textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update. Just incorporated the latest observations into the near term and updated the aviation discussion.

KEY MESSAGES

1. A weak disturbance will lead to some isolated snow showers early today, mainly in the mountains. Expect a very gradual cooling trend through the end of the work week.

2. Some slippery travel possible Friday night into Saturday with a minor snow event expected to bring a coating to 2 inches.

3. Well below normal temperatures return as the day progresses Saturday. Bitterly cold temps will combine with gusty winds to produce dangerous wind chills. An extreme cold watch is in effect for some zones.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

The next weak shortwave approaches early this morning in the wake of progressive ridging. Moisture will be even more limited with this system than the previous one, but there should be enough lift for some isolated snow showers in the mountains through at least the first part of the day. By the afternoon, surface high pressure moves in which should limit the coverage of snow showers later in the day. Friday should mainly be dry during the day.

Temperatures today will be just a little bit cooler than they were yesterday with afternoon highs ranging from the low to mid teens across the north country and western Maine mountains, to the 20s elsewhere. A few readings in the lower 30s will be possible over coastal areas. Decent radiational cooling may be possible in some spots tonight into Friday morning with light winds and weak high pressure in place. However, guidance is still a bit uncertain regarding how much cloud cover there will be so that will be something to watch. At the moment, lows Friday morning are expected to range from around 10 below zero across portions of northern NH and northwest/west central Maine, to around zero or a couple of degrees above south and along the coast. Highs on Friday will actually be a little bit warmer in the mountains and valleys while areas south of the mountains will actually be a touch cooler. The NBM has readings mainly ranging from the upper teens and lower 20s north, to the mid 20s south.

KEY MESSAGE 2 DESCRIPTION...

No significant changes to the light snow forecast for Friday night and Saturday. WAA out ahead of the next arctic air mass will aid in the development of light snow Friday night which will be on and off through Saturday as upper level low pressure moves overhead. The system will the moisture-starved, so a coating to two inches should cover it.

KEY MESSAGE 3 DESCRIPTION...

The next and probably most important key message is the return of arctic air Saturday into Monday. With the passage of the arctic boundary on Saturday, temperatures will likely steadily fall during the afternoon as winds increase. This will be especially true in the interior. Some snow squalls are not out of the question.

Latest forecast soundings indicate that wind gusts Saturday afternoon and night have the potential to gust around 35 MPH, if not briefly slightly more.

Temperatures remain below normal but start to recover Monday, and by Tuesday guidance favors returning to near or even slightly above normal temps.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through 12Z Friday...HIE should improve to VFR later this morning and then VFR conditions can be expected through Friday afternoon. That being said ceilings will thicken and lower heading toward daybreak Friday morning.

Outlook:

Friday Night: MVFR to local IFR conditions expected in light snow Friday night into Saturday.

Saturday: Areas of IFR or lower are possible in snow/snow showers especially near the coast early on. Second half of day westerly wind gusts of 25 kt or more possible.

Saturday Night: VFR conditions expected south of the mtns, local IFR conditions in the mtns. Westerly wind gusts of 30 kt or more possible.

Sunday: VFR conditions expected. Westerly wind gusts of 30 kt or more possible.

Sunday Night: VFR conditions expected.

Monday: VFR conditions expected.

MARINE

Today through Friday: Offshore winds will shift from out of the northwest to out of the north tonight, and eventually to out of the northeast by Friday. Winds will generally max out in the 10 to 15 knot range. Some light freezing spray will be possible this morning and again tonight into Friday morning.

A strong cold front will cross the waters Sat. Westerly winds will increase sharply and become gusty. Gale force conditions are possible, and as such a gale watch has been issued for all zones. Temps will also fall into the single digits and moderate to heavy freezing spray will develop beginning Sat night. The gusty winds and at least areas of moderate freezing spray continue into Mon.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Extreme Cold Watch from Saturday evening through Sunday afternoon for MEZ007>009. NH...Extreme Cold Watch from Saturday evening through Sunday afternoon for NHZ001>003-005-007. MARINE...Gale Watch from Saturday afternoon through Sunday afternoon for ANZ150>154.