textproduct: Gray - Portland

WHAT HAS CHANGED

Another set of Frost/Freeze headlines have been issued for tonight as temperatures again fall into the low to mid 30s.

KEY MESSAGES

1. Clear skies and calm winds this evening will allow temperatures to cool rapidly resulting in frost and freeze chances once again.

2. Widespread, soaking, beneficial rain takes aim at the area for the second half of the work week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Daytime cumulus should easily dissipate this evening once daytime heating wanes. Under approaching high pressure, surface winds should also subside rather quickly allowing rapid cooling amid the dry airmass (daytime dew point temps have largely been in the low to mid 20s areawide).

New frost and freeze headlines have been issued for tonight, this time encompassing much of southern ME and central NH.

Clouds will become a complicating factor into the overnight hours as the next weather system approaches from the Great Lakes. High cirrus is initially expected to enter NH late this evening, lifting NE across ME in the early morning hours. Points nearing central ME will see clouds the last, and it is these locations that have the best chance of cooling into the mid 30s. Better radiational cooling opportunities into the Fryeburg region could lead to temps into the lower 30s.

Expect to see lower and more dense cloud cover enter SW NH after midnight, and have excluded these areas from frost headlines at this time. However it will still be cool, falling into the upper 30s to around 40.

KEY MESSAGE 2 DESCRIPTION...

Main story continues to be another round of much needed rainfall targeting the area for the latter half of the work week. Generally speaking, abundant cloud cover and rainfall will keep temps below normal thru the end of the week. The event will get going Wed as a warm front lifts into the forecast area. An area of steady rainfall likely moves into southwestern NH during the first half of Wed and will lift thru the remainder of the forecast area into the afternoon. Wed night into Thu may feature a period where steady precip ends, or becomes more of a drizzle, as the dry slot lifts in the area. As the upper low captures the surface low, it will begin to pivot back towards the south and west. Ensemble guidance, especially the ECMWF, has shown a pretty marked southwest trend for precip over the last several days. The overall evolution of precip will be an increase in shower activity Thu in southerly flow, with the heaviest precip likely Thu night into Fri. This is actually pretty consistent across all ensemble suites. NBM already has categorical PoP for this period, so I do not see any reason to change that. Much of the forecast area is forecast to receive between 1 and 2 inches over the roughly 48 hours. There may be some localized amounts higher than that, but generally speaking we are in a rainfall deficit still and it will occur over long enough period of time that flooding is not anticipated. Once this storm moves away we may begin a warming trend and maybe even see some above normal temps.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18z Wednesday...Cu field continues through late afternoon, dissipating into the evening. Winds will also go calm into sundown. Will see a period of SKC before cirrus begins to build in from the SW overnight. This will gradually thicken and lower as a warm front approaches with SHRA late Wed morning. MVFR cig restrictions arrive into midday for NH terminals north of CON. This progresses east through the afternoon, with IFR cigs possible through the mountains and foothills.

Outlook:

Wednesday Night: Increasing chances IFR cigs expand across the interior and towards the coast Wed evening with some BR/FG possible amid SHRA.

Thursday: Areas of MVFR likely as rain becomes more widespread/steady.

Thursday Night: Areas of MVFR likely. IFR or lower conditions becoming more likely thru the night.

Friday: IFR conditions gradually improve thru the day.

Friday Night: VFR conditions expected.

Saturday: VFR conditions expected.

Saturday Night: VFR conditions expected.

Sunday: VFR conditions expected.

MARINE

High pressure builds over the region this evening with offshore winds near the coast subsiding.

Winds become onshore Wed and will gradually increase thru the day. This will build seas above 5 feet outside of the bays, and eventually gusts 25 to 30 kt are expected by Wed evening and overnight. While winds may diminish Thu and Fri, seas may remain above 5 feet into Fri. An approaching cold front over the weekend may allow southwest winds to freshen late Sat. Southwest winds are less likely to fully mix down, but some gusts near 25 kt are possible outside of the bays.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Freeze Warning from 2 AM to 9 AM EDT Wednesday for MEZ012-033. Frost Advisory from 2 AM to 9 AM EDT Wednesday for MEZ013-014- 018>028. NH...Freeze Warning from 2 AM to 9 AM EDT Wednesday for NHZ004. Frost Advisory from 2 AM to 9 AM EDT Wednesday for NHZ003-005- 006-009-010. MARINE...Small Craft Advisory from 2 PM Wednesday to 8 AM EDT Thursday for ANZ150-152-154.