This 4th of July weekend featured the best weather that our area has had for an Independence Day holiday in a very long time. Lots of sunshine, zero threat of rain and relatively low humidity made for great weather for lake trips, cookouts, fireworks and all of the usual things associated with the 4th of July.
Unfortunately, all good things must come to an end, and as most of us head back to work this week, we’ll do so with an increasing threat of thunderstorms, some of which could be strong and contain heavy rainfall.
First things first: The next two days are going to be gorgeous, though hotter. We’ll be near 90° on Monday and again on Tuesday, so if you like summer-like weather, these two days are tailor made for you. In true summer fashion, we’ll see a slight risk for diurnally-powered thunderstorms return to the forecast on Tuesday afternoon, but coverage should be skimpy. Most of us won’t see rain.
Wednesday onward: Beginning Wednesday, thunderstorm chances increase, with rain and storms likely each day for the remainder of the week and through the weekend. As we draw nearer to the time frame in question, it’s not looking quite as wet as it once looked like it might be. Thunderstorm coverage might be a little less thorough than originally anticipated, especially on Wednesday and Friday. But we’re almost certainly going to see rain at some point, and could see a lot of it, depending on how the storms set up.
Severe weather? Overall, the risk for severe weather is quite low this week. The Storm Prediction Center in Norman, Okla. has not outlined risks for severe weather in our region any day this week. But there could be some marginally strong thunderstorms with some isolated high wind gusts and some heavy rain — potentially leading to very isolated flash flooding — depending on how things shake out.
Progression of the pattern: Wednesday will feature the least rain chances of the second half of the work week and the upcoming weekend, with about a 40% to 50% chance of thunderstorms. These storms will be primarily diurnally-driven, meaning they’re fueled by the heat of the summer sun, as low-level moisture and instability increase, the upper ridge over our region weakens, and the weather pattern generally becomes more unsettled.
Then on Thursday, a cold front will approach from the northwest, which should lead to more widespread storm coverage.
On Friday, the frontal boundary will have cleared the region, but models are indicating mid-level drying and plentiful low-level moisture with quite a bit of instability. That’s going to lead to more thunderstorm chances, and Friday may actually bring the best chance of some isolated strong thunderstorms this week.
Then another upper level trough approaches for the weekend, helping to fuel thunderstorm chances on Saturday and Sunday.
Not a complete washout: No day this week will be a complete washout. The storms will come and go. One thing to keep in mind is that models often pump up summer rain chances in advance, then diminish them as the time frame draws nearer. We saw this last week, when we certainly saw thunderstorms but not the deluge that models had originally suggested.
We’re already seeing the same thing happen on the models this week, as most major forecast models trend towards less rainfall for the second half of the week. Both the GFS and the ECMWF show generally an inch of rain or less for our area (the ECMWF is closer to half an inch) through Friday evening. Of course, trying to nail down exactly how much rain is going to fall is fruitless, because this is going to be convective precipitation that isn’t picked up well at all by models. Wherever thunderstorms set up, more rain will fall. And the stronger the storm, the more rain a localized area will see. It’s impossible for models to predict in advance where those storms will set up. But the key takeaway from this is that we aren’t going to see rain all day, every day.
The bottom line: Rain chances will be on the increase every day this week after today, beginning with a 20% chance of afternoon thunderstorms on Tuesday and then increasing from there. Atmospheric conditions gradually become more favorable for thunderstorms as the week progresses, with storms likely each day by the end of the week and through the upcoming weekend. The risk of severe weather is low, but some marginally strong storms can’t be ruled out, which could produce isolated high wind gusts and heavy rain that could potentially lead to isolated flash flooding. No day will be a complete washout, however. Storms will generally be scattered to numerous, with Thursday likely bringing the most complete storm coverage.