AFD - Boston

Near Term

THROUGH TONIGHT
Key Messages...

* Rain moves offshore, but eastern MA and RI may struggle to reach the lower 60s with overcast skies persisting.

* A few t-storms possible west of Worcester this afternoon, but severe weather is not likely.

* Cooler and breezy overnight.

Isentropic forcing continues to produce widespread light rain showers over southern New England early this morning, though the heavier precipitation remains over eastern PA/NY. This is where, not coincidentally, mesoanalysis indicates the core of a 40+ kt 850 mb jet. As this jet (and associated forcing) shift east the heavier bands of rain will move through SNE generally between 7 AM and 5 PM. Once all is said and done most locations will have gotten a good soaking, between a 0.25" and 1.25" with the QPF bullseye over western/interior SNE; ensemble guidance paints a 60-70% chance of AOA 1" in the Worcester Hills and 80-95% chance in the Berkshires.

Some dry mid/upper level air works in by afternoon as the core of the jet moves off, so more breaks in the rain are expected, especially west, before a final round of showers and thunderstorms accompanies the cold front late afternoon/evening. Guidance continues to be pessimistic on breaks of sun during daylight hours (needed to increase the modest instability available, up to 500 J/kg SBCAPE) so severe weather is not expected. However, some thunderstorms are possible, mainly west of Worcester.

Tonight the cold front ushers in a much cooler and drier airmass as dewpoints drop from 60F to the 30s by 5am. It will become breezy, however, as CAA promotes deeper mixing. Low temps will be 10+ degrees cooler than the previous night, in the 40s.

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Short Term

SUNDAY
Key Messages...

* Cool and blustery conditions on Sunday

Sunday will be drier, but still cloudy thanks to the -23C 500mb cold pool and cyclonic flow aloft with the lingering trough. Strong gradient winds will also be increasing through the day as CAA promotes mixing down of a potent 45-50 kt 850 mb LLJ. A marginal Advisory may be needed for a portion of interior SNE. Most locations will be dry on Sunday, but a few instability showers are possible and some orographically forced precipitation may linger over the Berkshires for part of the day. .

Long Term

SUNDAY NIGHT THROUGH FRIDAY

Key Messages:

* Much warmer with dry conditions Monday and Tuesday. A few showers are possible Tuesday night into Wednesday morning ahead of an approaching cold front.

* Near seasonable temperatures Thursday and Friday. While Thursday is dry, rain chances return for Friday.

Sunday Night: Gusty NNW winds continues for part of the night, but the duration of the wind will largely depends how quickly we cool the boundary layer and lose the mixing. Guidance does show a robust 850mb jet with wind speeds aloft 50 to 60 knots, with the 00z NAM being the most robust with max wind speeds ~70 knots. While I do not think will mix up to 850mb, BUFKIT soundings mix upward 900mb which have winds close to 40 knots. For now, think wind gusts 30 to 40 MPH through midnight is a good assessment, with potentially near advisory level gusts 46+ MPH for the Berkshire high terrain.

Otherwise, the mid-level low moves out to the Gulf of Maine and drier air advects into southern New England, will have clearing skies and lows in the 40s and possible upper 30s for those AOA 1,000 feet.

Monday through Wednesday: After a gloomy weekend, nicer weather for Monday and Tuesday with high pressure and mid-level ridging. Monday night there is the potential for cooler temperatures because of radiational cooling, did blend in the cooler CONSMOS guidance which gave lows are in the upper 30s to low 40s across interior southern and known areas that radiate well along the I-495 corridor and Martha's Vineyard, elsewhere middle and upper 40s. The axis of the ridge shifts east Tuesday evening and a northern stream trough and cold front approaches from the west.

Temperatures rebound nicely both these days, low 70s for Monday, then mid to upper 70s on Tuesday. SW flow on Tuesday ushers in higher PWATs, ahead of an approaching mid-level trough and surface cold front. While a few showers Tuesday night into Wednesday morning are possible, it looks the best forcing with the cold front comes too late as the best moisture exits east of New England before the cold front arrives. The timing of the cold front will dictate the high temperatures for Wednesday, thinking it could be a slow moving front, which may allow the coast plain to warm up nicely into the low and middle 70s, while those interior locations only reach the upper 60s to low 70s. Cold front moves across the region and brings a shot of colder air across all of southern New England, widespread upper 30s to low 40s.

Thursday and Friday: Drier Thursday with weak high pressure briefly in control, but is quickly followed by unsettled weather and the return of rain on Friday.

Temperatures late week are seasonable in the low and middle 60s. .

Aviation

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

06Z TAF Update:

Through 12Z: Low confidence.

VFR/MVFR conditions, slowly decreasing through 12Z with the arrival of RA.

Today: Moderate confidence.

Widespread MVFR (with some IFR) in bands of steady moderate rain, which begins to move offshore around 18-20z. By then, clouds scatter to VFR-MVFR (perhaps still some straggling IFR along the south coast). Possible SCT SHRA/TS near/west of ORH after 20z Sat, although development and strength of any TS would depend on how quickly we see any breaks in OVC. If we do see any storms, they would likely be weakening as they move east of ORH. S/SW winds around 10-15 kt with occasional gusts to low 20s-kt range.

Tonight: High confidence.

Improvement toward SCT-BKN VFR with cold frontal passage, though some MVFR bases may develop overnight in western airports. Winds become W/WNW around 10-15 kt with gusts 25 kt (up to 30 kt high terrain).

Sunday: High confidence.

VFR. NW winds 10-15 kts. KBOS TAF...High confidence in TAF thru 07z, then moderate to low.

VFR with E/SE winds continuing thru 03z before becoming S around 10 kt. Mainly MVFR bases with 3-6SM RA developing after 10z Sat, possibly IFR at times. RA ends ~18-20z with slow improvement in cigs to borderline VFR levels. Another round of showers and perhaps a rumble or two of thunder is possible late afternoon to early evening

KBDL TAF...High confidence in TAF thru 05z, then moderate to low.

VFR with south winds around 10 kt. MVFR-possible IFR bases with 3-6SM RA developing after 09z, then tapering off around early to mid afternoon. Possible SCT SHRA/TS after 20z depending on how quickly improvement develops from AM rains.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR. Windy with gusts up to 35 kt.

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Slight chance SHRA, isolated TSRA.

Wednesday: VFR. Breezy.

Marine

Forecaster Confidence Levels:

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

Southerly flow continues to strengthen into the SCA range for today, with winds 25-30 kt and seas 4-7 ft. Rain and reduced visibilities expected until a sharp frontal passage this evening, bringing a windshift to W/NW around 15-25 kt. Sunday NW winds will gust 20 to 25 kts with seas of 3-6 ft.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas.

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

Monday Night: Winds less than 25 kt.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft.

Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers, isolated thunderstorms.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.