textproduct: Gray - Portland

SYNOPSIS

A strong cold front will barrel through the region during the day Thursday. Heavy snow showers and squalls along the front will give way to gusty winds into the overnight. Temperatures will fall from the 30s into the single digits and even below zero in places by Friday morning. Wind chills even at the coast will be below zero. High pressure will arrive later Friday and more seasonable temperatures return Saturday.

NEAR TERM /UNTIL 6 AM THURSDAY MORNING/

7 PM Update...Quiet weather continues tonight other than some high level clouds moving in ahead of the cold front that will cross the region Thursday.

Previously...

Quiet period of weather tonight as the atmosphere reloads after our storm. Temps will be cool but with increasing cloud cover and southwest winds that should prevent any extreme radiational cooling.

SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/

Thu around midday our next weather maker arrives in the form of a strong Arctic cold front. There may be some warm advection snow shower activity ahead of the front...but most of what precip does fall will occur along the front. Conditions look favorable for heavy snow showers/squalls along the front. It will be a well mixed and gusty environment with low static stability and temps falling thru freezing. The set up is ripe for snow squalls that make the roads a mess as readings fall into the 20s behind the front. It is not surprising that the snow squall parameter is lighting up across the region. I have blended some hi-res CAM guidance into the NBM to highlight the potential timing of showers thru the forecast area.

Behind the front it will get gusty. Bufkit soundings suggest 30 to 35 mph possible. The NBM was a bit too low based on these forecast...so I once again included some higher res guidance to beef the winds up.

The winds will also coming with plummeting temps. By Fri morning widespread single digits are expected going below zero north of the mtns. Ensemble guidance is all in agreement on an anomalous air mass...with extreme temps for this time of year possible. This matches up well with NBM forecasts of record or near-record temps...see climate section below. With the cold temps and continued gradient winds...wind chills may approach 20 below in the northern zones Thu night. Not sold that we stay that windy overnight so I will let the midnight shift get another look before issuing any cold weather headlines.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

Behind the arctic front, expansive high pressure will be settling in across the region to start the long term period. Frigid temperatures will be ongoing Friday morning with lows mainly in the single digits below zero across the north, to the single digits above south. While the pressure gradient will be relaxing, some winds in the 10 to 15 mph range will lead to some frigid wind chills sticking around through the morning hours.

Cold temperatures will hang around through the day under near zonal flow aloft. Highs will only range from the lower teens to lower 20s for most, but we could see a few single digits in/around the mountains and some mid 20s along the coast.

Low amplitude ridging will cross the forecast area Friday night into Saturday and then we transition back into southwest flow aloft as a closed upper level Hudson Bay low starts to rotate troughing into the region. While most of the forcing should generally stay out of our area, we could see enough of a glancing blow to bring in at least low chances of light snow (~20 to 30 percent) on Saturday. Highs on Saturday will be a little bit warmer, mainly ranging from the lower 20s to the lower 30s. Mean troughing sticks around through at least Sunday behind a surface cold front, potentially bringing some upslope snow showers to the mountains and vicinity. Highs will be another touch warmer on Sunday, mainly ranging from the mid 20s to mid 30s.

The start of the new work week will be chilly behind the front with highs mainly ranging from the lower teens to the lower 20s on Monday and the mid teens to the mid 20s on Tuesday. Monday and Tuesday mornings will likely see widespread wind chill values in the single digits below zero. A few areas in the higher terrain will probably see wind chills in the double digits below zero at times.

Looking ahead, the next chance for widespread precipitation looks to come mid to late week. That being said, it is still way too early for specific details this far out.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Short Term...VFR conditions thru tonight ahead of the next cold front. That Arctic boundary will drive thru the region Thu and bring a chance for heavy snow showers/squalls and brief local IFR or lower conditions. Behind the front surface wind gusts up to 30 kt are possible into Thu night. Northwest of the mtns some lingering MVFR CIGs are possible in upslope flow/snow showers.

Long Term...Winds should be relaxing Friday morning. A few snow showers will be possible on Saturday with some sticking around in and around the mountains on Sunday. Localized restrictions could be possible if any of these showers move directly overhead. Otherwise, mainly VFR conditions are expected along with winds generally below 20 kts.

MARINE

Short Term...Winds and seas continue to slowly diminish this evening...but the break in winds will be brief. A strong cold front will blast across the waters Thu afternoon and strong wind gusts are anticipated behind it. Gale warnings have been issued for all waters into Thu night. While waters are still relatively warm...the coming air mass will be quite cold and some pockets of freezing spray are not out of the question.

Long Term...Wind and seas should be relaxing Friday morning and into the weekend. Winds and seas should largely remain below SCA criteria through at least mid to late next week.

CLIMATE

This air mass on Fri morning will be anomalously cold and low temps will approach records. This will especially be true at PWM where the forecast is 4 degrees and the previous record is 7 in both 1989 and 1945. The forecast at AUG is 5 degrees and the previous record is 4 set in both 1989 and 1991.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning from 3 PM Thursday to 7 AM EST Friday for ANZ150- 152-154. Gale Warning from 3 PM Thursday to 1 AM EST Friday for ANZ151- 153.