Tonight: Clear Skies – Temps Drop into the Mid-60°s
Great evening ahead with above average temps.
Tuesday: Sunny, Small Chance of a Pop-Up Shower or Storm Late – Wake Up 60° High 85°
Tuesday will start out much like today; clear skies, temps in the 80°, wind gusts up to 20 mph.
As the day progresses, chances of pop-up isolated showers and storms increase. Why? Increasing humidity and associated instability.
The GFS model shows some showers possible in the evening:
But…the NAM4 and Euro models show:
The odds of a storm wandering overhead are low, but must be mentioned. Meteorology has not yet figured out when/where a storm will develop in these conditions .Best chance of these showers is north of I-40.
Wednesday: Rain, Possibly Storms in the Afternoon – Wake Up 63° High 82°
Rain chances increase Wednesday. The NAM4 does not show any rain so far (which isn’t unusual because it’s currently at the end of its range).
The Euro model shows some showers in the morning and then more rain in the evening, which lends confidence to the thought of higher rain chances Wednesday when compared to Tuesday.
The GFS model also likes our rain chances. It shows showers developing in the early afternoon and continuing into the late evening hours:
Are we talking strong/severe thunderstorms?
It’s kinda possible, but (right now) we think not.
The GFS model predicts pretty high CAPE (Convective Available Potential Energy):
This is CAPE approaching 2,000 j/kg. Translation: that’s more than enough “stuff” to make some storms.
*Update: NWS mentions ” what everything needs is a lifting mechanism…and we might just get that”. This is a slight change in the language they used earlier today. Still lots of uncertainty, but with most of the “ingredients” being present, if we get this lifting mechanism, our chances of severe weather could increase.*
We will also have a few other key “ingredients” present that could create some storms; however, the main “forcing” — the things setting them off — will remain well west of us. The main severe storm area of concern currently sits to our west. Storms are expected be ongoing as far east as the Mississippi river, then weaken as they work west toward I-65.
Because more of the big storm-making ingredients are believed to be well west of us, the Storm Prediction Center only includes us in a “general thunderstorm” outlook. There is still a lot of time left before these storms could arrive. There is a high level of uncertainty surrounding this event due to weather model variance.
Bottom Line: Still a lot of uncertainty. A lot could change by Wednesday. We will continue to keep you updated if anything does change. But, right now, looks pretty “meh” to us.
Extended Outlook: Rain Clears by Thursday Afternoon, Continues Through Friday
Making a specific forecast “call” this far away is a bad idea unless there is consistency inside the models and consistency among the models (and even then, it is still not smart). Such model consistency is rare — and we don’t yet have it to make a reliable Saturday forecast. But, undeterred by, you know, “science,” I’m sure your crap app is spitting out a forecast for Saturday’s Country Music Marathon. So, enjoy that.
The unexpressed truth from your app’s photo and percentage is that we don’t know, and neither does your crap app that’s guessing or hedging its bet.
Here is what we know:
The GFS model thinks light rain will be pushing into the area around race time:
The previous run of the GFS has the same thing, but, note: this is not very much rain.
It has 59° at race time, but humidity at 55°. By the end of the race, dewpoints will have climbed into the low 60°s. That makes a very humid and sweaty race. If this verifies, and there is reason to think it will, you will need more water Saturday than you’ve been using for training.
The European model has less rain than the GFS. It holds the rain/storm dynamics to the west, and sends them through later in the weekend (as a pretty potent storm system). So, for your run, the Euro model advertises clouds and maybe a stray shower.
The Euro, however, is internally inconsistent regarding humidity. In its most recent run, dewpoints remain in the mid 50°s for the entire run. Two runs ago, however, it starts and finishes the race with dewpoints at 60° then 67°. That’s an insane amount of humidity for a race, and a completely different solution to the humidity forecast than the prior run. This internal inconsistency in the Euro lends more credit to the GFS’s 55° dewpoint at the start, low 60°s at the end.
If in an elevator and asked about the marathon, I would say the only thing we think we know for sure is that humidity will be high. Rain chances are real, but assessing the risk right now is a fool’s errand.
NWS-Nashville chose “unsettled” to define the weekend outlook. They point out the above-described rain chances as “a couple of stronger-looking disturbances” but “it is too soon to know the details.” They did mention these systems (the strongest of which looks more likely Sunday) have the potential to set off severe weather anywhere from the plains, Mississippi–Ohio River–Tennessee Valleys. This includes us.
*Update: This weekend is still unsettled, but the NWS now mentions “there very well may be some isolated to scattered activity Saturday morning”. Seems to be growing confidence in the possibility of rain in the AM, but still too early to say for sure.*
Specifics will slowly fill in this week. Such is life in late April in Nashville.
This website supplements @NashSevereWx on Twitter, which you can find here.
Categories: Forecast Blogs