I am writing a special discussion to provide a deeper analysis on the upcoming days that will have a series of hazards in CT. For our new followers, a SCW Period of Interest is our way of highlighting time periods that bring increased chances of significant weather. It is a way to inform, not panic or hype up.
Let's get right to it.
Thursday--Hazards: Heat, Severe Thunderstorms, Flash Flooding
A heat wave by itself isn't usually a reason to issue a period of interest, and without the severe weather threat I probably wouldn't be writing right now. That said, people always underestimate heat, and it's actually the top weather related hazard that impacts people's health.
Today's heat fell just short of 90 with inland highs in the upper 80s. With lower humidity, it didn't feel too bad out there today. That changes in a big way tomorrow, as it is almost certainly day 1 of our heat wave, defined as three consecutive days of high temperatures 90 and above.
A ridge will bring a plume of heat and humidity over the region, meaning that we will see breezy conditions tomorrow advecting in higher temperatures aloft and at the surface, along with more oppressive humidity. The humidity is a lock, as we're expecting dew points into the 70s again.
Temperatures look to be in the low to mid 90s, and even at the shore you are likely to be close to or over 90 depending on wind direction. It will not feel any cooler given the very high humidity. Heat indices between 95 and 100 are expected statewide, so make sure you are taking precautions if you are outside for an extended period of time.
Temperatures could be a little lower if we have cloud cover hang on from an overnight thunderstorm complex that's expected to die out long before reaching CT, but it's going to be hot regardless.
Importantly, we will not see much relief Thursday night with elevated temperatures and high humidity. That has a compounding impact on the body. This is nothing new, but it is a reminder to check in on those without air conditioning, especially the elderly.
Tomorrow has the potential to be a very active day across the state, as the Storm Prediction Center (SPC) currently has a slight risk of severe weather for all of Connecticut. This has been up for multiple days, which is uncommon around here. Severe weather is inherently hit or miss, and has felt particularly so this summer where we have had multiple watches and not a lot of severe reports to show for it.
Every setup is different, and it's important to remember that heading into tomorrow. When we talk about severe thunderstorms, I've heard from some followers that they immediately think of the Midwest storms with violent tornadoes and large hail. That's not what we mean in New England when we talk about virtually all severe weather setups, even the ones with tornado watches, and if the setup were calling for that, rest assured we'd be sounding the alarm.
Severe thunderstorms are storms that produce winds at or above 58 mph or hail that is quarter size (1") in diameter or larger. Technically a tornado is a severe thunderstorm, but different warnings come out with those.
Tomorrow is a conditional severe weather day. What does that mean? Most of the ingredients for severe thunderstorms are there. We will likely see unseasonably strong shear as a "cold" front approaches with a weak surface low. We will see sufficient lift come with the same. We will see modest instability build with the heat that we are going to see and more than enough moisture in the air. The ingredients are there for strong to severe thunderstorms.
How can the severe potential come apart? If we have too much cloud cover that restricts instability from building too high, or if low to mid level lapse rates (change of temperature with height) are weak.
What makes me perk up a little more for tomorrow is the presence of helicity, or low level spin. Yes, that means an isolated tornado is possible in New England. That's not hype, it's just the reality of the setup. The SPC puts out chances for each hazard (wind/hail/tornado) and as of their latest forecast, wind was at 15%, hail was at 5%, and a tornado was at 2% for most of the state and 5% for the far northern part of the state. Low odds, but enough to take seriously.
As is usually the case for severe weather, we'll have to watch and see what things look like tomorrow. Storm timing looks to be between 2pm and 10pm with storms traveling from west to east generally. Below is the latest high resolution NAM depiction of noon to midnight tomorrow. Right now I think the best severe chances are north of CT, but any individual storms that develop tomorrow have the chance to quickly become strong to severe.
I know this is probably already going long, but let me just go one level deeper.
Let's see what it looks like tomorrow.
Finally, the flash flood risk. Not much needs to be said, but it has been all-time wet for many with this being at top 5 wet month at BDL. Although storms are likely to be moving at a faster pace, given the moisture in the air (PWATS over 2"!) any storms are likely to bring torrential rain. For northern CT in particular, that had flash flood warnings yesterday, watch out if you get storms over you.
One last note on Thursday. It seems a little odd to have severe potential as heat is building into the region. For us "old-timers" it's usually the case that we have storms to break the heat!
Not this time.
Friday doesn't look like a multi-hazard day, but it may very well be the hottest day of the year. The "cold" front on Thursday doesn't bring anything but more heat and humidity, and Friday is likely to see highs in the mid to upper 90s with heat indices between 95-105. The highest heat index is likely in the heat corridor between Springfield and Hartford, but it's going to be downright brutal across the state.
While there may be a very slight chance of a storm, I don't think we see much of anything statewide Friday, other than hazy, hot, and humid conditions. This is a day where you definitely want to take it easy if you are outside for any extended period of time. Watch out for pets, children, and the elderly. Unfortunately, the heat does not break Friday night either.
Originally, it looked like the cold front that would finally break the heat would arrive on Friday, but that is no longer the case. Now, Saturday is looking like a reflection of Thursday, meaning it will be hot and potentially very active.
A powerful cold front is going to bring us relief for Sunday, but first it has to push out the heat. Highs are likely to be in the low to mid 90s, but I'm wondering if Saturday is sneaky hot as the front advances. At any rate, expect heat indices between 95 and 100 again, providing plenty of energy for strong to potentially severe storms.
Right now, I think the primary risk on Saturday is strong winds and flash flooding as a line of storms associated with the front moves through the state during the afternoon and evening, but this is something that needs to be honed in on later this week. For now, however, the signal is there for another active day.
Overall, and active few days are ahead. We'll take it one day at a time here at SCW and will provide updates, but hopefully this gives you information to plan the next few days.
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