textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Dry today with seasonably cool temperatures.

- Fast-moving system expected to bring periods of rain Friday, followed by much colder and drier conditions Saturday.

- Quiet and seasonable weather Sunday through Tuesday.

DISCUSSION

KEY MESSAGE 1...Dry today with seasonably cool temperatures.

High pressure settles in over the region today along with a notably drier airmass. Initially breezy conditions early this morning will wane heading into the late morning/early afternoon. A cooler, more seasonable airmass moves overhead today, dropping 925 mb temperatures from the 16-18C range to generally just below 10C. This will be more supportive of highs back in the upper 50s and low 60s across southern New England. Humidity also notably drops as drier air moves in, dropping dew points into the 40s and PWATs to generally around 0.25".

KEY MESSAGE 2...Fast-moving system expected to bring periods of rain Friday, followed by much colder and drier conditions Saturday.

High pressure today drifts off to the east and offshore later tonight ahead of a strong northern stream shortwave trough progressing east through the Great Lakes and into the northeast. Compared to last night's guidance, the timing for this front appears to have slowed down slightly, though this is still expected to be a quick moving system. The associated surface low is slated to track through the Great Lakes region, deepening as it moves northeast and reaching the 1000 mb mark (and possibly lower) by Friday morning, centered over southeast Ontario. Ensembles are in strong agreement with this threshold being crossed especially as it tracks into northern NY and VT by early Friday afternoon. Deterministic global guidance takes it to around 995 mb by the evening hours. Out ahead of the low, a warm front is expected to track into the region which will be the main driver for our first round of rain. Based on the latest guidance, rain is expected to move in closer to the 4-8 AM time range from west to east, spreading over the region. Once the warm front moves through, the warm sector settles in overhead. 925 mb temperatures climb up again into the 16-18C range, especially in the afternoon, and anomalous PWATs increase up to around 1.75" with the moisture plume advected in by this system. Highs will be warmer than that of Thursday given this warm sector overhead during the day Friday, but not to the same level we saw Wednesday; highs will likely top out in the upper 60s with some places brushing 70. With the first round of rain out of the region by the afternoon, we're left with a muggy, breezy, and mild day. Some showers during this lull aren't out of the question, though, given the strong WAA.

Round two moves in toward the evening hours Friday ahead of the low's strong cold front. This front will provide strong forcing in an environment with bulk shear at 0-6 km expected to be at and above 50 kt. A southerly LLJ sets up over much of eastern MA, RI, reaching 40-50 kt at 925 mb and up to 60 kt over the region from the SW at 850 mb. CAPE values top out around 500 J/kg based on the latest CAMs and global guidance, so while widespread severe weather is not expected, some embedded thunderstorms are not out of the question. With regards to rainfall totals, ensembles appear to have trended totals down slightly, generally ranging between 0.30"-0.60". Probabilities for totals reaching or exceeding an inch within southern New England have dropped considerably, though the GEFS does have a 20% chance across much of MA and into northern CT. Even with these low probabilities, the chance that there could be some convective features combined with these high PWAT values keeps the chance for some locally higher rainfall totals in play.

Breezy winds are expected for Friday given the aforementioned LLJ, though latest guidance has trended the intensity down slightly. This appears to be driven by the presence of a low-level thermal inversion noticeable in forecast soundings. Generally, gusts to 30 mph seem most likely, though the waters may very well see gusts to the 35 mph range and higher given the warmer ocean temperatures.

As the cold front crosses southern New England Saturday morning, strong CAA kicks off in its wake. 925 mb temperatures fall below 0C heading by Saturday evening, and PWATs fall below 0.25" once more as colder, drier air sets in. Lows Friday night fall into the 40s and upper 30s (towards the high elevations). Highs Saturday may struggle to reach the low 50s across the interior and lows Saturday night will likely dip below freezing across the region, with the exceptions being areas closest to the coasts and urban areas. Though, those areas will likely be sitting just above freezing overnight, with low 40s possible for the Cape and Islands. In the midst of this colder air, strong NW winds prevail, gusting well into the 30 mph range with some gusts to 40 mph not to be ruled out.

KEY MESSAGE 3...Quiet and seasonable weather Sunday through Tuesday.

High pressure builds in Sunday and a more seasonably cool airmass moves into the region, and the tighter gradient between the strong exiting low and approaching high pressure slackens. This will allow winds to let up as well, diminishing slightly heading into the second half of the weekend and the start of next week.

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:

Through 12z...High confidence.

VFR. Gusts 20-25 kt for more eastern terminals through the rest of tonight. Sustained winds between 10-15 kt also expected, particularly for terminals that don't see gusts this morning.

Thursday...High confidence.

VFR. Brief period of gusty/high sustained winds possible across all terminals between 12z-15z before winds diminish through the rest of the day. Winds remain generally NNW, then shift more NE to E in the afternoon/early evening for coastal terminals.

Thursday Night...Moderate confidence.

Becoming MVFR to IFR with -SHRA moving in from west to east between 06Z and 12Z. S-SW winds develop with gusts nearing 20 kt closer to sunrise.

Friday...Moderate confidence.

IFR to LIFR with SHRA. Brief respite from SHRA possible in the afternoon hours, though low ceilings continue. Will need to monitor for the risk of some embedded TSRA and convective features. Gusty S to SW winds up to 30 kt with higher gusts possible near the coasts and higher elevations.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: Mainly VFR, with areas MVFR possible. Windy with gusts up to 30 kt. Chance SHRA.

Saturday: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt.

Saturday Night: VFR. Breezy.

Sunday through Sunday Night: VFR.

Monday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Seas around 3-5 ft on most waters through today, with dry weather and good visibility expected. Gusts should subside below SCA criteria by late this afternoon.

A frontal system brings SW winds back into the SCA range on Friday (25-30 kt), which will also bring periods of light to moderate rain reducing visibility through Friday early evening. A short period of small craft advisories will likely be needed once the existing SCAs expiring Thursday afternoon expire.

Looking ahead into Friday night and into Saturday...a period of strong northwest winds are forecast. We've issued a Gale Watch on most waters for Friday night into Saturday, with seas becoming increasingly rough at up to 12 ft. Dry weather is expected by Saturday.

Outlook /Friday Night through Monday/...

Friday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 10 ft. Rain showers likely.

Saturday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 10 ft. Chance of rain showers.

Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ230>234-250-251-254-255. Gale Watch from Friday evening through Saturday evening for ANZ230>237-250-251-254>256-280>283.