Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 212225 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 525 PM EST SUN DEC 21 2014 .SYNOPSIS... AN ONSHORE FLOW MAY TRIGGER SOME FLURRIES OR LIGHT SNOW MAINLY OVER SOUTHERN REGIONS RIGHT THROUGH TUESDAY. A SIGNIFICANT LOW PRESSURE SYSTEM SYSTEM WILL GRADUALLY ORGANIZE WEDNESDAY...BEFORE MOVING OVER THE GREAT LAKES. THIS COULD BRING WINDY CONDITIONS AND THE POTENTIAL FOR HEAVY RAIN AROUND CHRISTMAS EVE INTO EARLY CHRISTMAS MORNING. ANOTHER LOW PRESSURE SYSTEM WILL PASS BY TO OUR NORTHWEST LATE IN THE WEEK AND EARLY NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... AREAS OF LIGHT SNOW WILL CONTINUE INTO THIS EVENING HOURS ASSOCIATED WITH "OCEAN EFFECT" ONSHORE FLOW...AND ALSO DUE TO THE PROXIMITY OF A WEAK MID LEVEL LOW. IN GENERAL...WILL BE LOWERING POPS AS WE HEAD INTO THE LATE EVENING HOURS...WITH THE GREATEST CHANCE OF A SNOW SHOWERS ALONG AND NEAR THE COASTLINE. THE BEACH AREAS WILL NEED TO BE MONITORED HOWEVER...AS THERE IS SOME INDICATION OF A WEAK NORLUN TROUGH OVER THE REGION. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... SCATTERED SNOW SHOWERS AND FLURRIES WILL CONTINUE RIGHT THROUGH MONDAY NIGHT OVER SOUTHERN AREAS DUE TO A PERSISTENT NORTHEAST FLOW OVER THE MOIST GULF OF MAINE. MESO MODELS WITHIN THE 12Z MODEL SUITE CONTINUE TO HAVE A DIFFICULT TIME PICKING UP ON THIS LOW LEVEL MOISTURE AND PRECIP. HAVE THEREFORE RAISED POPS ABOVE ALL AVAILABLE GUIDANCE. A COLD AIR DAMMING SIGNATURE WILL BE FORMING BY MONDAY NIGHT. THEREFORE...THE PTYPE SHOULD BE ALL SNOW THROUGH THE SHORT TERM PORTION OF THE FORECAST...BEFORE THE WARM AIR POURS INTO THE REGION. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... THE WEAK ONSHORE FLOW CONTINUES INTO TUESDAY WITH LOW LEVEL MOISTURE DEEPEST ALONG THE COAST. ON TUESDAY THE WARMER ONSHORE FLOW DEEPENS AS THE HIGH MOVES FURTHER OFFSHORE ALLOWING A SOUTHEAST FLOW TO INCREASE...SO SCATTERED LIGHT INTERMITTENT PRECIPITATION EXPECTED...MOSTLY IN THE FORM OF RAIN EXCEPT SOME IN THE FORM OF LIGHT SNOW IN THE MOUNTAINS BEFORE CHANGING OVER TO RAIN EVEN IN THOSE AREAS. THE MAIN EVENT WILL BE THE ONSET OF THE HEAVIER PRECIPITATION LATE TUESDAY NIGHT AND ESPECIALLY CHRISTMAS EVE WHERE THE RAIN WILL BECOME HEAVY AT TIMES AS A STRONG WARM ADVECTION PATTERN DEVELOPS BEING ACCOMPANIED BY A STRONG LOW/MID LEVEL JET. THE MAIN UPPER LOW PASSES WELL TO OUR WEST AS IT MOVES THROUGH THE GREAT LAKES. QPF TOTALS FOR LATE TUESDAY INTO THURSDAY COULD BE IN THE 2-4 INCH RANGE. DUE TO VERY WARM AIR THIS WILL BE IN THE FORM OF RAIN EVEN IN THE MOUNTAINS. SOME FLOODING PROBLEMS MAY ARISE IN THE HEADWATERS BY WEDNESDAY NIGHT OR THURSDAY DUE TO THE COMBINATION OF SOME SNOWMELT AND THE HEAVY RAINS. ALL MODELS AGREE ON MILD TEMPERATURES...USED A BLEND OF THE MODELS. SYSTEM FINALLY EXITS TO THE NORTHEAST BY THURSDAY AFTERNOON AS A DRY SLOT MOVES ACROSS THE AREA FOLLOWED BY A COLD FRONT WITH A RETURN TO SEASONAL TEMPS FOR FRI. ANOTHER SYSTEM WHICH WILL BE WEAKER WILL APPROACH FOR THE WEEKEND. MODELS DIFFER IN RUN TO RUN CONTINUITY AND ALSO VARIANCES IN TIMING, STRENGTH, AND POSITION OF THIS SYSTEM. FOR NOW WILL BROAD BRUSH DUE TO ALL THE UNCERTAINTY AS WELL AS PTYPE. