“Where’s the Moisture Going to Come From, Dan?”

We’ve all had instances in our lives when someone said something to us that we’ll never forget.  Maybe it was a word of affirmation from your significant other or your child.  Perhaps it was one of your parents or grandparents congratulating you for something.  Or maybe it was neither good nor bad….the comment just got you thinking.

One such instance happened to me back in the year 1995, when I was a meteorology graduate student at Penn State.  A professor and I were looking at the weather maps on the map wall and I told him, “I think the Northern Rockies will get some showers tomorrow.”  We both had noticed an approaching storm, albeit weak, moving that way from the northwest.  He turned to me and said, “Where’s the moisture going to come from, Dan?”  I half-smiled uneasily because I was stumped.  I replied,”I don’t know” with a shrug of my shoulders.  My professor went on to explain that you can have all the rising air in the world…but if you don’t have moisture, you won’t get rain.  It’s that simple.  It hadn’t dawned on me how dry the air in the Rockies was, in advance of that approaching storm.

This conversation from 21 years ago stuck with me all this time in part because I was embarrassed…..but also because I learned a valuable weather lesson — one that can be applied to our forecast for tomorrow!

We’ve told you all week on Channel 4 there’s a good chance for showers and thunderstorms tomorrow…and there is.  However, because there won’t be a tremendous amount of moisture available for the approaching storm to tap into, our chance for severe weather is rather low.

Let me show you…

Here in the Mid State, our best source of moisture in the lower atmosphere is the Gulf of Mexico.  On days with a high chance for severe weather, our wind flow near the ground looks like this below…with moist air streaming our way from the Gulf.

DT_SEVERE RISK REGION2

However, tomorrow, notice that even though we’ll have a strong southwesterly wind all day, its origin won’t be the Gulf….it’ll be the Plains states — a normally very dry area.

DT_SEVERE RISK REGION3

SO….the folks at the Storm Prediction Center give us only a marginal threat for severe weather tomorrow afternoon & evening.  That’s the lowest in the scale of threats they have (scale of 1 through 5, it’s a 1).

DT_SEVERE RISK REGION

Despite the fact that our chance for severe thunderstorms (storms containing a tornado, at least 1″ diameter hail, and/or 58mph wind gusts) is rather low, I still expect downpours, some lightning and thunder, and a few storms with at least pea-dime size hail.

As for timing, 3pm looks like a good call along the TN River, around 5pm in Nashville, and 7pm over eastern Middle TN.  However, Lisa Spencer will update this timing tonight, on Channel 4 News at 10pm.

DT

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