textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Scattered shower and a few thunderstorms possible tonight.

- Strong cold front will bring a round of widespread showers late Sat night into Sunday, then drying out and turning colder Sun night.

- Mainly dry and unseasonably cool Mon-Tue, then moderating temperatures toward midweek. Next chance of showers will be Tue night into early Wed.

DISCUSSION

KEY MESSAGE 1...Scattered Showers and few thunderstorms possible tonight. Few showers possible late Friday afternoon, low probability (< 20%) for an isolated thunderstorm.

Ample warming this afternoon in western and central southern New England. Satellite imagery this afternoon shows cumulus starting to develop across those areas. A sign that at least marginal instability is present. Something to keep tabs on given that we have potential for scattered showers and thunderstorms in the forecast tonight in response to a shortwave trough. Winds aloft increase this evening which will bring in better bulk shear values. All that being said, we can still see a risk for scattered thunderstorms generally after sunset. Where higher instability and sufficient shear overlap in far west/NW MA, can't rule out a strong to severe storm. Overall CAMs show limited coverages of storms as they develop and move eastward after sunset. A round or two of scattered showers are also possible overnight and into early Friday morning.

Cooler day Friday compared the Thursday, especially for the locations that were well into the 80s in western southern New England on Thursday. Highs range in the 60s and 70s in west, central southerne new england and mid 50s to lower 60s further east. Isolated showers are possible, although lower confidence on exact location of the showers given the lower coverage. Instability will be marginal, but enough to support an isolated storm in the afternoon.

KEY MESSAGE 2...Strong cold front will bring a round of widespread showers late Sat night into Sunday, then drying out and turning colder Sun night.

Surface ridging in control on Sat will provide dry weather with temps more seasonable for mid April as onshore flow will prevail. Then a fairly robust upper trough will approach from the Gt Lakes with the attendant strong cold front moving through SNE during Sunday. A plume of PWATs 1.25-1.5" move into SNE in the pre-frontal environment Sat night into Sunday. Decent forcing for ascent ahead of the upper trough acting on this moisture will result in an area of widespread showers moving through the region late Sat night into Sunday which may be enhanced along and just ahead of the front. There is some elevated instability so can't rule out a few t-storms as well.

The front will move through western New Eng by midday and eastern MA during the afternoon. The column cools rapidly behind the front and there may be enough lingering moisture for showers to end as some snow showers in western MA, especially over the higher terrain but if it happens not expecting any accumulation. PWATs drop quickly from W to E late Sun and Sun night which will bring clearing skies and turning much colder in the strong cold advection pattern. Temps by Mon morning will drop to the low-mid 30s, with upper 20s over the higher elevations. Brisk W-NW winds will result in wind chills in the 20s around daybreak Mon.

KEY MESSAGE 3...Mainly dry and unseasonably cool Mon-Tue, then moderating temperatures toward midweek. Next chance of showers will be Tue night into early Wed.

Upper trough and core of coldest air aloft move through Mon into Mon night so it will be unseasonably cool during this period. 850 mb temps bottom out around -10C Mon night. Expect diurnal cu to develop Mon but dry weather with highs mostly in the 40s to near 50 in the coastal plain. Gusty W-NW winds will make it feel even cooler. Lows will drop into the 20s Mon night with diminishing wind as high pres builds into the region. Temps moderate slightly Tue but still chilly with below normal temps, then temps get back to seasonable normals Wed and Thu. Another northern stream shortwave may bring a few showers Tue night into early Wed, otherwise mainly dry weather through Thursday.

AVIATION /19Z THURSDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

Through 00z Friday: High confidence overall, though is low to moderate for Boston.

Mainly VFR. Stratus and mist still lurks offshore and is hugging the eastern MA coastline and could at times work its way back into BOS but it may not be that persistent, if it even does so at all thru 00z. Pop-up showers could develop near BDL and north of ORH as soon as 22z but would be more likely after 00z. SSW winds around 5-10 kt, with ENE/E winds for ORH, BED and BOS, with SE winds around 5 kt.

Tonight: Moderate confidence.

Mainly VFR; uncertain if BOS and BED see IFR/MVFR stratus layer return but would be more likely tonight as the boundary layer cools off. Couple periods of SHRA/possible TS: one 00z-03z mainly N/W of ORH, with a somewhat better chance after 06z Fri. Carried PROB30s for the time being since the coverage could be spotty. SW winds (E winds near the eastern coast) around 5-10 kt become light in all areas thru midnight then should come around to light northerly by daybreak.

Friday: Moderate confidence.

Mainly MVFR, possibly IFR from low ceilings, with periods of hit-or-mostly-miss showers. North to northeast winds 5-10 kt.

KBOS Terminal...Moderate confidence in TAF. VFR generally governs thru 00z, but stratus and mist lurk offshore and could at times bring periods of IFR. Better chance at IFR stratus coming in tonight. Mainly dry but risk for rain showers after 06z Fri. NE/E winds 5-10 kt flip to light southwest briefly overnight, then return to light northerly for Friday.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Tuesday/...

Saturday: Mainly VFR, with local MVFR possible.

Saturday Night: Mainly VFR, with areas IFR possible. Breezy. Slight chance SHRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

Sunday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, slight chance SHSN.

Monday: VFR. Breezy. Slight chance SHRA, slight chance SHSN.

Monday Night through Tuesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

High confidence through the weekend.

Seas 2-5 ft and winds less than 25 kts. SW winds shift to NE later Friday. Brief periods of marginal Small Craft Advisory seas possible late tonight/early Fri AM over the southern outer waters, though not expected to be widespread. Passage of stronger cold Front Sun should bring SCA conditions to at least outer waters Sun into Mon.

Outlook /Friday Night through Tuesday/...

Saturday through Saturday Night: Winds less than 25 kt.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely.

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

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, slight chance of snow showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

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