textproduct: Boston / Norton

WHAT HAS CHANGED

Increased confidence in a period of icing Saturday night into Sunday morning across the highest terrain of northern Massachusetts. Confidence increasing in a period of northwest wind gusts of 35 to 50 mph Sunday night especially during the overnight hours along with a brief shot of colder weather. Gale Watches also issued for all waters Sunday night into Monday morning. Milder temperatures return Tuesday and Wednesday before a pattern change to colder and perhaps some unsettled weather arrives by late next week.

KEY MESSAGES

- Period of showers and light rain tonight.

- Soaking rain arrives later Saturday into early Sunday. Rain for most areas with an increasing chance for icing across the highest terrain in Northern Massachusetts.

- Becoming windy & turning colder Sun night into Mon with a period of NW wind gusts of 35 to 50 mph possible later Sun night. Low risk for a brief snow squall too.

- Milder temperatures quickly return Tue and especially by Wed when highs may approach 50 in some locations.

- Turning colder Thu into Fri and will have to watch an offshore storm for the potential of mixed precipitation/snow if it tracks close enough to the coast.

DISCUSSION

KEY MESSAGE 1...Period of showers and light rain tonight.

Weak frontal boundary passes through southern New England tonight with a broken band of showers and steady rain. Still not expecting much in terms of totals or intensity although rain may extend into early Saturday morning across the Cape and Islands. As mentioned previously, the best forcing is displaced well north, across northern New England and southern Quebec. Still, a few light rain showers arrive across western Massachusetts and Connecticut between 5 PM and 7 PM, then central and eastern Massachusetts and Rhode Island between 7 PM and 9 PM. Despite higher than normal PWATs, do not expect much QPF, once again due to lack of forcing. Rain totals range between 0.1" and 0.2". Showers exit off the coast between 12 AM and 3 AM Saturday as the trailing cold front pushes through the region. Not as cold, lows are in the middle to upper-30s. Though, the Berkshires likely drop to the low-30s, here there would be a threat of black ice overnight.

KEY MESSAGE 2...Soaking rain arrives later Saturday into early Sunday. Rain for most areas with an increasing chance for icing across the highest terrain in Northern Massachusetts.

More significant system moves towards the region later Saturday. Parent low over the Great Lakes moves NE as a secondary low develops just S of New England. Notable feature with this system will be an enhanced SW jet will help transport above normal moisture into southern New England, around 230-280 percent of normal. This will set the stage for a soaking rain for southern New England. Rain will likely arrive in the afternoon spreading from south to north, tapering off early Sunday morning. Showers may linger across the south coast and Cape/Islands through the afternoon. There is still a decent range in QPF likely owing to track of the surface low. There continues to be a fairly wide range in the 25th-75th percentiles among ensemble guidance. For northern MA amounts range from 0.20- 0.50" and 0.40-1.0" for the south coast and Cape/Islands.

High-res guidance continues to highlight the chance for icing and/or mixed precipitation across elevated portions of northern Massachusetts Saturday night into Sunday. The trend in the 12z guidance suite has been to develop a secondary surface low just offshore. Northerly flow around this feature would help to keep a wedge of colder air over the interior through Saturday night. Warm nose aloft means a chance of freezing rain over a snow event. HREF Freezing Rain Accumulation Model (FRAM) has ticked up accumulations across the higher terrain of western Franklin and Hampshire counties with the 12z run indicating the chance of 0.05-0.10" amounts. Continued with the previous shift's thinking and blended in a portion of cooler guidance to account for the potential for the colder, around freezing temperatures. Still looking like a marginal thermal profile so holding off on a winter weather advisory for now.

KEY MESSAGE 3...Becoming windy & turning colder Sun night into Mon with a period of NW wind gusts of 35 to 50 mph possible later Sun night. Low risk for a brief snow squall too.

