Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 211627 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 1227 PM EDT TUE OCT 21 2014 .SYNOPSIS... LOW PRESSURE OVER THE EASTERN GREAT LAKES WILL MOVE TO THE SOUTHEAST TODAY AND WILL INTENSIFY SOUTH OF LONG ISLAND TONIGHT....BRINGING AN EXTENDED PERIOD OF RAIN TO THE AREA. LOW PRESSURE WILL MEANDER OFF THE SOUTHERN NEW ENGLAND COAST WEDNESDAY THROUGH FRIDAY BEFORE DRIFTING OFF TO THE NORTHEAST ON SATURDAY. A COLD FRONT WILL CROSS THE AREA SUNDAY FOLLOWED BY A RIDGE OF HIGH PRESSURE FOR MONDAY. && .NEAR TERM /TODAY/...
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1230PM UPDATE... HAVE UPDATE POP FORECAST AGAIN AS RAIN IS ARRIVING IN SOUTHWEST MAINE AND MUCH OF NEW HAMPSHIRE. EXPECT THIS AREA OF RAIN TO FILL IN MORE OVER THE NEXT SEVERAL HOURS. 9AM UPDATE... HAVE ALTERED POP TO BETTER REFLECT TIMING OF PRECIPITATION AS IT ARRIVES PRIMARILY THIS AFTERNOON. HRRR MODEL SEEMS TO BE HANDLING THIS WELL. LONG STRETCH OF MOISTURE ON WATER VAPOR SATELLITE IMAGERY IS SEEN TO BE EXTENDING ALL THE WAY FROM A TROPICAL LOW IN THE GULF OF MEXICO UP THROUGH THE WESTERN ATLANTIC AND INTO OUR REGION. THE STAGE IS BEING SET FOR A BIG PRECIPITATION EVENT. COASTAL AREAS WILL LIKELY GET THE HEAVIER RAIN FIRST THIS EVENING AS RAIN WRAPS IN FROM THE OCEAN AROUND A SURFACE LOW. HAVE MADE SOME MINOR MODIFICATIONS TO QPF FORECAST BUT THIS DID NOT RESULT IN SIGNIFICANT CHANGES. 6AM UPDATE... HAVE INCREASED POPS FOR THIS MORNING AS A FEW OF THE RAIN SHOWERS ARE FINALLY MAKING IT THROUGH TO THE SURFACE. NOT EXPECTING SIGNIFICANT ACCUMULATION UNTIL LATER. ORIGINAL DISCUSSION... LOW CURRENTLY OVER WESTERN NEW YORK WILL MOVE SOUTHEASTWARDS THROUGH THE DAY... WITH THE SHOWERS CURRENTLY IN NY SPREADING EASTWARDS ACROSS THE REGION. WHILE TEMPERATURES WILL HOLD STEADY IN THE 50S... THE CLASSIC COLD AIR DAMMING SIGNATURE IS EVIDENT IN THE ISOBARS... SO EXPECT LIGHT EASTERLY WINDS TO CONTINUE THROUGH THE COASTAL PLAIN... RESULTING IN COASTAL FRONT FORMATION. WARM AIR ADVECTION FROM THE DEVELOPING CYCLONE WILL RESULT IN LIGHT RAIN BY AFTERNOON... WITH THE HEAVIEST AMOUNTS ALONG THE COASTAL FRONT.
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&& .SHORT TERM /TONIGHT AND WEDNESDAY/... THE LOW WILL INTENSIFY SOUTH OF LONG ISLAND AND MOVE NORTHEASTWARDS OVER THE BENCHMARK INTO THE GULF OF MAINE DURING THE DAY ON WEDNESDAY. STEADY LIGHT RAIN WILL CONTINUE THROUGH THE DAY ON WEDNESDAY AND NORTHEASTERLY WINDS WILL INTENSIFY ALONG THE COAST WEDNESDAY AFTERNOON AS THE LOW DEEPENS. THE STRONGEST DYNAMICS MOVE IN WEDNESDAY NIGHT SETTING UP FOR HEAVY RAIN. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... FOCUS IN THE EXTENDED IS IN THE EARLY PART...AS LOW PRESSURE FEEDS MOISTURE OFF THE ATLANTIC INTO NORTHERN NEW ENGLAND. MODEL GUIDANCE IS IN FAIR AGREEMENT THAT SURFACE AND UPPER LOW WILL STACK AND DEEPEN WEDNESDAY NIGHT INTO THURSDAY. THIS IS PROGGED TO SEND A SIGNIFICANT SLUG OF PRECIPITATION INTO PARTS OF WESTERN MAINE AND ADJACENT NEW HAMPSHIRE. OPERATIONAL MODELS...INCLUDING THE ECMWF AND GFS...ARE FORECASTING 2 TO 4 INCHES TO FALL IN THE SPAN FROM 00Z THU THROUGH 00Z FRI. WITH EASTERLY FLOW UPSLOPING INTO THE MOUNTAINS AND COARSE MODEL RESOLUTION IT IS REASONABLE TO ASSUME LOCALLY HIGHER AMOUNTS POSSIBLE. AT THE MOMENT THERE ARE A LOT OF FAVORABLE PARAMETERS FOR A HEAVY RAINFALL EVENT ACROSS MUCH OF THE FORECAST AREA. THE 21/00Z GEFS FORECAST A -4 STANDARD DEVIATION 850 MB U WIND ANOMALY. SUCH A SEASONABLY STRONG EASTERLY JET IS A STRONG SIGNAL FOR HEAVY QPF...ESPECIALLY FOR THE EASTERN SLOPES. IN ADDITION...