textproduct: Gray - Portland

SYNOPSIS

Low pressure passes well south of New England through tonight bringing chances for light snow, mainly near the coast and southern NH. Another shot of cold air builds into the area Monday. A couple of weak disturbances bring chances for snow showers Monday night and again Wednesday. Temperatures will warm above normal the second half of the week as an area of low pressure tracks northwest of New England.

NEAR TERM /UNTIL 6 AM SUNDAY MORNING/

545 PM Update... Latest hi-res guidance and ensemble based information continues to show growing confidence that some light snow will impact the southern two thirds of the CWA beginning mostly after midnight tonight and lasting through Sunday morning. Forecast soundings show a nearly saturated -12C to -18C layer with decent cross hair omega within this layer. Despite low QPF of generally a tenth of an inch or less, snow- liquid ratios (SLRs) of between 12-15:1 will likely allow for some southern locations to receive between 1-2" of snow with perhaps some locally higher amounts. Given the cold antecedent airmass and road temperatures, this could result in locally slippery travel Sunday morning.

Went ahead and increased PoPs and QPF with this update based on this new information.

Previously... A weak wave aloft and a warm front will continuing lifting northward this afternoon into early this evening, providing the focus for some light snow. Most of the area could see flakes, but favored areas for a dusting of snow will be the Midcoast and across the north, except maybe an inch or two in the higher terrain.

For tonight, clouds will limit radiational cooling with temperatures mostly in the 10s and 20s for overnight lows. However, the main focus remains the potential for light snow as a positively tilted 500mb trough approaches from the Great Lakes and a low pressure begins to develop well offshore. There's still discrepancies among model guidance as to whether enough moisture will make it into the area for light snow to develop overnight, but the higher chances remains cross southern NH and coastal ME and possibly as far north as the foothills. Winds will also be switching to W/WNW overnight, and that may also contribute to some upslope snows in the north and mountains.

SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/

Chances for light snow continue into Sunday morning and maybe early afternoon along the coast before a push of drier air works in from the northwest. The mountains may also continue to see light snow from upsloping. Little in the way of accumulation is expected with this system, but portions of southern NH and ME coast could see up to an inch. Even with these very light accumulations, there still could be slick roadways.

Winds also become breezy in the afternoon and evening with the low pressure beginning to deepen and high pressure building in from the west, tightening the pressure gradient.

A cold night is ahead Sunday night as cold air advection continues with somewhat breezy conditions. Temperatures are expected to drop into the singles digits to 10s, but with the winds most of the area will likely see wind chills below zero by daybreak Monday. A chance for upslope snow showers continues in the mountains.

LONG TERM /MONDAY THROUGH SATURDAY/

Overview:

The first half of December has been much colder than normal and this can be attributed to persistent ridging over western North America. An onslaught of Pacific storms into the Pacific NW will continue the break down of the western ridge this week resulting in a near zonal flow pattern across the northern tier of the US. Temperatures will moderate by mid week and may spend a few days above normal into Friday. There will be multiple chances for precipitation through next weekend with a storm track that favors snow/mix to rain events.

Key Messages:

*Above normal temperatures likely Wednesday to Friday.

*Low pressure tracks north of the area Thursday into Friday bringing snow/wintry mix across the north and mainly rain south of the mountains.

Forecast Details:

A trough swings offshore Monday morning with gusty NW winds advecting colder air into the area. Highs will range from teens north to 20 south and with winds gusting up to 25 mph the wind chill will be about 10 degrees lower than the ambient air temperature. A weak wave approaching from SE Canada along with weak WAA will bring chances for snow showers, mainly in the mountains Monday night. Mid level ridging builds in Tuesday into Wednesday morning for mostly dry weather and the start of a warming trend. Low pressure passes north of the area Wednesday into Wednesday night bringing light precipitation across the north with snow showers in the mountains and a mix of rain and snow at lower elevations.

The pattern briefly becomes more amplified Thursday into Friday as trough digs into the Ohio Valley. This trough will spawn an area of low pressure that tracks west of New England into SE Canada. The lack of cold antecedent air will likely result in precipitation mainly in the for of rain south of the mountains Thursday night into Friday. Precipitation types become more tricky across the north as some model solutions suggest cold air quickly wraps into the system as the low occludes and others hint at pressure falls offshore. At this time range these finer details will take a few days to iron out. The attendant cold front crosses late Friday with temperatures return to near normal over the weekend.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Short Term...Brief restrictions are possible this afternoon and early evening from light snow showers, mainly at HIE and LEB. Tonight into the first part of Sunday, southern NH and coastal terminals may see MVFR to IFR restrictions from light snow. Mainly VFR Sunday afternoon and Sunday night with northwest winds becoming breezy on the order of 20-25 kt, possibly as high as 30 kt. The exception is the possibility of MVFR conditions at HIE due to an ongoing chance of snow showers through Sunday night.

Long Term...Outside of snow showers at KHIE Monday night and again Wednesday, conditions will mainly be VFR into Thursday morning. Low pressure brings potential for restrictions late Thursday through Thursday night.

MARINE

Short Term...SCA conditions continue into this evening, but winds and seas will subside and remain below SCA conditions overnight into most of Sunday. SCA conditions then return Sunday evening and Sunday night as northwest winds increases in response to deepening low pressure well offshore. Gusts to gale force are possible over the outer waters Sunday night.

Long Term...NW winds will gust to 30 kts Monday into Monday night. Winds and seas drop below SCA thresholds Tuesday. SW winds increase Tuesday night through Wednesday and may approach Gale force Wednesday as low pressure passes north of New England. Winds briefly turn offshore Wednesday night into Thursday morning before increasing out of the south late Thursday ahead of the next low pressure system.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until midnight EST tonight for ANZ150-152- 154. Small Craft Advisory until 10 PM EST this evening for ANZ151- 153.