Marine Weather Net

Provincetown MA to Chatham MA to Nantucket MA out 20 NM Marine Forecast


THIS AFTERNOON

W
WINDS
20
KNOTS

TONIGHT

W
WINDS
15 - 20
KNOTS

TUE

W
WINDS
10 - 15
KNOTS

TUE NIGHT

W
WINDS
10 - 15
KNOTS

The Marine Weather Forecast In Detail:
ANZ254 Forecast Issued: 116 PM EST Mon Jan 18 2021

SMALL CRAFT ADVISORY IN EFFECT THROUGH TUESDAY MORNING
This Afternoon...W Winds Around 20 Kt With Gusts Up To 30 Kt. Seas 4 To 6 Ft.
Tonight...W Winds 15 To 20 Kt With Gusts Up To 30 Kt. Seas 4 To 6 Ft.
Tue...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 5 Ft.
Tue Night...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 5 Ft.
Wed...W Winds 15 To 20 Kt, Becoming Nw 20 To 25 Kt In The Afternoon. Seas 4 To 6 Ft.
Wed Night...Nw Winds 20 To 25 Kt With Gusts Up To 30 Kt. Seas 5 To 8 Ft.
Thu...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 4 To 6 Ft.
Thu Night...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 4 Ft. A Chance Of Rain And Snow Showers.
Fri...Nw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 4 Ft.
Fri Night...Nw Winds 15 To 20 Kt. Seas 4 To 7 Ft. Seas Are Reported As Significant Wave Height, Which Is The Average Of The Highest Third Of The Waves. Individual Wave Heights May Be More Than Twice The Significant Wave Height.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
110pm EST Monday Jan 18 2021

Synopsis
Above normal temperatures will persist through Monday, but will be replaced by seasonably cool temperatures beginning Tuesday and continuing through the week. Several opportunities for light snow showers especially across the higher elevation of the interior. Snow showers may be a bit more widespread Thursday into Friday.

Near Term - Until 6pm This Evening
945 AM

Next mid level shortwave across mid Atlantic region will be moving off the coast and tracking south of New Eng later this afternoon. Impressive cold pool(a region of relatively cold air) aloft with this feature with 500 mb temps around -35C with the core of the coldest air just south of New Eng. Expect clouds to fill in across the region as the shortwave approaches and moisture in the 850-700 mb layer increases. A few rain/snow showers are possible with focus more likely to be south of the Pike through the afternoon where best low level instability is located. However, soundings show rather dry air in the lowest 3k ft so activity will be isolated to widely scattered and most locations should remain dry. If precipitation does make it to the ground, any rain showers will trend toward snow showers due to wet bulb cooling processes.

Temps will be several degrees above normal with highs ranging from mid/upper 30s interior high terrain to mid 40s coastal plain. But any shower activity that makes it to ground will result in temps falling into 30s. Blustery conditions developing with west wind gusts to 20-30 mph at times in deep and well mixed boundary layer.

Previous discussion... Another day of above normal temps, courtesy of temps already off to a mild start with 3 am temps only in the upper 30s and lower 40s. Overall fairly pleasant day by mid Jan standards, especially this morning with partial sunshine and temps rising thru the 40s, upper 30s high terrain. Although enough of a brisk west wind 10-20 mph with gusts up to 30 mph over Cape Cod and the Islands, to provide a Jan chill.

This afternoon clouds will build as next short wave trough approaches the region from the southwest. Cold temps aloft (-35C at 500 mb) associated with this trough will provide steep mid level lapse rates and TT around 55! This instability and cyclonic flow aloft will be sufficient for some low top convection in the form of scattered rain showers, snow showers high terrain given cold air aloft/steep low level lapse rates. This instability combined with thermal profiles may be sufficient for the risk of graupel. Not expecting precipitation to be very widespread as deep layer moisture is lacking. This dry air aloft will likely preclude any thunder as instability won't be fully realized. Hi res guidance suggest best chance for showers this afternoon and early evening will be across CT/RI and up to the Mass Pike. This seem reasonable as coldest air aloft/instability tracks across this region to the south coast and offshore.

