First, I'd like to share a few pics I received last night as showers passed over the area around 5-6pm. The high-based showers (meaning the base of the clouds was fairly high) with sun peeking through the clouds and a stable layer of air beneath the clouds made for some interesting sky-watching and even a double rainbow! The clouds with round "nobules" or "sacks" below them were mammatus clouds, which are more commonly associated with severe weather, but which also form when falling precipitation encounters a stable layer of air, thus making the cool formations on the base of the clouds.
|Mike H sent us these pics of the mammatus clouds on Twitter.|
|Joey Sulipeck took this great pic of the rainbows over Barbecue Fest|
|Posted by the Memphis Redbirds Twitter account right before the first pitch last night!|
Besides cool temps, the trough also has upper-level disturbances rotating around it. As we are in the base of that trough, the disturbances pass over and bring us rounds of precip, one of which occurred last evening. The next fairly strong one is due in tonight and will bring a better chance of showers overnight into the early morning Saturday. Though a shower is possible this evening, most rain will hold off until after midnight and end by mid-morning Saturday if not a bit quicker. one more, slightly weaker, disturbance arrives Saturday night, bringing another chance of rain late Saturday night into early Sunday.
That should be the last chance of rain for some time as the trough moves east and a summer-like ridge of high pressure build in behind it for next week. The transition from trough to ridge is shown in the animation below, which depicts forecast atmospheric pressure and wind at about 18,000' up every 24 hours from this morning through next Wednesday. The yellows/red over the center of the country are this morning and that is the huge trough (it looks like a dip, or trough, in the pressure pattern). You can see that that area of yellows/reds weakens and shifts north, while a hill, or "ridge," or light browns moves east across the southern U.S. The south-central and southeast U.S. is under that ridge by Tuesday and Wednesday as it strengthens (light brown becomes pink). As that happens, the ridge warms temperatures and suppresses precipitation. In other words, a hot and dry week is ahead!
|Loop of 500mb (18,000') pressure pattern and wind, showing a significant trough being replaced by a large ridge.|
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