If you’re out tonight to catch any last minute deals, temperatures will be in the 40s. Bundle up!
Under a dome of high pressure, we stay dry and find some more sunshine by Saturday and Sunday. Notice the afternoon high on Sunday in the low 60s: this will be a warm up influenced by a switch to southerly winds, also leading to an increase in atmospheric moisture.
Patchy fog is possible very early Friday morning, It’ll mix out quickly, and leave us ample sunshine.
A bit colder in the mornings this weekend. Mid 30°s Saturday morning will turn into near/below freezing temps before dawn Sunday morning.
This morning, we described the set-up (you can click back to that if you want). Basically, south winds Sunday will transport moisture into Middle Tennessee, effectively eliminating the Dry Air Monster.
Monday and Tuesday, a robust low pressure center will move across Missouri and toward the Great Lakes, that is, if you believe the latest run of the GFS model (12z):
This should make it rain here Tuesday.
Each run of the GFS tells a different story. Some runs send us a lot of rain; others, not so much. But each run consistently says yes, it will rain, and it should be more than we’ve seen in a long, long time.
The Euro model, which we aren’t allowed to show you, is encouraging. It has 1″+ of rain, pretty consistently.
Our NWS still thinks between 1″ to 2″ total, with more rain to our west than east. The Weather Prediction Center has us in the 1.25″ to 1.50″ category:
Thunderstorms or Severe Weather? Certainly not Monday. But Tuesday? Probably not, but it’s worth talking about.
To get severe weather, you need a lot of things to come together. Two main ingredients for severe weather are shear (Tuesday we will have more than enough of that) and instability (what we think we’ll be missing Tuesday).
Instability is measured many ways. Unstable environments make strong storms. To have an unstable environment, you need some “stuff” to make the storm, measured in joules per kilogram (j/kg) as CAPE: Convective Available Potential Energy. It’s kinda like making an omelette — you can have a chef, a stove, a skillet, and some ham and cheese, but if you have no egg, you won’t make an omelette.
Generally speaking, you need at least around 500 j/kg of CAPE to make storms, maybe a bit less than that in the high shear environment we will see Tuesday. Most model runs say we will have no CAPE, as in zero CAPE, nothing, but other model runs toss us 100 to 200 j/kg (like the GFS model below), which isn’t much, but will need to be closely watched.
Our NWS is not alarmed:
Models continue to show relatively weak CAPEs for Tuesday. However, with a howling low level jet of 50+ kts, we`ll have to keep an eye on things for next Tuesday just in case our atmospheric instability and thunderstorm chance increases.
As you sit around a table with your family today, remember: observe any Airing of Grievances on Festivus, not Thanksgiving.
Save it for December 23. Save it for Festivus, you guys.
Clouds today, maybe some fog very early Friday morning. I would not be surprised to some pre-dawn fog early Saturday because temps will be 37° and dewpoints 34°. This is a 3° dewpoint depression — look for those when looking for foggy conditions. I mention that only because it’s hunting season.
Mid 30°s Saturday morning will turn into near/below freezing temps before dawn Sunday morning. NWS won’t issue more Freeze Warnings for the rest of the winter, so you’re on your own.
Let’s make it rain. All images from the GFS model run this morning.
Step 1: Saturday’s north winds will blow in dry air. We can’t do anything with that. Sunday, we switch those to south winds, which blow in moist air.
That’s not exactly a juicy atmosphere, but it’s not dry. The Dry Air Monster cannot survive in it. He won’t be around to eat our rain like he did yesterday.
Our atmosphere is very dry, both at the surface and aloft. System to the west toting its own moisture, but our D.A.M. will eat much of it. pic.twitter.com/ONAFNltNfY
— NashSevereWx (@NashSevereWx) November 23, 2016
Step 2: How about a strong (991 mb) low pressure center passing to our northwest by mid-day Tuesday? Check.
So, those are two main — but not the only two — ingredients we need for active weather. I will now stop nerding and start translating.
We think 20+ MPH sustained winds, perhaps gusting over 30+. This will depend on the exact track of the low. Some of the models yesterday were going crazy with wind speeds. The GFS had winds at 5,000 feet moving around 60knots, which is crazy high and unlikely to happen, but even close to that is a lot of wind. We may need a Wind Advisory Monday and/or Tuesday.
There’s still uncertainty about how everything will shake out. It’s pretty complicated.
When? Right now I don’t think we will see much Monday. West Tennessee will see some maybe Monday night, but I don’t think it will get to us until Tuesday, probably in the morning. ETA is very uncertain.
How Much? Check out the uncertainty in the GFS model.
First, the 0z run of the GFS model this morning really screws us out of the rain with a point-three, but that would be three times the amount of rain we’ve seen from each of our past 2 events.
Then there is the most recent, but less reliable, run of the GFS — we hit jackpot between 1.2″ and 1.8″:
So, no real clear answer from the GFS, which has been going back and forth like this for a few days.
The Euro model, which we aren’t allowed to show you, is encouraging. It has 1″+ of rain, pretty consistently.
Our NWS thinks 1″ to 2″ total.
The Weather Prediction Center has us in the 1.25″ to 1.50″ category:
Thunderstorms or Severe Weather? Certainly not Monday. But Tuesday? Probably not, but it’s worth talking about.
Shear, both speed shear and winds turning with height, is very high, and we would be freaking out about it if there was going to be even a little convective available potential energy (CAPE). You can have severe thunderstorms and tornadoes in low CAPE, high shear environments, but you can’t if there is no CAPE, and we don’t think there will be any CAPE on Tuesday when the best storm dynamics arrive. However, a few model runs have suggested we’ll see around 200-300 j/kg CAPE (for example, this is what the 12z Euro said yesterday), possibly in response to a secondary low pressure center it thinks will form along the front. We usually want around 500 j/kg CAPE to start worrying. Note, however, the GFS does not have any CAPE at all, except for one model run yesterday where there was 3 j/kg, and the Euro runs also have shown no CAPE.
