textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes. High wind watches for RI and eastern MA and storm watches for the waters continue. Flood Watches may need to be issued today for the potential of flooding of rivers, small streams as well as urban and poor drainage areas.

KEY MESSAGES

- Mix of sun and clouds with seasonable temperatures today before conditions start to worsen tonight into Monday

- 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 Thursday and especially Friday.

DISCUSSION

KEY MESSAGE 1...Mix of sun and clouds with seasonable temperatures today before conditions start to worsen tonight into Monday.

Mid-level ridging persists today with surface high pressure as well before a warm front brings more unsettled conditions tonight into Monday. Strong winds from the day before have diminished considerably as ridging has built in overnight. Lighter winds from the SE can be expected this afternoon. Seasonable highs in the mid 40s along with a mix of sun and clouds will be the result today. This respite will be short-lived though as a warm front will lift north across southern New England. Showers will start to move into the region tonight, mostly after midnight, and SE winds will begin to strengthen behind the front. Lows tonight will fall mostly in the low 30s; upper 20s possible in the higher elevations.

KEY MESSAGE 2...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.

Guidance has continued to show significantly above average PWAT values for this time of year associated with this system and is supportive of total QPF approaching 2" for much of southern New England. Strong southerly flow ahead of a powerful low will kick up heading into Monday night, which will help advect in significant moisture. PWAT values approaching 1.5" are possible, and with the stronger forcing that comes with a strong LLJ, widespread amounts of rain to 2" are possible. The NAM has been depicting a fine line feature developing in the latest runs, too, and MUCAPE values around 500 J/kg could lend to isolated t-storms developing. These could lead to localized higher rain totals approaching 3"+ (more details on possible severe weather in KEY MESSAGE 3). This additional rain would also have a greater impact on the above normal stream levels we've been seeing with the snowmelt and rain we've seen lately, so some streams and rivers could see flooding. Spots of poor drainage in urban areas could lead to localized flooding as well.

KEY MESSAGE 3...A period of strong to damaging winds expected across portions of SNE Monday night.

While winds will be ramping up Mon afternoon, the main concern will be Mon night as a very impressive and anomalous low level jet develops ahead of a strong cold front and lifts across SNE. 3K NAM showing 90-100 kt at 925 mb moving up along the SE New Eng coast 03- 06z and exiting Cape Cod by 09z. Up to 80 kt extends back to the I- 95 corridor. The biggest challenge is determining how much of this wind will be able to mix down as we will have a low level inversion in place with NAM soundings showing a strong inversion over the Islands and adjacent waters which complicates the forecast. How mild it can get Mon evening as well as a potential fine line of convection will be a significant factor to damaging wind potential. High confidence that temps will reach the upper 50s with a chance temps could get to 60+ away from the immediate south coast. Soundings indicate damaging wind potential increases significantly if temps get to 60F or higher as inversion would weaken considerably. 3K NAM also indicating a fine line of convection along the front which seems more than reasonable given the strong low level convergence and elevated instability. Any fine line or pre- frontal convective elements would also increase damaging wind potential. It is interesting to note that CSU machine learning probs have severe wind probs and 2% tornado probs across SNE but think this is more of a reflection of damaging wind potential with the fine line as surface based convection is unlikely unless we can get temps to 62-63F with dewpoints 60+. At the very least, even if cooler temps win out with stronger inversion in place, taking 50 percent of the LLJ would suggest at least 45-55 mph gusts, with risk for 60-70 mph gusts and power outages if the inversion weakens. We will continue the high wind watch across RI and eastern MA where highest risk for damaging wind gusts, but wait until we get into the HREF window before potentially upgrading to warnings. Wind advisories will also likely be needed further west across CT and portions of central and western MA.

KEY MESSAGE 4...Mainly dry and trending much colder Tue into Wed, then moderating temperatures Thursday and especially Friday.

We will be in the post-frontal airmass on Tue with colder and much drier air advecting in from the west in the cold advection pattern. It will also be blustery with soundings showing a well mixed boundary layer supporting west gusts to 25-35 mph at times. The cold will peak Tue night into Wed as 850 mb temps drop to -15 to -18C around 12z Wed. Lows Tue night will drop into the teens and low 20s with Wed highs in the 30s. Winds will remain gusty into Tue evening then diminish late Tue night and Wed as high pres builds into the region. Temps then moderate Thu into Fri with temps getting back into the upper 40s and lower 50s for Fri. Looks mainly dry through the end of the week with chance of showers sometime Fri night or Sat as a frontal system approaches.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

12Z update...

Today...High Confidence

VFR. Winds becoming E/SE between 5 and 10 knots after 15Z.

Sunday Night...High Confidence

Deteriorating conditions Sunday night into Monday as a warm front lifts north over the region. MVFR/IFR ceilings and visibility developing after 06Z as light to moderate rain overspreads southern New England.

Monday...High Confidence

Mostly IFR with RA overspreading the region. Winds increasing and shifting more S through the day. Gusts to 35 kt possible heading into the evening hours. Some isolated TSRA cannot be ruled out, particularly in CT and RI. However, it does remain possible outside of those areas as well.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence

Outlook /Monday Night through Thursday/...

Monday Night: Mainly MVFR, with areas IFR possible. Strong winds with gusts up to 50 kt. RA, patchy BR.

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

Tuesday Night through Wednesday: VFR. Breezy.

Wednesday Night through Thursday: VFR.

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 today 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.

Outlook /Monday Night through Thursday/...

Monday Night: Low risk for storm force winds with gusts up to 50 kt. Rough seas up to 19 ft. Rain, areas fog, slight chance of thunderstorms. Local visibility 1 nm or less.

Tuesday: Strong winds with gusts up to 30 kt. Rough seas up to 15 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 through Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Wind Watch from Monday afternoon through late Monday night for MAZ005>007-013>024. RI...High Wind Watch from Monday afternoon through late Monday night for RIZ001>008. MARINE...Storm Watch from Monday afternoon through Tuesday morning for ANZ230>237-250-251-254>256.