textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. Gusty winds diminish this evening as high pressure builds in and dominates the pattern through Wednesday. Tonight will be the coldest night since last spring with Frost Advisories in effect across the north.

2. A front will bring the chance of rain Thursday, with rain chances continuing into the weekend amid cooler temperatures.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure centered over the eastern Great Lakes will migrate east this evening and crest over the area by Tuesday morning. Gusty NW winds will diminish this evening as the gradient softens and will likely go calm overnight. The combination of calm winds and clear skies will optimize radiational cooling leading to lows in the mid to low 30s across the north to lows in the low 40s near the coast and southern NH. Frost Advisories remain unchanged since the last forecast with localized patchy frost elsewhere in favorable radiational cooling spots. Valley fog will be likely tonight.

High pressure will provide fair weather Tuesday through Wednesday. A cool air mass will remain in place limiting highs to the upper 60s to low 70s Tuesday. Strong ridging over the Southeast will attempt to push northward Tuesday into Wednesday bringing warmer air into the region. This will result in lows Tuesday night mainly in the 40s and highs on Wednesday pushing well into the 70s.

KEY MESSAGE 2 DESCRIPTION...

In the wake of broad cyclonic flow exiting northern Quebec Wednesday, a wide upper jet develops through central Ontario. This strong zonal flow north of record max 500mb heights across the central and eastern CONUS will be responsible for a lot of the momentum entering northern New England mid to late week.

The upper flow prevents a lot of deeper moisture from advancing north, but there will be a disturbance rapidly exiting the eastern Great Lakes Thursday that could make use of some of this more humid airmass. Most model guidance introduces the chance of showers Thursday afternoon and evening across a portion of the forecast area, but there are many outcomes relating to footprint and rainfall totals. While PWATs climb, there is some hesitancy to claim the chance for heavy rainfall at this time. This is mainly due to how progressive the IVT plume is and the lack of substantial CAPE for convective enhancement. For now it's likely it will either be a period of rain passing Thursday afternoon, or some more intermittent showers.

Behind the passing cold front, NW winds become unidirectional for Friday. It will be more breezy, but temps may not sway too much cooler than Thursday as warm/moist airmass remains steadfast to the south, and dry air should promote mostly sunny conditions. Cooler temperatures will be more likely into next weekend as moisture rounds the top of high pressure to the south. This will lead to an increase in clouds, as well as rainfall chances.

AVIATION /15Z MONDAY THROUGH FRIDAY/

Through Tuesday night... Gusty NW winds diminish by 00Z this evening and will go calm overnight. Valley fog at LEB, HIE, and CON likely bring a period of LIFR late tonight until 12-14Z Tuesday morning. VFR prevails Tuesday with light winds. Valley fog cannot be ruled out Tuesday night while more in the way of clouds may limit development of fog. Otherwise VFR Tuesday night.

Outlook...

Wednesday: VFR, no sig wx.

Thursday and Thursday night: SHRA possible late morning through the early evening as a cold front moves through. MVFR cigs possible.

Friday: VFR, no sig wx. Breezy NW winds up to 15 kts.

MARINE

Gusty NW winds will be on a downward trend this evening. Winds and seas remain below SCA thresholds tonight through Wednesday as high pressure resides over the Northeast.

Winds and waves are expected to remain below SCA criteria Thursday and into the weekend. A cold front will bring winds NW after its passage Thursday night, remaining breezy Friday. Winds shift to become more onshore this weekend, with gusts approaching 20 kts. Some gusts near 30 kts are possible on the outer waters, but these may remain off the surface due to an inversion.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Frost Advisory from 2 AM to 8 AM EDT Tuesday for MEZ007. NH...Frost Advisory from 2 AM to 8 AM EDT Tuesday for NHZ001-002. MARINE...None