textproduct: Boston / Norton

WHAT HAS CHANGED

No changes to the forecast for this update cycle.

KEY MESSAGES

- Another warm and humid day today with a chance for isolated showers and storms.

- Dry and seasonable weather with low humidity levels this weekend into Monday.

- Heat and humidity return by midweek.

DISCUSSION

KEY MESSAGE 1...Another warm and humid day today with a chance for isolated showers and storms.

Cold front drops S from northern New England, crossing through northern MA this morning before slowing S of the Mass Pike by the afternoon. Front acts as a focus for showers and isolated thunderstorms along and S of the Mass Pike as the column dries out significantly behind the front. General risks with any limited thunder activity will be limited to lightning and locally heavy rain as lingering cloud cover limits CAPE values to >1000 J/kg. Could see locally higher shower and storm coverage on the east coast of MA with a sea breeze acting as a mesoscale lifting mechanism. Thus, have POPs around 20-35% this afternoon in those areas. The other story today will be hot and humid conditions as highs warm into the upper 80s to near 90 for much of the CWA. Highest heat index values will be along and S of the Mass Pike where dew point values will likely be near or above 70 degrees.

KEY MESSAGE 2...Dry and seasonable weather with low humidity levels this weekend into Monday.

Surface high pressure from Canada builds southward under cyclonic flow aloft. NW flow aloft will cool 850 mb temps to +13-15C, which translates to highs in the mid 70s to low to mid 80s. Should feel quite a bit more comfortable than what we've experienced over the last few weeks with low humidity levels and dry weather Saturday through Monday. Other than some cooler seabreezes near the eastern coast, it's shaping up to be a great weekend weatherwise.

KEY MESSAGE 3...Heat and humidity return by midweek.

A sprawling 594dm ridge over the central CONUS builds east through midweek. By Tuesday and especially Wednesday, temperatures become quite hot as 850 mb temps soar again into the +18 to +22C range. These values are similar (somewhat cooler by comparison) to our last extended spell of high heat/humidity. The potential could exist for temperatures in the 90s with high humidity levels perhaps necessitating a period of heat headlines for midweek. The risk for thunderstorms looks limited, with a better chance on Wednesday as NW flow aloft increases and a plume of elevated mid-level lapse rates builds in favoring stronger instability.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Through 12z Friday: Moderate confidence.

Generally VFR but starting to see IFR- LIFR stratus along the south coast; potential for MVFR- IFR ceilings as far north as PVD to OWD by 09z, but confidence is lower if it slips into BOS/BED. SW winds around 7-12 kt, with gusts to 25 kt eastern and southeast MA, though gusts subside to sustained SW winds 5-10 kt overnight.

Friday: Moderate confidence.

Main issue for the TAFs Fri is the timing of the cold front southward. Current indications are for winds turning NWly under 10 kt for BDL-ORH-BED-BOS between 13-15z with BKN/OVC VFR ceilings; winds turning NE under 10 kt at BOS early afternoon. Thinking area more favored to see SCT SHRA/TS is from HFD to PVD south and east after 17z, after overnight stratus disperses. A slower passage would put more TAFs at risk for SHRA/TS.

Friday Night: High confidence.

Lingering SHRA/TS moves offshore early Fri night to VFR conditions. Outside chance at river valley fog if skies can clear out. Winds become light northerly overnight.

KBOS Terminal...Moderate confidence. Thinking stratus near south coast should stay far enough south of the airport. Windshift to NW under 10 kt by 13-15z Fri, then turning NE under 10 kt with BKN VFR ceilings. Slower frontal timing will affect timing of windshifts Fri.

KBDL Terminal...Moderate to high confidence. PROB30 for TSRA thru 02z Fri, otherwise, VFR should prevail with a windshift to NW around 13-15z Fri.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday Night: VFR.

Monday through Tuesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Friday Night...High confidence.

A weak front approaches the waters from the NW this afternoon, but is not likely to pass the southern coastal waters until late Friday night at the earliest. A risk for scattered showers or thunderstorms tonight across the southern waters. Tranquil weather returns for the weekend under high pressure.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt.

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

Monday: Winds less than 25 kt.

Monday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft.

Tuesday: Low risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Areas of seas approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.