Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 190241 AAA AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 1041 PM EDT SAT APR 18 2015 .SYNOPSIS... WEAK LOW PRESSURE MOVES ACROSS THE AREA THIS EVENING WITH SHOWERS AND AN ISOLATED THUNDERSTORM AS IT DOES SO. HIGH PRESSURE BUILDS IN ON SUNDAY. AN INCREASING EASTERLY ONSHORE FLOW WILL PROVIDE COOL AND DAMP WEATHER MONDAY WITH RAIN CHANCES INCREASING AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. SIGNIFICANT RAINFALL AND COASTAL FLOODING ARE POSSIBLE WITH THIS SYSTEM MONDAY NIGHT AND TUESDAY. UNSETTLED WEATHER LOOKS TO DOMINATE MID TO LATE WEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... UPDATE...PCPN IS WINDING DOWN OUTSIDE OF THE UPSLOPE SHOWERS IN THE MTNS. WITH WLY GRADIENT PICKING UP...TEMPS SHOULD GRADUALLY BUT STEADILY FALL THE REST OF THE OVERNIGHT. NO OTHER MAJOR CHANGES PLANNED. PREVIOUS DISCUSSION...UPPER LEVEL SHORTWAVE TROUGH AND WEAK SURFACE LOW ARE MOVING THROUGH THE REGION THIS AFTERNOON. WIDESPREAD SHOWERS AND A FEW EMBEDDED THUNDERSTORMS HAVE DEVELOPED AND ARE TRACKING SOUTHEAST ACROSS THE AREA. HAVE ATTEMPTED TO SHOW PROGRESSION OF SHOWERS ACROSS THE AREA THIS EVENING VIA THE HOURLY PRECIPITATION CHANCES. IT IS LIKELY THAT PRECIPITATION COMES TO AN END ACROSS MOST OF THE AREA BY 00Z TONIGHT BUT SOME LINGERING SHOWERS ARE LIKELY TOWARD THE MIDCOAST. TOTAL PRECIPITATION OF 0.25 TO 0.50 INCHES ARE LIKELY. SOUTHWEST NEW HAMPSHIRE MAY GET SPARED FROM ANY PRECIPITATION THIS EVENING. HIGH PRESSURE BUILDS IN BEHIND THE DEPARTING LOW TONIGHT WITH LOW TEMPERATURES FALLING INTO THE 30S. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... HIGH PRESSURE MOVES INTO THE AREA SUNDAY WITH LIGHT WINDS AND A MOSTLY CLEAR SKY. SEA BREEZE FLOW BECOMES DOMINANT ACROSS THE COASTAL PLAIN IN THE AFTERNOON BECOMING MORE EASTERLY SUNDAY NIGHT AS HIGH PRESSURE LIFTS OFF TO THE NORTHEAST. HIGHS SUNDAY TOP OUT IN THE 50S... BUT COOLER NEAR THE COAST... AND GENERALLY FALL INTO THE 30S SUNDAY NIGHT. EXPECT ANY RAIN WITH THE APPROACHING SYSTEM TO HOLD OFF UNTIL AFTER 12Z MONDAY MORNING AS ALL FORECAST MODELS KEEP QPF OUT OF THE AREA UNTIL AFTER THAT TIME. && .LONG TERM /MONDAY THROUGH SATURDAY/... RIDGING ALOFT WEAKENS AND SHIFTS EAST MONDAY AS THE MEAN UPPER LEVEL TROUGH CARVES INTO A SUBSTANTIAL PORTION OF THE CENTRAL UNITED STATES. A WARM FRONT SURGES UP FROM THE SW MONDAY ALLOWING SHOWERS TO SPREAD INTO THE REGION BY MONDAY AFTERNOON. SECONDARY CYCLOGENESIS OCCURS OFF THE JERSEY COAST AND QUICKLY DEEPENS AS IT MOVES INTO THE GULF OF MAINE. HEAVIER RAIN ARRIVES TOWARDS LATE AFTERNOON AND OVERNIGHT... CONTINUING INTO TUESDAY. DYNAMICS WITH THIS SYSTEM ARE GOOD. A ROBUST LOW LEVEL JET WILL FEED MOIST THETA-E AIR INTO THE LOW HELPING TO BOOST PRECIPITABLE WATER VALUES TO NEAR AN INCH. FORECAST SOUNDINGS INDICATE WARM RAIN PROCESSES SHOULD BE ONGOING AT LEAST PART OF THE TIME AND TRAINING SHOULD ALSO BE OCCURRING. IT WILL BE COLD ENOUGH ALOFT TO SUPPORT 1-3 INCHES OF WET SNOW IN THE MOUNTAINS. WITH FORECAST QPF AMOUNTS IN THE 1-2" RANGE... FLOODING WILL BE THE MAIN CONCERN. THIS IS ESPECIALLY