Metro Detroit weather: Sizable severe storm risk this afternoon

Here’s what to expect

DETROIT – We have been very fortunate that all of the overnight thunderstorms were north of the advancing warm front -- those storms were what we call elevated, and did not produce any severe weather over southeast Michigan, although western Michigan wasn’t so lucky.

There is tremendous wind shear above us right now and, had any storms fired up during the post-midnight period, we might have had some tornadoes.

You undoubtedly noticed the sharp increase in humidity overnight, and that’s just the first ingredient of many that will combine to provide a sizable severe storm risk this afternoon.

70 mph wind gusts possible

A strong wind field aloft makes severe wind gusts (possibly to 70 mph) a high probability -- but there is one critical model difference that will dictate whether or not we get any tornadoes: some models keep the wind direction very similar (from the southwest) from the surface up through 20,000 feet, while others nudge the surface wind a bit closer to the south. This is a critical ingredient, because any clockwise shift of the wind as you go up increases what we call directional wind shear, which causes rotating storms, and that introduces the possibility of supercell thunderstorms with a tornado risk. Which model verifies will be interesting to watch -- and have significant repercussions on what we get.

Here are the risks:

Thunderstorm risk this evening

All that’s left now is a trigger to fire up the storms, and we have that in an upper level low pressure trough that will move from southwest to northeast across our area during the hottest part of the day. I’ve been concerned about this feature for two days now, and it’s going to be a major player today. It appears that our thunderstorm risk is between 4 p.m. and 8 p.m., and we should be mainly dry during the daytime prior to then.

The way these scenarios usually play out is that the tornado threat is greatest near the beginning of the severe event, when we just have individual thunderstorm cells. Once those storms congeal into a solid line of storms, the threat translates to a much greater chance of widespread damaging wind gusts, although a tornado is still possible. The strongest storms will also have large hail -- so make sure your car is parked in the garage or under a carport later this afternoon, if possible.

And also remember to keep your devices charged, as there will be power outages later today.

I talk all the time about having “layers of protection” – meaning multiple ways to receive warnings. The perfect combination is our Local4Casters Weather App (with notifications turned on) and a Midland NOAA Weather Radio. Why both? Because cellular networks sometimes fail during high impact severe weather events. Just ask the people of Joplin, Missouri about eight years ago, who had cell towers damaged by severe storms early in the day, before the ninth deadliest tornado in American history came roaring through late afternoon. Some people with weather apps on their phones did not get the tornado warning as a result, but those with weather radios did.

And remember that you can watch live radar on our app -- you’ll see the storms develop this afternoon, and track them yourself as they head your way.

Don’t forget to follow me on Twitter (@PGLocal4) for personalized updates this afternoon and evening.

Aside from the storms, it’s going to be a generally windy day, with south to southwest winds possibly gusting to near 40 mph, and with steamy highs near 90 degrees (31 to 32 degrees Celsius).

Storms move out early this evening, and you’ll notice the lower humidity coming in during the night, which will allow lows to drop into the low 60s (16 degrees Celsius). Southwest wind at 15 to 25 mph.

Thursday forecast

Partly cloudy, cooler and less humid Thursday, with highs in the mid to upper 70s (25 degrees Celsius).

Partly cloudy Thursday night, with lows in the upper 50s (15 degrees Celsius).

Friday forecast

Partly to mostly cloudy on Friday, with a few afternoon showers possible. Highs in the mid 70s (24 degrees Celsius).

Weekend outlook

The upcoming weekend looks dry, but cooler. Mostly sunny to partly cloudy on Saturday, with highs in the mid to upper 60s (19 degrees Celsius), and mostly sunny on Sunday, with highs in the low 70s (22 degrees Celsius).

**Don’t forget that the sun’s rays are now at their strongest of the entire year -- you can burn just as easily when temps are in the 60s as when it’s in the 80s -- use sunscreen if you or the kids will be spending meaningful time out in the sun**

It appears dry through next Friday, but with one caveat: an upper level low pressure area is going to develop to our east. Three of the four long range models I’ve looked at this morning (GFS, UKMET and CMC) keep it far enough east to maintain the dry forecast. One model (ECMWF) trends it farther west, which would give us more clouds and a shower chance on one or two days. But right now, I’m not seeing any real support for that solution, so I’ll stay with my dry week ahead, with steady warming through the week -- we’ll reach the upper 80s (31 degrees Celsius) by Friday.


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