textproduct: Gray - Portland

WHAT HAS CHANGED

Temperatures have continued to trend colder for Tuesday.

KEY MESSAGES

1. Rain ends this morning giving way to mild conditions today.

2. A back door cold front brings colder air tonight with low pressure crossing on Tuesday. Mainly a cold, beneficial rain is expected Tuesday while the mountains and lower elevations of central Somerset County will see some wintry precipitation.

3. Wednesday and Thursday turn drier and breezy before the next chance for widespread precipitation and gusty winds arrives Friday into Saturday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Low pressure south of Long Island, NY will scoot ENE this morning with steady rain largely coming to an end by day break. Mesoscale models are in good agreement that skies will be mostly sunny south of the mountains today while areas north of the mountains may remain mostly cloudy as a back door cold front approaches. It will be mild today with highs mainly in the 60s with spots south of the mountains making a run into the low 70s.

KEY MESSAGE 2 DESCRIPTION...

A back door cold front will march SSW through the area late today into Tuesday morning with high pressure building over the Canadian Maritimes. This high will be well positioned to set up cold air damming across the area Tuesday as an area of low pressure tracks east out of the Great Lakes. This low will move overhead Tuesday night and then offshore Wednesday morning. There is some subtle variability in the track of the low amongst guidance which will impact the swath of heaviest QPF as well as thermal profiles across the mountains and areas near the Canadian border in Maine. Latest guidance suggests a swath of +1 inches of QPF will be possible with a multi model consensus placing that swath from the White Mountains towards the Mid Coast and points north. To the south amounts drop off with far southern NH forecast to receive less than a quarter of an inch.

It will be a cold rain for much of the area with highs mainly in the 40s while thermal profiles in the mountains and points northeast may support a period of wintry precipitation during the day Tuesday. Around Jackman, ME profiles from the 00Z HRRR suggest the column will be cool enough for snow Tuesday morning with a transition to a wintry mix and then rain Tuesday evening. Farther to the SW profiles from the HRRR show a warm nose aloft with a sub-freezing layer generally between 6,000 feet and 1,500 feet. This would support freezing rain near mountain summits while valleys above 1,500 feet may see more in the way of sleet. As the low moves overhead Tuesday night profiles will likely warm enough for mainly rain with precipitation tapering off late Tuesday night into Wednesday morning.

KEY MESSAGE 3 DESCRIPTION... Low pressure exits off to the east on Wednesday with a trailing front bring as end to the precipitation as it does. It looks like the system has become more progressive, and most of the area should be dry by early morning. The Midcoast will likely be the last to clear later in the morning. Skies look to end up mostly sunny to partly cloudy south of the mountains by peak heating, so guidance suggests temperatures climb into the mid to upper 60s (and maybe even into the low 70s for southern New Hampshire). Northwesterly flow is going to keep clouds and showers banked up to the terrain so temperatures hang more in the 50s to near 60F. As showers continue into the night some of the higher elevations may see some light snow, but the clouds are going to keep lower elevations above freezing. Warmer 850 mb temperatures move in with the ridging aloft, so while south of the mountains sees mostly clear skies temperatures still only fall into the low to mid 40s.

The aforementioned low pressure system continues to deepen as it moves over the Canadian Maritimes on Thursday, which tightens the pressure gradient between it and the high pressure building in to our west. It is going to be a breezy day for sure with northwesterly wind gusts 25-35 mph, but guidance suggests we could tap into the 50kt low level jet aloft and see wind gusts near 40 mph at times. This is going to have to continue to be watched as positioning of the jet is going to make the difference and guidance has been trending in more eastward, but again confidence in wind gusts at least up to 35 mph is high.

We could see a rinse and repeat solution Friday and Saturday as another low pressure system takes a similar track to the first one, but the difference is that models have been pretty consistently depicting this one being stronger. Widespread rain is likely Friday into Saturday , but that is all I am willing to say about that at this point. What catches my eye more is the signal for potentially strong winds Saturday if this low bombs out in the proximity of Nova Scotia like most global models are depicting. The European and Canadian model have been especially bullish showing widespread 40+ mph gusts. The GFS doesn't quite show the strengthening the others do and therefore suggests a solution more similar to the Tuesday system. We will see how things trend, but a signal like that bears watching.

AVIATION /06Z MONDAY THROUGH FRIDAY/

Through tonight...Low cigs and rain will bring a mix of MVFR to IFR or lower through around 12Z this morning. Conditions improve this morning with VFR likely by mid day and lasting into the evening. Gusty NE winds develop tonight near the coast with cigs lowering to MVFR to IFR.

Outlook...

Tuesday-Tuesday night: Areas of IFR or lower in cigs and rain with some LLWS possible near the coast.

Wednesday: MVFR possible in the morning as rain gradually comes to an end from west to east, but a return to VFR is expected for most sites, although can't rule out a few additional showers to cause TEMPO MVFR in the afternoon. The exception will be periods of MVFR and rain showers at HIE. Northwest wind gusts to around 25 kt possible.

Wednesday night: Mainly VFR, except possible MVFR cigs and rain/snow showers at HIE. Northwest winds may remain gusty up to 25 kt.

Thursday: MVFR restrictions possible early in the day at HIE due to rain/snow showers. Otherwise VFR with breezy northwest winds gusting 25-30 kt.

Thursday night: Mainly VFR with lighter winds.

Friday: IFR to MVFR possible with increasing rain chances.

MARINE

Low pressure exits east this morning with winds and seas below SCA thresholds today. A back door front moves through the waters tonight bringing NE winds gusting in excess of 25 kts. Winds shift E to SE Tuesday as low pressure approaches from the west with gusts 20-25 kts with gusts approaching 30 kts near the Mid Coast late Tuesday into Tuesday night.

SCA conditions may occur Wednesday as a cold front crosses sometime in the morning with winds turning west to northwesterly. SCA level winds become more likely Wednesday night and Thursday, and possibly gales over the outer waters, as a secondary front crosses the waters and the pressure gradient tightens between low pressure over the Canadian Maritimes and high pressure building in from the west. There may be brief improvement Thursday night as the high builds overhead but will potentially be followed by more SCA conditions and possibly gales Friday into the weekend as another low pressure/front approach and cross through.

GYX WATCHES/WARNINGS/ADVISORIES

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