“Blerg” means it’s under 40° and raining, not snowing. This is not an official weather definition. We made it up.
Today is “almost” a blerg because the rain is mostly south and east of us, where it is expected to remain most of the day. Don’t be surprised if you get a shower/sprinkle or two, but don’t expect any real rain during the day.
A chilly rain, at that.
If you’re planning on a night out, a rain jacket, boots, and/or an umbrella would all be helpful.
How about four more days of it?
Sunday will start as a continuation of Saturday with showers encompassing most of the middle state.
High pressure remains well in control as we head into the evening hours tonight.
Through the night, expect for skies to begin to become cloudier. By tomorrow, skies will be mostly cloudy and once we reach tomorrow afternoon, we will become fair game for showers.
GFS 12z Run – Dry Conditions for next 36 hours
Through Saturday, high pressure will remain entrenched over the area, with westerly winds swinging around the north side of its center.
This brings us cooler and drier air to the two-county region through Friday. Then, changes start back up.
Waking up on Sunday morning, temperatures will be in the upper 30s to low 40s accompanied by some showers. This will be a cold rain, and if you’re traveling towards the Cumberland area, don’t be surprised to see a few snowflakes on the northern side of the plateau in the morning.
GFS 12z Run – Rain Returning Early Sunday
Several pieces of energy (shortwaves) will work their way across the Tennessee and lower Mississippi valley from Sunday through mid-week. There will be breaks in the rain activity here and there, one of these times likely being Monday morning. However, expect off and on rain showers starting Sunday morning, rinsing and repeating through the work week.
Rain totals through Tuesday morning could range from 1-2″:
Wednesday PM-Thursday AM: we are watching for a strong cold front to make its way here. Showers and thunderstorms will be likely with this system as a robust low pressure system develops over the Rockies and travels through the midwest into the Great Lakes region.
NWS Nashville on mid-week storm:
Another strong Midwest trough will move in Thursday next week, and again models are in pretty good agreement on magnitude but slightly off on timing. Late Wednesday night into Thursday morning looks to be the consensus on timing, so have high chance pops in for that timeframe. The upper trough also brings a very strong cold front to the region, so if some precip lingers behind the front, flurries or light snow showers will be possible for the mid state Thursday morning into the early afternoon. With highs only in the low 40s Thursday, it looks like we will get a small taste of winter at the end of the forecast.
After what has been a very busy weather week thus far, we look to end the remainder of the work week with nothing but clear skies.
Showers and thunderstorms from last night continue to move off to the east. The cold front has passed through our area. Some scattered showers were trying to follow behind it earlier today, but those have since dwindled out. Partly cloudy skies through the remainder of our Wednesday. Behind this aforementioned cold front, we can expect to see cooler temperatures overnight and through the rest of the week.
What does this mean for us? Simply put, it is discussing the northern movement of a better severe weather environment. The closer that warm front gets to Davidson/Williamson counties, the more unstable our atmosphere could potentially become tonight. We still think the *best* ingredients for tornado development is ever-so-slightly to our south, but this does not mean we are free from seeing severe weather or possibly a tornado.
The Wind
Let’s talk first about the wind…and oh my the wind. We are currently under a wind advisory through midnight tonight.
Sustained winds to start the day will be around 15-20 mph. This will increase to about 20-25 mph by the afternoon. Now these are just sustained winds. We could potentially see wind gusts upwards of 40 mph through the day. This wind is expected long before any stormy weather (which would bring even faster wind speeds).
South winds will blow slowly, gradually increasing as we get into tonight. Sunny today, high 60°, and dry, with dewpoints in the upper 20°s.
Big changes arrive Monday. There is a lot of meteorology to talk about (low pressures, wind gradients, instability/CAPE, shear, QPF, etc.), but I’m going to leave most of that out because I don’t want to drown out the message.
Rain arrives sometime Monday. We may see some light and scattered showers in the morning. After that, a much heavier rain (with questionable storm potential, see below) arrives.
ETAs for the heavier rain (and storm potential), by model:
GFS: 3 PM
EURO: 3 PM or so.
