Beautiful Day….PLUS Weather 101

Today will be an absolutely beautiful day!….so once I share what you can expect, I’ll explain a weather phenomenon that came up this morning which many of you have likely wondered about at one time or another.

First though, our weather…

The dense fog we had in spots this morning is mostly gone now (as of 7:30am)…and the sun is shining brightly!

DT VIDEO TVI

Temperatures are already recovering from their early morning levels in the 30s and lowermost 40s.

DT DMA TEMPS STILL1

Count on 100% of the possible sunshine today.  It’ll turn mild.  The wind will remain light, too (northwest, 5mph….and occasionally 10mph, at most).

9am temperatures should look like this.

DT 4 RPM 12KM Temperature2

Late this afternoon…

DT 4 RPM 12KM Temperature2b

For the Preds and Sounds games, weather couldn’t be any better!

NOW….as I noted above, earlier this morning we had many communities in the mid-upper 30s.  I commented on TV a few times that despite the cold, it wasn’t frosty at all because the air wasn’t dry enough.  Robert, a Channel 4 News viewer then emailed me with this related question:

“Since frost is ice crystals and water freezes at 32°; how do you get frost when it’s in the mid and upper 30’s. I’ve always wondered about that.”

This was my response to Robert:

“Hi Robert!
Great question.  Frost forms from vapor deposition — essentially water vapor in the air skipping over the liquid phase and freezing on contact with certain objects (deck railings, plant leaves, cars, etc).  While the temperature of the air in those instances may be in the upper 30s, the temperature of those objects is often lower, as long as the wind is light enough and the air is sufficiently dry (dew points in the 20s or lowermost 30s).  Objects like plant leaves can get colder than the air since they can cool more efficiently (through cooling from both sides). 
If the dew point is 33 degrees or above, dew will form on objects instead of frost as they cool down toward the freezing mark.  Once dew forms, the object stops cooling since dew formation is produced by condensation — a process that releases heat. 
This morning, dew points are in the upper 30s and lower 40s.  SO…dew has formed on objects, not frost.
Have a great day!  Tks for watching!
Dan Thomas
Meteorologist, WSMV-TV Channel 4 News”
SO….a little Weather 101 to begin your Sunday!  Fortunately, we’re not going to have to worry about frost anymore until autumn.  In fact, heat will return to the Mid State this week.  I’ll share more on that shortly, on Channel 4 News Today, from 8am until 9am.  Please join Alan Frio and me for that!
DT
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One Response to Beautiful Day….PLUS Weather 101

  1. Fred says:

    Excellent article! For additional bit of trivia, today, May 7th is the only date in May when temperature never reached 90 (highest is 89, occurring several times, most recently in 1986) and, in fact, the only such date between May 1 and October 10.

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