textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes were made to the forecast during this update.

KEY MESSAGES

- Cold front moves through the region this afternoon and exits tomorrow morning, scattered showers with embedded thunder are possible along with cooler temperatures.

- Drying trend second half of Thursday into Friday along with seasonable to slightly below seasonable temperatures.

- The weekend looks unsettled with a couple periods of showers, one Saturday and the other towards Sunday evening/Monday.

DISCUSSION

KEY MESSAGE 1...Cold front moves through the region this afternoon and exits tomorrow morning, scattered showers with embedded thunder are possible along with cooler temperatures.

A slow-moving cold front moves across southern New England starting this afternoon as it approaches western New England and exiting the region's coastal waters tomorrow morning. While not as windy as the last two days, expecting a period of gusty SW wind, 20-30 mph, due to a tight pressure gradient between the incoming front and surface high to the east. SW flow advects higher PWATs, values around 1.3", which is 1.5-2 standard deviations above normal. Rain arrives to western MA and northwest CT between noon and 2 PM, reaching eastern southern New England between 4-7 PM. Temperatures are noticeably cooler, in the upper 60s to lower 70s with dew points between 53- 57F, this should support of a few hundred units of CAPE and embedded thunder. Rain amounts generally are between 0.1-0.3" with localized amounts greater than 0.5" within thunderstorms. The cold front moves offshore tomorrow morning with showers linger for areas SE of I-95. Do think showers end before 8 AM, but could persist for Cape Cod and the Islands as late as 10 AM to noon.

KEY MESSAGE 2...Drying trend second half of Thursday into Friday along with seasonable to slightly below seasonable temperatures.

Late morning into early afternoon does feature drying conditions across southern New England and more typical temperatures for early May. CAA does advect a seasonable airmass and low PWATs, less than 0.3" by the afternoon. That said, we feel more confident that the second half of the day will be rain free with variable amounts of cloud cover and seasonable highs between the lower and mid-60s. A cool night ahead with northwest winds. These winds should help limit the potential for radiational cooling as there will be less in the way of cloud cover. Nevertheless, a cool night, urban areas have a nightly low in the lower to mid 40s while rural areas fall as low as the upper 30s. Eastern Berkshires could dip as low as 33-36F. Do warm up, though a tad cooler than average with breezy westerly winds Friday under a mixture of sun and clouds.

KEY MESSAGE 3...The weekend looks unsettled with a couple periods of showers, one Saturday and the other towards Sunday evening/Monday.

The next opportunity for rain arrives sometime early Saturday as a mid-level trough and weak surface low pressure system passes through the northeast. Raw type of day with highs in the lower 60s, wetting rain of a quarter of an inch of rain is possible, ensembles have the probabilities between 40-60 percent. Towards the end of the forecast period Sunday into early next week there are uncertainties, though the forecast for Sunday, Mother's Day, has improved, a bit of a lull in the action. The second system appears to be more of a rain-maker, due to potential phasing between a southern-stream 500mb vort max rippling through the Gulf Coast states with northern stream broader troughing north of the Gt Lakes region. Timing and details regarding this frontal system are still hazy but the timing looks to be more centered at absolute earliest late Sunday afternoon, but more probable Sunday night into Monday.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

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 through at least 09z. Some risk for MVFR stratus to develop from IJD-PVD-SE MA airports after 09z. SW winds 12-15 kt with gusts to 25 kt, with low level wind shear.

Today and Tonight: Moderate confidence.

Low-end VFR to MVFR conditions dominate today. Numerous showers will overspread the region from west to east, mainly during the afternoon hours, lowering to MVFR to IFR. Showers move offshore tonight. IFR conditions improve from west to east after midnight.

Thursday: High confidence.

VFR. Wind WNW 8-12 kt, localized sea breeze possible.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR.

Friday: VFR. Breezy.

Friday Night: VFR.

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

Saturday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA.

Sunday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Thursday...High confidence.

Small Craft Advisory conditions persist today, then gradually improve tonight. Showers expected to develop across the coastal waters this afternoon, then gradually taper off into Thursday morning from west to east. Seas remain elevated on the southern waters into early Thursday afternoon.

Outlook /Thursday Night through Sunday/...

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

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

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

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

Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230- 236. Small Craft Advisory until midnight EDT tonight for ANZ231>235- 237-251. Small Craft Advisory until 4 AM EDT Thursday for ANZ250. Small Craft Advisory until 8 AM EDT Thursday for ANZ254. Small Craft Advisory until 2 PM EDT Thursday for ANZ255-256.