Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 202150 AAA AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 550 PM EDT MON APR 20 2015 .SYNOPSIS... LOW PRESSURE MEANDERING NORTH OF THE GREAT LAKES WILL DRIVE A COLD FRONT TOWARD THE REGION TONIGHT. THE FRONT WILL SLOWLY CROSS THE REGION ON TUESDAY. LOW PRESSURE NORTH OF THE GREAT LAKES WILL GRADUALLY WEAKEN AS IT DRIFTS SOUTHEAST INTO NEW ENGLAND WEDNESDAY THROUGH THURSDAY. LOW PRESSURE WILL CONTINUE TO WEAKEN AS IT MEANDERS NORTH OF NEW ENGLAND FRIDAY THROUGH SATURDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... UPDATE...HAVE MODIFIED THE GRIDS THRU MORNING BASED ON LATEST HI-RES MODEL GUIDANCE. EXAMINING RECENT HRRR RUNS HAVE A LARGE AREA FAVORABLE FOR LIGHTNING DEVELOPMENT MOVING ACROSS THE REGION ON THE LEADING EDGE OF THE DRY SLOT NEAR MORNING. IN ADDITION...THE SPC SSEO PRODUCTS ALSO FAVOR A CLUSTER OR LINE OF TSTMS CROSSING THE FORECAST AREA NEAR 12Z. HAVE INCREASED THE PROBABILITY FOR THUNDER LATE TONIGHT AND EARLY TUE AS A RESULT. HAVE ALSO INTRODUCED SOME AREAS OF HEAVY RA TO THE GRIDS NEAR THE COASTAL FRONT AS WELL AS IN THE EAST SLOPES OF THE MTNS WHERE STRONG SELY LLJ WILL IMPINGE UPON THE TERRAIN. THIS LLJ...WHICH IS REALLY JUST GETTING UNDERWAY OVER SRN NEW ENGLAND PER KBOX 88D...WILL SLOWLY TRAVERSE THE COAST THRU ABOUT 06Z. THIS PUTS HEAVIEST PRECIP IN THE FORECAST AREA BETWEEN ABOUT 00Z AND 06Z. IN ADDITION TO THE HEAVY PRECIP...THIS LLJ MAY INDUCE SOME STRONG DOWNSLOPE WIND GUSTS NW OF THE WHITE MTNS. PREVIOUS DISCUSSION...THE FIRST BATCH OF RAIN FROM THIS MORNING WAS MOVING INTO EASTERN MAINE AS A WARM FRONT LIFTED NORTH INTO SOUTHERN CANADA. SO FAR ONLY A TENTH TO ABOUT A THIRD OF AN INCH OF RAIN HAS FALLEN TODAY WITH SOME ISOLATED HIGHER AMOUNTS. THIS MORNINGS GYX SOUNDING HAD PLENTY OF DRY AIR AND THIS INHIBITED RAINFALL FROM SPREADING FASTER FOR THE FIRST HALF OF THE DAY. STEADIER RAINS ARE NOW OVER SOUTHERN NH AND MOVING INTO WESTERN MAINE. THIS TREND WILL CONTINUE INTO THE EVENING HOURS. A SECONDARY CYCLONE WILL FORM TONIGHT OVER THE VIRGINIAS AND MOVE NE ALONG THE ATLANTIC COAST. AS IT DEEPENS IN THE GULF OF MAINE A LLJ WILL STRENGTHEN AND FEED MOISTURE RICH AIR INTO COASTAL NH AND MAINE. WARM RAIN PROCESSES AND TRAINING OF CELLS WILL SUPPORT HEAVY RAIN OVERNIGHT AND INTO TUESDAY. A FLOOD WATCH REMAINS IN EFFECT AS RAIN COMBINES WITH SNOWMELT TO BRING RIVERS AND STREAMS TO NEAR BANKFULL. WINDS WILL BE GUSTY... ESPECIALLY ALONG THE COAST... BUT WE SHOULD FALL SHORT OF WIND ADVISORY CRITERIA. COASTAL FLOODING WILL ALSO BE A CONCERN FROM PORTLAND WESTWARD AS EASTERLY FLOW INCREASES AND COINCIDES WITH THE ASTRONOMICAL HIGH TIDE. MORE INFORMATION ON THESE HAZARDS BELOW. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... MODERATE TO HEAVY RAIN CONTINUES INTO TUESDAY MORNING. MUCAPE VALUES INDICATE A SLIGHT CHANCE FOR THUNDERSTORMS BETWEEN 12-18Z TOMORROW AS THE COLD CORE OF THE UPPER LOW SWINGS BY OVERHEAD. DRIER AIR PUNCHES IN FROM THE SW MIDDAY TUESDAY. SOME LINGERING SHOWERS WILL BE POSSIBLE OVER THE MOUNTAINS IN UPSLOPE FLOW. HIGHS SHOULD WARM INTO THE UPPER 40S NORTH TO LOWER 60S SOUTH. ADDITIONAL SHOWERS WILL BE POSSIBLE TUESDAY NIGHT WITH CYCLONIC FLOW ALOFT. