Finally, Widespread Rain Today; Then Big Heat Thereafter

Good morning!

Today’s high temperatures will fall in the upper 70s to low 80s, under mainly cloudy skies and some showers moving in this morning. Winds will be SW 5-10 mph, except higher in thunderstorms. These showers are moving east into the region, accompanied by plentiful areas of steady rain and some areas of heavy rain.

radar 728 am.PNG
7:30 AM radar, courtesy National Weather Service website

In addition, an embedded thunderstorm or two is possible. When thunder roars, go indoors. But the main threat is some urban flooding, as the steadier to heavy rain is being sponsored by high PWATs streaming into the region along with high dewpoints. The high PWATs support some areas of very heavy rain, with values over 2″ flowing into the region:

pwats hrrr 13z.png
PWATs valid at 9 AM (13Z) on the 11Z HRRR, courtesy Pivotal Weather

Note – just because there is a 2″ or larger PWAT value doesn’t mean you’re going to see 2″ of rain at your house, but it does mean there is a strong potential for someone to see some heavy rain. Again, not necessarily 2″, but rather the potential itself for heavy rain is what needs to be the primary takeaway.

11z hrrr radar.gif
11Z HRRR, courtesy WeatherBell

The above is the 11Z HRRR’s thoughts on how precipitation will proceed. It shows the batch of rain coming and going, then a few showers and storms forming behind the batch. The potential for formation of more showers/storms after this batch exists – there is a shortwave aloft, there is definitely enough moisture, and there will be increasing instability despite the presence of some clouds. Severe weather is not likely as a result of decreasing shear, but there is a possibility of an isolated stronger storm with gusty winds with 0-6km shear of 25-35 kt in spots.

6z nam 0-6 shear.png
6Z NAM, 0-6km shear of 30-35 kt in spots, valid for 18Z (2 PM EDT) today, courtesy AccuWeather Pro
11z hrrr shear.png
The 11Z HRRR depicts 0-6 km shear more on the order of 20-30 kt, courtesy Pivotal Weather

The main threat in any cell that forms and isn’t overly weak is heavy rain, due to the aforementioned factors. As a result, urban flooding potential exists this afternoon as well in any cell with heavy rain.

A detracting factor to afternoon storms is weak mid-level lapse rates:

lapse rates 11z hrrr 18z.png
11Z HRRR 700-500 mb lapse rates valid 18Z courtesy Pivotal Weather

Generally, at least 6C lapse rates – preferably higher – are wanted to help with a storm threats and this is a swing and a miss in that department as much of the area hovers around 4.5 or 5 in this projection (with other high-res models spitting out similar output).

Any storm chance dwindles this evening as dry air aloft takes over, but there will be no relief in the low levels at the surface as dewpoints stay in the upper 60s to the low 70s.

High Heat Thursday-Saturday

With those dewpoints I just noted, combined with temperatures in the mid-90s tomorrow, there is a threat from this heat given heat indexes of 95-105. Similar conditions persist into Friday and likely Saturday. As such a heat advisory has been issued for Boston proper, plus areas to the north and south of Boston away from the immediate coast, between the NH border and areas just north of the South Coast,  12 to 7 PM tomorrow, with a strong possibility of expansion, as well as potentially future heat advisories for Friday and Saturday. I’ll have more on this later, but be in an air conditioned area if possible, and if an AC’d area is not available, or if you are working outside, drink plenty of water and take breaks. As for today, monitor the skies and head inside when threatening weather approaches. If driving and you encounter a flooded road, turn around, don’t drown.


Published by Nathan Coram

Hello! I'm Nathan Coram, a 20 year old meteorology student and weather geek, and am in my junior year at UMass Lowell as a meteorology major. I am the current Vice President of the UML American Meteorological Society Local Student Chapter. Prior to at UML, I attended the Dracut school system for my K-12 years, having graduated from Dracut High in 2018. I first got into weather with the December 2008 ice storm, which knocked out my electricity for 4 days. I had no idea how it could be raining and becoming ice immediately, and how rain can knock out power. (Now I do - warm layer aloft, cold air at surface). But I didn't really get into it until the heat of July 2010 and specifically a few severe weather events during that month, followed by the year 2011, which featured several high profile weather events. Since then I have had a growing interest, and am hoping to make it into the meteorology field, preferably with NOAA/NWS. But for now, I'm blogging here on Dracut Weather (also on Twitter and Facebook), helping with the UML Weather Center social media, and tweeting about the weather on my own account as well. Thanks for visiting!

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