The Wind
A Wind Advisory is in effect Monday from 9 AM to Midnight.
Wind speeds will increase Monday morning. By Monday late afternoon and evening, winds may gust between 40 and 50 MPH.
This will bring down tree limbs and blow around small objects, such as trash cans.
This will be the strongest wind we will have seen in a long time. It will render umbrellas useless.
The Rain…and Storms?
Dry air will try to fight off light showers Monday morning. Eventually, the showers will win, and light rain will start falling sometime — according to the HRRR model — after 8 AM:
This light/moderate rainfall should continue off and on through lunch and early afternoon.
Meanwhile, a squall line (or, to use a meteorology term, a QLCS: quasi linear convective system) will form in Arkansas, and move our way. The NAM4 model thinks the squall line will cross the Mississippi River into West Tennessee Monday around 3 PM:
Ahead of that line, a strong S/SW wind will transport increasingly wet/humid air into Middle Tennessee. This will fuel badly-needed rain activity.
Robust moisture transport might also support storms. As discussed this morning, substantial shear/helicity will greet the approaching squall line. Shear/Helicity refers to winds that increase and turn the further up the atmosphere you go; this can cause storms to rotate. There is no such thing as “maximum helicity,” but it’s so high it is off this scale:
Despite exceptionally high helicity, our severe weather concern is low because instability (aka “CAPE”) — an essential ingredient for storm-making — is missing.
That’s just not enough CAPE to cause problems.
If these models are off, and it turns out there is more CAPE/instability than projected, then a small tornado concern will emerge. Right now we do not think that will happen.
If we use the NAM4’s timing, expect the heaviest rain to arrive after dinner.
This is when the wind, and any potential severe weather concerns, will be greatest.
Don’t fixate on that timing. It will need to be adjusted as the HRRR model comes into range and, of course, we see what’s actually happening tomorrow on the radar. Locate updated and additional information on Twitter @NashSevereWx and/or your favorite local TV meteorologists. The more info, the better.
Seriously, Y’all, the Wind
It’s going to be nuts. A mesolow moving from near Memphis to near Bowling Green by Monday late afternoon and evening will expose us to a very tight pressure gradient. That means wind gusts running into the 40+ MPH range. Some models think winds will gust stronger than that.
The NAM4 has a reputation for being overdramatic, so even if you discount this by 25% — which is fair — this is still a lot of wind. Be ready for it.
So How Much Rain?
NWS-Nashville increased the forecast total from this morning’s forecast. They now expect 1.58″ in Nashville, and 1.62″ in Franklin. Our last biggest rain was 1.33″ in mid-September; this would be (obviously) more than that.
Warm & Dry Tuesday, Then Here Comes More Rain (Probably)
After a quiet day, late Tuesday evening should bring widespread showers and maybe a few thunderstorms. Models differ too much to provide actionable certainty, but, generally speaking,
- there should be more rain to our SE (where the drought is worse); we should still get some. Maybe 0.25″ to 0.50″.
- there will be strong (and maybe severe) thunderstorm potential, again, we think that will be confined to counties to our southeast.
Totaling both rain systems, the Euro predicts just over 2″ of rain. The GFS model predicts about a half inch less rain because it thinks the rain late-Tuesday/early Wednesday will miss us.
Rain should taper off Wednesday, then leave us dry Thursday, Friday, and Saturday.
The Weekend Guess
Chilly. Lows below freezing, highs around 50°. We may see some rain try and sneak in Sunday night, but it’s way too far away to say more than that.
Current Radar
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