textproduct: Gray - Portland

SYNOPSIS

A low is bringing accumulating snow, ice and rain to northern New England. The low moves out tonight, and will be followed by a cold front. This cold front passes through Thursday morning with a prolonged period of gusty winds in its wake through Friday. High pressure briefly builds in Friday night into Saturday before the next trough approaches from the Great Lakes.

NEAR TERM /THROUGH TONIGHT/

As of noon today, light snow has started across the region. Temperatures are on track, though AUG has been running a little cooler than anticipated. This afternoon's forecast is a challenging one, even only in the near term. Hi-res guidance has been consistently flip-flopping on icing, ice amounts and some guidance still has none over the area. However, upon monitoring temperature trends, especially in Augusta, the image becomes a bit more clear regarding the icing.

I opted to lean more heavily towards the HRRR's solution, which paints a broad swath of noticeable freezing rain totals across the foothills and central Maine. Low-level southwesterly winds this afternoon will allow for inefficient warm air advection, which will interact with stagnant and stubborn cold air at the surface. This should allow for a band of sustained freezing rain to occur in a swath from interior York, to Lewiston, Augusta and then northeast from there. This swath could see up to a tenth of an inch of ice, though up to a quarter of an inch can not be ruled out at Augusta and northeastward. I still think that freezing rain will stay confined to Maine, though a patchy glaze of ice can not be ruled out across Strafford and Merrimack counties either.

The snowfall forecast is still on track, with 3-6 inches expected across northern NH and northwestern Maine.

Skies will be quick to clear up across the south tonight, with southern NH likely waking up to mostly clear skies tomorrow morning, partly cloudy skies elsewhere. Low temperatures will vary quite a bit, from upper teens north of the mountains, to upper 20s along the coast.

SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/

The system exits the area tonight, and a pressure gradient will set up in its wake. The pressure gradient and strong mixing will allow for breezy to gusty winds to setup across NH and Maine on Thursday. These winds in addition to strong cold air advection Thursday afternoon will allow for temperatures to crash mid-day and will allow for a chilly and blustery second half of the day. Upslope snow showers are likely in the mountains and should continue through Friday morning. Blustery conditions will continue through Friday morning as well, with lows in the teens expected.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

By early Friday morning, an upper low will have moved up into the Canadian Maritimes with most of our forecast area remaining in cyclonic flow aloft. This will mean ongoing upslope snow showers across the mountains and forecast Froude Numbers are greater than 1 through the day on Friday. Thus, we could see some of these snow showers making their way out of the mountains and closer to the coast. This activity should diminish at night.

A very cold airmass will be in place with Friday highs only expected to range from the teens north, to the upper 20s south. A few lower 30s are possible along the coast. In addition to the cold airmass, winds will remain fairly gusty given modest pressure rises and cold air advection through the day. Forecast soundings generally suggest 35 to 45 knots of wind at the top of the mixed layer with the highest winds expected along coastal areas and the higher terrain. A few wind gusts in the 35 to 45 mph range seem reasonable during the early to mid afternoon with soundings suggesting that we will see diminishing values after 21z or so. These winds will make it feel much colder with apparent temperatures only expected to range from around 5 below zero over portions the north country, to the mid to upper teens south.

Upper ridging and high pressure move in Friday night into Saturday which should keep most of the area dry, although some guidance keeps a few mountain snow showers in the forecast. Lows Saturday morning will once again be chilly, ranging from the upper single digits above zero to the low to mid teens. However, we will rebound a little bit during the afternoon as the ridge axis moves across the region. Forecast highs will mainly be in the lower 20s north, to the low to mid 30s south. Winds will also be light and variable with high pressure in place at the surface.

We then transition back into southwest flow aloft on Sunday as the next trough/upper low approaches. This system will bring our next widespread low to medium precipitation chances (20 to 40 percent). An easterly trend has continued in most of the ensemble guidance and confidence is growing that the associated surface low will not deepen until it is well out to sea. This scenario would mean mainly light snow for most of our area. There are still a few scenarios that bring in some heavier precipitation to coastal areas, but these are low probability solutions at this time.

Highs on Sunday will be similar to Saturday, but we are likely to see another round of arctic air move in Sunday night into Monday behind a cold front associated with the aforementioned upper low/trough. Monday morning lows will mainly range from around zero across portions of the north, to the lower teens south. Afternoon highs will only range from the lower teens to the lower 20s (a little bit colder in the higher terrain and a little bit warmer along the coast). Tuesday will then see a modest warmup as most guidance suggests an upper ridge axis moving across the region.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Short Term...Lowered restrictions are expected due to rain, snow and freezing rain through tomorrow morning. VFR expected afterwards, though HIE may continue to see lowered restrictions due to upslope snow.

Long Term...Mainly VFR Friday through Sunday. WNW winds will gust up to 35 kts on Friday. There are low chances for light snow Saturday night into Sunday that will bring the potential for the next period of restrictions.

MARINE

Short Term...Near-Gale force southerly winds will continue through tonight. Tomorrow morning, winds shift to westerlies, strengthening to at least Gale Force winds. These winds will continue past Friday morning. 5-9ft seas are expected through the entire forecast period.

Long Term...Gales out of the west are likely to be ongoing Friday morning. Winds and seas drop below SCA thresholds Friday night into Saturday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory until 1 AM EST Thursday for MEZ007>009- 012>014. Winter Weather Advisory until 1 AM EST Thursday for MEZ018>021- 033. NH...Winter Weather Advisory until 1 AM EST Thursday for NHZ001>006. Winter Weather Advisory until 1 AM EST Thursday for NHZ008>010. MARINE...Gale Warning until 1 PM EST Friday for ANZ150-152-154. Small Craft Advisory until 1 AM EST Thursday for ANZ151-153. Gale Watch from Thursday evening through Friday afternoon for ANZ151-153.