37ºF

Frost Advisory Friday for part of southeast Michigan

And some improving news for the holiday weekend!

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DETROIT – You know the drill by now: clear skies, a cold and dry air mass overhead, and light wind will promote maximum efficiency in our surface cooling Friday -- a situation known as radiational cooling.

I've been watching dewpoint temperatures closely Friday afternoon -- dewpoint is the temperature that you'd have to cool the air down to in order for it to become completely saturated, so the bigger the spread between the temperature and the dewpoint, the drier the air is. And there's a very important thermodynamic rule involved here: the temperature can never fall below the dewpoint. So, in situations like we'll have Friday, dewpoint can be used to approximate what the low temperature will be since the temperature will fall to just above that dewpoint.

As of the time I am writing this article (4:45 PM), dewpoints across our area are generally in the 28° to 32° range, so the writing's on the wall: frost will develop in some areas.

The National Weather Service has issued a Frost Advisory for our counties north of 8 Mile. The most likely spots to get some frost are north of M-59, but not everybody will get it as there are a number of local effects that impact whether or not you'll get frost.

The bottom line is that if you have tender plants that you don't want to risk losing, you'll need to cover them (or move them into the garage if they are portable, such as hanging baskets). Use burlap or an old sheet -- prop it up on stakes above BUT NOT TOUCHING the plants. What this does is reflect heat radiating up from the ground back down, which prevents frost when temperatures are close to freezing. This does not work in temps well below freezing, but we won't drop that far Friday. And by the way, early season perennials (such as tulips) and hardy flowers (such as pansies) can handle this cold -- no need to worry about them.

Freeze Warnings have once again been posted for areas up north, so I repeat my concern about our state's tart cherry crop…the nation's best…since the blossoms are already out due to the early spring warmth. I wrote earlier this week about this happening to those cherry farmers back in 2002 and 2012, and how we lost 90% of our tart cherry crop in 2012 as a result of the freeze that followed. Let's hope it's not that bad this time.

Once we get past Friday's frosty temperatures, get ready for a spectacular start to the holiday weekend! Saturday will feature sunny skies, with highs reaching the low 70s in most areas (21° Celsius for you Canadians reading this). South-southwest wind at 5 to 10 mph. I've been targeting this day all week long to plant my flowers…hope to get all nine flats planted! And by the way, if you'll be out in the sun, don't forget your hats and sunscreen. THE TEMPERATURE DOES NOT IMPACT THE INTENSITY OF THE SUN'S RAYS, WHICH ARE HIGH THIS TIME OF YEAR. You and your kids will burn if not protected. If you want to see a very cool and dramatic scientific demonstration I did to show the sun's impact on your skin, check it out here.

Mostly clear Saturday evening, with some increase in high cirrus clouds later at night. Warmer, with lows in the mid 50s.

Becoming mostly cloudy on Sunday, but it should be a dry day and very pleasant, with highs in the mid 70s.

There's a chance of showers and thunderstorms Sunday night as a warm front crosses the area. Lows near 60.

Monday is still tricky, but the trends are encouraging. As long as the Sunday night warm front continues progressing north, it's possible that we'll start the day mild, muggy and dry…that would be GREAT news for all of the Memorial Day parades that morning, and especially for me as I co-emcee the Farmington Memorial Day Parade in downtown Farmington. My co-emcee, Kelly Duca, and I will be set up near the intersection of Grand River and Farmington Roads announcing the various groups and bands that parade by. I'm really praying that the rain holds off -- Ben Bailey cheerfully tells me that I'm "wishcasting" here!

As long as the scenario that I'm seeing in the computer models pans out, the shower and thunderstorm chances should hold off until sometime during the afternoon when we warm up and the atmosphere becomes more unstable -- but this is a razor thin margin of error that I'll keep an eye on over the weekend. Highs near 80°.

If you have any outdoor plans Monday, keep checking the radar on our Local4Casters weather app (FREE in the app store, just search under WDIV if you don't have it yet). Also remember to follow me on Twitter at @PGLocal4, so you can receive my personalized weather updates.

And here's one final reminder: remember what Memorial Day really stands for, and show that spirit. Go to your local parade and salute the veterans parading by, fly your flag (I'll have mine out all weekend), and pause for a moment and give silent thanks to those who gave their lives so that we could live ours. Enjoy the day, but please don't forget its true meaning.

As I mentioned yesterday, the weather pattern for the rest of the week is quite muddled, with shower and/or thunderstorm chances virtually every day, although it won't rain all day every day. It will stay warm, though, with highs generally in the vicinity of 80°, and lows in the 60s.


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