textproduct: Gray - Portland

WHAT HAS CHANGED

Expanded Winter Weather Advisories to northern Grafton and northern Carroll for light freezing rain tomorrow. Otherwise forecast remains on track.

KEY MESSAGES

1. Another round of soaking rain is expected Sunday, with a wintry mix possible in the mountains.

2. After a cooler and mostly dry Monday, expect low to medium chances for light snow or rain on Tuesday. The rest of the work week will feature warming temperatures and mainly dry conditions with precipitation chances possibly increasing Friday into the weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A warm front will move northeastward tonight, allowing for a deep warm layer in the low-levels to develop. Cold air will linger at the surface across the interior, and will allow for the potential to see freezing rain and some sleet over the mountains by Sunday morning. The cold air dam will break quickly on Sunday morning as the cold front moves in from northwest to southeast. This will allow for a transition from wintry mix to all rain across interior areas. By the time the cold front arrives in northern New England, there will be very little instability to work with, so the front will likely pass in the form of some scattered to numerous showers in the first half of the day Sunday. Freezing rain accumulations in this setup will likely be higher in the mountains, because the warm air aloft looks to be up near 700mb, compared to the 800-850mb warm air positioning that is more commonplace earlier on in the winter. This may allow for slick travel in the White Mountain notches, and have expanded the Winter Weather Advisory further south.

Things dry out behind the cold front for most, but northwesterly winds may churn up some upslope rain and snow showers in the mountains. Temperatures are expected to sharply cool off for the start of next week.

KEY MESSAGE 2 DESCRIPTION...

Broad mean troughing will be in place to start the work week across the eastern half of the CONUS. This will mean cooler temperatures and increasing clouds, especially in and around the mountains with a stiff westerly breeze in the forecast. This pattern could also lead to some isolated/scattered mountain snow showers through the day with mainly dry conditions elsewhere. Highs will range from the low to mid 30s north, to the upper 40s and lower 50s south.

The next wave then approaches on Tuesday as the main trough axis moves overhead which will lead to our next low to medium precipitation chances. While some rain may mix in across southern New Hampshire and coastal Maine, a dusting to a half inch or so will be possible over much of the rest of New Hampshire and portions the Foothills and Interior of Maine. The highest terrain could potentially see an inch or two. Precipitation should move out by the evening hours.

High pressure then dominates the weather pattern Wednesday before the next longwave trough starts to approach the region and we transition back into southwest flow aloft to end the work week. While specifics are still unclear this far out, it looks like we will see the next chances for precipitation in the Friday through Sunday timeframe.

Regarding temperatures, cool highs remain in place on Tuesday with highs ranging from the upper 20s and lower 30s north, to the low to mid 40s south. The warmup then begins in earnest on Wednesday and by Friday highs are forecast to range from the upper 40s and lower 50s north, to the low to mid 60s south (mid to upper 50s across the Midcoast). While NBM spread increases considerably by the end of the week, it does appear that above to well above normal temperatures should stick around through at least the weekend.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

VFR is expected this afternoon, but restrictions will lower overnight as rain and some wintry mix moves in. Patchy fog Sunday morning will sustain poor restrictions and conditions do not look to improve until Sunday night.

Outlook:

Monday/Monday night: VFR conditions with daytime WNW wind gusts between 25-30 kts possible. Low chance of a snow shower at HIE.

Tuesday/Tuesday night: VFR conditions are currently favored but there is a low to medium chance (30-50%) for some light rain/snow along with lower ceilings. The greatest potential for this is currently across southern TAF sites. Westerly winds at 5-15 kts.

Wednesday/Wednesday night: VFR conditions expected. Southwesterly winds at 5-15 kts.

Thursday/Thursday night: VFR conditions expected with a mountain shower possible at night at HIE. Southerly winds at 5 to 15 kts.

MARINE

SCA easterly winds are expected this afternoon and tonight. Winds will shift to SCA westerlies when the cold front passes over the Gulf of Maine Sunday afternoon. Westerly SCA winds continue through Monday morning. Seas of 3-5ft this afternoon will increase to 5-10ft by the end of the day Sunday. Seas relax back down to 3-5ft for Monday morning.

Winds become northerly Tuesday through Wednesday morning with potential gusts in the 25-30 kts range. After winds calm down during the day Wednesday, seas and winds increase again through the end of the week starting Wednesday night.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from midnight tonight to 10 AM EDT Sunday for MEZ007>009. NH...Winter Weather Advisory from midnight tonight to 10 AM EDT Sunday for NHZ001>004. MARINE...Small Craft Advisory until 8 PM EDT Sunday for ANZ150-152-154. Small Craft Advisory from 8 PM this evening to 11 AM EDT Sunday for ANZ151-153.