Updating Wednesday's severe storm potential

Plus, a nice stretch of weather to follow


DETROIT – Any isolated showers around late this afternoon and this evening should quickly fade near sunset, leaving us quiet for the balance of the night.

It's going to be another warm, muggy one, with lows near 70° (22° Celsius for you Canadians). Very light south-southeast wind.

Wednesday is the day I've been targeting for several days now, and it should begin on a quiet note -- you have no worries during the morning hours. We should start partly cloudy, then see more cloud cover by midday into the afternoon. Any sunshine we get is bad news, because more sun equals more heat, which makes the atmosphere more conducive for thunderstorm development. Right now, I expect highs to reach the mid 80s (29° Celsius), which should be sufficient for thunderstorms to develop ahead of an advancing cold front.

Severe storm risk Wednesday afternoon

As I discussed yesterday, we have a severe storm risk Wednesday afternoon and early evening, but this is by no means a slam dunk -- there are both positives and negatives for severe weather to develop. Positives (meaning good for storm development) include a warm, very moist air mass, and very strong (for this time of year) upper level storm system to our west that will have strong wind aloft associated with it. Negatives include increasing cloud cover, which could limit our temperature rise, and weak surface convergence (which you need to initiate the violent lift upward of parcels of air that become thunderstorms).

The wild card, to me, is what we call a pre-frontal trough. Basically, this is like a very weak cold front with converging wind that advances well out ahead of the main cold front. Under the right conditions, these pre-frontal troughs can generate thunderstorms and, sometimes, these storms are the ones to worry about…not the ones associated with the cold front itself. The problem today is that one of my high resolution models generates these pre-frontal trough storms, and another does not. This will be the key to the forecast because, if these scattered storms do develop, some of them may even be capable of generating some rotation. However, another scenario could be that showers and NON-severe storms develop ahead of the pre-frontal trough, stabilize our atmosphere behind them, and basically kill any chance for severe storms ahead of the main cold front.

The bottom line is that we DO have a severe storm risk Wednesday, so plan accordingly if you have outdoor plans -- particularly during the afternoon and evening. If you have a weather radio (and you SHOULD have one), make sure it's set, plugged in, and has a fresh battery. If you haven't downloaded the FREE Local4Casters app, get that done today so you have instantaneous radar at your fingertips all day long to monitor storm development. And by the way, not everybody has a smartphone -- if you don't, then you can get the same awesome radar display on a customizable map right at the top of the weather page on ClickOnDetroit.com.

If you don't already, follow me on Twitter at @PGLocal4 -- I tweet out radar and severe weather updates. Finally, if you do see some severe weather or damage and can SAFELY snap a photo or shoot a quick video, don't forget to pin it on our Storm Pins map -- we can get those on TV right away (and, the National Weather Service monitors Storm Pins -- so you help them a LOT, too). Storm Pins can be downloaded for free from the app store and, like our weather app, just search under WDIV -- it's right there.

Showers and storms should end for a while Wednesday night, and then rain showers return with the cold front later at night. Lows in the mid 60s.

Thursday forecast:

Some lingering rain showers may start your day on Thursday, mainly if you are east of I-75, but they should be gone by 9:00 or 10:00 AM and the rest of the day should be partly cloudy, breezy and cooler -- with lower humidity, too. Highs in the mid 70s.

Mostly clear Thursday night, with lows in the upper 50s.

And then, we start a stretch of spectacular summer weather for an extended period of time. I expect plenty of sunshine and no rain, with the exception of a Sunday night cold front that may bring some showers, through the end of next week. Highs should generally be in the low 80s (perhaps warmer middle to end of next week), with the coolest day being next Monday with highs in the 70s. Overnight lows should generally be in the low 60s -- comfortable enough to sleep in. Enjoy!

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