textproduct: Boston / Norton

SYNOPSIS

One more day of dangerous heat and humidity is in store for the region today. An approaching cold front may bring hit or miss showers and thunderstorms today, but much of the day will be dry. The cold front will bring and end to the heat and humidity later tonight with beautiful dry weather Friday and Saturday. Another cold front will likely bring a round of showers and embedded thunderstorms to the region late Saturday night and/or Sunday along with the return of some humidity. This will be short-lived though as a dry and very pleasant airmass moves back in time for the start of the next work week.

NEAR TERM /UNTIL 6 PM THIS EVENING/

Key Messages...

* Hit or miss showers/t-storms today...but much of the day is dry * One more day of dangerous heat/humidity...Heat Indices 95-100 * Any Severe weather threat today should be isolated/localized

Details...

Today...

A shortwave and its associated cluster of showers & t-storms across the mid-Atlantic states early this morning will lift northeast. The guidance indicates that the convection may weaken as it moves northeastward into lingering mid-level ridging. However...diurnal heating may try to offset that later this morning into the mid- afternoon. Therefore...hit or miss showers and thunderstorms may cross the region this morning and into the mid afternoon. We then will need to watch for the approaching cold front and perhaps another risk for isolated/widely scattered convection late in the afternoon and evening. However...subsidence behind initial shortwave and a lot of mid level dry air will probably keep this as an isolated convective threat. Modest instability will quickly develop with Capes on the order of 1500 to 2500+ J/kg along with 25 to 30 knots of effective shear. A fair amount of 0-1 KM helicity will also develop on the order of 100 to 200+ units.

Despite a lot of favorable parameters for severe weather...there is a significant limiting factor. The mid level lapse rates are poor and the forcing is quite limited in our region with the better of it across northern New England. The HREF is also showing rather limited 2-5 KM UH swaths which might be a red flag. That being said...given the parameters in place if some mesoscale processes can come into play there will be an isolated/localized severe wind threat and even a low risk for a weak tornado given the 0-1 KM helicity. But any severe weather threat should be isolated/localized given the limited forcing. We also should mention that with Pwats near 2"...brief torrential rainfall will also be possible with any thunderstorm.

Outside the convective threat...the majority of the day will feature heat and humidity. High temps will be in the upper 80s to lower 90s allowing heat indices to reach into the 95 to 100 degree range. Heat Advisories remain in place through 7 pm this evening.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/

Key Messages...

* Relief from heat & humidity later tonight with a NW breeze * Mostly sunny Fri with low humidity and highs 80-85

Details...

Tonight and Friday...

Any isolated shower & thunderstorm activity this evening will come to an end later tonight. Otherwise...the main story will be relief from the heat and humidity behind the cold front later tonight and Friday. This much drier air will be ushered in on a northwest breeze which may gust to around 25 mph later tonight into Friday morning. Low temps tonight will be in the upper 60s to the lower 70s...but with relief from the humidity. This will be followed by mostly sunny & beautiful weather for Fri with highs mainly between 80 and 85 and very comfortable humidity levels. Quite the change from the last few days.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Key Messages...

* Dry & very pleasant Fri night and Sat with comfortable humidity

* More humid with a round of showers & embedded t-storms sometime late Sat night and/or Sun with locally heavy rainfall

* Dry pleasant weather returns Mon/Tue/Wed with comfortable humidity

Details...

Friday night and Saturday...

A ridge of high pressure builds over the region resulting in very pleasant weather Fri night into Sat. Low temps Fri night will probably drop into the lower to middle 50s in the outlying locations given light winds/mainly clear skies and a dry airmass in place. Highs on Sat will be in the 80s with very comfortable humidity.

Saturday night and Sunday...

The next shortwave/cold front will approach southern New England from the west late Sat night into Sun. This will be associated with the return of some humidity and Pwats increasing to around 2 inches. The forcing with this system looks quite impressive for July standards...so we may see a round of fairly widespread showers and embedded t-storms sometime late Sat night and/or Sun.

Monday through Wednesday...

A ridge of high pressure builds in behind the latest cold front for the start of the next work week. This will bring mainly dry and very pleasant weather to the region. Highs will mainly be in the upper 70s to the middle 80s although by next Wed may be on the warmer side of those numbers.

AVIATION /07Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

06z TAF Update...

Today...Moderate confidence.

Deep moist southerly flow was allowing IFR-LIFR in mainly low clouds with some fog near the Cape/Islands to overspread much of the region early this morning. These low clouds should mix out later this morning and afternoon allowing many locales to improve to VFR...although lower cigs may flirt with the Cape/Islands at times through the day. Otherwise...we may have a few brief showers & t- storms cross the region today but the vast majority of the day will feature dry weather. SW winds may gust to between 20 and 25 knots by afternoon.

Tonight and Friday...High confidence.

Any isolated shower & t-storm activity should come to an end this evening. Otherwise...VFR conditions as a dry NW flow of air takes over later tonight into Friday. NW winds may gust between 20 and 25 knots behind the cold frontal passage overnight into the first half of Friday before diminishing.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: VFR.

Saturday: VFR. Breezy.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, chance TSRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, chance TSRA.

Sunday Night through Monday: VFR.

MARINE

Forecaster Confidence Levels...

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

Today through Friday...High confidence.

Gusty southwest winds near 25 knots develop across our near shore southern waters this afternoon given good mixing ahead of an approaching cold front. We opted to issue a small craft advisory for those near shore southern waters given it is peak boating season. We also expect marginal SCA seas to develop with long southerly fetch across the southern outer-waters by this evening into Friday so we have headlines for that too. Lastly...behind the cold expect a round of NW wind gusts of 25 knots overnight into Fri morning across our northern waters...where we will have additional small craft headlines.

Outlook /Friday Night through Monday/...

Friday Night through Saturday: Winds less than 25 kt.

Saturday Night through Sunday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

Sunday Night: Winds less than 25 kt. Slight chance of rain showers.

Monday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Heat Advisory until 7 PM EDT this evening for CTZ002>004. MA...Heat Advisory until 7 PM EDT this evening for MAZ003>007- 010>021-026. RI...Heat Advisory until 7 PM EDT this evening for RIZ001>007. MARINE...Small Craft Advisory from midnight tonight to 2 PM EDT Friday for ANZ230-250-251. Small Craft Advisory from noon today to 8 PM EDT this evening for ANZ231>237. Small Craft Advisory from 2 PM this afternoon to 2 PM EDT Friday for ANZ254>256.