textproduct: Gray - Portland

SYNOPSIS

A clipper system affects the region tonight with light accumulating snow that will last into Thursday morning. Mainly dry and cold weather is expected through the weekend into early next week, with the pattern looking to become more active again thereafter.

NEAR TERM /THROUGH TONIGHT/

Impacts and Key Messages: * Light accumulating snow beginning around the midnight hour may make for some slippery travel heading home from New Year's Eve festivities. * Briefly heavy snow showers or squalls are possible in southern New Hampshire and far southern Maine in the early hours of Thursday morning.

Low pressure rides a stationary boundary into the region tonight accompanied by a sharp shortwave trough. Some light flakes may be falling during the countdown to the New Year as a warm front begins to move northward across the area, but the snow won't really start accumulating until just afterward. This may create some slippery travel for those heading back from New Year's festivities. For much of the interior snow will remain relatively light through sun rise, amounting to a half inch to an inch, but models have been showing a good signal for some coastal enhancement as low pressure deepens in the Gulf of Maine. Coastal areas look to see a more moderate snowfall heading into the early morning hours of Thursday with amounts more on the order of 1-2 inches through sunrise. It is also worth noting that some briefly heavy snow showers or even squalls are possible as the cold front sweeps through southern New Hampshire and far southern Maine toward sunrise.

SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/

Impacts and Key Messages: * Light accumulating snow and potentially slippery travel continues in some areas into Thursday morning. Hi-res guidance continues to hint at an inverted trough forming Thursday morning, but the signal is much weaker than last time. Still, the deepening low will provide coastal enhancement in the form of additional moisture with the onshore flow, so moderate to locally heavy snow looks likely for the Midcoast through the morning, with light snow continuing for the rest of the area. Snow tapers off as the low pulls away to the north Thursday evening. When all is said and done a widespread 1-3 inches looks like a good bet, with amounts on the Midcoast piling up more in the 4-6 inch range. Winter Weather Advisories have been issued for these areas. Locations around Penobscot Bay and on the islands stand the best chance of seeing locally higher amounts greater than 6 inches, but confidence is low on where that heavier moisture axis is going to set-up.

Skies clear and winds calm overnight leading to efficient radiational cooling Thursday night. I went ahead and blended in some cooler guidance to account for this and ended up with low temperatures bottoming out in the single digits in southern New Hampshire and the coastal plain. The interior and foothills are going to bottom out in the -5F to 0F range, and the north gets as low as -5F to -10F.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

Overview: Cold but quiet weather through the first half of the weekend. A quick clipper system will pass through Saturday night into Sunday bringing light snow and preserving cold temperatures in the region for early next week. Towards the middle of next week, moderating temperatures seem likely with one or two disturbances to watch for precipitation.

Details: The pressure gradient through NH and southern ME will widen as low pressure continues to exit north Friday. West winds will still be present though, with some gusts 15 to 20 mph. Into the weekend, gusts become more diurnal with daytime mixing.

Unchanging west flow will keep temps cool and below normal Friday through Monday. This will also help advect moisture from the Great Lakes Friday night into early Saturday morning. This may produce a few snow showers in the mountains, but otherwise repeat downslope drying through the Greens and Whites should keep the interior and coast dry until a quick clipper Sat night.

Pace and available moisture will both be preventative of any significant accumulation as the quick clipper passes. Mean QPF is just a few hundredths ending Sunday morning. Upper and mid level jet dynamics will be somewhat supportive of sfc low pressure deepening into the Gulf of Maine after midnight, so can't rule out a few streamers of enhanced QPF in vicinity of better convergence. But at this time it may be too little too late as the disturbance keeps moving east with little low level support.

Remains some differences in guidance for a follow up clipper Mon night into Tues, and this is shown in NBM PoPs with a rather drawn-out period of unsettled conditions. As this system approaches, think there will be better temporal definition with the event. Until then, GFS solutions quickly dry another clipper cutting south of the Great Lakes where Canadian and Euro solutions hang onto the moisture into New England. This may wind up being another nuisance snow similar to Sat night as not significant jets populate the region leading to lesser net lift for notable accumulations.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Short Term...VFR conditions continue into tonight, before widespread light snow will bring about IFR restrictions tonight. For most terminals a return to VFR should occur around 12Z Thursday, but further east terminals like RKD and AUG may hold onto restrictions closer to 18Z. VFR is then expected to prevail through Thursday night.

Long Term...West winds continue with some gusts to 20 kt Friday and lighter into the weekend. MVFR ceilings hang on in northern NH and the US/CAN border, mainly N and NW of the Whites. Light SN may accompany these lower ceilings, but unsure on exact vis impact at this time Fri night. Series of quick clipper systems could bring lowered ceilings and vis to a wider region Sat night and again Mon night with light snow.

MARINE

Short Term...SCA conditions continue into tonight with a brief break overnight. A front sweeps across the waters early Thursday morning bringing a return to SCA conditions and by the afternoon, gale force wind gusts. Gales last through Thursday night, but SCA conditions continue into Friday morning. Moderate freezing spray is expected Thursday night into Friday morning as well.

Long Term...SCA conditions likely continue through Saturday as west wind regime and cool air mass continues. Other than two quick clipper systems Saturday night and again Monday night, no large pressure systems to impact the waters through early next week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 1 AM to 7 PM EST Thursday for MEZ022-025>028. NH...None. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ150- 152-154. Gale Warning from 1 PM Thursday to 7 AM EST Friday for ANZ150>152-154. Freezing Spray Advisory from 10 PM Thursday to 1 PM EST Friday for ANZ150>154. Small Craft Advisory until 7 PM EST this evening for ANZ153.