textproduct: Boston / Norton

WHAT HAS CHANGED

Updated Aviation section.

High temperatures away from the southeast coast could threaten daily records for March 10th. Dreary weather Wednesday but turns mild overnight with periods of rain. Increased winds Thursday with temperatures cooling off late in the week.

KEY MESSAGES

- Sunny and quite warm today with near record high temperatures away from the southern coast, although quite a bit cooler with low clouds along the southern coast.

- Cloudy, dreary Wednesday as backdoor cold front returns north as a warm front. Much cooler daytime highs Wednesday northern MA compared to CT/RI. Then a mild night Wednesday night with periods of rain as cold front moves in.

- Lingering showers ending Thu, then becoming blustery and turning colder in the afternoon.

- Chance for rain and elevation snow showers late Fri into Fri night, then becoming windy and turning milder again late Sunday into Monday with potential for widespread showers.

- Snowmelt will continue but with lack of significant rainfall only minor river flooding possible.

DISCUSSION

KEY MESSAGE 1...Sunny and quite warm today with near record high temperatures away from the southern coast, although quite a bit cooler with low clouds along the southern coast.

Areas of fog and stratus to advance along the south coast and much of southeast New England. Fog could be locally dense at times but its northern extent should be stunted by at least modest SW winds. This moisture is trapped underneath a very strong temperature inversion, so even though fog is expected to disperse early Tue, potential exists for at least residual low clouds to lurk around into the afternoon as that moisture remains trapped beneath the inversion. This casts some uncertainty on how warm temps may get along the south coast and coastal southeast New England; although the coolest readings should still be recorded in these locations, in the upper 40s to low 50s.

Elsewhere, expecting a particularly warm day by early-March standards. WSW winds will combine with full sun and continued warm advection (850 mb temps rise to +12 to +14C) and lead to soaring temps. Given highs yesterday reached into the 60s with a few spot 70 degree readings, highs today should be some 3-5 degrees warmer and support readings well into the 60s, with lower to even mid 70s in the CT and Merrimack Valleys. Some daily records could be challenged, best chance being Hartford/Windsor Locks and Worcester; unlikely to see records at Providence given cooling marine influence. Toughest call is Boston; should see strong enough SWly winds to keep a seabreeze offshore and kept highs right around 70, which is just under the daily record. If a seabreeze does develop, highs along the eastern MA coast will end up being several degrees cooler.

KEY MESSAGE 2...Cloudy, dreary Wednesday as backdoor cold front returns north as a warm front. Much cooler daytime highs Wednesday northern MA compared to CT/RI. Then a mild night Wednesday night with periods of rain as cold front moves in.

Challenging forecast Wed especially with respect to highs. As the case early this AM, Tue night will be met with returning fog and low clouds from the southern coastal waters into portions of CT- RI- SE MA. Lead wave of weak low pressure passes to our north Tue night and should reinforce cooler temps, which will drain southward as a backdoor cold frontal boundary into northern and especially northeast MA. This backdoor front will be marked by a NE wind shift to go along with dreary conditions and very light rain/mist. Uncertain when this backdoor front may slip into SNE but could occur as soon as the pre-dawn Wed hours. It eventually returns northward through the day on Wed as a warm front though. As shown in higher res 2-m temps, this creates quite a temperature contrast across SNE, with daytime temps struggling to rise above the mid/upper 40s north/northeast MA while areas south and west of the boundary could again rise into the mid 60s. Other than drizzle or very light rain, most of the day is generally drier than not.

Then a stronger wave of low pressure looks to pass to our north Wed night, but strong warm and moist advection takes place ahead of this frontal system's associated cold front on SWly low level jet nearing 50 kt. PWATs rise to as much as 1.5" Wed night and 850 mb temps continuing to warm to at least +14C. Even some elevated instability, as can be expected in these nighttime strong warm/moist advection regimes, although its scope varies between the GFS/NAM quite a bit. 00z NAM profiles are pretty impressive and could support thunder but much more paltry in the GFS. Raised PoPs to likely for Wed night ahead of the cold front. Not expecting a significant amount of QPF with this wave but this will need to be monitored.

KEY MESSAGE 3...Lingering showers ending Thu, then becoming blustery and turning colder in the afternoon.