NAM: 6 PM
NAM4: 7-8 PM
How Much? This will be the heaviest rain we have seen in months.
Our last big rainfall was September 17 to 18th, when we got 1.33″. We’re forecast to get that much Monday.
The Euro model has 1.3″, with some areas getting more. The GFS, below, generally agrees with the Euro:
I have to mention one run of the NAM4 model was showing only 0.5″, so I suppose there is some bust potential for a 1″+ rain on Monday. Most models have us over 1″.
Officially, our NWS is going with 1.19″ in Nashville and 1.26″ in Franklin.
We do not expect thunderstorms in the morning. It’s the arrival of a squall line that has potential to cause problems. We expect it to arrive sometime after dark. We aren’t exactly sure when, but we will have a better idea about this tonight and tomorrow morning.
Here’s the NAM4 model’s view of it:
This system has strong storm dynamics. “Forcing” is there to kick things off and make the squall line.
The winds aloft, measured in shear or “helicity,” will be strong, even exceptionally strong. Helicity measures the amount of “spin” in the atmosphere to support the rotation that makes severe thunderstorms, and, if other conditions are right, tornadoes. Check out how high helicity is on the GFS model Monday night at 6 PM:
The reason we are not freaking out about is because of missing of moisture and instability, measured in “CAPE” (Convective Available Potential Energy).
At the same time we will have very high helicity, the CAPE is barely even visible. You may have a hard time seeing it, so I outlined it:
That’s about 100 j/kg of CAPE. It’s just not enough to make a big, bad storm.
HOWEVER, what if the models are wrong? What if CAPE is 300 j/kg? In those cases, and when other things align, we’ve had severe weather, even tornadoes. To be very clear, I do not think we will have any severe weather. There’s not enough CAPE. Some models show an inversion aloft. And the helicity is probably too strong even if we get more CAPE than expected — if you lift up a thin parcel of air and try and make a tornado with it, that helicity is so strong it would probably just shear the top of it smooth off, rather than spin it.
So, we will be watching the CAPE tomorrow. One key element of CAPE is the dewpoint. Right now, the predicted dewpoint is 56°.
If that dewpoint starts creeping toward 60° tomorrow afternoon, our concern will increase.
So, my concern level is low. There are other reasons to discount a storm threat, but we won’t go into those. Just know that the helicity — rotation or spin the further up you go in the atmosphere — will be high, and there will be some rain around, so we will need to watch this tomorrow very closely. My gut says it’ll just be rainy and really windy, but stay tuned. If my gut is wrong, it’ll get messy around here.
@WendyMonday has tweeted to @NashSevereWx for years, so every time we’re going to get a Wind Advisory on a Monday….we say it’s a Wend….so yeah, you get it.
Monday will be Wendy Monday for sure. NWS has already said it will issue a Wind Advisory.
20-30 MPH sustained winds, gusting to 40 MPH. For those of you who live at a higher elevation, expect 40-50 MPH winds.
Use today to secure any inflatables or stuff that can be blown around.
Also, if you’re out in the rain, wear rain-tolerant shoes, and a rain jacket, because the wind will destroy your umbrella if you aren’t careful.
Also, secure your God’s Frisbee.
That’s all I have to say about that.
This is running long, so I’ll leave you to read the excellent forecast discussion from NWS-Nashville this morning:
It`s this second wave [Wednesday] that could bring another 1 to 2+ inches of rainfall to our southern and eastern counties. All totaled, between Monday`s and Wednesday`s rain, all of Middle Tennessee could see 2 to 3 inches, with some higher totals for those southern and eastern counties -- all of which need it, desperately. What we will have to watch closely is any of it piling up in a short period of time. The ground is so hard and dry, run-off from this heavy rainfall could create some flooding issues, so please keep this in mind.
Overall, a nice weekend is ahead if you need to finish any yard work or holiday decorating.
Sunday is the pick day with highs in the low 60s. Why so warm? A high pressure system currently over the Ohio/Tennessee Valley slides east and we end up on the backside, where warm southerly flow begins to work in.
