURES NEAR OR JUST BELOW SEASONAL NORMALS...VULNERABLE TO AN ONSHORE FLOW. WITH A LONG FETCH OF SOUTHERLY FLOW OVER THE WESTERN ATLANTIC ON THE EAST SIDE OF THE CUT OFF LOW... THIS WOULD PUT US IN A FAVORABLE POSITION FOR SEEING A HEAVY PRECIPITATION EVENT IF AND WHEN A MORE SUBSTANTIAL SURFACE LOW CAN FORM AND TRACK NORTHWARD TOWARD THE AREA. THE LATEST ECMWF DEVELOPS JUST SUCH A SYSTEM ON THURSDAY... THOUGH GIVEN THE DIFFICULTY IN TIMING THE MINOR WAVES WITHIN A CUT OFF LOW... THIS SYSTEM COULD AFFECT OUR AREA ANYTIME FROM THURSDAY THROUGH SATURDAY SO WE CANNOT BE TOO CONFIDENT ON TIMING OF THE BEST RAIN CHANCES AT THIS POINT IN TIME. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... SHORT TERM...VFR THRU SUN MORNING. SHOULD SEE CONDS DROP TO MVFR IN THE AFTERNOON...ESPECIALLY ACROSS NH. COULD SEE SOME LATE IFR MOVE IN AT THE COASTAL TERMINALS LATE SUNDAY AS WELL. LONG TERM...SHOULD SEE A GOOD PERIOD OF IFR CONDITIONS AS EARLY AS SUNDAY NIGHT BUT FOCUSED MAINLY ON THE MONDAY TIME FRAME. CONDITIONS IMPROVE TO VFR TUESDAY AS LOW PRESSURE DEPARTS TO THE EAST. && .MARINE... SHORT TERM...WIND WILL BE VERY LIGHT OVERALL...BUT WILL TURN ONSHORE NEAR THE COAST AND INCREASE TO ABOUT 10 KTS THIS AFTERNOON IN SEA BREEZE CIRCULATIONS. LONG TERM...LOW PRESSURE DEVELOPING JUST SOUTH OF NEW ENGLAND ON MONDAY WILL TRACK EASTWARD NEAR THE GULF OF MAINE. DEPENDING ON THE STRENGTH AND TRACK OF THE LOW... THIS COULD PROVIDE A PERIOD OF STRONGER EASTERLY WINDS. THIS EASTERLY FLOW WILL PRODUCE A FAVORABLE FETCH FOR LARGER WAVES IN THE GULF OF MAINE MONDAY INTO EARLY TUESDAY. && .FIRE WEATHER... ONSHORE FLOW WILL KEEP RH MODERATE TODAY OVER THE COASTAL PLAIN. ACROSS THE FOOTHILLS AND MOUNTAINS A MUCH DRIER AIR MASS WILL BRING RELATIVE HUMIDITY VALUES DOWN TO 25 TO 30 PERCENT THIS AFTERNOON. WINDS WILL BE VERY LIGHT...BUT FUELS REMAIN DRY SO FIRE DANGER MAY STAY ELEVATED. MUCH OF THE AREA WILL SEE RAINFALL SUNDAY INTO MONDAY...WITH WETTING RAINS POSSIBLE FOR MANY OF THOSE LOCATIONS. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$

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