Cold front will be moving through SNE Thu morning then offshore in the afternoon. Pre-frontal showers expected and timing of FROPA will determine how quickly the showers exit. Best chance of showers in the morning will be in the east where later FROPA arrival, then drying out in the afternoon as PWATs crash. Strong cold advection behind the front so after a mild start temps will fall from the 50s in the east through the 40s in the afternoon, while interior locations will see temps fall through the 40s and into the 30s higher elevations. The strong cold advection will also result in gusty W-NW winds. Soundings show a relatively shallow mixed layer but excellent mixing will support gusts 25-35 mph. Winds will slowly diminish Thu night with lows dropping into the 20s.

KEY MESSAGE 4...Chance for rain and elevation snow showers late Fri into Fri night, then becoming windy and turning milder again late Sunday into Monday with potential for widespread showers.

Another fast moving northern stream shortwave and attendant clipper system will track to the north late Fri into early Sat. Bulk of the QPF will be to the north but modest low level jet and increasing moisture suggest a period of rain and elevation snow showers will impact the region late Fri into Fri night, especially northern MA. Minor snow accums are possible over the Berkshires. Then drying out Sat behind the cold front as much drier air moves in.

A more amplified trough approaches from the west Sunday into Monday with a stronger low level jet advecting anomalous PWATs (approaching 1.5") northward into SNE. This will likely bring a more widespread rainfall event Sun night into Monday and can't rule out locally heavy rainfall given the LLJ and PWAT anomalies. Something that will need to be monitored as rivers and streams will be running high from the recent accelerated snowmelt. Any heavy rainfall could introduce flooding concerns. Another surge of mild air and gusty winds expected Sun night into Mon with the southerly low level jet.

KEY MESSAGE 5...Snowmelt will continue but with lack of significant rainfall only minor river flooding possible.

Snowmelt will become more accelerated Wednesday night as dewpoints climb into the 50s and most of the snowpack outside of the Berkshires will likely be depleted by Thursday. However, we are not expecting much rainfall Wed night into Thu so only expecting minor flood stages to be observed as a worst case scenario. Guidance continues to indicate the most likely spots to see flooding are along the Connecticut River by next weekend with addition of S. RI rivers by early next week.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

12z TAF Update: High confidence.

VFR with SW flow today and early tonight.

Near Cape Cod and Islands, LIFR improves this morning but it's possible ACK holds onto fog and low clouds all day. For now we are showing improvement around 16z but there is a 30-40% chance that doesn't happen. Either way, LIFR returns to these areas around or just after sunset and persists all night.

Elsewhere, MVFR and IFR cigs develop overnight as winds shift to E/NE with some improvement during day Wed.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...

Wednesday: MVFR/IFR conditions possible. Breezy. Slight chance RA, patchy BR.

Wednesday Night: Mainly VFR, with local IFR possible. Breezy. Chance RA.

Thursday: Mainly VFR, with local MVFR possible. Windy with areas of gusts up to 30 kt. Chance RA.

Thursday Night through Friday: VFR. Breezy.

Friday Night: Windy with gusts up to 30 kt. Chance RA, chance SN.

Saturday: Windy with local gusts up to 30 kt.

MARINE

Forecaster Confidence Levels...

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

Sub-SCA wind and wave conditions prevail through the daytime hours Wed. SW winds around 10-15 kt with seas 2-3 ft, though seas build to 2-4 ft Wed. Main concerns for mariners are the risk for nighttime fog both overnight and again Tue night into Wed, and also a NE windshift for mariners navigating the northern waters Wed.

SCAs likely to be needed Wed night as seas rise over 5 ft on all waters. Gusts could also punch into SCA range but more than likely to be tempered by a strong inversion.

Outlook /Wednesday through Saturday/...

Tuesday Night: Winds less than 25 kt. Patchy fog. Areas of visibility 1 nm or less.

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain, patchy fog.

Wednesday Night: Strong winds with areas of gusts up to 30 kt. Areas of rough seas. Chance of rain.

Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain.

Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.

Friday Night: Strong winds with gusts up to 35 kt. Areas of rough seas. Chance of rain.

Saturday: Strong winds with gusts up to 30 kt. Areas of rough seas.

CLIMATE

Record highs for Tuesday, March 10th...

BOS...71...1878 PVD...72...2016 BDL...72...2016 ORH...67...2020

Average high for 3/10 is 40-45.

BOX WATCHES/WARNINGS/ADVISORIES

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