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... SHORT TERM...MAINLY VFR THROUGH MONDAY NIGHT...HOWEVER THERE MAY BE BRIEFLY MVFR CONDITIONS IN SCATTERED SNOW SHOWERS SOUTHERN LOCATIONS. LONG TERM...MVFR CONDS EXPECTED TUE AND THEN LOWERING TO IFR TUE NIGHT AND LIFR CONDITIONS WED INTO THU. CONDITIONS IMPROVE BY LATE THU TO VFR. && .MARINE... SHORT TERM...WINDS AND SEAS WILL REMAIN MOSTLY OUT OF THE NORTHEAST THROUGH MONDAY NIGHT. WINDS AND SEAS WILL REMAIN BELOW SCA CONDITIONS. LONG TERM...STRONG LOW PRESSURE WILL MOVE WELL TO THE WEST AND WILL CAUSE WINDS TO INCREASE TO GALES TUESDAY NIGHT THROUGH WEDNESDAY WITH BORDERLINE STORM FORCE WIND GUSTS POSSIBLE WEDNESDAY NIGHT. SEAS COULD BUILD IN EXCESS OF 15 FT OVER THE OUTER WATERS BY WEDNESDAY NIGHT OR EARLY THURSDAY. GUIDANCE LOOKS LOW ON BOTH WINDS AND SEAS WHICH IS TYPICAL FOR THESE TYPE OF EVENTS. && .HYDROLOGY... MODELS CONTINUE TO BACK OFF ON RAINFALL TOTALS FOR THE CHRISTMAS EVE/EARLY CHRISTMAS MORNING EVENT...BUT AREA STILL IN THE 1 TO 3 INCH RANGE. HOPING THE SNOWPACK IN THE MOUNTAINS AND FOOTHILLS WILL TAKE IN SOME OF THE 1 TO 2 INCH RAINFALL AMOUNTS IN THAT AREA...BUT STILL EXPECTED RAPID RISES IN THE HEADWATERS. OVER SOUTHERN LOCATIONS...2 TO 3 INCHES OF RAIN EXPECTED. IN ANY CASE...FLOODING IS A DISTINCT POSSIBLY CHRISTMAS EVE AND CHRISTMAS MORNING ASSOCIATED WITH THE HEAVY RAIN AND SNOWMELT. && .TIDES/COASTAL FLOODING... ASTRONOMICAL TIDES ARE AT THEIR PEAK FOR THE MONTH. THIS...IN COMBINATION WITH STRONG SOUTHERLY DEVELOPING GALES (WITH POSSIBLE STORM FORCE GUSTS) WILL LIKELY ALLOW FOR ABOUT A 1 FOOT STORM SURGE. WITH BUILDING WAVES IN THE 15 FOOT RANGE...EXPECT A FEW AREAS TO HAVE COASTAL FLOODING...SPLASH-OVER AND BEACH EROSION. NART WAVE RUN-UP MATRICES ARE ALREADY PREDICTING THE POTENTIAL FOR COASTAL FLOODING...OVERWASH AND EROSION ACROSS MOST LOCATIONS IN MAINE AND NEW HAMPSHIRE BASED ON OUR CURRENT STORM SURGE AND WAVE PREDICTIONS. THE QUESTION IS HOWEVER...WHEN WILL THE PEAK WINDS AND SEAS ARRIVE? RIGHT NOW IT IS TOO EARLY TO TELL IF THIS PERIOD OF INCLEMENT WEATHER/OCEAN CONDITIONS WILL ARRIVE NEAR THE TIME OF HIGH TIDE. THE MIDDAY TIDES ON CHRISTMAS EVE AND CHRISTMAS DAY ARE THE HIGHEST AT 11 FEET...WHILE THE 1 AM CHRISTMAS MORNING HIGH TIDE IS LOWER AT 10 FEET. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$

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