Sunday: Perfect Weekend Continues . . .
Low 60°s today at BNA will actually be mid/upper 60°s under direct sunlight. That’ll change soon.
Clouds Arriving Monday
That was a good week and a half of winter. Spring begins Monday.
Some models have a few showers dripping from afternoon clouds Monday afternoon, but they are few and mostly east of us. You may see a few drops but I doubt we will see a rainout.
Winds turn south, jacking the temp into the mid 70°s.
Rain, Maybe Storms, Tuesday
The Storm Prediction Center has outlooked us as a 1 on the scale of 0 to 5 for severe weather Tuesday.
The high-res, regional models are not yet in range of this event. This prevents a more detailed forecast. Here’s what we think we know. Observe all uncertainties.
When: Afternoon/Evening. NAM3 model has a some morning rain, but nothing supportive of strong thunderstorms. Global models expect an afternoon/evening event, in the form of a line of storms located along the Kentucky/Tennessee border by late afternoon, moving our way kinda along I-24 into the evening.
Tornadoes? Probably not. The GFS model is showing a low-end tornado environment Tuesday night, with plenty of moisture (dew point 63°). instability (CAPEs around 1,000 j/kg), low cloud bases (LCLs under 200m), but not very much shear (bulk shear is 45 kn). The shear is “speed shear,” meaning the winds are only going faster the further up you go, but they really aren’t turning all that much. Surprisingly, the NAM model is not all that different from the GFS. Even the Euro is on board with this idea. We aren’t ruling them out, but now there is no reason to sound alarm about tornadoes. We will need to watch it as the models resolve themselves. I am sure the models do not have it “exactly right.” Storm type forecasts like this are always full of uncertainty.
Damaging straight-line winds are the primary storm threat. The storms should form one long line or a series of line segments capable of damaging straight-line winds.
Hail, too? Yes, certainly possible. In the heavier storms, there should be enough shear aloft to support hail. This is less likely than the wind threat.
Lightning? I expect to see some lightning in these storms.
Rainout Alert? Yes. Our NWS thinks we will see 0.14″ of rain by 7 AM Tuesday, and another 0.36″ by 7 PM Tuesday night. This should wreck all practices Tuesday night, especially since we expect the storms to be arriving by late afternoon/early evening Tuesday.
Rest of the Week: Weekend Storms?
Tuesday’s storms will be riding a cold front, which will have passed by noon Wednesday, taking the temp down to the mid 40°s Wednesday morning and not quite to 60° Wednesday afternoon. Expect to stay dry from Wednesday afternoon through Friday around noon.
There’s been a lot of interest in a weekend storm system. No one really know what it is going to do. We get the brunt of these storms when the center passes north of us — but not too far north — ideally for storms, you want the center to run northeast along the Ohio River. The medium-range models have been struggling to figure this out. Last Thursday the models predicted the storm’s center to be as far north as the Great Lakes. Today, some model runs have it centered south of us. Neither the GFS nor Euro models put the center in the “right” place for severe weather for us, but the variability is massive, and if you take the average of the two it will cause us some problems either Friday or Saturday. This is one of many reasons we talk so much about forecast uncertainty. To quote today’s forecast discussion from the Storm Prediction Center: “Uncertainty is substantial at this range in the forecast period.”
If you say: “shoot me straight, what’s it going to do?”
Categories: Forecast Blogs