Our NWS is not alarmed:
Models continue to show relatively weak CAPEs for Tuesday. However, with a howling low level jet of 50+ kts, we`ll have to keep an eye on things for next Tuesday just in case our atmospheric instability and thunderstorm chance increases.
Current Radar
Fun Fact of the Day
We’ve seen a lot of records set this year, but this may be the cherry on top. With our freeze this past Sunday, this is Nashville’s longest growing season on record. Nashville went 259 days (Mar. 5-Nov. 20) between freezes according to our local National Weather Service Office.
Current Radar
HRRR Model 7AM-Midnight (18 hour loop)
The above HRRR model shows rain arriving around midnight, but very low dew point values will “eat” that precipitation. We don’t think it’ll even make it to the ground. As you can see below, very dry air is dominating the SE U.S.
Current Radar
Most of us will dip down into the upper 20s overnight and into Tuesday morning.
A few more clouds are possible on Tuesday but sunshine will be the main story once again. The reason for our increased warmth will be due in part to the previously mentioned high pressure migrating east.
Official low overnight is 26°, but we should be closer to 20° in rural/outlying areas.
No more Freeze Watches and Warnings. NWS only warns the first few.
A WIDESRPEAD HARD FREEZE OCCURRED ACROSS THE MID-STATE THIS MORNING...WITH MANY LOCATIONS REPORTING 600 AM TEMPERATURES BETWEEN 23 AND 27 DEGREES. AS A RESULT OF THE WIDESPREAD NATURE OF THIS HARD FREEZE THE NATIONAL WEATHER SERVICE AT OLD HICKORY WILL DISCONTINUE ISSUING FREEZE WATCHES AND WARNINGS...AS WELL AS FROST ADVISORIES...UNTIL THE GROWING SEASON RESUMES NEXT SPRING. SOME OF THE FREEZING TEMPERATURES REPORTED THIS MORNING INCLUDE... ASHLAND CITY...26 DEGREES... HENDERSONVILLE...27 DEGREES... FAIRVIEW...23 DEGREES... FRANKLIN...23 DEGREES... ANOTHER HARD FREEZE IS FORECAST FOR TONIGHT...WITH TEMPERATURES EXPECTED TO BE EVEN A FEW DEGREES COLDER THAN THOSE EXPERIENCED THIS MORNING. A FEW SPOTS BY SUNRISE MONDAY MAY EVEN SEE LOWS IN THE UPPER TEENS.
Many areas hit the 20°s overnight. We’ll warm rapidly today toward 50°, thanks to abundant sunshine.
Our local National Weather Service office only issues Freeze Watches and Freeze Warnings for the first few freezes of the fall. That doesn’t mean it won’t freeze again. They just don’t want to overwarn you.
A WIDESRPEAD HARD FREEZE OCCURRED ACROSS THE MID-STATE THIS MORNING...WITH MANY LOCATIONS REPORTING 600 AM TEMPERATURES BETWEEN 23 AND 27 DEGREES. AS A RESULT OF THE WIDESPREAD NATURE OF THIS HARD FREEZE THE NATIONAL WEATHER SERVICE AT OLD HICKORY WILL DISCONTINUE ISSUING FREEZE WATCHES AND WARNINGS...AS WELL AS FROST ADVISORIES...UNTIL THE GROWING SEASON RESUMES NEXT SPRING. SOME OF THE FREEZING TEMPERATURES REPORTED THIS MORNING INCLUDE... ASHLAND CITY...26 DEGREES... HENDERSONVILLE...27 DEGREES... FAIRVIEW...23 DEGREES... FRANKLIN...23 DEGREES... ANOTHER HARD FREEZE IS FORECAST FOR TONIGHT...WITH TEMPERATURES EXPECTED TO BE EVEN A FEW DEGREES COLDER THAN THOSE EXPERIENCED THIS MORNING. A FEW SPOTS BY SUNRISE MONDAY MAY EVEN SEE LOWS IN THE UPPER TEENS.
Current Radar
Make sure to bundle up with wind chill values in the mid 40s, falling rapidly through the evening.
Clear skies, windy and cold.
7 PM Kickoff: 41° (Wind Chill of 35°)
10 PM: 36° (Wind Chill of 30°)
Winds: NW at 5-10 mph
The heater and extra blankets will surely be appropriate for overnight tonight into Sunday morning. A freeze warning has been issued by NWS Nashville:
...FREEZE WARNING IN EFFECT FROM MIDNIGHT TONIGHT TO 9 AM CST SUNDAY... THE NATIONAL WEATHER SERVICE IN NASHVILLE HAS ISSUED A FREEZE WARNING...WHICH IS IN EFFECT FROM MIDNIGHT TONIGHT TO 9 AM CST SUNDAY. THE FREEZE WATCH IS NO LONGER IN EFFECT. * TEMPERATURE...MOST AREAS WILL HAVE LOWS IN THE MID TO UPPER 20S. * IMPACTS...SENSITIVE OUTDOOR VEGETATION MAY BE KILLED BY THE FREEZING TEMPERATURES. PRECAUTIONARY/PREPAREDNESS ACTIONS... A FREEZE WARNING MEANS SUB-FREEZING TEMPERATURES ARE IMMINENT OR HIGHLY LIKELY. THESE CONDITIONS WILL KILL CROPS AND OTHER SENSITIVE VEGETATION.
Current Radar
The night is finally here that we have been longing for, because we need the rain.
Timing of showers/thunderstorms
As of right now, most models are trending towards a 10 PM ish or later arrival for the majority of the showers.
