Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 181921
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
321 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 /TONIGHT/...
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 /SUNDAY AND 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 FRIDAY/...
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 /19Z SATURDAY 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.

&&

.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...NONE.
NH...NONE.
MARINE...NONE.

&&

$$

KIMBLE/HANES


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