textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. High pressure brings fair weather with lower humidity over the weekend and into early next week. The exception will be the chance for rain across the north Sunday afternoon and into the evening.

2. There are multiple chances for rain next week; the best of which are Tuesday afternoon through Wednesday night.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Behind the exiting cold front, morning valley fog will dissipate. High pressure eases into the Northeast through the morning, sagging south across the Mid-Atlantic by the late afternoon. This will bring a very pleasant day with mostly sunny skies and light winds up to 12 mph. There is plenty of dry air aloft, but a sharper inversion atop the boundary layer and light winds should prevent this drier air from mixing down.

Clouds may begin to thicken aloft come Saturday evening and overnight. Broad low pressure to the north will help advect moisture into the region from the west as the high's influence weakens. Mid level jet will be poised across the St Lawrence Valley, and the entrance region will near the US/CAN border by Sunday afternoon. Added moisture and lift will bring the chance for showers into the evening. For now this is focused across the north as a front drops south, with uncertainty on coverage south of the foothills into the overnight period. Some instability may be available for thunderstorms, but greater confidence rests with a chance of showers.

Under unidirectional NW flow, dry air flushes back in Monday for another dry and mostly sunny day.

KEY MESSAGE 2 DESCRIPTION...

Fast WNW 500 mb flow overspreads the Northeast U.S., on the periphery of a strong ridge to our south. It will be a favorable setup for disturbances to ride the ridge and bring some rain chances to New England next week. At the surface, should see a stationary front setup in our vicinity Tuesday. This feature may lift northeast into our region as a warm front with low-level southerly flow and moisture, before a cold front on Thursday brings drier air back with winds turning westerly.

Precipitation looks more hit-or-miss on Tuesday, before widespread rains arrive Wednesday. The more widespread chance for rain on Wednesday-early Thursday will be with a surface low moving through the flow. Most ensemble members have it tracking right over New England. One key factor to watch will be the warm front position, which will dictate if it is a more stratiform or convective rain. The ECMWF brings the warm front north into our region, while the GFS keeps it well southwest. This also will have an impact on temperatures, which for now are low confidence, but leaning towards a low diurnal range with the clouds/rain.

Rain chances drop from Thursday onward with drier northwest low-level winds developing behind a cold front. Cannot rule out an isolated rain chance from a shortwave rounding the ridge late week, but for now ensembles suggest rain-free conditions are more likely.

AVIATION /01Z SATURDAY THROUGH WEDNESDAY/

Through tonight...Valley fog develops and lingers thru sunrise. VFR today with WNW winds around 10 kts. This shifts SW becoming light overnight. Drier air may limit the coverage of overnight valley fog.

Outlook...

Sunday-Sunday night: Mainly VFR, except low cigs and SHRA bring potential restrictions at HIE. SHRA advance from the north in the evening and overnight.

Monday-Monday night: Mainly VFR, no sig wx.

Tuesday-Wednesday: Lowering cigs and SHRA likely bring periods of at least MVFR.

MARINE

NW flow arrives behind an exiting cold front this morning. These turn SW by this evening, continuing into Sunday.

Gusts increase to 20 kts Sunday afternoon as a front approaches from the north. Winds briefly turn offshore behind the front Sunday night and become light and variable through Monday. A front south of the waters slowly moves north through mid week allowing for increasing SE winds.

GYX WATCHES/WARNINGS/ADVISORIES

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