textproduct: Gray - Portland

WHAT HAS CHANGED

Snowfall totals have increased resulting in coastal Rockingham County being upgraded to a Winter Storm Warning. No other changes to the remaining headlines in effect.

Increased PoPs some for southern areas based on latest observational trends.

KEY MESSAGES

1. Light snow has developed across much of the area early this morning. Periods of light snow will continue on and off into this afternoon. Across southern New Hampshire into coastal York County periods of moderate to heavy snow are likely due to ocean enhancement from the pre dawn hours into early Saturday afternoon. Slick travel will be possible across much of the area and difficult travel for areas in the Winter Storm Warning and Advisories.

2. A frigid airmass will push across the Northeast this weekend, resulting in dangerous wind chill values tonight and Sunday night. Widespread temperatures below zero overnight are expected, with gusty winds making it feel like the teens below zero from the coast to the foothills, and 20 to 30 below zero for the western third of the forecast area.

3. Temperatures moderate through the balance of next week to near normal. The next chance for some light precipitation will arrive Tuesday night into Wednesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Light snow has developed across much of the area as of this writing as an approaching short wave is spreading forcing for ascent over New England. Models have not captured this early snowfall well and there continues to be a significant spread in the location of moderate to heavy snow associated with an inverted trough that develops over the next 6 to 12 hours. Overall, the NBM and HREF have generally increased QPF over past runs and this is represented in the latest forecast. Areas from Cape Porpoise to Cape Ann and towards the lower Merrimack Valley seem to be favored for seeing variable snowfall rates approaching 1 inch per hour after sunrise through early afternoon.

There has not been much change in the mesoscale meteorology with strong lift and decent moisture within the dendritic growth zone that will produce snow ratios of 15:1 to 18:1. Again close to the coast some low level instability will bring the potential for snowfall rates pushing 2 inches an hour with the latest HREF show a slight uptick in these probabilities. The combination of early light snow and uptick in QPF has resulted in Storm Total Snowfall increasing uniformly across the forecast area. For areas within the Winter Weather Advisory amounts will be in the 3-5 inch range with amounts decreasing to the north and east. Snowfall amounts across eastern Rockingham County into far southern York County are forecast to be 6-8 inches with potential for locally higher amounts. I have upgraded coastal Rockingham County to a Winter Storm Warning based on these higher snowfall amounts, but it should be noted that areas around the warning could see amounts in excess of 6 inches.

Snowfall will gradually taper off this afternoon.

KEY MESSAGE 2 DESCRIPTION... Forecast is still on track for Saturday and Sunday nights to feature well below normal temperatures and gusty winds, resulting in dangerously cold wind chills.

A deepening mid-level trough over the eastern US will allow for bitterly cold air to move into the area Saturday evening. A cold front moves through the area Saturday afternoon, bringing some snowfall. After the frontal passage, gusty northwesterly winds will kick in, allowing for an arctic airmass to advect across the northeast.

The combination of both a bitterly cold airmass and gusty winds will create a couple exceptionally chilly nights Saturday and Sunday night. The coldest of this airmass looks to anchor itself across just west of the area, so the coldest readings across NH and Maine should be across western NH and interior western Maine. Low temperatures are generally expected in the single digits, below 0F across the west and above 0F out to the east in the Midcoast and Central Maine. The additional wind gusts should allow temperatures to feel as cold as -25F across western areas, -15F elsewhere.

Wind chill values this cold can lead to frostbite in as little as 10 to 20 minutes on exposed skin. Any outdoor activities Saturday night should be accompanied with plans if getting stranded outside is a possibility. This is especially true for higher elevations, particularly the Whites, where wind chill values could fall to 30 to 40 below given stronger winds here.

KEY MESSAGE 3 DESCRIPTION... High pressure builds in Monday and settles south of New England Tuesday. This will set up milder southwest flow over New England allowing for a warming trend. Global models are in decent agreement that a low amplitude short wave will track east out of the Great Lakes Tuesday night that will bring our next chance at widespread precipitation centered on Wednesday. Temperatures will be close to freezing as this system approaches so the track of any surface low will determine precipitation types. Latest available NWP guidance suggest a weak low passing over southern New England that would result in light snow.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Through 12Z Sunday: Ceilings continue to lower through this morning with light snow. Periods of moderate to heavy snow possible locally at KPSM and KMHT. KPWM to KAUG will be the edge of MVFR/VFR to the east and IFR to the west in SN through this afternoon. A cold front will begin pushing across the forecast area during this afternoon. This will result in a quick increase in NW winds gusting 25 to 30 kt with perhaps some BLSN. At the moment, this looks to impact NH TAF locations the most through this evening.

Outlook...

Sunday Night: Mainly VFR conditions with some MVFR CIGS possible at KHIE. NW gusts to 25 kts through early evening. No sig wx.

Monday: VFR. No sig wx. NW winds 10 to 20 kts.

Monday night and Tuesday: VFR. No sig wx.

Tuesday night: VFR, ceilings will be thickening and lowering. Light SN possibly approaching the region.

Wednesday: Light SN possible.

MARINE

Northeast flow increases this morning with gusts approaching 25 kts by early afternoon. Periods of moderate to heavy snow are likely through the morning that will bring sharp reductions in visibility. Snow ends this evening as strong cold front crosses. Behind the front, NW winds will bring Gale conditions and moderate freezing spray into Sunday. Offshore winds remain around 30 kts into Sunday night with continued moderate freezing spray. High pressure builds in Monday and Tuesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Cold Weather Advisory from 6 PM this evening to 10 AM EST Sunday for MEZ007>009-012-013-018-019-033. Winter Weather Advisory until 6 PM EST this evening for MEZ023. NH...Cold Weather Advisory from 6 PM this evening to 10 AM EST Sunday for NHZ001>006-009-010-012-013. Winter Weather Advisory until 6 PM EST this evening for NHZ008>010-012-013-015. Extreme Cold Warning from 6 PM this evening to 10 AM EST Sunday for NHZ007-008-011-015. Winter Storm Warning until 6 PM EST this evening for NHZ014. MARINE...Gale Warning from 2 PM this afternoon to 1 PM EST Sunday for ANZ150>154. Freezing Spray Advisory from 7 PM this evening to 7 AM EST Monday for ANZ150>154.