textproduct: Gray - Portland

WHAT HAS CHANGED

Little has changed in the short term portion of the forecast as very cold air is is expected to pour into the region during the day today, particularly the afternoon. Cold weather headlines remain in effect. Confidence continues to grow for a impactful snow storm Sunday through Monday across the forecast area.

KEY MESSAGES

1. An Arctic blast will bring dangerously cold weather to the region this weekend. Sub-zero wind chills begin Friday night and last through the day Saturday. It will still feel below zero come Sunday morning despite lighter winds. Frostbite and hypothermia can onset quickly at these temperatures for anyone with exposed skin or inadequate shelter.

2. A significant snow storm will bring widespread accumulating snowfall to the region late Sunday through Monday. All snow is expected, which will bring hazardous travel conditions through the Monday morning commute. The greatest snowfall amounts are likely across the southern half of the forecast area.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION:

Arctic cold front located over eastern Ontario and southwestern Quebec early this morning will move southeastward and across our region during the afternoon and evening hours today. Brutal cold will pour into New England in the wake of this front late today and tonight on gusty NW winds. Wind chill values will be dangerous and well below zero for most of the forecast area. As such, extreme cold weather warnings and advisories remain in effect for tonight into Saturday morning.

In addition, several CAMs show the potential for scattered to numerous snow showers and squalls this afternoon which could cause for locally slippery travel and brief very low visibilities.

KEY MESSAGE 2 DESCRIPTION: Guidance tonight displays a strong area of low pressure exiting the Mid-Atlantic coast Sunday evening, tracking outside of Cape Cod Monday, and towards/just east of Nova Scotia by Monday evening. This would bring a broad precip shield of snow south to north across the forecast area Sunday afternoon/evening through Monday evening. Cold temperatures in place will ensure an all snow event, with increased snow ratios creating a fluffy snow character. Residence time of net lift and moisture will bring persistent snowfall, with potential embedded banding increasing snow rates and localized amounts. While a fluffy and impactful, significant snowfall is of increased confidence, we are still a couple days removed from the event to solidify snow totals, periods of enhanced rates, and locations of these two. That said, at least 6 inches of snow is likely for much of the area, with higher amounts most likely towards the southern half of the forecast area.

The system will have brought significant travel disruption to much of the central CONUS, with its East Coast chapter being the final act. Within this winter storm, there are a handful of notable features. Strong jet dynamics will be present ahead and during this storm. A digging trough across the Midwest sets in motion the strengthening of mid/upper jet across the TN Valley, with exit region into New England. This couples with entrance region of departing upper jet across the Canadian Maritimes, creating a broad area of lift across northern New England as low pressure deepens off the coast.

Anomalous moisture transport will be moving across the south and then up the East Coast. Upwards of 1400 kg/m/s of IVT tracks across the Deep South and then the Mid-Atlantic coast, supplying the deepening storm with plenty of moisture feed. The mere proximity to this moisture advection will mean a powerful conversion when the cold airmass overhead can support snow to liquid ratios north of 15 to 1. NBM mean brings values towards 18-20 to 1 into the region.

A trend towards double digit totals can't be ignored for a portion of the southern forecast area, but would like to emphasize that at this range shifts in track can mean a lot for any individual location's storm totals. Will continue with previous Winter Storm Watch area at this time, but extended probabilities do support future expansion of a Watch for much of the CWA.

AVIATION /02Z FRIDAY THROUGH TUESDAY/

Today: VFR expected this morning but occasional brief MVFR/IFR conditions in snow showers is expected. Westerly winds will gust around 25 kt much of the day across southern NH followed by the rest of the CWA getting 25 to 30 kt gusts later on in the afternoon.

Tonight: VFR expected.

Saturday: VFR prevails at all terminals. WNW winds at 15-20 kts.

Sunday and Sunday Night: VFR Sunday morning transitioning to MVFR and then at least IFR Sunday afternoon as snow overspreads from south to north. IFR to LIFR likely Sunday night in moderate to heavy snow.

Monday and Monday Night: IFR to LIFR likely Monday as moderate to heavy snow continues. Snow gradually ends Monday night while IFR likely continues with improvement possible into Tuesday morning.

Tuesday: VFR likely.

MARINE

SCA westerly winds are expected this morning. Gales then develop by this afternoon and continue into early Saturday morning. Heavy freezing spray will be possible at times tonight into Saturday, especially off the Midcoast and they bays where water temperatures are colder. Winds and seas drop below SCA thresholds late Saturday night.

Northeast winds increase Sunday as low pressure tracks from the Mid Atlantic towards Cape Cod. Northeast winds will likely bring Gales over the waters Sunday night into Monday night as low pressure slowly tracks along the outer Gulf of Maine with seas building in excess of ten feet. Winds shift northwesterly Monday night through Tuesday with SCAs likely needed for these NW winds.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Extreme Cold Warning from 1 AM to 10 AM EST Saturday for MEZ007>009-012>014-033. Cold Weather Advisory from 1 AM to 10 AM EST Saturday for MEZ018>028. Winter Storm Watch from Sunday afternoon through Monday evening for MEZ018-019-023-024. NH...Extreme Cold Warning from 1 AM to 10 AM EST Saturday for NHZ001>006-009. Cold Weather Advisory from 1 AM to 10 AM EST Saturday for NHZ007-008-010>015. Winter Storm Watch from Sunday afternoon through Monday evening for NHZ005>015. MARINE...Gale Warning until 7 AM EST Saturday for ANZ150-152. Heavy Freezing Spray Warning from 10 PM Friday to 11 AM EST Saturday for ANZ150>153. Small Craft Advisory until 7 AM EST Saturday for ANZ151-153. Small Craft Advisory until 1 PM EST Friday for ANZ154. Gale Warning from 1 PM Friday to 7 AM EST Saturday for ANZ154. Freezing Spray Advisory from 10 PM Friday to 10 AM EST Sunday for ANZ154.