textproduct: Gray - Portland

WHAT HAS CHANGED

Lowered forecast high temperatures on Sunday from the NBM based on latest forecast guidance.

KEY MESSAGES

1. No significant weather impacts expected through Saturday. Onshore flow develops Saturday for cooler conditions and cloudier skies south of the mountains with possibly dense fog Saturday night.

2. Widespread rain and falling temperatures on Sunday. Light snow accumulations possible across the mountains and far north Sunday afternoon and evening.

3. Cool and dry conditions to start next week, but the long- range pattern remains unsettled deeper into the week.

4. Minor coastal flooding possible during the Saturday night/early Sunday morning high tide cycle.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Short wave trough over New England slides east through late this afternoon with any lingering showers over southern NH coming to an end. High pressure builds over the Canadian Maritimes tonight and will press southwestward into the forecast area Saturday morning. Northeast winds around the high will shift more onshore Saturday. These winds will advect marine air into the coastal plain with skies turning mostly cloudy south of the mountains. Highs will range from the 60s along the CT Valley where there will be more sunshine to the low 50s near the coast.

Onshore flow will continue into Saturday night with more moisture being advected into the region by a trough approaching from the west. This increase in moisture will bring potential for dense fog along the coastal plain Saturday night.

KEY MESSAGE 2 DESCRIPTION...

Low pressure will track across southeastern New England and over the Gulf of ME on Sunday before exiting to our northeast over the Canadian Maritimes Sunday evening. This area of low pressure combined with a passing cold front will bring widespread rainfall to the region with generally between 0.25-0.75" of QPF expected. A non- diurnal temperature trend is likely on Sunday as the front crosses with temperatures initially into the 40s before falling into the middle and upper 30s from northwest to southeast. Latest forecast guidance suggests that the column may cool quickly enough for rain to mix with or even transition to some wet snow during the afternoon before ending Sunday evening, especially across the interior and over the mountains. Given the high mid- April sun angle and marginal sfc temperatures, accumulations during the daytime will be tough to achieve unless snowfall rates are over 1"/hr or so (which is unlikely). Nevertheless, a slushy coating is possible across western NH and up through the foothills and points north. The mountains and towards the Canadian Border have the best chance for a slushy 1-3". Precipitation will end Sunday evening with low temperatures into the 20s and 30s.

KEY MESSAGE 3 DESCRIPTION...

Colder than average temperatures will persist on Monday as H8s hover around -10C. This combined with some cloud cover will limit high temperatures to the 40s in most locations, although NW wind gusts up to 25 mph will make it feel colder. Most areas should remain dry but some upslope rain/snow showers are possible across the mountains. Radiational cooling is possible Monday night with mainly clear skies and low temperatures into the 20s. Another dry day is likely on Tuesday as an H5 s/wv ridge moves overhead. Temperatures will remain cool into the 40s and lower 50s.

Shower chances then increase once again Tuesday night through Wednesday as the next trof of low pressure arrives from the west. Cool and at times unsettled weather then looks to prevail through the remainder of the week as cutoff low pressure meanders near or east of New England.

KEY MESSAGE 4 DESCRIPTION...

The combination of high astronomical tides and surge of up to around 1/2 foot may bring total water levels to near minor flood stage during the late Saturday night/early Sunday morning high tide cycle. The greatest threat will be from Portland and points south.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through Saturday...Mainly VFR through 06Z tonight. Clouds thicken and lower after 06Z with cigs lowering to MVFR and then IFR by Saturday morning for all sites except KHIE and KLEB. KLEB will be on the western periphery of the marine cloud deck and may drop to MVFR at times. Cigs will gradually lift and scatter through the day Saturday before another push of marine air arrives bringing lowering cigs from the coast to points inland Saturday afternoon and evening.

Outlook...

Saturday night: Low cigs and fog will likely bring IFR/LIFR to all sites Saturday night with some rain showers.

Sunday/Sunday Night: IFR restrictions likely through at least 00Z Monday with LIFR possible due to RA and low ceilings. RASN is possible at KHIE. NW wind gusts up to 25 kts. Improvements likely Sunday night.

Monday/Monday Night: VFR conditions with NW winds at 10-20 kts during the daytime before becoming light and variable at night.

Tuesday/Tuesday Night: Lowering ceilings during the day with restrictions possible at night due to -SHRA and lower ceilings. SE winds at 10-15 kts.

Wednesday: Mainly VFR conditions likely.

MARINE

Winds and seas remain below SCA thresholds through Saturday night with NE flow turning more onshore Saturday and then southerly Saturday night.

A few gusts up to around 25 kts are possible Sunday/Sunday night across the coastal waters with seas of 3-5 ft. Otherwise, winds and seas will largely remain below SCA criteria through Tuesday. Increased winds and seas are then possible towards the middle of next week.

GYX WATCHES/WARNINGS/ADVISORIES

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