-3 STANDARD DEVIATION 250 MB U WIND ANOMALIES SIGNAL THAT SLOW FORWARD MOVEMENT OF THE SYSTEM IS LIKELY. THIS IS NOTABLE CONSIDERING THE OPERATION GFS IS FAIRLY PROGRESSIVE WHEN COMPARED TO THE 21/00Z ECMWF. SREF MEAN QPF AT KPWM IS JUST ABOVE 3"...WITH A CLUSTER OF MEMBERS NEAR 4". ECMWF ENSEMBLES ALSO SHOW NEARLY HALF OF THE 51 MEMBERS AT OR ABOVE 5" TOTAL QPF THRU THURSDAY. THAT BEING SAID...SOME MODEL GUIDANCE SUGGEST SOME DRY SLOT ISSUES WRAPPING AROUND THE SYSTEM WHICH COULD SIGNIFICANTLY AFFECT PRECIPITATION. GIVEN THAT THE HEAVIEST RAINFALL IS STILL MORE THAN 48 HOURS OUT...WOULD LIKE ANOTHER SUITE OF GUIDANCE BEFORE MAKING ANY HEADLINE DECISIONS. WILL ALLOW THE DAY SHIFT TO REVIEW LATEST GUIDANCE IN THIS CASE. EVENTUALLY LOW PRESSURE MEANDERS OFF TOWARDS THE CANADIAN MARITIMES. WEATHER WILL REMAIN UNSETTLED THOUGH...AS NORTHERN STREAM SHORTWAVE TROUGH RACES SE ACROSS CANADA AND DRIVES A COLD FRONT THRU NEW ENGLAND ON SUNDAY. THE UPPER LOW CROSSING THE AREA WILL LEAD TO SCATTERED SHOWERS...ESPECIALLY ACROSS THE HIGHER TERRAIN. WILL HAVE TO MONITOR TRENDS...AS ECMWF IS COOLER THAN THE GFS...AND ONLY A DEGREE OR SO FROM BEING SNOW ACROSS THE MOUNTAINS. HIGH PRESSURE WILL THEN TAKE CONTROL FOR EARLY NEXT WEEK. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... SHORT TERM... VFR CEILINGS WILL REMAIN THROUGH THE MORNING... BEFORE CEILINGS DESCEND ALONG THE COAST AS RAIN MOVES IN TONIGHT. BY TONIGHT... IFR CONDITIONS ARE EXPECTED ALONG THE COAST... WHILE LEB AND HIE MAY REMAIN MVFR. WEDNESDAY WILL SEE ALL LOCATIONS REMAIN IN IFR. LLWS WILL BE A CONCERN FOR PWM...RKD... AND PSM. LONG TERM...IFR CONDITIONS PROBABLE WEDNESDAY NIGHT THRU THURSDAY IN RAIN...HEAVY AT TIMES. COASTAL TERMINALS WILL SEE GUSTY NE WINDS AT OR ABOVE 25 KTS AT TIMES. KHIE WILL ALSO SEE DOWNSLOPING WINDS THAT COULD BE GUSTY AT TIMES FROM THE E. MVFR CONDITIONS LIKELY LINGER THRU THE WEEKEND...WITH SCT SHOWERS POSSIBLE IN THE MOUNTAINS ON SATURDAY AND SUNDAY. && .MARINE... SHORT TERM... WINDS/SEAS WILL BE CALM FOR TUESDAY..BEFORE BUILDING AHEAD OF THE STORM TUESDAY NIGHT. SUSTAINED GALE FORCE WINDS ACROSS THE OUTER WATERS FOR WEDNESDAY...WITH GUSTS TO GALE IN THE BAYS. SEAS WILL BUILD TO 10 TO 12 FT IN PROLONGED NORTHEASTERLY FLOW. LONG TERM...GALE FORCE WIND GUSTS ARE LIKELY WEDNESDAY NIGHT INTO THURSDAY. SCA CONDITIONS WILL LINGER INTO SATURDAY...BEFORE HIGH PRESSURE TAKES CONTROL OF THE WATERS. && .HYDROLOGY... MAIN STEM RIVERS WILL NEED TO BE MONITORED CLOSELY MID TO LATE WEEK. MOST SMALL RIVERS AND STREAMS WILL LIKELY HAVE SHARP RISES AS WELL. THE HEAVIEST RAINFALL IS EXPECTED TO BE OVER SOUTH-CENTRAL MAINE AND THE NORTHEAST FACING HIGHER TERRAIN. AGAIN...MOSTLY 2-3 INCHES QPF WITH LOCALIZED AMOUNTS APPROACHING 5 INCHES. && .TIDES/COASTAL FLOODING... ASTRONOMICALLY LOW TIDES WILL PREVENT WIDESPREAD COASTAL FLOODING PROBLEMS... HOWEVER PROLONGED NORTHEASTERLY FLOW MAY RESULT IN AROUND A 1 FT SURGE. COMBINED WITH 10FT WAVES THIS MAY CAUSE BEACH EROSION AND SPLASHOVER... ESPECIALLY IN NEW HAMPSHIRE AND YORK COUNTY MAINE. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...GALE WARNING FROM 2 AM WEDNESDAY TO 8 AM EDT THURSDAY FOR ANZ150>154. && $$ NEAR TERM UPDATE... KIMBLE

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