textproduct: Gray - Portland

SYNOPSIS

High pressure slides offshore tonight allowing a warm front to push across the area. A large low pressure system across the Great Lakes drift east Monday bringing mixed precipitation and hazardous travel conditions. This is followed by a strong cold front Monday night. High pressure briefly returns on Wednesday, with periods of reinforcing cold air through the end of the week.

NEAR TERM /THROUGH TONIGHT/

3 PM Update...Opted to upgrade central New Hampshire to winter storm warnings as confidence is increasing in portions of this area seeing the higher end ice accumulations greater than 0.5", but less then 0.75". This combined with mixed precipitation and expected gusty winds within the warning area will create an elevated power outage threat.

Previous Discussion... Impacts and Key Messages: * A messy winter storm with a period of freezing rain is going to bring hazardous travel to the area Sunday night.

Not too much has changed in regards to thinking with this system. Models have come into pretty good agreement on a start time of around 10pm for precipitation working into southwestern New Hampshire. BUFKIT profiles suggest the warm nose is going to be well established at this point, starting things off as freezing rain. Precipitation expands northeastward, overspreading the area by daybreak Monday. Temperature profiles still look colder in interior Maine, so I would expect more of a mix as it pushes into that area. After a very cold night last, and temperatures staying well below freezing through much of tonight, untreated roads and walkways are going to be primed for ice accumulation. Anyone out and about in the overnight hours should use extreme caution as it looks like it is going to be slippery.

SHORT TERM /MONDAY THROUGH MONDAY NIGHT/

Impacts and Key Messages: * A messy winter storm with a period of freezing rain is going to bring hazardous travel to the area through at least the Monday morning commute. * Gusty winds Monday night may pose a limited power outage threat depending on how much ice accumulation locations see.

The Monday morning commute is going to be a tough one for many. Models are being far too generous with surface warm air and I have continued to blend in colder guidance. It has been noted that this cold air dam setup is on the weaker side, but my gut tells me it will hold through the commute. The immediate coast has the best chance of starting to see a transition to rain early, but interior locations likely hold on to freezing rain through a good chunk of the morning. The biggest note in trends with the hi-res models is the fact that they have been more progressive with this system, with precipitation tapering off by Monday evening. Combined with QPF in the 0.5-0.75 range, this is going to help keep ice accumulations comfortably below warning criteria. However, because I am not discounting the cold air dam and the latest runs of the CAMs don't have the dry slots they were showing during the day Monday in yesterday's runs, ice accumulations 0.25" up to 0.5" are not out of the question, and therefore the Winter Weather Advisories continue unchanged. I do believe higher end amounts stay more isolated to the terrain.

A potent upper low passes to our north Monday night, with an 80kt low level jet rounding it's base. The core of this jet stays off to our southeast, but ensemble means suggest 40-50kt winds on the fringes of the jet move over our area. Looking at BUFKIT profiles, lapse rates aren't super steep, but momentum transfer suggests widespread wind gusts 25-35 mph able to reach the surface. While these winds aren't the most impressive, areas that do end up seeing significant ice accumulations will have a limited power outage risk. Low temperatures Monday night fall into teens across much of the area, so windchills will feel more like the single digits by Tuesday morning.

LONG TERM /TUESDAY THROUGH SUNDAY/

- Cold with periodic moisture starved shortwave passages & upslope mountain snow

Strong cold air advection behind the exiting system will have favorable momentum transfer tapping into a low level jet ~50+kt, resulting in blustery westerly surface winds around 20-35 mph Tuesday. This will drop wind chills down in the single digits from the foothills south, and negative values further northward. Fortunately winds gradually weaken Tuesday night as temperatures continue to plummet.

Cyclonic NW flow pattern will dominate the remainder of the week as the area is under a deep upper low over eastern Canada. This will support reinforcing shots of cold air. Each shortwave & reinforcing cold front push will bring some snow chances, particularly in the mountains. Model ensembles are coming together on a shortwave rotating around the trough late Wed-Thu which could bring light snowfall to all areas. However, the source region being dry will limit any accumulations. There is high confidence that this will be a cold stretch with high heating degree days. The trough is projected to become less amplified by the weekend, with at least some moderation in temperature. Light snow is still possible Saturday Night-Sunday with the continued shortwave crossings through the main trough.

AVIATION /20Z SUNDAY THROUGH FRIDAY/

Short Term...VFR conditions prevail through the day before things go down hill quickly tonight. Freezing rain will begin to move into the area around 03Z overspreading New Hampshire terminals by 06Z and southern Maine terminals by 09Z. Mixed precipitation is possible at times as well bringing periods of IFR visibilities. Widespread IFR is likely Monday as ceilings lower. Conditions improve Monday night as precipitation tapers off. Westerly wind gusts 25-30 kts are expected Monday night in the wake of the system.

Long Term...Periods of sub-VFR CIGs will be likely Monday with periods of mixed precipitation ahead of the approaching cold front. A period of gusty southwest winds looks likely Monday, night through Tuesday with gusts 20-30 kt. VFR conditions to return Monday night.

MARINE

Short Term...Sub-SCA conditions are expected through tonight, but southerly winds will ramp up, with gusts above 25kts, quickly as rain overspreads the waters associated with a frontal passage. Monday night behind the front, winds shift westerly with gusts ramping up to Gale force. During this time seas are also expected to build to 5-8 ft.

Long Term...The front is progged to push across the waters Monday evening with strong NW winds developing bringing a period of Gale Force winds across most waters Monday night. Seas are progged to build up to 6- 10 ft through Tuesday, with improving conditions late Tuesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 10 PM this evening to 7 PM EST Monday for MEZ007>009-012>014-018>028-033. NH...Winter Weather Advisory from 10 PM this evening to 7 PM EST Monday for NHZ001-002-010>015. Winter Storm Warning from 10 PM this evening to 7 PM EST Monday for NHZ003>009. MARINE...Gale Warning from 7 PM Monday to 7 AM EST Wednesday for ANZ150- 152-154. Gale Warning from 10 PM Monday to 7 AM EST Wednesday for ANZ151-153.