textproduct: Gray - Portland

WHAT HAS CHANGED

Boosted PoPs over southern NH given expanding area of light returns on regional radar win region of upper level diffluence and ample llevel moisture. Given abundant llevel moisture and morning observations...have also expanded fog mention across the area. No other significant changes at this time.

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.

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. Stationary boundary will develop just off the Maine coast today that will be a focus area for steady rain and potentially some localized heavy downpours. 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 this afternoon into Saturday morning. 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 precipitation amounts ranging from near 2" for Penobscot Bay Islands to only a quarter of an inch for the CT River Valley.

KEY MESSAGE 2 DESCRIPTION...

As the consolidated low moves northeast, it will slow and expand in size, keeping us on the periphery into next week. This will help bring cooler temperatures back to the region as well as additional light precipitation. The airmass will continue to cool aloft with 850 mb temperatures bottoming out at -1 to -5C by Monday evening. This should translate to daytime highs in the 40s across the mountains with 50s towards the interior and coast for much of the week. Cyclonic flow continuing through midweek and a fair amount of cloud cover should keep lows on the milder side, likely in the 30s to low 40s, with radiational cooling limited.

With cyclonic flow in place, with a series of hard-to-time waves will move through the flow. This suggests shower chances for the first half of the week, driven by cold air aloft. More clarity on the timing/impacts of each wave should become clear in the coming days. Pattern recognition suggests the best odds for cloud cover and precipitation to be across the White Mtns. and far interior portions of the forecast area, with a lesser chance towards the coast. Freezing levels just off the deck suggest wet snowflakes may mix in for northern zones, with light accumulations in the mountains possible.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Through 12Z Saturday: Restrictions will continue to stay down in most places as a developing coastal low brings rain, fog and low stratus into the area. These conditions will allow for sustained IFR/LIFR across most places. Some improvements are possible at LEB or HIE during the day Friday after fog mixes out but showers will only allow for improvements to MVFR there.

Outlook... 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...None.