AFTERNOON UPDATE (posted 1:30pm)
Things are shaping up to be stormy later this afternoon. The stubborn cloud cover finally started to break up late this morning, allowing temperatures to warm up significantly — high temperatures are still likely to crack 90 degrees. That sets up a warm and unstable air mass, and there are storms moving into that air mass as I type this. The Storm Prediction Center expanded the “Slight Risk” area to include most of the Midstate…
…and the SPC also posted a Severe Thunderstorm Watch until 9pm:
The latest run of the HRRR model is still too fast for my analysis, but I think it has a good handle on the storm pattern, even if it’s an hour or two too aggressive:
I’d bet on storms approaching Nashville around 5pm, rather than the 4pm depicted in that loop. Either way, that’s bad news for the evening rush hour. The threats remain the same — damaging straight-line winds and large hail from the severe storms, intense cloud-to-ground lightning and heavy rain from ALL storms.
WEATHER (posted 9:00am)
On the surface, today’s weather looks almost identical to yesterday’s and Monday’s — hot and humid, with scattered afternoon storms. The difference is that today’s storms could become severe, especially from mid-afternoon through this evening.
Some cloud cover this morning has been trying to put the brakes on our warm-up, but the June sunshine will burn through that and push us up to the low 90s before the best chance of thunderstorms arrives:
Factor in the humidity, and the heat index will be pushing 100 once again.
Like we have the past couple of days, we’ll start to see some pop-up storms appearing on the radar by late morning to around midday. The strongest storms will develop to our northwest and head in a bit later in the afternoon — the specific timing is variable, depending on which forecast model you believe. The RPM model rapidly intensifies the storms and pushes them through the Midstate, with the heftiest thunderstorms moving through Metro Nashville around rush hour this afternoon:
The HRRR model moves the storms through even faster, with the strongest storms in the first half of the afternoon:
I lean more toward the RPM at this point, but with this type of scenario we have to take it literally hour-by-hour.
The severe threat is greater today, especially along and north of I-40. The wind field throughout the depth of the atmosphere is a little more organized, the upper levels of the atmosphere are a little drier, and there’s a weak boundary off to our north to help trigger the storms — all of those factors are important. The Storm Prediction Center has included the northwestern Middle Tennessee and most of southern Kentucky in a “Slight Risk” (level 2 of 5) for severe thunderstorms, with the rest of the Midstate in a “Marginal Risk” (level 1 of 5):
That’s a northward adjustment compared to their earlier outlooks, and I’m not sure I buy the reduced risk for the I-40 corridor. The main threat will be damaging straight-line wind gusts over 60mph. The hail threat can’t be ruled out, but there’s a LOT of warm air that the hail will have to fall through before it hits the ground. The tornado threat is almost zero, and the storms should move quickly enough to keep flooding from being a major problem:
This isn’t an off-the-charts risk by any means, but we’ll still keep a close eye on any storms that show up on the radar this afternoon and evening.
Once today’s storms scoot off to the south, we’ll be left with just a very limited storm chance tomorrow and Friday. I think the best chance will be late Thursday night and Friday morning as a weak cold front (really more of a wind shift line) moves through. Thursday looks exceptionally hot (Nashville’s record high for June 16 is 100)…
…and the heat index will likely exceed 100 degrees in most locations Thursday afternoon.
The change in wind direction on Friday is very good news for us — northerly winds will bring slightly cooler air in…but more importantly, they’ll bring less-humid air in as well. It will still be hot this weekend, but “tolerably hot” thanks to the lower humidity levels:
Some mid-week nerdiness…
- The southwestern United States will be unbelievably hot later this week. (When Phoenix is threatening its all-time record high temperature, that’s saying something.)
- Believe it or not, that kind of heat can cause airport delays. Just the heat!
- Meanwhile, it snowed in Hawaii. (On top of a 13000-foot mountain, but still.)
- The “tipping point” when renewable energy sources will become cheaper than fossil fuels might only be about ten years away.
- When I talk to kindergarten and first-grade classes, I show a thermometer that has both Fahrenheit and Celsius markings, and I explain that the United States is the only country that uses the F side of the thermometer. Which begs the question: why has the United States been so slow to adopt the metric system?
- The Mars rover Opportunity is wrapping up its study of a valley on the red planet.
- Elsewhere on Mars, the rover Curiosity has found mineral evidence of explosive volcanic eruptions in the distant past, which has surprised researchers.
- A rare meteorite was recently discovered in Sweden, which could help astronomers re-create a cosmic collision that happened a long, long time ago.
- What the world looks like if you’re a polar bear.
- Scientists just got one step closer to solving one of biology’s greatest mysteries.
- Calling someone a “bird-brain” might actually be a compliment.
- Can’t make this up: Australia hopes to clear its rivers of an invasive species of European carp by giving the fish…herpes. Yup.