Metro Detroit weather: Frost advisory in effect tonight as temperatures drop

Positive news for Mother's Day?

By Paul Gross - Meteorologist

DETROIT - In addition to the frost advisory, we have some potentially positive news about Mother’s Day. We’ll get to that in a moment.

But first, we know that some people get a little impatient and have to jump the gun and get those flowers in the ground. You’ll never catch a Local4Caster planting tender annuals this early. We know that frost is a possibility in early May.

In fact, even in the third week of May most record lows are near or right at freezing, and the latest official freeze in recorded Detroit weather history occurred on May 29, 1966

Quoting the great philosopher, Yogi Berra, “it ain’t over until it’s over.” We usually wait until Memorial Day weekend to do our planting, as long as there are no big-time cold spells in the forecast for that last week in May.

Clear skies for the first two-thirds of tonight, combined with a cool, dry air mass and light wind, means that conditions overnight will be quite favorable for radiational cooling -- a very efficient process that transfers low level heat upward.

Some clouds will move in after midnight will slow the temperature drop, so it’s a race against time between the plummeting temps and the incoming clouds, which will stabilize temps. Accordingly, the National Weather Service has issued a Frost Advisory tonight as a precaution. The advisory covers all Local 4 counties except for Wayne, Monroe and Lenawee.

Temperatures in the advisory area will drop into the mid to upper 30s (2 to 3 degrees Celsius), with areas not in the advisory holding in the upper 30s to near 40 degrees (4 degrees Celsius).

As always, low elevation areas stand the best chance of seeing some frost. This happens because the cooler air is denser (“heavier”), and tends to sink toward lower spots.

In essence, the cooling feeds upon itself. The cooler it gets, the more likely it is that this air sinks into a low area, which then cools even more. Overall, the best chance to see any widespread frost is north of I-69, with frost mostly just in lower areas south of there.

But wherever you live, if you have tender annuals already out, then you may want to move them in the garage if they are in pots, or cover them -- just put some stakes in the ground and have an old bedsheet or layer of burlap on top of the stakes (don’t let the cover touch the plants).

Saturday will start with at least partial sunshine, but clouds will increase and thicken through the afternoon. At least it’ll remain dry for the Race 4 the Cure and Birmingham Art Fair. Highs should reach the upper 50s (15 degrees Celsius), as long as the thicker clouds hold off until afternoon. Wind will blow from the northeast at 5 to 10 mph.

Saturday’s sunrise is at 6:17 a.m., and Saturday’s sunset is at 8:43 p.m.

Mostly cloudy Saturday night. We could see partial clearing late at night, with lows in the low 40s (5 to 6 degrees Celsius).

Now, we have some (hopefully) good news about Mother’s Day. The computer models have suggested for several days now a very complex evolving weather pattern, where an upper level disturbance to our southwest deepens into an upper level low pressure area that moves into the Ohio Valley region.

Historically, the models have great trouble handling this type of pattern evolution until the day before the upper low develops, but we’re seeing enough in today’s models to project with moderate confidence a dry Sunday morning, with rain chances developing from south to north during the afternoon. The northern half of our area may even hold off the rain until Sunday night!

We strongly urge you to frequently check the customizable radar on the free Local4Casters weather app if you have outdoor Sunday plans. If you’re one of the few who doesn’t have the app (many people say it’s the best weather app they’ve ever seen), just go to the App Store and search under WDIV.

Remember that when you open the app, it opens right up to the radar. And also remember that our app follows you wherever you go (even to Europe) and gives you the radar and forecast for where you happen to be at that moment. 

Highs Sunday should only reach the mid 50s (13 degrees Celsius), and it may become a little breezy with wind from the northeast.

Wind from the northeast to east Sunday into Sunday night, combined with the already high St. Clair River levels, means that another round of flooding is possible for the Harsens Island-Algonac-Marine City-Pearl Beach area. Accordingly, the National Weather Service has extended the Areal Flood Warning for this area until 2:45 p.m. Monday.

Rain is likely Sunday night, with lows in the mid 40s (6 to 7 degrees Celsius). 

Showers likely on Monday means that it’ll be a great day to come see us at WeatherFest at the Southfield Public Library. If you’ve never been to WeatherFest, we’re proud to partner with the National Weather Service, the Southfield Public Library and the Young Meteorologists Program for a great day of learning and fun.

The event is open to the public between 1 p.m. and 6 p.m. Check out all the details here. We hope to see you there!

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