textproduct: Gray - Portland

WHAT HAS CHANGED

Minor update to near term forecast to reflect observational trends.

KEY MESSAGES

1. Snow tapers off this afternoon. A strong cold front will bring much colder temperatures to the region through Sunday night. Accompanying this airmass will be gusty winds that will create dangerously cold wind chill values tonight. Frostbite can begin shortly after direct skin exposure at these values.

2. There is a chance of light snow Tuesday into Wednesday. The timing may be such that it impacts the evening commute on Tuesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... While much of the sharper convergence with enhanced reflectivity and snowfall rates settled south of the forecast area today, there was a narrow corridor that set up. This was between morning onshore flow and the advancing front from the west. This ended up being through the Merrimack Valley where visibility was a mile or less for much of the mid morning to early afternoon.

The incoming front isn't very 'clean' in regards to satellite or radar presentation, but it has been notable in the wind field and advection of drier air to bring an end to moderate snow rates. The winding nature of it will keep some light snow going across northern NH and western ME for a couple more hours.

For this evening, north winds increase and temperatures plummet. There hasn't been much change in the forecast as far as temperatures and resulting wind chill values go, and headlines remain in place. To the west, winds have been running a bit above guidance, so did increase overnight wind speeds which again brings some of the lower wind chill values into the lowlands. Forecast winds did lower for points along/near the Maine/CAN border. This results in values barely meeting Advisory criteria for the region, but not enough to remove the hazard altogether. Coldest wind chill values of 30 to 40 below will be felt at higher elevations and throughout the Whites given their exposure to stronger winds.

Daytime highs Sunday have trended 'warmer' but a day in the single digits to low 20s with a brisk wind won't feel much different. This combo of temp and wind results in wind chill values in the single digits above and below zero through the day.

For Sunday night, winds continue with the cold airmass still overhead. The tighter pressure gradient will have departed, but there will still be an embedded wave that pivots through the exiting cyclonic flow. This will keep Sun night breezy, but not expecting the same magnitude of gusts like tonight. Can see the need for additional cold weather headlines for Sunday night as wind chills fall into the teens below zero across the interior and foothills to and 20s below zero in the mountains and north/western valleys.

KEY MESSAGE 2 DESCRIPTION... Shortwave trof/closed upper low approaches the region Tue. Warm advection ahead of it will support lift in a saturated snow growth region. This should result in a band of snow translating across the forecast area on a roughly northwest to southeast oriented axis. About 90 percent of ensemble members show accumulation less than 4 inches, but the current timing is for Tue evening. This could be a tricky during the commute, especially as we lose any melting influence of the sun thru the cloud cover. I could see a need, if the timing remains consistent, for an impact- based advisory for parts of the area due to roads becoming snow covered during a peak travel window.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through Sunday: Conditions have largely improved to VFR with VFR likely to prevail into Sunday. A cold front has now crossed much of the area with gusty NW winds to around 20 to 30 kts, continuing Sunday. Winds slacken into Sunday evening, but steady winds should continue. Otherwise VFR.

Outlook...

Sunday Night: VFR expected with WNW winds 10 to 20 kts.

Monday: VFR conditions expected.

Monday Night: VFR conditions expected.

Tuesday: Increasing clouds and lowering CIGs but mostly VFR expected thru evening.

Tuesday Night: Areas of IFR in light snow.

Wednesday: IFR conditions improving but may continue to be local IFR or lower in snow showers.

Wednesday Night: VFR conditions expected.

Thursday: VFR conditions expected.

MARINE

A strong cold front will bring Gale conditions tonight. The combination of cold airmass and gusty winds will create an extended period of moderate freezing spray through Sunday and Sunday night. Winds slacken Sunday, but may again approach Gale come Sunday evening for waters along the Midcoast.

Winds and seas will continue to diminish Mon. Some lingering moderate freezing spray is anticipated before winds and seas come down, and cold temps depart the region. Otherwise winds and seas expected to remain below SCA thresholds.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Cold Weather Advisory until 10 AM EST Sunday for MEZ007>009- 012-013-018-019-033. NH...Cold Weather Advisory until 10 AM EST Sunday for NHZ001>006- 009-010-012-013. Extreme Cold Warning until 10 AM EST Sunday for NHZ007-008-011- 015. MARINE...Gale Warning until 1 PM EST Sunday for ANZ150>154. Freezing Spray Advisory until 7 AM EST Monday for ANZ150>154.