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... BROAD UPPER LEVEL CLOSED LOW WILL KEEP WEATHER UNSETTLED IN THE NORTHEAST THROUGH THE WEEK AND INTO THE WEEKEND AS IT GRADUALLY SHIFTS EAST. EXPECT SEVERAL LOBES OF ENERGY TO ROTATE AROUND THIS SYSTEM AND INTO THE NORTHEAST. ANY MORNING SUN ON WEDNESDAY WILL QUICKLY GIVE WAY TO CLOUDS AND SHOWERS AS THE FIRST OF THESE DISTURBANCES SWINGS INTO THE REGION. EXPECT THESE SHOWERS TO PERSIST INTO WEDNESDAY NIGHT AS A WEAK SURFACE LOW SLOWLY CROSSES THE REGION. STEADIER PRECIP WILL COME TO AN END AS LOW PRESSURE LIFTS INTO THE MARITIMES ON THURSDAY. EXPECT CLOUDY SKIES AND SCATTERED SHOWERS THURSDAY THROUGH FRIDAY WITH HIGHS IN THE 40S TO LOWER 50S. SHOWER ACTIVITY WILL DIMINISH OVER THE WEEKEND BUT SKIES WILL REMAIN MOSTLY CLOUDY WITH RAIN OR SNOW SHOWERS POSSIBLE MAINLY IN NORTHERN ZONES. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... SHORT TERM...MVFR WILL DETERIORATE TO LIFR AND IFR SHORTLY AS HEAVIER RAIN MOVES IN. RAIN MAY BE LIGHTER AT KHIE WHERE WE WILL SEE THE RAIN SHADOW EFFECT. ALSO SOME SNOW MAY MIX IN LATE IN THE NORTH. EAST WINDS MAY GUST TO 35 KTS AT TIMES. SOME IMPROVEMENT BY MID MORNING TUESDAY AS RAIN MOVES EAST. LONG TERM...AREAS OF MVFR CEILINGS WEDNESDAY THROUGH FRIDAY. && .MARINE... SHORT TERM...EASTERLY WINDS AND SEAS CONTINUE TO BUILD TONIGHT. A GALE WARNING REMAINS IN EFFECT THROUGH 2 PM TUESDAY. WINDS WILL DECREASE BUT A SCA WILL LIKELY BE NEEDED FOR WAVES THROUGH WEDNESDAY EVENING. LONG TERM...SCA`S MAY BE NEEDED THURSDAY AND FRIDAY. && .FIRE WEATHER... ONSHORE FLOW TODAY BRINGS MORE MOISTURE AND EVENTUALLY RAIN TO THE AREA. A SOAKING RAIN IS EXPECTED LATE TODAY AND TUESDAY. && .HYDROLOGY... A WIDESPREAD 1 TO 2 INCHES OF RAIN IS EXPECTED FROM THIS AFTERNOON THROUGH TUESDAY. HOWEVER...GIVEN STRONG MOISTURE INFLOW...LOCALIZED AMOUNTS OF UP TO 3 INCHES COULD OCCUR. THIS WOULD LEAD TO FLOODING PROBLEMS...ESPECIALLY IN AREAS WHERE SNOW MELT IS STILL OCCURRING. A FLOOD WATCH REMAINS IN EFFECT. && .TIDES/COASTAL FLOODING... AS EASTERLY WINDS CONTINUE TO INCREASE...SEAS WILL BUILD 10 TO 15 FT. HIGH TIDE ON APRIL 21 IS AT 1:21 AM WITH A PREDICTED HEIGHT OF 11.4 FT MLLW. HOWEVER...ONSHORE WINDS ARE EXPECTED TO RESULT IN A 1- 2 FT STORM SURGE. THE COMBINATION OF WIND, WAVES AND HIGH TIDE WILL RESULT IN OVERWASH AND POSSIBLE INUNDATION FOR THE BEACHES OF THE SOUTH COAST OF MAINE AND NEW HAMPSHIRE. FARTHER DOWNEAST THE EASTERLY WIND DIRECTION IS LESS FAVORABLE FOR ONSHORE INUNDATION. EVEN SO THE SIGNIFICANT WAVES MAY RESULT IN SOME COASTAL FLOODING AND A COASTAL FLOOD ADVISORY HAS BEEN POSTED THERE. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...FLOOD WATCH THROUGH WEDNESDAY MORNING FOR MEZ007>009-012>014- 018>028. COASTAL FLOOD ADVISORY FROM 11 PM THIS EVENING TO 3 AM EDT TUESDAY FOR MEZ025>028. COASTAL FLOOD WARNING FROM 11 PM THIS EVENING TO 3 AM EDT TUESDAY FOR MEZ023-024. NH...FLOOD WATCH THROUGH WEDNESDAY MORNING FOR NHZ002>015. COASTAL FLOOD WARNING FROM 11 PM THIS EVENING TO 3 AM EDT TUESDAY FOR NHZ014. MARINE...GALE WARNING UNTIL 2 PM EDT TUESDAY FOR ANZ150>154. && $$ NEAR TERM...LEGRO

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