textproduct: Boston / Norton

WHAT HAS CHANGED

A Wind Advisory was issued for the portion of Southern New England not within the High Wind Watch. The Storm Watch has been converted to a Storm Warning for all waters. A Flood Watch has been issued for the potential of some minor river and stream flooding as well as localized poor drainage flooding in urban areas.

KEY MESSAGES

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

- A period of strong to damaging winds expected across portions of SNE Monday night.

- Mainly dry and trending colder Tue into Wed, then moderating temperatures Thu and especially Fri.

- Period of showers possible sometime Fri night and/or Sat with a trend to drier/chillier weather Sun or Sun night.

DISCUSSION

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

The upcoming storm system will pose two hazards for southern New England, the first of which we'll address is potential for heavy rain, flooding, and some embedded thunderstorms. A deepening low pressure system crossing the Great Lakes on Monday will direct a plume of deep moisture out ahead of it while strong dynamics both at the surface and in the middle/upper atmosphere will together bring a prolonged period of rain, heavy at times. As the warm front lifts north on Monday SNE will be placed in the warm sector featuring temperatures as warm as the low 60s and dewpoints well into the upper 50s! Warm advection showers will begin to overspread the region in the pre dawn hours on Monday. The environment is conducive to widespread light to moderate rain with embedded convective elements given 200-500 J/kg of elevated MUCAPE. These would contribute to localized heavy downpours as well as thunder. It should feel like a true Spring day, especially in those locations that make it into the 60s. Rainfall continues through the day and overnight hours, coming to a head with a potential fine line of convection (depicted in most hi-res guidance) ahead of the cold front which moves through between midnight and 5am. Anomalous moisture content in the atmosphere (PWATs near 1.5" or 3-4 SD above normal) combined with similarly anomolous jet dynamics (80-90kts at 925mb) will squeeze out a good soaking of rain, widespread 2" likely with as much as 3+" possible under any soaking t-storms. A Flood Watch has been issued for the area, given recent snowmelt combined with a decent rainfall will likely lead to rises to minor flood stage on some rivers and streams as early as Tuesday morning. Can't rule out some localized poor drainage flooding under t-storms as well.

KEY MESSAGE 2...A period of strong to damaging winds expected across portions of SNE Monday night.

The other (and likely more impactful) threat from this storm system is that those impressive jet dynamics make their way to the surface as damaging wind gusts during a ~6 hour window Monday night with the passage of the cold front. As mentioned above, the wind will be screaming just overhead with some guidance indicating as much as 80- 90 kts at 925mb between 03 and 09Z. The difficulty, as is usually the case with southerly flow events like this, is that we'll have a stout inversion in place to about 950mb which will have to be overcome to bring the strongest of those winds down. This will depend heavily on just how warm temperatures get late Monday. Regardless, winds will ramp up on Monday gusting 35-45 mph. The best shot at the damaging winds comes along and ahead of the cold front, especially if that fine line of convection forms and can help to drag the strongest gusts down. A High Wind Warning is in effect for RI and eastern MA which has the best shot at a ~3 window in any given location for damaging gusts of 60-70 mph. Best case scenario if we don't reach these speeds, gusts of 45 to 55 mph are likely so Wind Advisories have been issued for the rest of the region.

KEY MESSAGE 3...Mainly dry and trending colder Tue into Wed, then moderating temperatures Thu and especially Fri.

Strong cold air advection aloft works into the region Tue morning behind the cold frontal passage. This will be offset somewhat by some mid March sunshine...although we do expect some diurnal CU too in especially across the interior and can not rule out a passing brief spot flurry/snow shower. Tue afternoon temps will mainly be in the lower to middle 40s in the lower elevations with 30s in the higher terrain. It will also be blustery with westerly wind gusts on the order of 25 to 35 mph...so it will feel colder. The cold air peaks Tue night into Wed with 850T dropping to between -15C to -18C. This is a decent shot of cold air for the second half of March. Low temps Tue night will bottom out in mainly in the teens with a few urban centers in the 20-25 degree range. Wind chills early Wed morning will be in the single digits to the lower teens! Despite plenty of sunshine Wed...Highs will be held mainly in the 30s but with much less wind as high pressure builds overhead.

After a rather cold start early Thu morning...temps will begin to moderate as high pressure moves east of the region allowing return southwest flow to develop. Highs Thu will still be in the 40s...But expect highs to reach into the 50s on Fri ahead of an approaching cold front.

KEY MESSAGE 4...Period of showers possible sometime Fri night and/or Sat with a trend to drier/chillier weather Sun into Sun night.

A cold front approaching from the west may bring a period of showers sometime Fri night and/or Sat depending on the specific timing. Behind this cold front...think things will trend drier and chillier sometime Sun or Sun night. Quite the ways out though so this is certainly subject to change.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18Z update...

This afternoon...High Confidence

VFR. Winds E/SE 5 to 10 knots.

Tonight...High Confidence

Deteriorating conditions tonight into Monday as a warm front lifts north over the region. MVFR/IFR ceilings and visibility develop after 05/7Z as light to moderate rain overspreads southern New England.

Monday...High Confidence

IFR in expanding RA. Winds increase through the day, shifting to become more southerly, gusting 30-35 kts late afternoon and evening. Scattered TSRA is increasingly likely particularly in CT and RI.

Monday Night...High Confidence.

Peak of the winds, gusting gusting 40-55kts for several hours. S winds become more SW and W by 12Z. RA/TSRA possible through 07-12z, ending from west to east.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence

Outlook /Monday Night through Friday/...

Tuesday: VFR. Windy with gusts up to 35 kt.

Tuesday Night through Wednesday: VFR. Breezy.

Wednesday Night through Thursday Night:

Friday: Slight chance RA.

MARINE

Forecaster Confidence Levels...

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

Through Monday Night

Seas calm to 1-3 ft through the day afternoon as high pressure settles overhead. Winds today over the waters shift more to the SE into the afternoon but remain around 10-15 kt, occasionally gusting to 20 kt over the southern waters. Winds ramp back up tonight into Monday as a powerful low pressure system approaches from the west. Seas increase considerably headed into Monday night, 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 likely approach storm conditions Monday night. Storm Watches have been upgraded to Storm Warnings for all waters.

Outlook /Tuesday through Friday/...

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to 14 ft.

Tuesday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Rough seas up to 12 ft.

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

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

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...Flood Watch from late tonight through Tuesday morning for CTZ002>004. Wind Advisory from 2 PM Monday to 8 AM EDT Tuesday for CTZ002>004. MA...Flood Watch from late tonight through Tuesday morning for MAZ002>022-026. Wind Advisory from 2 PM Monday to 8 AM EDT Tuesday for MAZ002>004-008>012-026. High Wind Watch from Monday afternoon through late Monday night for MAZ005>007-013>024. RI...Flood Watch from late tonight through Tuesday morning for RIZ001>007. High Wind Watch from Monday afternoon through late Monday night for RIZ001>008. MARINE...Storm Warning from 8 PM Monday to 5 AM EDT Tuesday for ANZ230- 236. Storm Warning from 5 PM Monday to 8 AM EDT Tuesday for ANZ231>235-237-250-251-254>256.