textproduct: Boston / Norton

WHAT HAS CHANGED

High Wind Watches have been upgraded to High Wind Warnings across eastern MA and RI.

KEY MESSAGES

- Periods of heavy rain with embedded t-storms today, especially tonight, may lead to river and small stream flooding. Poor drainage in urban areas could flood as well.

- A period of strong to damaging winds across SNE tonight.

- Mainly dry and trending colder Tue into Wed.

- After a cold start early Thu morning temps begin moderating especially by Fri. Mainly dry weather over this time.

- Unsettled weather at times Fri night into early next week... but timing remains uncertain. Temps tricky this weekend depending on the location of a boundary in the vicinity of SNE. Temps trending colder than normal early next week.

DISCUSSION

KEY MESSAGE 1...Periods of heavy rain with embedded t-storms today, especially tonight, may lead to river and small stream flooding. Poor drainage in urban areas could flood as well.

We're in the thick of a wet and windy storm system that will continue to impact the region through sunrise on Tuesday. After a bout of heavy and widespread rainfall this morning we're in a relative lull this afternoon as the warm front has lifted into northern New England. This has placed us into a warm and moist airmass with temperatures as warm as the low 60s while dewpoints have risen well into the 50s. A very strong LLJ (80-90 kts at 925mb over southeast MA) will act on very anomalous moisture (PWATs near 1.5" or 3-4 SD higher than normal) to continue to squeeze out copious amounts of rainfall over the next 12-15 hours. Following this lull in intensity we'll see a resurgence of heavy rainfall this evening and overnight ahead of the cold front. Rainfall amounts will also be juiced by any convection that occurs given the environment with 400-600 J/kg of elevated CAPE. The best chance for thunder is CT/RI and central MA. When all is said and done still expecting widespread 2 to 3 inches of rain with 3-4 inches possible in those locations that experience a t-storm. River Flood Warnings have been issued for some area rivers, given recent snowmelt combined with a decent rainfall will lead to minor flooding. Additionally, some localized poor drainage flooding is possible, especially under any convection.

KEY MESSAGE 2...A period of strong to damaging winds across SNE tonight.

The other threat from this system is a period of strong, potentially damaging winds. As was mentioned previously, the jet dynamics with this system are very strong. This means we'll have an impressive low level jet screaming overhead just above a temperature inversion. Model soundings show an impressive inversion to near 950 mb which is typical this time of year with southerly wind events. The question is always just how much of that jet can be tapped into to pull down to the surface. The best way to tap into these winds is typically 1) warming the surface, the warmer the temp the better mixing and 2) the winds being pulled down by heavy downpours, especially in convection. The best shot for this event will be a fine line of convection accompanying the cold front after midnight tonight coincident with the core of the jet overhead. Thus, while winds will be increasingly gusty today, gusting 35-45 mph by the evening, the real chance for damaging winds will be in a ~3-4 hour window from roughly midnight to 4am. Wind gusts as high as 65 mph are possible in the southeast MA/RI area. Can't even rule out a gust to 70 mph in the Providence to Plymouth corridor. This is the favored location because, while the core of the jet is further south over the Cape/islands, southerly flow off the water keeps temperatures cooler in these areas so mixing isn't as efficient.

KEY MESSAGE 3...Mainly dry and trending colder Tue into Wed.

The cold front exits east offshore well before sunrise on Tuesday ushering in a cooler and drier airmass through Wednesday. Expect mostly sunny skies mixed with some diurnal cumulus thanks to the cold pool that moves in aloft. 925 mb temps drop from 13 C on Monday to -3C on Tuesday so we can expect a significant cooldown, 10-15 degrees in highs from Monday to Tuesday and even moreso on Wednesday. Highs Tuesday will be in the low to mid 40s while Wednesday will be in the 30s.

KEY MESSAGE 4...After a cold start early Thu morning temps begin moderating especially by Fri. Mainly dry weather over this time.

Large high pressure shifts east of the region Wed night & Thu. Conditions will still be favorable for a good night of radiational cooling Wed night...so expect low temps mainly in the teens and 20s. Return southerly flow and plenty of March sunshine should allow highs on Thu to recover back into the low to mid 40s by afternoon.

A warm front crosses the region late Thu night into early Fri morning with perhaps a brief passing rain/snow shower or two. Otherwise...expect a further moderation in temps with highs on Fri potentially 50+.

KEY MESSAGE 5...Unsettled weather at times Fri night into early next week...but timing remains uncertain. Temps tricky this weekend depending on the location of a boundary in the vicinity of SNE. Temps trending colder than normal early next week.

A couple pieces of northern stream shortwave energy will result in unsettled weather at times Fri night into early next week. Specific timing is uncertain...but appears one potential for showers will be Fri night/early Sat associated with a shortwave/cold front. Perhaps another round of unsettled weather later this weekend into early next week...but timing/confidence on that is low given a large model spread in timing and track.

A boundary in the vicinity of southern New England makes the temperature forecast tricky this weekend. Highs may be in the upper 30s and 40s north of the boundary and between 55 and 65 to the south of the boundary. We probably will end up mostly on the cooler side of those numbers especially in north/northeast MA given climo this time of year...but plenty of time to sort that out. Regardless...temps likely trending colder early next week given amplifying New England upper trough indicating by the long range ensembles.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

00Z update...

Tonight...High Confidence.

IFR. Peak of the winds, gusting gusting 40-55kts through 06-09z. S winds become more SW and W by 12Z. RA with embedded TSRA possible through 07-12z, quickly ending from west to east.

Tuesday...High Confidence

VFR. Region clears out behind cold front. Gusty W winds around 25-30 kt are left in its wake.

Tuesday night...High Confidence.

VFR. W winds 5-10 kts.

KBOS Terminal...Moderate confidence.

KBDL Terminal...Moderate confidence.

Outlook /Wednesday through Saturday/...

Wednesday through Wednesday Night: VFR.

Thursday: VFR. Breezy.

Thursday Night: VFR. Slight chance SHSN.

Friday: VFR. Slight chance SHRA.

Friday Night: VFR. Chance SHRA, chance SHSN.

Saturday: VFR. Breezy. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday night...

Winds ramp up this afternoon into tonight as a powerful low pressure system approaches from the west. Seas increase considerably headed into tonight, reaching up to 15 ft and even close to 20 ft in the southern waters by 06z Tuesday. Seas 7-10 ft will be more common in the eastern waters. Winds will very likely reach storm conditions tonight. Storm Warnings are in effect for all waters.

Seas decrease to around 12 ft for Tuesday as the cold front exits over the waters. W winds remain gusty to around 35 kt through the day Tuesday. Winds and seas diminish significantly Tuesday night.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt. Areas of rough seas.

Wednesday Night: Winds less than 25 kt. Seas up to 5 ft.

Thursday through Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Friday Night through Saturday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Flood Watch through Tuesday morning for CTZ002>004. Wind Advisory until 8 AM EDT Tuesday for CTZ002>004. MA...Flood Watch through Tuesday morning for MAZ002>022-026. Wind Advisory until 8 AM EDT Tuesday for MAZ002>004-008>012- 026. High Wind Warning until 6 AM EDT Tuesday for MAZ005>007- 013>024. RI...Flood Watch through Tuesday morning for RIZ001>007. High Wind Warning until 6 AM EDT Tuesday for RIZ001>008. MARINE...Storm Warning until 5 AM EDT Tuesday for ANZ230-236. Storm Warning until 8 AM EDT Tuesday for ANZ231>235-237-250- 251-254>256.