textproduct: Gray - Portland

SYNOPSIS

An upper level disturbance will cross New England this afternoon bringing a round of snow showers and potential squalls. After high pressure quickly moves near the region Saturday into Saturday night, low pressure and a cold front will draw moisture and precipitation back into the region Sunday into Sunday night. High pressure then tracks through New England Monday and Monday night.

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/

630 PM Update...The coverage and intensity of snow showers has continued to diminish this evening with the passage of a short wave trough. Upslope snow showers on western slopes of the mountains will continue overnight, however. Breezy and cold conditions continue to be expected overnight.

Previously...

A well-defined 500mb shortwave continues to trek through New England this afternoon, providing the lift for snow showers with the primary focus remaining on the potential for heavy snow showers and/or squalls. The environment continues to be favorable with SPC mesoanalysis depicting steep low-level pretty much areawide lapse with snow squall parameters also increasing. Current radar imagery suggests watching portions of southern NH closely as there is a steady stream of lake-effect moisture. The last couple runs of the HRRR are also favoring western ME from the foothills southward over the next couple of hours especially Fryeburg-Lewiston/Auburn-Augusta-the Midcoast, but will see how things play out. Outside of snow showers, it will be mostly cloudy and breezy with gusts of 25-35 mph, possibly up to 40 mph.

Snow showers are expected to largely diminish south of the mountains after 4-5PM as the sun goes down and with the shortwave passing to the east. Winds will stay up through this evening and tonight with gusts of 20-25 mph at times, which results in wind chills in the teens. For the mountains and portions of the CT Valley, upslope flow will keep snow showers going through the night, and there may be a bit of spillover into the foothills as Froude numbers remain elevated.

SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/

Cold air advection continues on Saturday with low pressure across the Canadian Maritimes. It will again be on the breezy side with gusts up to 30 mph based on forecast soundings, which will make it feel chillier than the actual temperature. Current forecast has wind chills staying the 20s south of the mountains and in the teens in the mountains.

The mountains will see more upslope snow showers at least through the morning as upslope flow remains, but these should taper off through the afternoon as high pressure starts to build in. The overall airmass will be drier, but Froude numbers support some spillover of clouds downwind of the mountains and possibly some flurries.

The high pressure settles in for Saturday night bringing light winds. Temperatures could drop pretty quick if skies are clear enough early on, but increase clouds are expected to level off temperatures or even bring them up a bit as the night goes on. Lows should be mostly in the 20s, but a few spots may get down into the 10s.

LONG TERM /SUNDAY THROUGH FRIDAY/

This afternoon's discussion has been shortened to focus on active weather in the near-term forecast.

11/28 1200PM UPDATE...Extended forecast remains on track, with minimal changes necessary. Forecast guidance is continuing to point in the stormier direction for Tuesday afternoon's winter weather. Both Euro and GFS snow probabilities show that there is still a 30-40% chance of seeing at least 6 inches of snow across New Hampshire and Maine. At this time, we are more uncertain about the intensity of the low over the track of it. It will probably snow across a wide swath of New Hampshire and western Maine on Tuesday. Honing in on how intense the low could be will give us more defined answers to whether we are talking about widespread Winter Weather Advisory snowfall or a more defined winter storm bringing over 6 inches of snow.

Previously... Precipitation moves in Sunday morning, with snow likely in the mountains but mostly rain elsewhere. A couple inches of snow is not out of the question north of the mountains, but snow will struggle to accumulate in the foothills and south. Precipitation should clear out of the area for most by Sunday evening, with some lingering snow showers expected to persist across the interior through Monday morning.

High pressure returns on Monday with mostly dry conditions likely, along with clearing skies. However, this period of quieter weather will be brief.

Monday night, a low pressure system looks to develop over the Ohio River Valley, and move eastward. Cyclogenesis looks favorable as the low looks to position itself in the left exit region of a weak upwind jet streak, as well as the right entrance region of a much stronger jet streak downstream. This should allow for increased upper-level divergence and lower pressure falls within the low. Uncertainty still remains with storm track, but models have come into stronger agreement that winter weather is likely Tuesday, and this system has a solid chance of becoming the first notable widespread winter storm for the region. Despite the large spread on intensity, ECMWF and GFS Ensemble snow probabilities show at least a widespread 40% chance to see greater than 6 inches of snow across New Hampshire and western Maine. Snow may be heavy at times and substantially skewer visibility during the day Tuesday.

Wednesday and Thursday look drier and higher pressure works into the area. A couple isolated snow showers can't be ruled out across the interior.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Short Term...Scattered snow showers, some potentially heavy, or even snow squalls could bring instances of IFR or lower visibilities should any pass over a terminal this afternoon. Outside of these, conditions will be primarily VFR with gusty winds of up to 30 kt. Snow showers should wane 21-22Z this afternoon, except at HIE, where occasional restrictions could persist through tonight. Winds may continue to gusts around 20 kt at times through tonight. For Sat-Sat night, mostly VFR is expected with gusty west winds continuing, but these will become light later in the day through Saturday night as high pressure builds in.

Long Term...Lowered restrictions are likely Sunday, with the heaviest restrictions possible in the north due to snow. Restrictions will stay down through Monday morning. VFR prevails through the remainder of Monday, and into Tuesday morning. Restrictions lower on Tuesday due to an possible winter storm.

MARINE

Short Term...Westerly gales will persist over the outer waters through tonight with SCA conditions in the bays. Once the gales subside, SCA conditions are likely over the outer waters through Saturday afternoon across the bays and then over the outer waters into Saturday evening. High pressure brings improving conditions Saturday night with conditions staying under SCA levels.

Long Term...Light and variable winds are likely to continue through Sunday afternoon. Seas lower from 3-5ft to 2-3ft in this timeframe. SCA thresholds are likely Sunday night through Monday morning, with some gales possible during this time frame as well. Marine conditions improve on Monday but SCA thresholds may return again by Tuesday night.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning until 7 AM EST Saturday for ANZ150-152-154. Small Craft Advisory until 7 AM EST Saturday for ANZ151-153.