textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Warmer temperatures expected today with increased humidity levels.

- Scattered showers possible Thursday evening into Friday morning, followed by dry conditions Friday.

- Rain chances return for the second half of the weekend. There remains uncertainty in the details such as coverage, timing, amounts.

DISCUSSION

KEY MESSAGE 1... Warmer temperatures expected today with increased humidity levels.

Patchy fog possible early this morning, but should burn off with sunrise. High pressure in place will keep things mainly dry today. The exception is a line of light showers moving through upstate NY early this AM. At most this line may bring a sprinkle and period of clouds as it moves through this morning.

Expect a warmer day with a touch more humidity. A strong upper level ridge/high remains positioned across the southeast CONUS, subtly building into the northeast. Warmer mid-level temperatures advect in within the SW flow with 925mb temperatures 16-18C. This should yield highs in the mid and upper 70s with low 80s in the valleys (seasonably warm for mid-Sept). There will also be some moisture advection as well within the SW flow which will bring dewpoints back up into the low 60s. This will make it feel more humid than the previous day or two.

KEY MESSAGE 2...Scattered showers possible Thursday evening into Friday morning, followed by dry conditions Friday.

The first part of Thursday should remain dry with shower chances increasing later in the day as a weak shortwave trough approaches. Ahead of this shortwave, a plume of anomalous moisture advects in from the west. PWATs run around 180-200 percent of normal or more directly put, PWAT values 1.7-1.9". This has also been signaled as anomalous across the NAEFS guidance. Despite the anomalous moisture, the lift/forcing with this wave is weaker. Most guidance tracks the better forcing further north (New England). Being further from the stronger forcing will likely limit the potential for widespread heavy rain across the region. For timing, showers become more likely late afternoon into early evening, continuing through early Friday morning. For rain totals, ensembles show low probabilities (< 15%) for rain totals greater than 0.50". Amounts generally range from a trace to a few tenths across the GFS/ECMWF/Canadian are their ensembles. If this wave tracks further south as a small portion of guidance has been indicating, amounts will likely trend higher so this will continue to be monitored. There is potential for some elevated instability Thursday night which could result in an isolated heavier downpour, but otherwise the model consensus leans toward a period of showers with overall lighter amounts.

A drier airmass pushes in behind the exiting shortwave Friday which will gradually clear clouds through the day. Temperatures are likely to be in seasonable ranges in the 70s. A cooler airmass sinks across the region by Saturday bringing the return of Fall-like temperatures. Surface high pressure dominates bringing dry conditions.

KEY MESSAGE 3... Rain chances return for the second half of the weekend. There remains uncertainty in the details such as coverage, timing, amounts.

Confidence in the pattern decreases for the second half of the weekend into early next week. Ensembles continue to indicate potential for a shortwave trough to drop southward across the northeast Sunday into Monday. The strength/track of the trough and how it interacts with a surface high over the Great Lakes has varied across guidance leading to uncertainly in rain chances, timing, and amounts. If the shortwave tracks closer to southern New England the lift associated with the wave combined with a plume of anomalous moisture will better support rain across the region Sunday. However, there are also solutions that favor a stronger high pressure that would suppress the system further south/west resulting in more limited shower chances. Still plenty of details to iron out, but should become more clear as we get closer.

Surface high pressure shifts across eastern Canada into early next week. There are indications across ensemble guidance for another disturbance to push through potentially bringing a period of showers in the Tue-Wed timeframe. Confidence remains on the lower end with question on how the high pressure suppresses the incoming system and moisture advection.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Today and Tonight...High confidence.

VFR. SW winds near 8-12 kts, "strongest" for Cape/Islands terminals. At BOS, low chance for a late day sea breeze (after 18Z) out of the SSE/SE. Not included in BOS TAF due to low confidence. Mid-level cloud deck begins to move in overnight into early Thursday morning.

KBOS Terminal...Moderate confidence in TAF.

There is still a low probability for a sea breeze to come in late day (after 18Z). Most model guidance keeps SW winds 8-10 kts in the boundary layer today which would more likely favor the "no sea breeze" scenario. However, if winds end up a few kts lighter a SSE/SE sea breeze may be able to sneak in late day. Due to the low prob, kept out of TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Wednesday Night: Mainly VFR, with local MVFR possible.

Thursday: Mainly VFR, with local IFR possible. Slight chance SHRA.

Thursday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA.

Friday through Friday Night: VFR. Breezy.

Saturday: VFR.

Saturday Night: VFR. Chance SHRA.

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Surface high pressure continues with SW winds 10-15 kts today and Thursday. Occasional gusts 18-22 kts are possible both days in the afternoon/evenings.

Outlook /Thursday through Sunday/...

Wednesday Night through Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Chance of rain showers.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.

Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

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