TRUE IN POOR DRAINAGE AREAS COVERED WITH SNOW AND LEAVES AND ALSO ON AREA RIVERS WHICH REACH BANKFULL AND WHERE ICE BEGINS TO MOVE. WINDS ALONG THE IMMEDIATE COASTLINE MAY REACH 30 MPH. DRIER SW AIR PUNCHES IN BY TUESDAY NIGHT ALLOWING FOR PRECIPITATION EROSION FROM SW TO NE ACROSS NH AND CENTRAL MAINE THROUGH WEDNESDAY MORNING. A SERIES OF SHORT WAVES FOLLOW ON THE HEELS OF THIS ONE AS THE UPPER LEVEL TROUGH MOVES EAST AND SLOWS OVER THE GREAT LAKES AND THEN THE NORTHEAST. THIS MAKES FOR A RAINY AND CLOUDY END OF APRIL. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... SHORT TERM...SHOWERS EXIT THIS EVENING AND VFR CONDITIONS RETURN. LIGHT WINDS SUNDAY TRANSITION TO A SEA BREEZE FLOW SUNDAY AFTERNOON AND BECOMES EASTERLY SUNDAY NIGHT. LONG TERM...IFR OR LOWER CEILINGS AND LOW VISIBILITIES EXPECTED IN RAIN LATER MONDAY THROUGH TUESDAY. SOME IMPROVEMENT FORESEEN TUESDAY NIGHT AND WEDNESDAY WITH LESSER CHANCES OF RAIN ALONG THE COAST. ON THURSDAY ANOTHER AREA OF LOW PRESSURE SPINS UP ALONG THE COAST BRINGING SCATTERED SHOWERS. && .MARINE... SHORT TERM...LIGHT PRESSURE GRADIENT KEEPS WINDS RELATIVELY LIGHT TONIGHT EVEN AS WEAK LOW PRESSURE CROSSES THE WATERS. NORTHERLY FLOW BEHIND THE LOW TRANSITIONS TO EASTERLY SUNDAY NIGHT AS HIGH PRESSURE SHIFTS NORTH AND EAST. LONG TERM...A GALE WATCH HAS BEEN ISSUED FOR LIKELY GALE FORCE WINDS MONDAY NIGHT INTO TUESDAY ALONG WITH RAPIDLY BUILDING SEAS AS LOW PRESSURE MOVES INTO OUR REGION. && .FIRE WEATHER... AFTER A WETTING RAIN OVER MUCH OF THE AREA TODAY... DRIER AIR WILL MOVE IN AGAIN TONIGHT AND TOMORROW. A SEA BREEZE DEVELOPS IN THE AFTERNOON ON SUNDAY... KEEPING HUMIDITY LEVELS HIGHER OVER THE COASTAL PLAIN. BUT TO THE WEST OF THE MOUNTAINS THE HUMIDITY WILL FALL BELOW 30 PERCENT IN THE AFTERNOON SUNDAY BUT LIGHT WINDS SHOULD PREVENT ANY ELEVATED FIRE WEATHER CONDITIONS. ONSHORE FLOW ON MONDAY BRINGS MORE MOISTURE AND EVENTUALLY RAIN TO THE AREA. A SOAKING RAIN IS EXPECTED MONDAY NIGHT AND TUESDAY. && .HYDROLOGY... A WIDESPREAD 1 TO 2 INCHES OF RAIN IS EXPECTED MONDAY AFTERNOON THROUGH TUESDAY. HOWEVER...GIVEN STRONG MOISTURE INFLOW...LOCALIZED AMOUNTS UP TO 3 INCHES COULD OCCUR. THIS WOULD LEAD TO FLOODING PROBLEMS...ESPECIALLY IN AREAS WHERE SNOW MELT IS STILL OCCURRING. && .TIDES/COASTAL FLOODING... HIGHEST TIDE OF THE MONTH OCCURS SUNDAY NIGHT AT 11.6 FEET IN PORTLAND. LIGHT WIND FLOW AT THE TIME SHOULD PREVENT ANY SIGNIFICANT FLOODING PROBLEMS. HOWEVER... THE TIDE MONDAY NIGHT REACHES 11.4 FEET WITH A STRONGER EASTERLY FLOW OVER THE GULF OF MAINE. ONSHORE FLOW AND BUILDING SEAS WILL INCREASE THE THREAT OF COASTAL FLOODING FOR THE HIGH TIDE MONDAY NIGHT AND A COASTAL FLOOD WATCH HAS BEEN ISSUED TO HIGHLIGHT THIS THREAT. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...COASTAL FLOOD WATCH FROM MONDAY EVENING THROUGH LATE MONDAY NIGHT FOR MEZ023>028. NH...COASTAL FLOOD WATCH FROM MONDAY EVENING THROUGH LATE MONDAY NIGHT FOR NHZ014. MARINE...GALE WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY AFTERNOON FOR ANZ150>154. && $$ NEAR TERM...LEGRO

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