Tuesday, May 24, 2016

Early summertime weather pattern is here! What about Bonnie?

The atmospheric patterns have shifted, changing from very pleasant and dry weather over the weekend to a more humid and warmer setup with increasing chances of thunderstorms, more akin to early summer.

At the upper levels, which drives how the rest of the atmosphere behaves, a large ridge of high pressure extends from the Southern Plains northeast towards the Great Lakes and is shifting east into the eastern U.S. Meanwhile, a large scale trough over the western U.S. will also push east into the Plains by this weekend.

As of Tuesday evening, a ridge of high pressure at the upper level (30,000') (which looks like a hill in the black contoured lines above) is situated from the western Gulf Coast towards the Great Lakes, causing weather systems in the Plains to move northeast around the ridge and somewhat protecting the Mid-South.
The mid levels respond with a high pressure ridge building briefly over the Mid-South for the middle of the week before moving east, as southerly flow ahead of a mid-level trough of low pressure also moves into the Plains.

By later in the week (Friday night, as shown), the upper level ridge shifts east and the mid-levels (18,000', shown here) respond with southerly air flowing into the region as storm system are allowed to get closer to the Mid-South with the ridge shifting east.
Finally, near the surface, the Bermuda high pressure cell maintains its grip on the southeastern U.S. with the Mid-South positioned on the western periphery of it. Lower pressures dominate the Plains.

Near the surface (5,000'), the Bermuda High (high pressure centered over the southeastern U.S. coastline), keeps weather systems from intruding too far east. Being on the periphery of the high, the Mid-South sees increasing chances of rain from east to west, with areas west of the Mississippi River having higher chances than those of us east of the river. 
Overall, this setup favors a southerly stream of warm, Gulf moisture-laden air into the Mid-South, which is increasing our humidity levels, as well as a stormy pattern (including some severe weather) to our west. As those storm systems encounter higher pressure east of the Mississippi River, they move northeast, up the west side of the ridge. We're left in the middle - with an active pattern to the west and dryness to the east.

Occasionally the systems to the west brush the area and bring us thunderstorm chances, but those are hard to determine more than 24-36 hours out which will fall apart as the encounter the ridge to our east and which will bring elevated chances of thunderstorms. Thus we are left with low chances of thunderstorms each day, some of which may not actually materialize and some which could bring a strong storm or two, as well as localized downpours!

It appears the best chance of more widespread storms in the metro may be in the Thursday night to Friday night time frame as the Plains trough is able to move into western parts of the Mid-South before high pressure re-builds heading into the weekend.

Total rainfall from Friday morning to Saturday morning according to the GFS model is nearly 0.5", so rain chances are expected to be higher to end the week before they fall again heading into the weekend. 
There also are some indications that this afternoon's storms just to our north could build south, or send out an outflow boundary that results in the formation of new storms closer to the metro this evening. Stay tuned to our social media feeds for the latest on this possibility. Most models are firmly opposed to the idea, so we'll see! Get our latest thoughts via the MWN Forecast.

Heading into the weekend, as mentioned, high pressure begins to build once again, reducing rain chances to low end "chance" possibilities, as a possible tropical or subtropical system develops off the southeast U.S. coastline. Atlantic hurricane season begins next Wednesday, but with Alex having developed in January, Mother Nature may not wait until June 1 to throw another named storm our way!

The American GFS model projects an area of low pressure over the Gulf Stream off the SC coastline on Sunday evening. Could this end up being Tropical Storm Bonnie?
Finally, you may know that we rolled out a brand new version of MWN StormView Radar on Sunday night. We've gotten lots of positive feedback on the new interface, features, and mapping! You'll get the full "interactive" experience on the desktop version of MWN, but the interactive version also works on mobile (the previous one did not). We also have a dedicated mobile version with 3 different zoom levels available via MWN Mobile. The new radar map also appears on the MWN mobile apps. For more on how to use the interactive features, check out this video tutorial I put together.

Latest regional view from MWN StormView Radar
I also must offer a big "Thank you!" to our inaugural sponsor of the new and improved StormView Radar, Levitt Shell! If you haven't taken in a free summertime, family-friendly concert at the Levitt Shell at Overton Park, plan to do so this year! And if you have, you're in for a whole new experience as the Shell has been completely renovated to enhance the patron and performer experience! We'll be keeping an eye on the weather for this summer's concerts as MWN is the Official Weather Partner of the Shell. You might even see StormView Radar on their video screens during one of your visits! Thanks Levitt Shell for a great partnership!

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

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