textproduct: Gray - Portland

WHAT HAS CHANGED

No notable changes were made to the ongoing forecast. However, Freeze Warnings were issued for Androscoggin and parts of Cumberland County to reflect strong radiational cooling expected there. Frost Advisories from the previous forecast update remain in place elsewhere.

KEY MESSAGES

1. Coldest air mass of the season so far spreads overhead today and tonight. Frost is likely.

2. Warmer weather arrives for Wednesday and especially Thursday. A cold front may bring a few showers on Thursday.

3. High pressure likely over the weekend with seasonable temperatures. Low pressure may bring unsettled weather at the start of next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Today, satellite imagery shows mostly clear skies over NH and Maine south of the mountains. Upslope flow over the mountains are allowing gravity waves to form, allowing for mostly cloudy skies north of the mountains. Gusty northwest winds are expected this afternoon, though these winds will taper off overnight as high pressure briefly moves overhead. This brief period of calm conditions could allow for deep radiational cooling Tuesday night, especially south of the mountains where skies are clearer. Low temperatures could fall near freezing even along the coast. Opted to issue Freeze Warnings for interior Cumberland and Androscoggin counties, as these counties are most likely to see below freezing temperatures due to exceptionally calm winds. Kept the Frost Advisory elsewhere, as light winds may persist through the night in Augusta and along the immediate coast.

KEY MESSAGE 2 DESCRIPTION...

High pressure passing New England to the south will allow for southwest return flow during the day on Wednesday. These winds could get quite breezy along the coast, with gusts of 25mph possible in Casco Bay and Midcoast. This should allow for a sharp rebound from the near freezing temperatures likely to be seen in the morning. Temperatures look to be in the upper 50s across central Maine, with mid-60s elsewhere. A frontal passage will move across New England early Thursday morning, with some showers possible with its passage. Despite the frontal passage, high pressure to the south will allow for the continuation of southerly winds and the warmer temperature trend into the day on Thursday. Temperatures look to be in the upper 60s and lower 70s forecast then.

KEY MESSAGE 3 DESCRIPTION...

High pressure moves overhead for the weekend. Approaching high pressure should allow for some cold air advection and northwesterly winds on Friday. These winds will help keep temperatures seasonable on Friday and Saturday. The aforementioned high pressure system is projected to move to the southeast on Saturday, allowing for warmer southerly return flow again. This return flow, and mid-level ridging is likely to bring above average temperatures on Sunday and into early next week.

Model guidance has also suggested a low pressure system could move in Monday afternoon and bring unsettled weather to the area. A lot of uncertainty remains at this time, but it does appear that this system could be the next opportunity to see meaningful rainfall.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Mostly clear skies this evening will allow for VFR conditions to continue through Wednesday. MVFR restrictions are possible Wednesday night as a frontal boundary moves over the area. Chances are greater to see lower restrictions north of the mountains.

Outlook: Thursday: MVFR in the morning due to showers. VFR in the afternoon.

Friday-Saturday: VFR Expected.

Sunday: VFR Expected.

MARINE

SCA level northwesterly winds and 3-5ft seas will decrease this evening as high pressure moves over the Gulf of Maine. Calm winds are expected overnight and will flip to southerlies on Wednesday, shifting to southwesterlies on Thursday. SCA issuance is possible as gusts could approach 25kts on Wednesday and Thursday. Winds shift to westerlies and lighten on Friday. Seas of 2-4ft are expected through the weekend.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Freeze Warning from midnight tonight to 8 AM EDT Wednesday for MEZ019-020. Frost Advisory from midnight tonight to 8 AM EDT Wednesday for MEZ021>028. NH...Frost Advisory from midnight tonight to 8 AM EDT Wednesday for NHZ010-012-013. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ150>154.