textproduct: Gray - Portland

SYNOPSIS

The first widespread winter storm is expected to bring a plowable snow to much of the region for Tuesday and Tuesday night. The weather will briefly turn quieter on Wednesday before an Arctic cold front brings snow squalls and breezy conditions Thursday afternoon and evening before temperatures turn sharply colder to end the week. Additional snow shower activity is possible again this weekend as a series of disturbances cross the region.

NEAR TERM /THROUGH TONIGHT/

Upslope snow showers are finally winding down and those that remain are confined largely to north of Dixville Notch and Rangeley.

The overnight will be quiet as high pressure settles over the area. Temps should radiate well early on...but high clouds will eventual win out and steady that drop. It will still be a chilly night however...with widespread readings in the teens.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/

***First Significant Winter Storm Arrives Tuesday Morning***

After a season of mainly light snowfall in the mountains and periods of upslope snow showers...the first widespread significant storm is expected Tue and Tue night.

There continues to be a narrowing of the forecast envelope towards a consensus...but significant questions remain and could seriously impact snowfall totals.

Broadly speaking model guidance agrees that this system will feature a strong jet streak in excess of 180 kt centered northeast of the forecast area. This will place us in the right entrance region of enhanced lift due to warm advection. Models also agree that the H8 mid level low will close off...but H7 remains an open wave until the storm center is closer to Nova Scotia. With that in mind I expect the mid level forcing to be good for the local area and getting better thru the event. The set up still favors a robust laterally quasi-staitonary band of snow somewhere in the forecast area. At this time I anticipate that to settle somewhere over southern NH and along or just inland of the western Maine coastline. Under the band snowfall rates may be intense at times...and 1 inch per hour or more is possible. Snowfall amounts could drop off quickly to the northwest of that due to confluence aloft and subsidence outside of the band itself.

That creates some uncertainty on the northern extent of heavy snowfall. I could see totals coming under what I have forecast...but given it will be the first plowable accumulation for many there will likely be significant travel impacts regardless. The same is true near the coast...where the NBM is insistent on warm temps and changeover to rain. I prefer colder solutions just based on the storm track and heavy precip lowering temps thru the latent cooling of melting. I did split out the coastal zones from the winter storm warning to mention the rain threat...and even if it did occur significant impacts to travel justify the headline. In the mtns and north I have issued a winter weather advisory for lighter snowfall amounts.

Late Tue night the storm will pull away and winds flip northwesterly and become gusty. That will bring a quick end to snowfall.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Key Messages: * Temperatures are expected to remain at or below normal through the long term period.

* Arctic front will bring the potential for snow squalls Thursday afternoon and evening...followed by bitterly cold wind chills Thursday Night.

* Uncertainty with regards to any potential weekend storminess. Recent trend favors a lower chance for impactful weather this weekend.

Details: Mid/upper level vortex centered around Hudson Bay will remain stationary into the weekend before splitting with a chunk sliding towards the south and east by the end of this forecast period. Shortwave features rotating around this broader trough form the focus for potential impactful weather through this period with a potent Arctic cold front poised to sweep through the forecast area Thursday afternoon and evening. The next wave looks to approach over the weekend...with significant spread in the guidance with regards to the degree of phasing between this wave and the southern stream...which yields a variety of possible solutions through this period. Regardless of the weekend outcome... guidance spread decreases heading into the beginning of next week with a return to chilly northwest flow aloft.

Thursday: Arctic frontal timing Thursday afternoon suggests decent llevel instability may be in play to support snow squalls. At the same time...good isallobaric push behind the front along with H9 winds around 30kts support 30-35mph gusts along and behind the front as T8s drop below -20C Thursday night. Expect lows in the single digits Thursday night in this airmass....with wind chills below zero throughout the forecast area overnight.

This Weekend: A series of shortwaves will rapidly move through the region this weekend. The guidance trend over the past 24-48 hours has been less phasing between the northern and southern streams which would result in a drier solution for Saturday...followed by another arctic cold frontal passage Sunday with additional snow showers /squalls?/ possible with temperatures turning well below normal as we begin the new work week.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Short Term...VFR conditions prevail thru tonight. Precip rapidly approaches Tue morning and conditions will largely drop from VFR to IFR or lower as it arrives. I anticipate mostly snow for the TAF sites...but there is a threat that rain may mix at PSM...PWM...and RKD if the strongest and farthest northwest storm tracks end up verifying. Regardless IFR conditions are most likely during the storm as well as a period of snow for all terminals south of the mtns that may be heavy at times. Snowfall rates may exceed 1 inch per hour along with visibility one quarter mile or less. As the storm pulls away we return to VFR except for HIE where MVFR CIGs continue. In addition surface wind gusts in excess of 25 kt are possible...especially closer to the coast.

Long Term...VFR conditions expected Wednesday through Thursday morning. Strong cold front brings the potential for isolated/scattered MVFR/IFR restrictions in snow squalls Thursday afternoon and evening with gusty northwest winds in it/s wake through Thursday night. VFR conditions Friday with gusty northwest winds diminishing during the day. Most likely solution is for VFR conditions to continue into Saturday...but there is a low chance for additional snowfall...or snow shower activity.

MARINE

Short Term...Gusty northwest winds continue this afternoon with SCAs on all waters. High pressure will crest overhead tonight and allow winds and seas to diminish for a brief period. Then a strong/deepening coastal storm will cross the edge of the Gulf of Maine and bring another round of increasing winds. SCAs are likely...but a small period of gale force wind gusts are possible overnight Tue. I have issued a gale watch for those areas outside the bays for that threat.

Long Term...Winds diminish Wednesday with lingering SCA waves into Wednesday night with winds shifting southwesterly and strengthening back to 25- 30kts from the southwest Thursday morning before shifting northwest with gale force gusts becoming increasingly likely by Thursday afternoon and through Thursday night. Winds and waves subside on Friday...and currently look to remain below SCA levels into Saturday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 8 AM Tuesday to 4 AM EST Wednesday for MEZ007>009. Winter Storm Warning from 8 AM Tuesday to 4 AM EST Wednesday for MEZ012>014-018>028-033. NH...Winter Weather Advisory from 8 AM Tuesday to 4 AM EST Wednesday for NHZ001>003. Winter Storm Warning from 8 AM Tuesday to 4 AM EST Wednesday for NHZ004>015. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ150>154. Gale Watch from Tuesday evening through Wednesday morning for ANZ150-152-154.