Rapidly intensifying low pressure will be lifting into the Canadian Maritimes Sun night. This will allow for a brief shot of windy and cold weather to work into the region. Strong CAA along with Bufkit support a period of northwest wind gusts of 35 to 50 mph later Sun night. It is possible we may briefly reach Wind Advisory criteria in some locations. In addition...there will be a low risk for a localized snow squall too. Impressive shortwave energy along with modest 1000 to 700 mb lapse rates...but low level moisture may be limited. So right now calling it a low probability...but something to watch.

Otherwise, main story is dry but windy and colder weather. Low temps by daybreak Monday will be in the 20s with highs only recovering into the 30s during the afternoon. Wind chills probably range from the high single digits to the middle teens by daybreak Mon.

KEY MESSAGE 4...Milder temperatures quickly return Tue and especially by Wed when highs may approach 50 in some locations.

The upper trough is fairly progressive and surface high pressure will quickly be moving east and away from the mid-Altantic states. This will result in the quick return southwest of milder air back to the region. Highs on Tue should be back into the 40s and by Wed some locations may even reach 50. Dry weather probably dominates...but shortwave energy may result in a few showers late Tue night/Wed morning.

KEY MESSAGE 5...Turning colder Thu into Fri and will have to watch an offshore storm for the potential of mixed precipitation/snow if it tracks close enough to the coast.

Long range guidance is in agreement in the likelihood of a pattern change back to colder weather by late next week. How quickly this happens and the magnitude of this remains uncertain...but appears that a -EPO will be developing. This will result in ridging over the Pacific and a northeast trough developing...so temperatures will be turning colder Thu and Fri. We will also need to watch the development of an offshore low pressure system Thu into Fri. If it comes close enough to the coast...the potential would exists for mixed precipitation and/or snow. A lot of the guidance currently favoring a glancing blow/miss...but there is a large spread in the individual ensembles and it would not take too much of a shift northwest to change things significantly. It is way too early to say much more and probably will be at least a few days until we have a better idea.

AVIATION /19Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High -greater than 60 percent.

TAF Update: 18z

Tonight... Moderate Confidence.

Areas of SHRA move in from west to east 22z-00z, conditions briefly lower to IFR, showers diminish between 03-06z, improving back to VFR 06-09z, while MVFR lingers on the Cape and Islands through 09z-12z. Wind shifts to the west to west- northwest between 04z-10z, winds speeds are 5 to 10 knots, slightly higher for coastal terminals.

Saturday... Moderate Confidence.

VFR to start, then lowering to MVFR from south to north, along with showery rain, mainly after 18z/21z. Light north wind becomes east at 5 to 10 knots.

KBOS Terminal... Moderate Confidence.

Moderate confidence in MVFR developing thru the evening.

KBDL Terminal... Moderate Confidence.

MVFR to IFR ceilings developing this evening into the overnight.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR. Strong winds with gusts up to 45 kt. Slight chance SHSN.

Monday: VFR. Strong winds with areas of gusts up to 45 kt.

Monday Night through Tuesday: VFR. Breezy.

Tuesday Night through Wednesday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Today through Sunday.. High Confidence.

Elevated seas continue tonight 4 to 6 feet, localized areas of 7 feet on the outermost southern waters. Showery rain overnight, not expected to be at all impactful. Saturday morning winds go light and flip to the east as a quasi-stationary front lifts from the south to the north, rain accompanies this front as well during the early to mid-afternoon. Increasing winds later Sunday as CAA increases behind a cold front. Gale conditions will be possible by Sunday night.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 13 ft. Slight chance of rain showers, slight chance of snow showers.

Monday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas.

Monday Night through Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

Tuesday Night: Strong winds with areas of gusts up to 30 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Gale Watch from Sunday evening through Monday morning for ANZ230>237-251. Small Craft Advisory from 7 PM this evening to 3 AM EST Saturday for ANZ235-237. Small Craft Advisory from 7 PM this evening to 7 AM EST Saturday for ANZ250-254>256. Gale Watch from Sunday evening through Monday afternoon for ANZ250-254>256.