textproduct: Gray - Portland

WHAT HAS CHANGED

A Winter Weather Advisory has been issued for the Western ME mountains and foothills of western ME from Wednesday morning through Wednesday evening for a wintry mix of freezing rain and sleet.

KEY MESSAGES

1. Well above to even near record highs will contribute to significant snowmelt and additional ice movement on area rivers the rest of today.

2. Low pressure likely brings a wintry mix and slick travel from the foothills of western ME northward Wednesday morning into portions of Wednesday night. A brief period of wintry mix can't ruled farther south toward Augusta and Lewiston and west into northern NH.

3. An unsettled pattern continues into the weekend and early next week. Snow, wintry mix and rain are all possible.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... A very warm rest of the day is in store with plenty of sunshine and light winds. We'll continue to monitor area rivers for rises as ice movement and breakup is likely, especially over NH. Most will remain mild tonight, but a backdoor cold front will begin to cool things down from NE to SW overnight with the western ME mountains likely below freezing before sunrise Wednesday, possibly the foothills and Augusta area in ME as well. Patchy fog may develop overnight as moisture increases.

KEY MESSAGE 2 DESCRIPTION... The colder air will set the stage for a round of wintry precipitation as low pressure approaches Wednesday morning into Wednesday night in and around the mountains of western ME. A Winter Weather Weather Advisory has been issued for these areas for a mix of sleet and freezing rain and the threat of slick travel. Although there is less certainty toward the foothills of western ME with today's hi-res guidance, I have leaned toward the colder guidance with the CAD and erred on the side of caution to put an Advisory there as well. It's possible there may be a brief period of mixed precipitation as far south as LEW-AUG and west into northern NH...but will let the next shift take another look at things.

Timing and coverage of precip is of lower confidence, especially with southward extent as better forcing will reside across the north. Hi-res guidance suggests that precipitation may come in waves rather than just being steady so a fairly wide net has been cast on the time of the advisory.

While still remaining cool, temperatures should remain above freezing elsewhere to keep precip type as rain with fog at times.

Temperatures will gradually warm from south to north Wednesday evening/night as a warm front lifts northward that will make any lingering wintry precip switch to just rain. Expect there to be at least patchy fog as moisture continues to increase ahead of the front, and fog could be dense in some places.

The frontal passage has trended earlier for Thursday, mostly likely in the morning. A brief changeover to light snow is possible with the cold air moving in, but the more noticeable thing will be the gusty winds behind the front and temperatures dropping through the day. Based on forecast soundings, wind gusts of 30 to 40 mph look like a good bet as mixing increases behind the front.

KEY MESSAGE 3 DESCRIPTION... Over Friday, a colder system should move eastward across the Great Lakes. The low will approach New England by Saturday. Temperature profiles across the region show that precipitation should be rain/snow, with colder temperatures prevailing aloft. The dominant precipitation type will be snow, though some rain may mix in across southern NH and in coastal areas. Likewise, any meaningful snow accumulations are only possible across the interior, with most snow melting on surfaces across the south/coast. A lot of uncertainty remains, as the system is fairly weak and several ensemble members do show a drier passage of the low, with many people potentially seeing very little in the way of precipitation amounts.

Soon after the aforementioned low exits the area, another more dynamic system follows suit. On Sunday, a warm front from this system appears to move northward across the region, bringing possibly more light snow. After the warm front passes over the region, temperatures will warm up rapidly aloft. Rain may develop behind the warm front, bringing notable precipitation across the region early next week. There appears to be a potential for the system to cause river rises and ice jams as snow continues to melt across NH and Maine this week.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday...VFR should hold through at least this evening, but increasing moisture will cause conditions to deteriorate overnight with MVFR to IFR possible with fog and low stratus...possibly drizzle as well.

IFR to LIFR is then likely Wednesday morning and afternoon with fog, rain, and low stratus continuing. There could be a period of wintry mix at AUG, but the rest of the TAF sites are not expected to have wintry precipitation at this time.

Outlook: Wednesday night-Thursday...LIFR to IFR remains likely, but conditions should start to improve from west to east behind a cold front either late Wednesday night or Thursday morning. However, there could be a brief change to snow. Otherwise, VFR returns Thursday afternoon with gusty west winds (these may begin as early as Thursday morning) with 30-35 kt possible.

Thursday night: Mainly VFR expected.

Friday: VFR, but chances for restrictions/precipitation increase late in the day across northern and western terminals.

Friday night: IFR possible with light snow, especially north and west.

Saturday - Saturday night: Most sites return to VFR by the afternoon.

Sunday: Possible restrictions later in the day as another system approaches the region.

MARINE

Through Thursday...SCA conditions return Wednesday through Thursday with a brief period of gales possible late Wednesday night into early Thursday as southerly winds increase ahead of a strong cold front. A period of westerly gales may occur behind the front Wednesday afternoon. Marine fog may also return tonight, but is more likely Wednesday and Wednesday night.

Marginal westerly gales may continue into Thursday night with southerly gales then possible ahead of an approaching system Friday night. High pressure then presses in late Saturday night into Sunday, and then another low pressure system approaches the region later Sunday into Monday.

CLIMATE

Temperatures today will approach daily record highs at long term climate sites.

Site Location Forecast Temperate Record Temperature Record Year Augusta 66F 64F 2016 Concord 71F 72F 1878 Portland 66F 66F 2016

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 8 AM to 11 PM EDT Wednesday for MEZ007>009-012>014. NH...None. MARINE...Small Craft Advisory from 6 AM Wednesday to 6 AM EDT Thursday for ANZ150>154.