textproduct: Gray - Portland

WHAT HAS CHANGED

No real significant changes were needed for this forecast package. Widespread light to moderate snow continues to fall early this afternoon with accumulations mainly on grassy surfaces thus far. We are still monitoring the potential for the development of a narrow band of locally heavy snow late this afternoon or this evening over western Maine. A snow squall is not out of the question.

KEY MESSAGES

1. Pockets of light to moderate snow will continue this afternoon with chance for a snow squall late this afternoon or the evening, mainly over western Maine.

2. A warming trend starts Thursday with temperatures climbing above normal Friday into this weekend. Even warmer temperatures are possible early next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A compact shortwave continues to traverse the base of a mean longwave trough axis crossing through the region early this afternoon. A surface low will also move into the Gulf of Maine this afternoon with CAMs suggesting that a narrow band of precipitation will develop on the north and west side. RAP soundings suggest that we could see a little bit of elevated instability on the order of 100 J/kg or so of MUCAPE, so this band will feature convective elements and possibly a rumble of thunder or two. The convective element could also lead to some brief heavy bursts of snow or even a snow squall or two. Some rain, sleet, or graupel could mix in at times.

Precipitation will move out mid to late evening with clouds diminishing overnight. This will make for some chilly lows by Wednesday morning, ranging from the single digits and lower teens north, to the upper teens and lower 20s south. Wednesday will then feature high pressure and plenty of sunshine. Afternoon temperatures will still be a little bit on the cool side but warmer than today with highs in the mid to upper 30s north, to the mid to upper 40s south. This pattern should also lead to favorable conditions for afternoon dewpoints mixing out into the upper single digits or lower teens. Widespread minimum relative humidity values in the 20 to 30 percent range appear likely with some upper teens even possible over southern New Hampshire. Thankfully, light winds and recent wetting precipitation should keep fire weather concerns in check.

KEY MESSAGE 2 DESCRIPTION...

Southerly flow increases Thursday into Friday as high pressure shifts east due to a cold front approaching from the west. This will usher in a warmer airmass into New England with temperatures climbing into the 40s and 50s for highs on Thursday and then 50s and 60s on Friday. The lower of these temperatures each day will be along and just inland from the western ME coast with flow off the very chilly Gulf of Maine.

As the front approaches late in the day Friday, it will bring increasing chances for rain showers to the area into Friday night. These will taper off overnight and probably be over by daybreak Saturday with ensemble means generally having rainfall amounts in the 0.10" to 0.25" range.

High pressure builds in behind the front for the weekend, bringing dry conditions other than a chance of upslope rain and snow showers in the mountains on Saturday. Temperatures come down slightly on Saturday, but most will still see 50s for highs, except 40s in the mountains. By Sunday the high slides to the south and east, bringing in a low-level southerly flow, possibly bringing temps back closer to 60 degrees across southern NH and parts of the Maine interior. Coastal Maine may end up being cooler on Sunday than on Saturday.

Going into early next week, global models are in good agreement in low pressure moving across the Great Lakes and a frontal boundary gradually approaching from the north and west. There is signal for the boundary to potentially stall out somewhere in the vicinity, but where is the key. If the front stays farther to the north and west, the deepening southwest flow could bring very warm temperatures well into the 60s and 70s Monday and Tuesday. Conversely, if the front sags into the area it will be cloudier, cooler, and more showery. As it stands right now, northern areas have the higher shower chances. Not surprisingly, the spread in the ensemble temperature guidance is quite large, but the NBM 25th percentile does shift more confidence toward the warmer temperatures as it still has highs reaching the 60s Monday and possibly even warmer Tuesday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Widespread IFR to MVFR conditions continue in light to moderate snow and low ceilings. Brief LIFR conditions will be possible at times under any heavier pockets of snow. Precipitation will gradually diminish from west to east late this afternoon and into the evening and ceilings will also scatter out for most sites by the overnight hours. VFR will then prevail the rest of the night and through the day on Wednesday.

Outlook:

Wednesday night: VFR.

Thursday: VFR. Southerly winds may gust 20-25 kt.

Thursday night: Mainly VFR. Some potential for IFR stratus or fog at RKD-AUG-PWM.

Friday: IFR stratus and fog are again possible early in the morning or in the evening at the western ME terminals. There will also be increasing chances for rain showers in the afternoon, especially at LEB and HIE.

Friday night: Increasing chances for MVFR to IFR restrictions as a cold front brings rain showers. Also can't rule out IFR to LIFR fog/low stratus for the coastal terminals and AUG.

Saturday-Sunday: Mainly VFR, except MVFR possible at HIE on Saturday.

MARINE

Winds and seas should remain below SCA thresholds thru the afternoon. By this evening, northeast winds will start to gust to SCA criteria. High pressure then moves over the waters on Wednesday bringing tranquil conditions to the waters.

Thursday-Tuesday...High pressure shifts east Thursday as low pressure passes well to the north of the waters. This will send a cold front through the waters Friday into Friday night with the possibility of a another low developing along the front. Southerly gusts may reach SCA levels Thursday into Thursday night and possibly again late Friday into Friday night behind the cold front. High pressure brings improvement over the weekend, and then SCA conditions are possible from late Sunday into early next week as south to southwest winds increase with the high shifting to the south and east and a frontal boundary gradually approaching from the north and west.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT Wednesday for ANZ150>154.