Metro Detroit weather: 2 severe chances on Saturday

What about the rest of the holiday weekend?

By Paul Gross - Meteorologist

DETROIT - Finally -- the holiday weekend is here, and it’s going to start with a bang as we have two different severe weather risks on Saturday. The first arrives tonight between midnight and dawn, as thunderstorms ahead of a strong warm front cross the area.

The most unstable part of an air mass ahead of any warm front is aloft -- we call storms in this environment “elevated convection.” In this situation, it’s very tough to get severe wind gusts down to the surface. However, large hail is definitely a possibility with these overnight storms.

Here is the Storm Prediction Center’s severe risk graphic for tonight:

Temperatures will initially drop into the upper 50s (15 degrees Celsius) overnight, but rise sharply after the warm front passes by. In fact, by 8:00 a.m. most of us will be in the mid 60s (18 degrees Celsius), as wind shifts from the east to the south and advects in that warmer air.

The overnight storms should move out by 8:00 or 9:00 a.m., and we’ll probably have a few hour break from any widespread convection (storms). However, given how unstable the atmosphere will become, we cannot rule out a scattered midday storm.

The next batch of storms will pop up mid-afternoon and quickly move eastward. These will be different storms than the overnight ones: they will fire up in the warm sector behind the warm front. It will be very unstable from the surface all the way aloft, and we call these storm “surface based convection.” In this environment, both severe wind gusts and large hail are likely. However, if any individual storms explode before the line of storms develops (we call those “discrete cells”), then there might be a small window for a tornado -- but please understand that this is a low threat. Once the storms congeal into a solid line, which should happen quickly, then this is mainly a wind and hail threat.

Here is the Storm Prediction Center’s severe risk graphic for Saturday:

We cannot emphasize enough to make sure that your weather radio is on alert mode, and check the radar often on our free weather app to see where the storms are. If you are one of the few who doesn’t have our app, just go to the app store and search under “WDIV” -- the Local4Casters weather app is right there. Many, many people have told us that our app is hands down the best weather app available.

Highs Saturday should reach the low 80s (28 degrees Celsius), you’ll notice the higher humidity, and a southwest wind at 15 to 25 mph.

The storms end by late afternoon / early evening on Saturday, and the rest of the night should be quiet, with lows in the low 60s (16 to 17 degrees Celsius).

Sunday remains tricky -- that front sags to our south, but it doesn’t appear it’ll proceed far enough south to remove the rain chance -- at least for the southern half of the area. Those of you north of M-59 are the lucky ones -- you may hang onto a dry day. But farther south, shower and thunderstorm chances, especially by afternoon, increase. Highs will reach the mid 70s (24 to 25 degrees Celsius).

Memorial Day looks dry -- until evening when that front -- the gift that just keeps on giving -- makes a move back at us. Hopefully, we’ll keep things dry until late afternoon, after which the rain approaches. Highs Monday in the mid 70s (24 degrees Celsius).

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