textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. Wetting rainfall continues through the first half of tonight followed by a drying trend into Thursday.

2. A cool and unsettled pattern begins Friday bringing slightly below normal temperatures, and keeping precipitation in the forecast.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Latest surface analysis places a stationary front southwest to northeast across northern New England with a wave of low pressure along the front near Albany, NY. Steady rainfall has overspread much of the interior and will make its way to the coast over the next hour or two. Latest satellite data has yet to capture any lightning while 100 J/kg of elevated CAPE may allow for a few rumbles of thunder and heavier bouts of rainfall through this evening. No significant weather impacts are expected with this rainfall as amounts are on the order 0.25 to 0.5 inches south of the mountains and 0.5 to 1.0 inches in and north of the mountains. Steady rain will end NW to SE early tonight with a drying trend after midnight. Lows tonight will range from the upper 30s north to upper 40s south.

Thursday will be partly to mostly sunny with steady WNW winds. These winds will gust 20 to 25 mph early afternoon and will relax into the the evening. Highs will range from the 50s north to mid 60s near the coast.

KEY MESSAGE 2 DESCRIPTION... Mean troughing is going to dominate the extended forecast period as an Omega Block develops centered over the North Atlantic. Several waves moving through the larger trough are going to bring continued chances for showers and wetting rains into next week, along with slightly below normal temperatures with flow mostly west/northwesterly.

Diurnally driven showers are possible Friday afternoon as a shortwave moves through the area and 500mb temperatures drop to near -30C. Coverage should be low as surface temperatures also only end up in the 50s outside of the mountains with 850mb temperatures dropping near to just below freezing. The best chance for showers at this point looks like it is going to be in and around the mountains as the upslope component adds some extra lift. Skies clear for the evening and look to remain clear for the first part of the night as shortwave ridging moves overhead, so could see temperatures drop quickly with lows falling into the upper 30s and low 40s south of the mountains and near freezing to the north.

The next best chance of widespread rain is going to be Saturday as low pressure passes to our north and drags a warm front through the area. Ensemble members from global models suggest this being a lighter event with the majority showing less than half an inch of QPF. The GFS ensemble has a few wetter members, but is also the outlier being the only model showing a secondary coastal low developing. The rest of the models are showing a battle with high pressure to the northeast resulting in more dry air intrusion. On a note from the tail end of the hi-res window, the RRFS is showing the possibility of some embedded heavier showers, but without seeing the full event it does appear to be on board with the generally lower amounts, showing dry slots forming.

Perhaps the better time period to keep an eye on will be early next week as a good signal for widespread wetting rains is already showing up in the ensembles. Deterministic global models are in surprisingly good agreement that low pressure is going to be riding along a frontal boundary up into the Northeast. Where they currently differ is on the strength of the low as it reaches our area, but they are all positioning it more or less off the coast Monday afternoon which would lead to some enhanced moisture. This is showing in the ensemble members as each global model camp has several suggesting over an inch of QPF with each also having a few around two inches. We will have to keep a close eye on trends as this looks like it could be the more significant system, but the good news is that regardless it looks like we will be continuing to put a dent in our drought.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through Thursday: Low CIGs and reduced visibility in rain will bring MVFR to IFR conditions at all TAF sites this evening. Conditions will start to improve west to east between 00Z and 06Z, except at HIE, AUG, and RKD where low CIGs likely linger until around 12Z. Elsewhere an improvement to VFR is likely between 06Z and 08Z. VFR is likely Thursday with WNW winds gusting to around 20 kts early afternoon. Winds diminish Thursday night with mainly VFR.

Outlook...

Friday: Generally VFR with MVFR conditions possible in afternoon rain showers, but confidence in impacts and coverage are low.

Saturday: Moderate confidence in MVFR conditions as light rain moves into the area in the morning, lasting through the day. Low confidence in IFR restrictions during the night as fog and/or low clouds could develop in the wake of the rain.

Sunday: Conditions improve to VFR during the day, but likely return to MVFR for the night as another system approaches the region.

Monday: Moderate confidence in MVFR conditions as rain overspreads the area once again. Can't rule out some brief IFR visibilities as this system may contain bouts of heavier rain, but confidence in that is low at this time.

MARINE

South winds gust to 25 to 30 kts through midnight before dropping below 25 kts as they turn more westerly. Elevated seas will maintain SCA conditions into Thursday morning. Winds and seas will stay below SCA threshold Thursday into Thursday night.

Wind gusts look to generally remain less than 25kts over the coastal waters from Friday into the middle of next week. However, we will likely see brief periods of wave heights building to 5-6ft Sunday and Tuesday as systems pass near or through the Gulf of Maine.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ150>152- 154. Small Craft Advisory until 3 AM EDT Thursday for ANZ153.