textproduct: Gray - Portland

WHAT HAS CHANGED

Little has changed for this forecast package as we turn our focus to the Sunday/Sunday night system.

KEY MESSAGES

1. Widespread snow and rain event expected late tonight through Sunday night with a plowable snow likely for much of the area, especially away from far southern New Hampshire and the immediate coast. There is some potential for lighter snow to linger into Monday.

2. Active weather week continues For Tuesday and beyond with multiple precipitation chances and temperatures at or a bit below normal for late March.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Upper level troughing crosses the region this morning and then we deamplify a little bit as we transition back into northwest flow aloft by the late afternoon hours. After some lingering light rain and/or snow this morning, most of your Saturday should be dry with similar temperatures to yesterday and breezy northwest winds. Highs are forecast to range from the low to mid 30s north, to the mid to upper 40s south. A few lower 50s will be possible over southern New Hampshire and far southwest Maine.

We transition to near zonal flow aloft Saturday night into Sunday as the next weak wave approaches, riding a polar front. Isentropic ascent will spread across the forecast area Sunday morning/afternoon leading to widespread high chances of precipitation (70 to 90 percent) across all of New Hampshire and most of western Maine. Various members of the global ensembles continue to suggest the development of a secondary low along the front on Monday, but there has been a trend where many of these members keep most of the associated precipitation out over the waters. Either way, cyclonic flow aloft will at least lead to lingering snow showers on Monday and if a secondary low does form along the front, we could have another push of moisture before it moves out to sea.

Precipitation should start out as all snow late tonight and into Sunday morning but we will likely see a transition to a brief wintry mix or just plain old rain across southern New Hampshire and coastal Maine during the afternoon hours with everything changing back to snow by late Sunday evening. Not much has changed regarding potential totals. NBM 5.0 24-hour snow probabilities for 4 inches of snow or greater generally range from 50 to 70 percent along and north of the Foothills of Maine and central New Hampshire. Increasing that threshold to 6 inches and we dip mainly into that 20 to 50 percent range with the larger percentages over the higher peaks. Thus, confidence is fairly high that we will see a swath of accumulation in the 3 to 6 inch range by Sunday night with some locally higher amounts possible over the higher terrain. Accumulations are a bit more uncertain south where we could mainly see rain when precipitation is at the heaviest, but a slushy couple of inches seems like a reasonable solution here. Given the potential for slick travel and plowable snow, Winter Weather Advisories are likely to be needed. If the secondary low develops along the front, we could see even more snow on Monday so this period will bear close watching.

Temperatures on Sunday will be around seasonable averages for this time of year with highs in the low/mid 30s north, to the mid/upper 40s across southern New Hampshire, and in the upper 30s/lower 40s over coastal Maine. Monday's highs will be closer to below average readings behind the front with highs in the upper 20s and lower 30s north, to the mid to upper 30s south. A few lower 40s will be possible over southern New Hampshire.

KEY MESSAGE 2 DESCRIPTION...A mid-level trough will remain over head next week, with high pressure moving in early in the week. This should allow for below-normal lows, though sunnier skies should keep high temperatures feeling warmer. On Wednesday, a cold front looks to move southeastward across NH and Maine. Instability ahead of the front could lead to the development of snow squalls in the afternoon, especially in the mountains. Snow squalls could lead to some slick mountain passes Wednesday evening.

By the end of the week, ensembles are perhaps a little more confident in a much broader low moving from west to east Thursday night and into Friday. While models are more confident in the existance of the system, models are less confident on precipitation types. At this time, mostly snow appears to be more likely north of the mountains, with rain, snow or wintry mix possible south of the mountains.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Through tonight: While most of the steady precipitation has moved out, expect widespread LIFR/IFR conditions to continue under low ceilings and drizzle/fog early this morning. The one exception may be over southern New Hampshire (CON and MHT) where ceilings only dip into MVFR categories. Northwest winds will bring drier air into the region later this morning, leading to VFR conditions through the rest of the day and into tonight.

Outlook (Sunday through next week):

Sunday: IFR restrictions expected due to rain and snow.

Monday: VFR, though brief restrictions are possible with snow showers.

Tuesday: VFR expected.

Wednesday: Brief periods of IFR possible in the afternoon, mainly across the interior with snow showers.

MARINE

Winds shift to out of the northwest this morning morning as a low departs. Breezy winds and elevated seas will allow SCA conditions to continue through this afternoon.

An active pattern is expected for Sunday through the coming week, which will result in nearly continuous SCA conditions through the week. There is a low probability for gale force wind gusts in the Wednesday- Thursday timeframe depending on the location and strength of developing low pressure over or just east of the Gulf of Maine.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ150-152- 154.