textproduct: Boston / Norton

SYNOPSIS

High pressure builds into the region later tonight into Saturday with less wind and cool conditions. A frontal system will bring mainly rain Saturday night, then drying out and becoming windy Sunday. Blustery and cool weather prevails early next week, then diminishing wind and continued dry weather into midweek as high pressure builds in from the west.

NEAR TERM /THROUGH SATURDAY/

Key Point

*Cold but less windy overnight. Wind chill values in the low 20s.

One last round of weak shortwave energy moves through the region this evening before the stalled upper-level trough and cold pool move well offshore. Not anticipating anything other than increased cloud cover this afternoon and evening, as dry low-level air will make it difficult for any rain to reach the ground. Clouds begin to decrease tonight, leaving skies clear by midnight. With decreasing wind overnight, expecting good radiational cooling tonight, with lows dropping into the low 20s to even the upper teens in the higher terrain of northwest Massachusetts.

SHORT TERM /SATURDAY NIGHT/

Key Points

*Continued cool and dry weather Saturday *Rain moves into the region from west to east Saturday evening

Weak upper-level ridge pushes the cold pool away from the region for Saturday, but the cold start will keep highs from exceeding 50F for much of the region. A warm front enters the region on Saturday afternoon, but rain from this front wont arrive until Saturday evening, as mid-level dry air will take time to erode. Thus, only expecting increasing clouds during the day.

Better forcing and moisture arrive Saturday evening, allowing rain to begin falling from West to east, with widespread steady rain across the region before midnight. Previous high-resolution guidance runs had some residual cold air in place as the rain arrived, resulting in some mixed P-types; however, guidance has since backed off on this, as wet bulb temperatures will be above freezing when the rain arrives. Deterministic and ensemble guidance are in good agreement, with QPF totals ranging from 0.25 to 0.5 inches, with pockets of up to 0.75 inches possible. Overnight lows remain a bit milder compared to the previous night, only bottoming out in the low to mid-30s with the warm air advection.

LONG TERM /SUNDAY THROUGH FRIDAY/

Key Messages:

* Rain ending early Sunday morning, low chance for showers into the afternoon, otherwise dry and windy through Monday.

* Mainly dry conditions along with below normal temperatures Tuesday into Thursday.

* Return of seasonable temperature and unsettled conditions Friday. The system that brings rain Saturday night into Sunday morning is moving northeast with the low pressure system strengthening as the center heads towards the Canadian Maritimes. Post frontal dry and cold air advects in from the northwest along with gusty conditions due to the strengthening pressure gradient as high pressure builds to the southwest of New England. Widespread rain ends early as PWATs fall to less than 0.3", cannot rule out spot rain and/or flurry from a passage of a robust shortwave Sunday afternoon.

What is more notable during the Sunday and Monday timeframe are the expected gusty conditions. Cooling temperatures aloft on Sunday aids with steep 1000mb-850mb lapse rates of 8-10C/km, resulting in a well mixed boundary layer. Assumptions are 80 percent of the momentum can transfer from 850mb to the ground, lending to gusts of 30 and 40 mph from the west-northwest. It is reasonably possible areas across the high terrain of northwestern Massachusetts could gust over 50 mph. A quick look at DESI utilizing HREF show probabilities of 20 to 40 percent of these gusts for the east slopes of the Berkshires. And slightly lower chances for Cape Cod and islands with probabilites between 10 and 30 percent. Something to monitor as these gusts near the threshold for a wind advisory. For mariners, Gale Watch has been issued for all waters beginning late Sunday morning through Monday evening for west-northwest gusts 30 to 40 knots.

Fairly quiet Tuesday into Thursday as the mid-level low moves from northern New England towards the Labrador Sea. Northwest flow regime remains, shortwaves races through the region through Wednesday night leading to a daily chance for hit-or-miss sprinkles and/or flurries. Late week, Thursday into Friday becomes unsettled with the next opportunity for widespread precipitation. Temperature-wise, will have below normal daytime highs and overnight lows through Thursday, with near normal conditions by the end of the week.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

00Z Update...

Tonight and Saturday...High confidence.

VFR through the period. Sct-bkn diurnal strato-cu 5-7k ft this evening clears tonight but ocean effect clouds lingering over the outer Cape. Winds NW 5-10 kt tonight becoming W-SW 5-10 kt tomorrow afternoon.

Saturday Night...Moderate Confidence

Gradually lowering CIGS as Rain ahead of our next system begins to approach the region. General consensus for rain timing seems to be arriving from west to east between 00z - 04z. Rain could be moderate at times and bring CIGS down to IFR level, but not confidence in CIGS becoming LIFR with SW winds.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt.

Sunday Night through Monday: VFR. Windy with gusts up to 35 kt.

Monday Night: VFR. Windy with local gusts up to 30 kt.

Tuesday through Tuesday Night: VFR. Breezy.

Wednesday: VFR.

MARINE

Forecaster Confidence Levels...

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

GALE WATCH IN EFFECT FOR SUNDAY AND MONDAY

Tranquil boating conditions are anticipated tonight into tomorrow as high pressure brings light westerly winds and rain-free weather. Seas decrease to 1-3 feet through Saturday. A warm front will bring rain to the waters on Saturday night, before a cold front clears the rain out and brings strong, gale-force winds on Sunday and Monday. Seas on Sunday and Monday could approach 8-12 feet.

Outlook /Sunday through Wednesday/...

Sunday: Moderate risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Slight chance of rain.

Sunday Night: gale force winds with local gusts up to 45 kt. Rough seas up to 14 ft.

Monday: gale force winds with gusts up to 40 kt. Rough seas up to 13 ft. Slight chance of rain.

Monday Night: Strong winds with gusts up to 40 kt. Areas of rough seas.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Wednesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Gale Watch from Sunday morning through Monday evening for ANZ230>237-250-251-254>256.