Metro Detroit weather: Storms, heat and humidity

Small chance for overnight thunderstorm

By Paul Gross - Meteorologist

DETROIT - If you’ve been watching the radar on our Local4Casters app (you can download it for free from the app store. Just search under “WDIV”), you saw a massive area of thunderstorms approaching Lake Michigan Thursday morning. It indeed looked ominous.

But it doesn’t look nearly as impressive now as it did earlier, which is counterintuitive to many of you. Why is it weaker now, during the hottest part of the day, than when it was cooler? Because this is a specific type of thunderstorm cluster called a mesoscale convective system (MCS). They blow up at night as the low level jet stream (LLJ) strengthens -- this fuels the system and keeps it going all night.

Then, when the LLJ starts weakening as the day progresses, the batch of storms becomes less organized. Sometimes, the entire massive cluster of storms is gone within a few hours. So, while some thunderstorms are possible across Southeast Michigan this afternoon, and a few could become severe with strong wind gusts, don’t expect anything resembling what the radar looked like earlier.

There’s only the small chance for an overnight thunderstorm, so we shouldn’t get rocked out of bed tonight. However, the heat is on, so is the humidity, and it’s only going to get a lot worse over the next two days.

Humid air does not cool nearly as well as dry air, so lows tonight will only fall into the upper 70s (26 degrees Celsius), and remember that it’ll take all night to get there. We’ll be in the 80s most of the night. Not surprisingly, the National Weather Service has issued an Excessive Heat Warning until 8:00 p.m. Saturday.

Friday (TGIF!) will be dangerously hot and humid, with afternoon highs reaching the mid to upper 90s (35 to 37 degrees Celsius), and the humidity making it feel like 105 to 110 degrees (41 to 43 degrees Celsius). Scattered thunderstorms are possible once again. The best chance during the first half of the day appears to be near and north of I-69, with chances farther south later in the day.

Generally speaking, the farther south you are, the lower your thunderstorm risk. But any storm that does pop up, especially in the afternoon, could have strong wind gusts, so keep an eye on things on our app’s radar.

The sunshine and high heat and humidity also means that Friday will be another Ozone Action Day. Believe it or not, there are a few common sense things you can do that actually make a tremendous difference in reducing the emissions that are turned into ozone by the sunshine, heat and humidity:

  1. This is an easy one: Avoid fueling your vehicle until evening, and don’t top off the tank, which releases additional fumes into the air.
  2. If you have the ability, carpool or use public transportation (or walk or bike to work or on your errands), as every vehicle that doesn’t operate is less exhaust that gets into the air.
  3. Avoid using gasoline powered lawn equipment until evening, because those don’t have the pollution controls that vehicles do, so they are actually big emitters of exhaust.
  4. Reduce electricity use at home and work. This is pretty simple: The less power we use, the less electricity our coal burning power plants have to generate, which reduces their emissions.

Friday’s sunrise is at 6:14 a.m., and Friday’s sunset is at 9:05 p.m.

Warm and oppressively muggy Friday night, with lows in the upper 70s to near 80 degrees (26 to 27 degrees Celsius). By the way, we’re keeping a very close eye on that overnight low:Tthere have only been three occasions in recorded Detroit weather history in which an overnight low has not dropped below 80 degrees (27 degrees Celsius). We’ll be very close to that dubious achievement.

Dangerously hot and humid once again on Saturday, with another thunderstorm chance. Highs in the mid-to-upper 90s (35 to 37 degrees Celsius), with the humidity making it feel like 105 to 110 degrees (41 to 43 degrees Celsius).

Now for some good news: A cold front with substantial relief will approach either Saturday night or Sunday morning. Shower and thunderstorm chances continue ahead of the front, and then taper off behind it. It’s not clear how long the rain chance will extend into Sunday. We’ll try to get more specific about that tomorrow.

However, after another oppressively warm and muggy Saturday night, we should start noticing some relief from the heat and humidity by later in the day Sunday.  In fact, if the front moves through quickly enough, we could even salvage Sunday afternoon, with highs in the mid 80s (29 to 30 degrees Celsius).

As mentioned yesterday, it appears that we’ll then have a spectacular stretch of summer weather all next week.

In case you missed them yesterday, here are some heat wave tips that will really help:

  1. Close your drapes and blinds during the daytime hours. Just keeping the sun from shining through the windows helps a lot. It’s like moving the inside of your house into the shade.
  2. If you have air conditioning, make sure that your furnace filter is clean.  A clean filter means that your furnace’s motor more efficiently pushes that cooler air throughout your house.
  3. Heat stresses us, especially the very young, very old, and those in poor health. Know your limits. If you don’t have air conditioning, it’s important to relieve that heat stress.  Perhaps spend some time at an air conditioned mall, or a friend / relative’s house.  If nothing else, a cool shower or bath certainly can help cool you off.  Just find a way to interrupt the heat’s stress and give yourself some recovery time. Most heat-related health issues result from extended periods of heat stress.
  4. Stay hydrated, and make sure that you’re hydrating with water and sports drinks. This is critical, because we sweat more when it’s hot, and this draws a lot of fluids out of our bodies. Avoid caffeine and alcohol, because they dehydrate you -- the exact opposite of what you want during a heat wave.
  5. Wear cotton or linen clothing, as these natural fibers absorb sweat and allow your skin to breathe. Synthetic material, like polyester and rayon, don’t breathe, and trap sweat on your skin, which makes you more uncomfortable.
  6. This one may surprise you, and it comes from my colleagues at the BBC in London! You probably already know that, if you’ll be out in the hot sun, you should wear light colored clothing (preferably white). This helps reflect solar radiation, and keeps you cooler than dark colored clothing. However, if you’ll be inside or in solid shade, dark clothing actually is better because it absorbs heat from your body and radiates that heat out into the environment around you, especially if there’s a light breeze. Yes, indoors or in the shade, black clothing actually helps keep you cooler!
  7. If it’s too hot for you, it’s too hot for your pets. Please make sure they have relief from the heat, and a dependable supply of clean, cool water to drink. Also, remember that the pavement will become very hot, and especially so for asphalt surfaces. If you are taking your fur baby for a walk, keep him or her on the grass. You wouldn’t walk on that hot pavement barefoot, so why would you force your pet to?

Heat stroke

Heat stroke occurs when our internal body temperature rises to an unsafe level -- above 105° (41° Celsius). If you notice somebody in the heat exhibiting the following symptoms, call 911 immediately:

  • Hot, dry skin (no sweating), despite the heat. The skin may also be red.
  • Severe headache or dizziness
  • Nausea and/or vomiting
  • General weakness or severe muscle cramps
  • Confusion
  • Disorientation
  • Loss of consciousness
  • Rapid heartbeat and rapid, shallow breathing
  • Seizures

After calling 911, start first aid which, in this case, is simply trying to cool the person. If possible, put them in a tub of cool water. If that’s not possible, dampen their skin and fan them, or sponge them with cool water.

You can even use the cool water from a garden hose. Another very effective thing to do is putting ice packs under the armpits and in the groin area.

It’s vitally important to get the person’s core body temperature down as best you can until the EMS arrives. Even just moving them into some air conditioning helps. At the very minimum, at least get them into the shade.

If you know any elderly people who live without air conditioning, or somebody with very young children, please check on them when we hit the peak of this heat wave.

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