textproduct: Gray - Portland

WHAT HAS CHANGED

Trended up precipitation amounts along the immediate coast through the weekend. Tight precipitation gradient is still expected.

KEY MESSAGES

1. Two rounds of rain are expected to bring beneficial rainfall Friday through Saturday night with heaviest amounts expected for the immediate coast with lighter amounts for mountains.

2. Cooler temperatures arrive later this weekend through the middle of next week areawide. There will be multiple chances for light precipitation, including light snow or snow showers for the higher peaks of the White Mountains into early week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Wet pattern expected over the next 48 hours. Broad southwest flow ahead of an approaching upper level shortwave trough that reach the region for the weekend. First round of shower activity this afternoon will push out the region by this afternoon with cloudy skies and continued low level moisture fetch remaining in its wake. Stationary boundary will develop just off the Maine coast tomorrow that will be a focus area for steady rain. Still enough spread in the guidance to support the potential that the outer islands and necks could be on the edge of the heavier rain axis tomorrow afternoon into Friday night. Trended up the rainfall amounts a bit for the first wave tomorrow closer to the main guidance as enough guidance has trended just slightly westward again. A brief break in the rain is possible Saturday morning before the upper level approaches and captures some of the coastal moisture fetch. Its even possible a surface low pressure system will develop in the Gulf of Maine, increasing low level dynamics for a developing deformation zone across the region Saturday night. This will be the prime window for rainfall chances across the interior through midday Sunday as the developing surface and upper level features move eastward by Sunday afternoon ending the widespread rainfall. Overall expecting close to 2" for Penobscot Bay Islands with only a quarter of an inch for the CT River Valley.

KEY MESSAGE 2 DESCRIPTION... As the consolidated low moves northeast, another wave in tow will dive out of Ontario/Quebec through New England Sunday night into Monday. This will help bring cooler temperatures back to the region as well as additional light precipitation. Daytime highs look to top out in the 40s across the mountains with 50s towards the interior and coast for much of the week.

While downstream precipitation could be light to none with this wave, it may be an effective upslope precipitation setup for the western Whites. Combined with cooler temps, its possible for some light snow or snow showers to occur for the Whites and US/CAN border mountains. Will need to monitor how far north or south the core of moisture passes through the Northeast given some variability in guidance at this time. This will determine if accumulations are expected at elevation, as well as if any of the rain showers will feature measurable amounts from the foothills to the coast.

Then, the pattern through midweek supports additional chances for light precipitation, arriving on northwest flow. With limitations on moisture source, measurable precipitation outside of the mountains appears limited, with upslope precip potentially continuing on and off through Wednesday or Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Through 18Z Friday: An organized slug of moisture is moving across NH and Western Maine at midday today bringing with it showers and MVFR visibility. Rain will push out from southwest to northeast through afternoon hours with just spotty rain coverage expected behind. Confidence isn't high enough to put any other periods of rain in the TAF through 18z tomorrow. Will have to watch Rockland for addition rain towards the end of the period tomorrow. MVFR cigs are expected to lower to IFR by tonight as moist onshore flow continues.

Outlook... Friday Night-Saturday: MVFR conditions likely areawide, with coastal terminals having a higher chance of seeing IFR conditions in rain that may be heavy at times.

Sunday-Monday: Returning to VFR conditions except for Whitefield and the mountain region due to upslope rain/snow showers.

Tuesday-Thursday: Mostly VFR for all terminals outside of the mountains where upslope showers continue with NW flow.

MARINE

Small window of SCA conditions expected tonight across the Central Coastal waters. By Sunday a surface low will be developing over the Gulf of Maine with the potential for SCA conditions as NW winds increase behind the departing low. A prolonged period of offshore winds with west to northwest flow is expected next week, with the potential for short periods of SCA conditions.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 4 AM EST Friday for ANZ150-152.