textproduct: Boston / Norton

SYNOPSIS

Thunderstorms and isolated flash flood risk continues through this evening before winding down with the loss of daytime heating. Increased confidence in heat index values climbing above 95F Tuesday through midweek allows for a heat advisory to be issued starting at 11am Tuesday and going through 7pm Thursday evening.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/

Key Points:

* Warm and muggy conditions continue tonight

* Hot and humid conditions begin Tuesday

Tonight:

Front passes during the first half of the overnight with little relief. Muggy conditions continue with dewpoint values only falling into the lower 70s for much of the region.

Tuesday:

* Heat Advisory goes into effect for most of the region starting at 11 am

* Little relief overnight with continued high humidity

Building ridge of high pressure brings the return of hot and humid conditions Tuesday. Guidance has 925 temperatures increasing from 19C today to 24C tomorrow afternoon. At the surface, this translates to high temperatures climbing into the upper 80s and low 90s for most areas Tuesday afternoon. While these temperatures are far from unheard of, dewpoint values will climb into the lower to mid 70's resulting in heat index values around 95 above. The greatest likelihood of this will be for inland areas away from the Cape and Islands. Low temperatures will remain quite mild and dewpoints high. Elevated low temperatures spell trouble for those without access to proper sources of cooling and relief from the day's high temperatures.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Key Messages:

Key Messages:

* Hot and humid during the middle of this week, with elevated heat indices around 95-100F. Heat Advisories for Tuesday into Thursday for most of southern New England. Heat Advisory may be needed for Friday too. * Becoming more unsettled late Thursday-Friday with increasing chances for showers and thunderstorms.

Most of this portion of the forecast will see southern New England om the warm and very humid side of a cold front. This front will take its time to move from the Great Lakes and Saint Lawrence River valley until it finally attempts to cross our region Friday night. The holdup is a large high pressure off the southeast USA coast. The position of this high pressure will keep pushing heat and humidity our way.

Heat Advisories already posted for most of southern New England for the middle part of this week. It may need to be extended into Friday as well. Slightly cooler conditions anticipated once this front passes by this weekend into early next week, but that should mean right around average temperatures for this time of July.

The heat and humidity should mean at least a low risk for mainly afternoon and evening thunderstorms. There remains a better signal for more organized forcing later Thursday and a weak trough shifts in from the west. This will bring higher chances for more widespread showers/storms. Weak winds aloft will support slower storm motions and given the high amounts of moisture signal a threat for flash flooding. We'll have to keep eyes on that as we go through this week. Friday is a more complicated forecast dependent upon the timing of the aforementioned front.

Looking ahead to this weekend, this front doesn't get too far south of our region, and could return as a warm front sometime Sunday into Monday. That could trigger another round of showers and possible thunderstorms.

AVIATION /18Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z Update:

Monday: Moderate Confidence

A line of slow moving showers and thunderstorms forms or moves into western MA and CT in the mid to late afternoon, continue to move east through about 10pm to midnight. How far east convection gets is still uncertain, with terminals inside the I-95 corridor possibly being spared.

Monday Night: Moderate Confidence

After remaining showers and thunderstorms dissipate, winds turn SSW brining in yet another round of low stratus and fog. Highest confidence near the south coast and CT river valley. Less certain in and around Boston.

Tuesday: Moderate Confidence

VFR outside the Cape and Islands where IFR stratus may hang on much of the day. Low chance for a weak shower or thunderstorm.

KBOS Terminal...Moderate confidence in TAF.

Stratus lifting 13z-14z, then VFR. Thunderstorms will struggle to reach the terminal this evening, likely just left over showers, thus continued with the PROB30 -SHRA.

KBDL Terminal...Moderate confidence in TAF.

MVFR stratus deck becoming IFR before sunrise. The stratus deck took longer then anticipated to burn off yesterday, however, winds turn more SSW today which should allow it to lift mid morning. VFR this afternoon with slow moving heavy showers and thunderstorms.

Outlook /Wednesday through Friday/...

Tuesday Night: Mainly VFR, with local IFR possible. Patchy BR.

Wednesday through Wednesday Night: VFR. Slight chance SHRA, slight chance TSRA.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA.

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday: VFR. Chance SHRA, chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Today through Tuesday...High confidence.

Weak pressure gradient will keep winds/seas below Small Craft Advisory thresholds through Sunday: seas 2-3 ft with E winds over the southern waters and SE winds over the eastern waters up to 15 kts during the afternoon hours, remaining light in the overnight hours. Main concern for mariners will be areas of fog tonight that may redevelop again tonight. Inland Thunderstorms are unlikely to affect the waters this evening. Winds turn more SW on Tuesday between 10-15 knots.

Outlook /Wednesday through Friday/...

Tuesday Night: Winds less than 25 kt. Patchy fog. Local visibility 1 nm or less.

Wednesday: Winds less than 25 kt.

Wednesday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, slight chance of thunderstorms.

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

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Flood Watch until midnight EDT tonight for CTZ002. Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for CTZ002>004. MA...Flood Watch until midnight EDT tonight for MAZ002-003-008>011. Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for MAZ003>007-010>021-026. RI...Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for RIZ001>007. MARINE...None.