Short Term - 6pm This Evening Through 6pm Tuesday
330 AM

Tonight... Short wave ridging behind departing trough will result in decreasing clouds and dry weather. Cooler with modest cold air advection behind departing short wave. Lows in the 20s, 15-20 across northwest MA. Modest WNW wind, except somewhat gusty over Cape Cod and the Islands.

Tuesday... Broad low amplitude trough begins to impact the region with occasional cloudiness, but mainly dry weather prevails. Cooler than today with highs 35-40, just a few degs above normal. Modest west wind 10-15 mph. Overall, another fairly tranquil mid January day.

Long Term - Tuesday Night Through Sunday
Highlights... * Mostly dry with periodic light snow showers Tuesday night through Saturday. Best chance of more widespread light snow is Thursday night/Friday but not expecting much

* Seasonably cool temperatures generally in the 30s

Details... No big storms in the extended forecast to speak of, though the pattern remains unsettled with periodic chances for light snow/rain showers through the first half of the weekend. There is no shortage of disturbances rotating through the mid level flow over our area, but none are deep or moisture laden enough to be of much consequence.

Tuesday night a subtle warm front lifts into the region ahead of a mid level trough followed by a weak cold front on Wednesday. The cold pool(a region of relatively cold air) aloft will lead to near adiabatic low level lapse rates while a 300 mb jet also provides some broad lift. All these features together should provide enough lift to keep things rather unsettled with some widely scattered light snow and rain showers Tuesday night and Wednesday. Again, lacking moisture, not expecting much more than a coating out of these. Good mixing will allow for gusty winds up to 25 to 30 mph. Cloudcover decreases Wednesday evening and overnight as drier post frontal air filters in from the NW. This may allow for some radiational cooling overnight but may be limited depending on how quickly clouds return and also by a boundary layer that is looking breezier and less likely to decouple than it was 24 ago. Nevertheless, it will be the coldest morning of the forecast, dropping into the teens and single digits.

A subtle ridge builds in early Thursday drying things out before the next shortwave and surface low crosses southern New England Thursday night and Friday. A 150 kt 300 mb jet will provide synoptic lift but again lacking moisture we won't see much appreciable snowfall out of this. By Saturday high pressure approaches but low pressure over Nova Scotia may increase the pressure gradient bringing gusty and cold NW winds. Best chance for scattered snow showers over the weekend is Saturday before ridging returns on Sunday.

Marine
330 AM

Today through Tuesday...High Confidence.

WSW winds this morning shifting to W this afternoon with speeds of 15-20 kt, gusting to 25 kts. Thus SCA (Small Craft Advisory) for all waters except Boston Harbor and Narr Bay, where winds will remain below 25 kt. West winds diminish tonight and Tue. Other than a few showers late this afternoon and evening, dry weather and good vsby prevail.

Strong low pressure over Quebec will gradually lift north tonight through Monday. Gale Force Westerly wind gusts will diminish by midnight across most of the waters as pressure gradient weakens. However, they will need to be replaced with SCA (Small Craft Advisory) right through Monday night. Enough mixing and chilly air aloft will generate enough mixing for continued westerly wind gusts of 20 to 30 knots and rough seas.

Outlook /Tuesday Night through Friday/... Tuesday Night: Winds less than 25 kt. Local rough seas.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Slight chance of snow showers.

Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas.
Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow showers.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, chance of snow showers.

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
MARINE...
Small Craft Advisory until 4am EST Tuesday for ANZ232>235-237- 250. Small Craft Advisory until 9pm EST this evening for ANZ230. Small Craft Advisory until midnight EST tonight for ANZ231-251. Small Craft Advisory until 7pm EST this evening for ANZ236. Small Craft Advisory until 8am EST Tuesday for ANZ254>256.