textproduct: Gray - Portland

SYNOPSIS

Low pressure tracks SE across northern New England this evening into Wednesday morning. This system will bring several inches of snow across much of the area with significant snowfall along the coastal plain of Maine. High pressure builds in Wednesday afternoon into Thursday morning. A cold front crosses Thursday evening with sub-zero wind chills likely Thursday night. A warm front approaches late Friday that will bring chances for light snow into Saturday morning.

NEAR TERM /THROUGH TODAY

Key Messages:

-Snow moves in from southwest to northeast today with deteriorating travel conditions by this evening.

Discussion:

Surface low pressure will exit Quebec today before moving over the Gulf of ME tonight within the left exit region of a LLJ. This area of low pressure will bring widespread snowfall to the region, which will advance from southwest to northeast through the day before arriving towards the Mid-Coast of ME by early this evening. Forcing for ascent during the day will be fairly weak with limited QPF, and therefore through sunset only 1-2" on average of snowfall is likely. High temperatures will range from the upper 20s to middle 30s from north to south, and this could allow for a little rain to mix in at times, mainly along the coast.

SHORT TERM /TONIGHT THROUGH WEDNESDAY/

Key Messages:

-Periods of moderate to heavy snowfall is expected tonight for portions of the western ME coast. Snow ends Wednesday morning into the early afternoon.

-Gusty northwesterly winds on Wednesday are expected, with some blowing and drifting snow possible.

Discussion:

Snowfall rates are expected to increase later this evening through the overnight hours along the ME coast as an inverted trof/Norlun Trof develops with light to at times moderate snow elsewhere. Latest forecast soundings show strong omega/lift within a saturated DGZ with some increasing LL instability developing and strong LL convergence. There is the potential for snowfall rates between 1- 2"/hr across portions western ME tonight, which will result in very hazardous travel conditions. Latest hi-res guidance shows between 0.50-1.00" of QPF, mainly from Portland, ME and points east towards the Mid-Coast of ME. This QPF combined with snow-liquid ratios of between 12-15:1 yields a wide swath of 6-8" of snow from Cumberland county to Kennebec county with pockets of 8-12" just inland from the coastline. Based on this latest guidance and the overall run-run consistency, went ahead and upgraded the existing winter storm watch to a winter storm warning. Elsewhere, generally between 3-6" of snow can be expected with lesser amounts towards southern NH of 1-3" due to less in the way of forcing and lower QPF. The winter weather advisory remains largely unchanged but did add Grafton County in NH based on the latest forecast.

Snow will gradually end from west to east on Wednesday morning but it may linger through at least part of the afternoon across western ME. Northwesterly winds will increase in its wake with gusts up to 25-30 mph possible. This could result in some blowing and drifting snow since snow character is expected to be fairly dry, especially away from the immediate coastline. High temperatures on Wednesday will primarily be into the 30s.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Overview: The mid tropospheric flow pattern across the CONUS will continue to feature a persistent ridge centered over the Great Plains through the end of the week. Disturbances riding the northeast flank of the ridge will bring a couple of chances for light precipitation Thursday into Saturday. The central US ridge temporarily breaks down late week as Pacific energy pushes inland across western North America. This will lead to a more robust trough swinging across the Great Lakes late in the weekend which will coincide with a growing upstream block near Greenland associated with a -NAO.

Key Messages:

*Light snow Friday afternoon into Saturday morning could bring slick travel. Particularly across southern NH where ensemble probabilities of greater than 1 inch of snow are around 60 percent.

*There is a growing signal for a widespread wintry precipitation event Sunday that will bring potential for travel impacts.

Forecast Details:

A cold front will cross the area Thursday bringing chances for snow showers, mainly in the mountains. Before the front crosses temperatures will rise into the mid 20s north to mid 30s across the south with a mix of sun and clouds. NW winds ramp up Thursday evening in the wake of the cold front. The combination of gusty NW winds and colder air moving into the area will bring wind chills below zero across the entire area by Friday morning.

High pressure building in from the north will allow for mostly sunny skies Friday morning with clouds increasing late in the day as the next upper level disturbance approaches. This feature will produce an area of low pressure over the Ohio Valley that tracks ESE to a position south of Long Island, NY Saturday. There is a large spread in the track of this feature amongst ensembles with several members keeping measurable precipitation south of the region. There are also several members that bring accumulating snow to much of the area with amounts approaching Advisory criteria across southern NH. The latest NBM brings chance PoPs (30-50%) across western Maine and northern NH and likely PoPs (60%) across southern NH, which seems to be a good compromise given the spread in ensembles.

There will likely be a break in precipitation Saturday afternoon through Saturday night before a more robust trough approaches from the Great Lakes. The current model consensus with this feature is for one area of low pressure to track into SE Canada with second low forming near coastal New England. This set up would likely yield snow with potential for a wintry mix while these finer details will take several days to iron out at this time range.

AVIATION /04Z TUESDAY THROUGH SATURDAY/

Short Term...SN will overspread the region today into this evening with deteriorating flight restrictions to IFR/LIFR. Periods of +SN and 1/4SM viz is possible overnight, mainly at KPWM, KAUG, and KRKD. Winds will generally be out of the E-NE at 10-15 kts. Conditions will gradually improve on Wed but restrictions may persist with SN at KPWM, KRKD, and KAUG through part of the afternoon. Gusty NW winds will develop with gusts up to 25 kts possible. No LLWS is anticipated.

Long Term...VFR likely prevails for most Wednesday night into Saturday. Some -SHSN will bring potential for restrictions at KHIE Thursday. There is potential a system will bring lowering cigs and light snow late Friday into Saturday morning with the highest confidence for restrictions at KLEB, KMHT, KCON, and KPSM.

MARINE

Short Term...Winds and seas will remain below SCA levels today into tonight. Gusty NW winds are expected on Wednesday with gusts up to 30 kts and seas building to 6-8 ft outside of the bays with 1-4 ft in the bays.

Long Term...Winds will be below 25 kts from 00Z to 18Z Thursday while seas will run greater than 5 feet. A cold front crosses late Thursday with NW winds gusting 30-35 kts into Friday morning. Winds and seas drop below SCA thresholds Friday afternoon into Saturday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 1 PM Tuesday to 1 PM EST Wednesday for MEZ007>009-012>014-018-023-033. Winter Storm Warning from 1 PM Tuesday to 1 PM EST Wednesday for MEZ019>022-024>028. NH...Winter Weather Advisory from 1 PM Tuesday to 1 PM EST Wednesday for NHZ001>006-009-010. MARINE...None.