textproduct: Gray - Portland

WHAT HAS CHANGED

Rain chances Sunday continue to be focused along the Maine Midcoast. There has been a trend back east in the present forecast, so rain totals have relaxed along the NH Seacoast through Casco Bay.

KEY MESSAGES

1. Rain showers and higher elevation snow today with continuing rain chances Sunday, particularly for the coast and ME Midcoast. A passing thunderstorm can't be ruled out across southern NH today. Clouds and showers likely keep daytime temperatures cooler this weekend.

2. A period of warm and breezy conditions are likely Monday through Wednesday next week with temperatures peaking on Tuesday in the 70s.

3. 3. Unsettled weather returns late Tuesday into Friday with periods of rain.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A weak wave passing through northern New England today will keep rain in the forecast for much of the area. Through the mountains, this means some flakes mixing in. However the chance for accumulating snow is limited to the higher summits of the Whites and perhaps towards the US/CAN border mtns. Either way, would expect to see subfreezing wind chills lasting through the weekend in the higher terrain.

After an initial push of rain through NH overnight, scattered rain showers look to linger until sunset. The passing low will be the primary forcing for precip this morning and into the early afternoon as it lifts northeast through southern ME. Cool air aloft wrapping behind the circulation will allow for steepening lapse rates late morning through the afternoon, therefore creating a somewhat convective environment across south and central NH and possibly into far southern ME. CAPE is nothing to get too excited about, a meager 100-200 j/kg, but the low freezing level and lapse rates around 6 to 7 c/km could support stout cu capable of some lightning. Can't rule out a passing graupel shower either, but very strong shear vs. this amount of CAPE could deter deeper cells altogether.

In tow, moisture continues to stream north ahead of low pressure in the open Atlantic that will continue to rapidly deepen. Fog develops along the Midcoast later this evening and overnight ahead of additional rain brought by this low for Sunday. The coast of Maine will fall along the western edge of the precip shield as it travels just east of Nova Scotia. A persistent shift west had been noted in the past 24-36 hours of QPF guidance, but the last two NBM runs have begun to taper back east. This seems to trade a broader coverage of light QPF along coastal to interior NH/ME, for a quarter to half an inch of QPF towards Penobscot Bay. Thus a sharp cutoff of measurable precip results west to east. Its possible that the pivoting rain shield remains just off the coast Sunday for the NH Seacoast up through Casco Bay. NBM percentiles are most confident for a region from the Midcoast inland to the I95 corridor seeing the greatest precip.

KEY MESSAGE 2 DESCRIPTION...

Height rises will start the week ahead of a deepening trough. This looks like it will open up the region to southwest WAA starting Monday and lasting into Wednesday. 850mb temperatures around +14C and strong enough gradient flow to prevent sea breezes suggest a mild stretch. 60s are likely on Monday and 70s on Tuesday before cooling slightly on Wednesday as cloud cover should begin to increase, but some 70s could be possible again for southern NH.

KEY MESSAGE 3 DESCRIPTION...

Cold front approaches from the west on Tuesday then stalls over the region for several days. This keeps daily rain chances in the forecast although it will not be raining the entire time.

Depending on the frontal timing Tuesday, could see a few thunderstorms make it into the northwest part of the forecast area late in the day before weakening by evening. Guidance suggests modest instability will be in place.

We then see the front stall out overhead, with daily chances for rain as several surface lows ride along a trough axis that will be taking on an increasingly negative tilt. The pattern becomes rather amplified by late week. The meridional flow suggests a tropical connection leading to locally heavy rainfall potential. Precipitation will generally be stratiform and steady however, easing flood concerns. Thursday is one day to watch specifically as some model guidance have been honing in on it for a stronger surface low to impact the region as the trough axis finally ejects offshore.

NBM mean has a strong signal at this point even with the long lead time of >1 inch of rain. Will have to watch how this trends, but with green-up coming into full gear, this will be optimal timing to help drought conditions as surface water depletion will begin to kick into full gear over the next few weeks.

AVIATION /02Z SATURDAY THROUGH WEDNESDAY/

Through 06z Sunday...A round of showers will lift north into the area into daytime. Expect MVFR to IFR ceilings, with highest chances of IFR remaining west of CON to LEW to WVL. These IFR ceilings should improve to MVFR south to north early this afternoon. Not expecting much vis restriction due to SHRA, but can't rule out pockets of 4SM. RASN mix could reduce vis across the western ME mountains.

Expect MVFR cigs to pull north of southern NH/PWM by mid afternoon, lingering towards AUG and the ME Midcoast into the evening. These then lower to IFR cig/vis in stratus/fog towards PWM/IWI/RKD into Sat night.

Outlook:

Saturday night-Sunday: Restrictions likely as moisture increases from a low pressure passing well to the south and east. Highest probabilities for IFR are currently for the western ME terminals due to low stratus, fog, and rain showers, but if the low trends farther west, chances for restrictions will increase across NH. North to northwest winds could also gust to 20-25 kt at times. Improvement is possible later in the day Sunday.

Sunday Night: Mainly VFR, MVFR cigs could be possible late Sunday night across the north.

Monday through Wednesday midday: Mainly VFR expected, with gusty southwest winds.

Wednesday Night through Friday Morning: Unsettled weather expected with rain showers on Wednesday transitioning to widespread rain by Thursday. Periods of IFR and LIFR conditions possible due to low ceilings.

MARINE

Seas subside through today as high pressure becomes centered south of the Gulf of Maine. Winds turn more north to northwesterly Saturday night and into Sunday as strong low pressure passes south and east of the waters. SCA level gusts near the waters, with passing open Atlantic low that may bring gusts to near gale force over the outer waters.

Period of enhanced winds expected to begin later Monday and last into Mid-week. Southwest winds increase in response to building high pressure over the Atlantic seaboard. Currently feel model guidance is a little to robust on speeds due to more limited mixing heights as SST remain around 50 degrees. Either way, SCA are guaranteed, and Gale Warnings especially Wednesday can't be ruled out.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.