textproduct: Caribou

WHAT HAS CHANGED

Increasing confidence in timing of abrupt return of cold air Thursday night into Friday morning - and hence likelihood of a flash freeze.

Low chance of a winter storm Sunday night into Monday but significant uncertainty still exists in the ensembles.

KEY MESSAGES

1) Rain with fog tonight and Thursday (Wintry mix with fog far NW) will result in reduced visibilities at times, making travel potentially difficult. In the far NW, wintry mix could make any untreated roadways slippery as well, especially at higher elevations.

2) Flash freeze likely Thursday night into Friday morning from NW to SE, with possibly 1-3 inches of snow on top of that across the North. A rapid fall off of temperatures will cause the rapid freeze of slush and wet surfaces into ice. This will make for difficult travel for any untreated surfaces, especially those covered by any snowfall across the North.

3) Active weather pattern this weekend through early next week, including a low potential for a significant winter storm Monday, but significant uncertainty on storm track and evolution.

DISCUSSION

KEY MESSAGE 1... Rain with fog tonight and Thursday (Wintry mix with fog far NW) will result in reduced visibilities at times, making travel potentially difficult. In the far NW, wintry mix could make any untreated roadways slippery as well, especially at higher elevations.

KEY MESSAGE 1 DESCRIPTION... Northern stream shortwave ridging transiting the area this evening, will hold the bulk of the precipitation off until after midnight across the North, with rain moving in across central and southern regions this evening the region in response to a northern stream shortwave undercutting that ridging. During this time frame, strengthening onshore flow will advect in milder, moister air from the Gulf of Maine, allowing for patches to possibly areas of fog to develop. Rain overspreads the North mainly after midnight, with a wintry mix over NW zones. There could be a period of some freezing rain in the transition to a more rain/snow mix (likely elevation dependent with areas above 1500 ft more likely to be snow than rain) - however confidence in this is not high enough to issue a winter weather advisory at this time. Fortunately any freezing rain is forecast to occur in the sparsely populated area west of the route 11 corridor in the North Woods. Will continue to monitor and will address with an SPS or short fused advisory if confidence in occurrence increases. Precipitation tapers off from S to N as the 925-850 mb warm front lifts to the N mainly in the afternoon on Thursday. This could leave patchy drizzle in its wake, but confidence in this is not high enough to reflect in the forecast at this time.

Also confidence in how low visibilities will get in the patches to possibly areas of fog is not great - likely will get into the 1-3 mile range but could fall below 1 mile. Locally dense fog cannot be completely ruled out, especially over the deeper snowpacks across the North.

Temperatures should slowly rise or hold steady through the night, with lows likely to occur this evening, with lows mainly in the 30s. On Thursday, temperatures will rise only a few degrees, if that across the North with a rise of around 5 degrees farther S. Temperatures begin to rapidly fall off across far NW zones later in the afternoon to the low-mid 20s with any lingering precipitation there becoming fairly quickly all snow as the cold front moves to the east.

KEY MESSAGE 2...Flash freeze likely Thursday night into Friday morning from NW to SE, with possibly 1-3 inches of snow on top of that across the North. A rapid fall off of temperatures will cause the rapid freeze of slush and wet surfaces into ice. This will make for difficult travel for any untreated surfaces, especially those covered by any snowfall across the North.

KEY MESSAGE 2 DESCRIPTION... A closed mid-upper level low moves over Maine Thursday night then exits to the east Friday morning. There is some question how far S the center of this low gets. This will determine over how much of the roughly northern 1/2 of the area will see lingering snowfall Thursday night into Friday morning. There is the potential for 1-3 inches of snow across at least portions of the North during this time frame. If it occurs, it will fall on top off any slush or untreated wet surfaces which rapidly froze as temperatures plummet Thursday night/early Friday morning. This will make travel potentially dangerous late Thursday night and for the Friday morning commute across the North.

Temperatures fall off into the single digits to mid teens across the North by Friday morning and to the mid teens to lower 20s elsewhere. Wind chills by Friday morning should be from around 5 below to around 10 above across the North and low to mid teens elsewhere as NW winds increase overnight with gusts of 20-35mph. Some patchy blowing snow possible Friday in response to the gusty winds, mainly in the northern agricultural areas.

KEY MESSAGE 3... Active weather pattern this weekend through early next week, including a low potential for a significant winter storm Monday, but significant uncertainty on storm track and evolution.

KEY MESSAGE 3 DESCRIPTION... A positive PNA will contribute to a pattern of longwave troughing over the central and eastern US with a ridge over the western US. This should result in a relatively active pattern for Maine this weekend through early next week. Low pressure passing through the area is likely to bring some light precipitation to the region this weekend but most notably there is a weak signal in the deterministic and ensemble models for a potentially impactful winter storm during the Sunday night -Monday time frame. While the GFS is showing a powerful storm just offshore in the Gulf of Maine, ensembles are far less bullish with less than 25% of the GEFS and EPS members showing an impactful winter storm so currently have quite low confidence. Working against such a storm is an expected neutral to slightly positive NAO which would generally favor a stronger, more zonal jet stream, keeping the low weaker and farther offshore. Behind this system, ensembles point towards cold air moving in with below average temperatures.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR to get started, except MVFR at KFVE which should improve to VFR later this afternoon. Conditions deteriorate to MVFR then IFR tonight and remain at IFR or lower through the remainder of the TAF period. Other than possibly a period of rain/snow mix late tonight/early Thursday morning at KFVE, the precipitation type should be all rain. Any gusty winds should abate by mid- late afternoon then winds become light and variable throughout early this evening, and remain so through the TAF period.

Late Thursday afternoon...IFR or lower possible. S-SW winds G15-20KT possible late.

Thursday night...Improving to MVFR North and MVFR at southern terminals. SW winds G15-20KT possible.

Friday...Intially MVFR/IFR with -SN at northern terms, mainly in the morning. VFR south. Expecting VCSH/-SHSN but mainly trending to VFR conditions. Cannot rule out SCT MVFR cigs at northern terms in the afternoon. W winds 5 to15 kts with gusts up to 25 kts. DRSN possible at northern terms for the afternoon hours.

Fri Night...VFR. W winds becoming S around 5 kts.

Saturday...VFR/MVFR northern terminals. MVFR/IFR southern terminals in light snow and possibly rain. S/SW winds 5 to 10 kts.

Sat Night...VFR/MVFR with IFR also possible. -SN possible but confidence is low. Winds light and variable.

Sunday...VFR/MVFR with a low chance of IFR. -SHSN possible but confidence is low. Winds W/SW 5 to 10 kts.

Sun Night...VFR/MVFR with a low chance of IFR, especially for southern terminals. -SN possible, especially for southern terminals. NW winds 5 to 10 kts.

MARINE

Have cancelled the SCA over the intra-coastal waters as winds and seas have fallen below SCA thresholds. For the coastal ocean waters have continued the existing SCA through 1AM tonight, mainly, if not entirely for seas. Conditions become sub-SCA throughout overnight and remain so Thursday morning. Winds could increase to SCA levels over the coastal ocean waters Thursday afternoon and on all waters Thursday evening. Gales are likely Thursday night, including the southern most portion of the intra-coastal waters, so have issued a gale watch starting at 6z Friday.

Winds decrease below gale criteria Friday evening with small craft winds continuing through Saturday evening. Small craft conditions borderline through Sunday but should return Sunday night. Seas decrease from 6 to 10 ft Friday to 4 to 6 ft Saturday night through Sunday night. Light freezing spray expected Friday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory until 1 AM EST Thursday for ANZ050-051. Gale Watch from late Thursday night through Friday afternoon for ANZ050>052.