textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes to the forecast with this update.

KEY MESSAGES

1. A cold front will cross the region tonight. Significant drought relief is unlikely. Northwest winds will gust up to 35 mph during the afternoon Thursday.

2. Mostly dry weather is expected to continue through Saturday, with cold temperatures early Saturday morning. Shower chances return Sunday and continue through at least the first half of next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

As a sign of the changing seasons, the warm front has definitely gotten bogged down trying to lift thru the forecast area today. That is providing a focus for some sprinkles that continue to work east southeast across the area. They are fighting some dry air still, so not much accumulation is taking place just yet.

Slowly but surely we saturate and more showers will begin reaching the ground. I think nearly everywhere will accumulate some rainfall thru tonight, but I do not see significant drought relief in store for anywhere. There highest totals will be in the higher terrain where some upslope enhancement is possible on the southwest facing slopes. Even then I have a hard time seeing much more than 0.5 to 0.75 inches. Rain will end from northwest to southeast by sunrise.

Northwesterly winds will then increase with daytime heating. Forecast soundings continue to indicate that mixing up to 30 kt is possible, so I have maintained the trend of bumping up NBM wind gusts for widespread 30 to 35 mph gusts. The upper trof and coldest air aloft are not forecast to cross the area until Thu evening. So daytime temps will be quite warm, especially near the coast where some downslope warming helps get readings into the 80s.

KEY MESSAGE 2 DESCRIPTION...

Low pressure makes it's exit off the Canadian coast and into the northern North Atlantic Friday. Meanwhile, high pressure begins to make it's way into the Northeast which briefly tightens the pressure gradient and makes for a breezy day with gusts 20-25 mph. Northwesterly flow brings in a colder airmass aloft with 850 mb temperatures only around +5 to +8 C. Full sun should allow us to mix down the full potential with high temperatures in the 60s north of the mountains, and low to mid-70s south of the mountains. Temperatures are going to quickly drop Friday night as winds go calm and clouds remain sparse. I think we easily decouple with at least widespread low to mid-40s a very likely solution by early Friday morning. I have blended in some cooler MOS guidance to reflect this, but I wouldn't be surprised if we have to go even colder as more hi- res guidance that better handles raditational cooling becomes available.

High pressure slides overhead Saturday coinciding with upper level ridging, allowing for high temperatures to end up in the 70s across the area as 850 mb temperatures rise to +10 to +12 C with continued clear skies aiding in maxing out mixing potential once again. High pressure slides east through the day and the resulting southwesterly flow advects a warmer and more moist airmass into the region. Low temperatures Saturday night stand to end up in the upper 40s and 50s as clouds increase through the night.

Global models have come into good agreement on a cold front approaching the area Sunday which brings about our next chance for showers, albeit low. The signal in the ensembles is increasing, but it is still is not great so continued low chance PoPs seem appropriate. High pressure returns to start next week off dry, but another signal is emerging toward midweek and this one initially appears stronger. Models have some subtle timing differences, but all suggest another seasonably strong low dragging a front through the Northeast. Trends will continue to be monitored.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through Thursday...A mix of VFR and MVFR CIGs currently across the forecast area while we wait for rain to move in this evening and overnight. Based on multi-model consensus, it looks like the majority of the forecast area will drop to MVFR conditions tonight, with maybe parts of southern NH staying VFR. There may be some local IFR conditions in parts of the Connecticut River Valley and Midcoast with lower CIGs. Rainfall does not look heavy enough to significant impact VIS, but showers/rain will be possible from evening thru the early morning hours. This will coincide with a modest LLJ aloft. However the winds will be generally unidirectional and for that reason I have not included LLWS in the TAFs. Behind the initial cold front Thu northwest winds will be gusty thru the day. All TAF sites can expect 25 to 30 kt gusts until around sunset.

Outlook:

Thursday Night: VFR conditions expected. Valley fog likely at LEB and HIE.

Friday-Saturday: Mainly VFR. Valley fog possible at HIE and LEB by Friday night.

Sunday-Monday: Generally VFR, with MVFR possible in showers.

MARINE

Southwest winds will continue to increase thru tonight. A SCA remains in place for the bays and coastal waters. The strongest winds/gusts will move east early Thu, but winds shift to northwesterly and remain gusty thru the afternoon. This will keep seas on a rather slow decline. Generally sub-SCA conditions are expected as high pressure is over the waters through this time period. Fronts moving off the coast early in the week and toward the middle of next week may create some briefly rough conditions, but this will depend on their strength.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday for ANZ150-152-154. Small Craft Advisory from 8 PM this evening to 8 AM EDT Thursday for ANZ151-153.