Remember the Meow Meow Lullaby? “Meow, meow, meow, meow, meow, meow. Meow, meow, meow, meow, meow, meow.”
That’s what I feel like when describing this summer’s weather pattern: “Rain, rain, rain, rain, rain, rain. Rain, rain, rain, rain, rain, rain.”
It hasn’t rained non-stop, of course, but there have been far more days with substantial rain chances than without, and the days that are sunny without rain chances have mostly been like today — on the cool side. That’s great if you hate the typical Tennessee summer, not so great if you think the best thing about the Mid-South is the four distinctive seasons.
In other words, spring has already had its chance and fall will get its chance soon enough, so let’s have some summer!
Well, I have bad news if you fall into that category: it isn’t happening anytime soon.
A dry northwesterly flow has produced gorgeous weather since Tropical Storm Cindy got out of the way to end last week, but after a weak system produces a slight chance of rain and a reinforcing shot of cool air tomorrow, we’re going to see the southerly flow return, which will bring warmer temps by the end of the week but which will also bring more humidity and a return of the daily rain chances.
So with a holiday weekend on tap, what are the chances it’s going to be a wash-out? With the 4th of July falling on a Tuesday, many folks will extend their celebrations all the way out to Friday evening, creating what is in effect a five-day holiday period. It certainly isn’t going to rain constantly from Friday to Tuesday, but any day during that period will likely produce a 50/50 chance for showers and thunderstorms.
But it gets worse. The National Weather Service says there is a chance for substantial rainfall for some areas.
Here’s the setup: A low pressure system is going to move across the Ohio Valley to our north, dragging an attendant cold front towards our region. This frontal boundary will be rather weak, without a lot of oomph behind it, which will likely result in it stalling out somewhere around our area. In fact, it may not quite make it to our area before stalling out.
That’s good, right? Nope, bad. Because when it stalls out, that provides the perfect avenue for pieces of shortwave energy to ride right along the boundary, providing considerable opportunities for thunderstorms to develop.
So, for now, it appears that the high pressure area currently delivering all the sun and cool temps will begin to slide off to the east by the middle of the week, with chances of scattered thunderstorms beginning on Thursday and increasing each day through the weekend. By Sunday, as that frontal boundary hangs out somewhere in the region, showers and storms may go from scattered to widespread. And while Sunday could potentially be the wettest day overall, it appears there will be excellent chances for storms to continue Monday and Tuesday, July 4.
For now, the NWS is forecasting a 20% chance of thunderstorms on Thursday, a 40% chance on Friday, and a 50% chance Saturday, Sunday and Monday.
In a forecast discussion this morning, the NWS’s Morristown weather forecast office noted that some areas could see training of storms, which would result in a lot of rain for those areas. And, again, that statement refers primarily to the upcoming weekend. But while it does appear storms will decrease in coverage on Monday and Tuesday, it seems likely that we’ll see at least a 50/50 chance of thunderstorms both of those two days.
Here’s a look at the total rainfall estimate of the GFS forecast model, beginning Thursday and continuing through sunset Tuesday evening:
More troubling, here’s the Canadian model for the same time period:
As you can see, the GFS shows around an inch or so of rain for us, while the Canadian shows twice that, with 5-inch amounts not too far to our north.
A couple of caveats: Both of these models are low-resolution models that do not handle convective precipitation very well. If we see a couple of thunderstorms in the same place between Thursday and Tuesday, there’s a chance we’re going to wind up with more than an inch of rain. On the flip side of the equation, the Canadian is not nearly as accurate as the GFS. It is almost always wetter, and almost always wrong when it is. Case in point: the tropical depression that just rolled through here on Friday.
The bottom line: Daily thunderstorm chances return by Thursday, and at least Saturday and Sunday could prove to be soggy, with 50/50 chances for thunderstorms on July 3-4 as well.
Further out, the GFS model shows 90s overtaking the region after the 4th…which is almost laughable at this point.