Metro Detroit weather: Challenging weekend forecast

APBA Gold Cup and Pure Michigan 400 weekend is here

DETROIT – Every summer weekend is a big one in my book, but this one is extra special due to the hydroplane races on the Detroit River and the big NASCAR race at Michigan International Speedway, not to mention a big Tigers series at Comerica Park against Mike Trout and the Angels. There’s lots going on around town.

The weekend forecast has become somewhat challenging, because we don’t have any solid weather features (such as a strong front) crossing the area. Rather, very small-scale features will impact our thunderstorm chances, and I’m seeing some disturbing differences in some of the computer models. I’ve mentioned many times in the past that the models sometimes don’t get a good handle on these small features, and I’ve also always been very honest about communicating this uncertainty to you.  So, here’s what we’re dealing with this weekend:

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Friday night will be quiet and dry, with partly cloudy skies. Lows should drop into the mid-60s -- that’s 18 degrees Celsius for our Canadian friends -- with calm air.

Partly cloudy to start our Saturday, and then clouds increase during the afternoon, with highs in the mid 80s (29-30 degrees Celsius) and a light southeast wind. And this is also where we start running into difficulties with the models.

Most of them try to limit us to a stray thunderstorm in the late afternoon or evening hours – with a better chance north and west of our area. However, my high-resolution, in-house RPM brings a pretty significant cluster of storms through southeast Michigan by mid to late afternoon.

Forecast soundings (upper air forecast data) don’t help, either – the GFS model suggests they would be “routine” thunderstorms, while the SREF forecast soundings suggest a strong severe weather potential.  So what to do if you’ll be outside at any of the big events?

Make sure that you have the FREE Local4Casters weather app downloaded on your phone. Just search under “WDIV” in the app store. When you open the app, it opens right onto the radar page, which you can pan or zoom with your fingers.

Check the app often for any developing storms -- particularly Saturday afternoon and evening.  Also remember to follow me on Twitter at @PGLocal4, as I’ll tweet personalized updates whenever possible.

Saturday’s sunrise is at 6:54 AM, and Saturday’s sunset is at 8:15 p.m.

Shower and thunderstorm chances continue Saturday night, with lows an uncomfortable 70 degrees (21 degrees Celsius).

Sunday brings us another disagreement in the models.  Some models (such as the ECMWF) end the Saturday night storms Sunday morning, and leave us dry in the afternoon. However, the GFS and RPM insist that we’ll have a dry morning with some scattered storms in the afternoon (but not everybody getting one) so, once again, keep an eye on our app’s radar, and my Twitter feed for updates. Highs in the mid-80s (30 degrees Celsius).

It will become partly cloudy Sunday night, with lows in the upper 60s (20 degrees Celsius).

It will be partly cloudy and still humid on Monday, with highs in the mid to upper 80s (30 degrees Celsius).

It will be partly cloudy and muggy Monday night, with lows near 70 degrees (21 degrees Celsius).

It will be partly cloudy and humid on Tuesday, with a chance for some afternoon thunderstorms ahead of a strong cold front.  Highs in the mid to upper 80s (30 degrees Celsius).

Showers and thunderstorms end at some point after the front comes through Tuesday night, with lows in the mid-60s (18 degrees Celsius).

Then comes a stretch of days with pleasant temperatures, plenty of sunshine, and low humidity. Mostly sunny Wednesday through Friday, with highs between 75 degrees and 80 degrees (25-27 degrees Celsius), and overnight lows generally between 55 degrees and 60 degrees (13-16 degrees Celsius).

It’s a little early to try and get specific about Labor Day weekend in terms of precipitation, but looking at this afternoon’s ensemble models suggests only a scattered thunderstorm chance at some point, and warmer temperatures returning to the area. Naturally, I’ll keep an eye on the trends, and start getting specific next week.