textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Dry & chilly tonight with widespread frost outside the urban centers. Sunny & becoming breezy Wed with milder high temps reaching well into the 60s. Much milder Wed night with S-SW winds holding low temps mainly in the upper 40s-lower 50s.

- Very low chance of a spot shower Thursday, otherwise a mild day. An early look at the holiday weekend favors dry weather, though late Sunday into Monday bears watching for rain.

DISCUSSION

KEY MESSAGE 1...Dry & chilly tonight with widespread frost outside the urban centers. Sunny & becoming breezy Wed with milder high temps reaching well into the 60s. Much milder Wed night with S-SW winds holding low temps mainly in the upper 40s-lower 50s.

Large high pressure builds overhead tonight. This coupled with the dry/cool airmass and mainly clear skies will result in good radiational cooling and unseasonably chilly temps tonight. Low temperatures should bottom out well down into the 30s in many locations with even some upper 20s in the normally coolest low-lying areas of western MA. Frost and even freeze headlines are in effect for much of the region outside the urban heat islands. The mild spot will be downtown Boston...where low temps will only drop into the middle 40s.

This high pressure system moves east of the region on Wed. This results in a return southwest flow of milder air to work back into the region. Sunny skies and 925T warming to around +10C by afternoon will allow for a very nice recovery in temps. Highs should reach the lower 60s in the high terrain with middle to upper 60s in most other locations. It will become a bit breezy Wed afternoon with Bufkit soundings supporting SW wind gusts of 20-25 mph...but still a very nice day.

A modest southwest LLJ of 30-40 knots ahead of an approaching cold front Wed night will prevent surface winds from decoupling. This will result in a much milder low temperatures that what is on tap for tonight. Low temps will only drop into the upper 40s and lower 50s in most locations.

KEY MESSAGE 2...Very low chance of a spot shower Thursday, otherwise a mild day. An early look at the holiday weekend favors dry weather, though late Sunday into Monday bears watching for rain.

There aren't many changes to the extended forecast. As previously mentioned, a vertically stacked low near Hudson Bay will send a few subtle shortwaves through New England Thursday. Limited moisture should preclude significant rainfall, though a spot shower cannot be ruled out. The NBM doesn't show this particularly well, but CAMs do indicate low-end PoPs during the day Thursday associated with a surface cold front. Southwest flow aloft also brings somewhat elevated PWATs into the region. Thus, felt it best to introduce Slight Chance (15-20%) PoPs. This is far from a washout, with much of the region and day remaining dry, though the setup does favor a few spot showers. Otherwise, dry weather prevails Friday through the start of the holiday weekend.

Forecast uncertainty increases late Sunday into Columbus Day and will depend largely on potential tropical development over the Bay of Campeche. Development of AL92 is expected, and if named would become Isaias. Some guidance brings remnant tropical moisture north into southern New England sometime late Sunday night or Monday, while other solutions keep it suppressed to our south as a strong 1030 mb high extends across much of southern Canada. Plenty of time to watch trends, with no reason to alter outdoor plans at this point.

Temperatures remain fall-like with highs mainly in the middle to upper 60s, except upper 60s to mid 70s Thursday. Overnight lows are mostly in the upper 40s and 50s, though cooler upper 30s to middle 40s are possible Friday night into Saturday morning. Even cooler conditions are possible where effective radiational cooling develops beneath the surface high.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

18z TAF Update...High confidence.

VFR conditions continue through Wednesday night. WNW winds diminish tonight and become Light W or completely decouple. Winds then shift to the SW Wed into Wed night with some 20-25 knot gusts expected Wed afternoon.

KBOS Terminal...High confidence in TAF

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday: VFR. Breezy. Slight chance SHRA.

Thursday Night: VFR.

Friday: VFR. Breezy.

Friday Night through Saturday Night: VFR.

Sunday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Tonight through Thursday night...High confidence.

Lingering WNW small craft wind gusts quickly diminish by early evening as high pressure builds in from the west. Winds then shift to the SW Wed into Wed night. Some SW wind gusts of 20-25 knots expected Wed afternoon and night. Later shifts may need to consider some small craft advisory headlines Wed PM...but felt it was too marginal for a late 2nd/3rd period event.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Friday Night through Saturday Night: Winds less than 25 kt.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Frost Advisory from 11 PM this evening to 9 AM EDT Wednesday for CTZ002>004. MA...Frost Advisory from 11 PM this evening to 9 AM EDT Wednesday for MAZ004>006-009-011>013-017-018-020-021-026. Freeze Warning from 11 PM this evening to 9 AM EDT Wednesday for MAZ002-003-008-010. RI...Frost Advisory from 11 PM this evening to 9 AM EDT Wednesday for RIZ001-003-006. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ250- 254.