Significant Rain Likely – Warm Day First

Good morning! Let’s just cut to the basics of today’s forecast, because we have a significant rain event on the horizon.

Today will be partly sunny to start with increasing clouds throughout the day, and pretty much the exact same high temps as yesterday, maybe a nudge cooler. 70-80, region-wide, locally cooler in the highest elevations, a hair warmer in some spots in CT and perhaps isolated spots in eastern MA, with south winds to 10 mph again. Some isolated showers with a widely isolated rumble of thunder may occur late this morning into this afternoon, with eventually full-on widespread rain entering this evening into overnight tonight.

Let’s get into a discussion of hazards with this storm.


Let’s start with the timing for this storm. The widespread shield of rain will enter the region sometime this evening into the early overnight. A true washout is expected throughout New England tomorrow, no way around it. Precipitation will finally leave the region Thursday, probably around midday.


A widespread 2-4″ of rain is likely across New England, with locally higher amounts possible within embedded thunderstorms, which will be possible due to elevated instability, particularly across Southern New England and adjacent Southern NH, starting Wednesday morning and continuing throughout the day. That instability will be on the elevated side, but it will not be high CAPE by any means; however, rather good shear is in place, meaning a strong to maybe even embedded severe thunderstorm is not out of the cards: (both images below are for the same time, at 1 km and 3 km. Not pictured, but 6 km shear is also rather strong).


Something interesting to note is there will be high helicity values for many. A spin-up tornado cannot be 100% ruled out; however, this is not an immediate concern, rather an interesting observation.

nam-hel--usne-36-C-hel3000_white nam-hel--usne-36-C-hel1000_white

Lifted index and lapse rates are looking better at the lower levels in the morning, however. More severe updates this evening.

The main story, however, is the 2-4″ of rain. Some of the smaller rivers may see rapid rises, but urban flooding is the main threat (especially in any embedded thunderstorms), as well as poor drainage and low lying areas. Main stem rivers, such as the Merrimack, Connecticut and Charles, should stay in their banks. An areal flood watch is out for a substantial portion of New England for this storm, in dark green on the map below.


Coastal Flooding

Yes, this storm also has a coastal flood threat, even if rather minor. There could be some localized minor splashover during astronomical high tide Wednesday, as a result of increasing seas and said high tide. Wednesday evening, there may be a more significant coastal flood threat, and more coastal flooding is possible through the rest of the week.


This storm will not be a big wind producer, at least not near the surface. Expect northeast winds 10-15 mph, with highest gusts to 25-30 mph, locally higher in the evening for both sustained and gusts. HOWEVER, the exception will be within thunderstorms, where gusts near or even over 45 mph are possible. Can’t completely rule out an isolated severe wind within those, as mentioned.

Current Alerts: Flood Watch for Southern Vermont/Far Western MA/Northwest CTFlood Watch for Northern CT/Western, Central and Northeast MAFlood Watch for Central VermontFlood Watch for NH and Southwest Maine; Coastal Flood Watch for NH and Southwest Maine Coast.

Have a great Tuesday!


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