textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. Cold temperatures overnight and early Saturday morning may allow for patchy frost development in northern zones.

2. Low pressure forming near southern New England followed by a cold front will bring periodic rain chances Saturday night through Sunday night. High pressure then brings mostly dry conditions Monday through Wednesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... High pressure slides overhead tonight allowing for strong radiational cooing across the area. With Mt. Washington's observed dewpoint sitting at the freezing mark early this afternoon, it is not out of the question for some the more sheltered northern valley locations to realize this as a low temperature by early Saturday morning. I don't believe any frost/freeze headlines are warranted here as any occurrences of either should be limited in scope, but certainly anyone with sensitive crops or plants that live in the north should take protective measures as temperatures are expected to drop into at least the mid-30s. Patchy valley fog is likely as well. South of the mountains will stay warmer, but not by much as the foothills and better radiating locations fall into the upper 30s. The coastal plain and southern New Hampshire stay the warmest with temperatures in the 40s.

As high pressure slides off to the east Saturday, upper ridging takes hold and the resulting southwesterly flow should help temperatures climb a few degrees higher than what we are seeing out there today. It will be more noticeable in the north as temperatures climb into the low to mid-70, with valley locations climbing into the upper 70s with downsloping winds. The coastal plain will end up pretty similar to today as the seabreeze will be able to come ashore and keep those areas in the low 70s. Overall, clear skies and dry air will make for a pretty quintessential fall day.

KEY MESSAGE 2 DESCRIPTION...

Ridging aloft over the Northeast will give way to broad troughing Saturday night through Monday. Embedded waves within the trough will spread forcing for ascent over the area for rain chances while the disconnect between waves will limit the chances for continuous rainfall through the period.

The first primary wave will slide across the Mid Atlantic Saturday night and then south of New England Sunday. This wave will advect deep moisture into the region with ensembles showing mean PWATs of 1.5 to 2 inches pushing into areas south of the mountains by Sunday morning. A majority of ensemble (mainly GEFS and CMC) members suggest a compact area of low pressure will track across southern New England and will focus the heaviest of rainfall south of the area with a sharp drop off in QPF to the north. There are some members that bring at least moderate rainfall in to southern NH and far SW Maine with a sharp cut off in QPF near the foothills. The ECMWF camp is a bit different in that several members do not close off a surface low allowing light to moderate rainfall to spread north into the mountains. Regardless of the range of solutions there are no flood concerns with the main focus on seeing how much rain we can get to put a dent into ongoing precipitation deficits.

The latest NBM brings chance PoPs into the area Saturday night with PoPs increasing to likely along the coastal plain Sunday morning. PoPs decrease Sunday afternoon as there likely will be a lull in precipitation before the next wave crosses Sunday night. This wave will send a cold front through region that will bring another shot of measurable rainfall. All together, rainfall amounts will be around 0.15 to 0.35 inches with southern NH and York County seeing potential for greater than 0.5 inches.

The cold front will push offshore Monday morning with high pressure building in through at least Tuesday and possibly Wednesday. High pressure overhead Monday night will bring favorable radiational cooling conditions that will allow for northern valleys to drop into the 30s for lows.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...VFR expected at most terminals overnight. IFR conditions are anticipated overnight at LEB and HIE as valley fog develops under calm conditions. Once the fog clears early tomorrow morning, VFR prevails at all terminals through the day Saturday.

Outlook:

Saturday Night-Sunday: Lowering cigs and SHRA will bring potential for at least MVFR, while periods VFR will be possible during the day Sunday.

Sunday night-Monday: MVFR possible Sunday night trending towards VFR by Monday morning.

Tuesday-Wednesday: VFR expected, except conditions will be favorable for valley fog at LEB and HIE.

MARINE

High pressure slides over New England through Saturday for quiet conditions on the waters. Southerly winds increase Saturday night through Sunday as a trough approaches while winds and seas remain below SCA thresholds. A cold front crosses Sunday night shifting winds offshore with winds and seas still remaining below SCA thresholds. High pressure then builds in Monday through Wednesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.