The last two weeks have featured very hot weather here in the Cumberlands and across Tennessee...more or less typical summertime weather, made to feel hotter by our cool start to the season. But if lots of sun, lots of heat and lots of rain-less humidity is your idea of good summer weather, you better get out and soak it up today, because a pattern change is about to begin.
The heat ridge that has been in place over our region will begin to slide out of the way today, giving thunderstorms an opportunity to develop. The flow will switch, allowing an airmass that is more moist and more unstable to begin to develop. There is a far greater chance that we won't see rain this evening than there is that we will, but there is a chance for spotty thunderstorms or showers to develop close to dark or shortly thereafter, representing the best rain chance we've had this week.
Rain chances will really begin to increase tomorrow, with the new air mass in place. Precipitable water values are very high, even for this time of year -- almost two inches. (Precipitable water is a measure of the moisture depth in the atmosphere. Essentially, it means this is how much rain we would receive if all there were sufficient dynamics in place to wring out all the moisture in the form of rainfall.) Instability should be plentiful, with CAPE values nearing or exceeding 3,000 J/kg. With weak wind fields in place, thunderstorm coverage will be more limited than it might otherwise be, and there will be very little threat of severe weather. However, with that much moisture in the atmosphere, heavy downpours are possible both Saturday and Sunday wherever thunderstorms do develop.
The best rain chances, if this morning's run of the GFS forecast model is correct, may not come until Monday, as a frontal boundary finally slides through the region. After that, we'll see cooler air than we've experienced the past couple of weeks. It's still gonna be warm, with highs generally in the mid 80s from Sunday through the end of next week, just not as hot as it has been.
The GFS is consistently very wet for the 3-5 days as the calendar flips from July to August. This morning's run showed more than four inches of rain for that general time frame, while other runs of the same model have shown as much as six inches of rain. Nailing down particulars at this point is impossible, but it'll be interesting to see how the pattern evolves as we get into what is traditionally the hottest month of the year. Because the more rain we see, the less heat we will see...as a general rule, of course.
For now, it doesn't look like we'll see heat on the same level we've experienced it this week until about a week into August, at least. It's at that point that the GFS model tries to start building the heat ridge back up, but that's a long ways off and it's way too soon to say for sure that this will happen.
The new long-range forecast from the National Weather Service's Climate Prediction Center, released yesterday, has the entire continental U.S. blanketed in above-average temperatures for the month of August, for what it's worth.
The main thing, for now, is that we're getting ready to see a return of above-average rainfall. The CPC is forecasting above-average rainfall chances for the next 14 days.
Eye to the Sky is a weather blog by Independent Herald editor Ben Garrett. Garrett is a weather enthusiast who has long blogged about interesting weather on his personal website. He is not a professional forecaster or a meteorologist and information on this blog should not be considered a substitute for forecasts, advisories or other products from the National Weather Service.