textproduct: Gray - Portland

WHAT HAS CHANGED

A frost advisory has been issued for most of the coastal plain for tonight.

KEY MESSAGES

1. Coldest air mass of the season spreads overhead today and tonight. Frost is likely. Warmer weather arrives for Wednesday and especially Thursday. A cold front may bring a few showers on Thursday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure and a cool air mass continues to build across the forecast area today. The result will be sunny skies but continued breezy weather. Forecast soundings support wind gusts of 20 to 30 MPH today, but the trend should be downward during the afternoon as the cold air advection wanes. Highs will only be in the 40s in the mountains today, with 50s elsewhere.

Winds becoming light along with clear to mostly clear skies will support strong radiational cooling. Widespread frost is likely, even toward the coast. Therefore, we have hoisted a frost advisory for the zones that remain active this season (the season ends Oct 11). The exception is for the NH Seacoast where temperatures may stay up a little bit more. Some areas in the frost advisory may need to be upgraded to a freeze warning today.

Otherwise, a warming trend begins Wed and peaks Thu. Highs by Thu should be well into the 60s, with 70s at lower elevations. A cold front looks to move through Thursday with scattered showers.

The surface trough moves off to the east Friday, but continued upper level troughing is going to provide the forcing for upslope showers in the mountains through Saturday morning before high pressure crests over the region by the afternoon. 850 mb temperatures in the 0 to +3 C range will allow for seasonable afternoon temperatures in the 50s and 60s each day. High pressure moves off to the east Sunday, and with continued ridging aloft, dry weather should continue through at least the daylight hours. Southwesterly flow brings 850 mb temperatures up around +10 C so Sundays highs likely mix into the 60s areawide. Significant uncertainty is then introduced heading into early next week as global models have a trough swinging out of the Great Lakes Region and generating an area of low pressure of the Mid-Atlantic, but at different times and intensities. The 19Z NBM suggests this would be the next chance of meaningful precipitation with around 50% probabilities areawide of greater than a tenth of an inch of rainfall in the Monday-Tuesday window. This will be a period to watch to see how models trend.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Restrictions: VFR conditions are expected to dominate the forecast through Wednesday.

Winds: Northwest winds 15-20G25-30KTS are expected for the day today before becoming light tonight.

Outlook:

Thursday: Generally VFR with scattered showers possible, mainly in the mountains.

Friday-Sunday: VFR conditions expected.

MARINE

SCAs needed all waters through this evening before a ridge of high pressure builds towards the region from the west with diminishing winds. A few NW gusts to near gale force are possible over the eastern waters Tuesday morning.

Sub-SCA conditions are expected Friday through the weekend as high pressure settles over the waters. Depending on the track and timing of low pressure early next week SCA conditions are possible.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Frost Advisory from midnight Tuesday night to 8 AM EDT Wednesday for MEZ019>028. NH...Frost Advisory from midnight Tuesday night to 8 AM EDT Wednesday for NHZ010-012-013. MARINE...Small Craft Advisory until 8 PM EDT Tuesday for ANZ150>154.