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Submitted by Tim Buckley on Tue, 05/10/2011 - 10:42am.
Lots going on weather-wise across the country today, so lots of odds and ends here in the blog! First of all, we've got a stubborn and persistent "Omega Block" happening; we've got smoky skies and fires here in North Carolina, and we've also got historic flooding in the lower Mississippi. Let's get going...
Omega Block Forecasting Woes
First of all, this type of pattern can either be a friend or foe to meteorologists. What we're finding across the country right now is a nearly stationary weather pattern called an Omega Block. I talked about this a little bit before on the show, and here on the blog back in Novemeber. But it's worth looking at it again, because this time it's a frustrating setup for us.
So here's that Omega block setup we were talking about:
You'll notice the "center" of the block stretches from Minnesota right down the Missippi to the Gulf Coast. This is the region in the blocking pattern that we typically see the nice sunny weather (EASY forecasts!). Back in November, we were in this position for over a week during a blocking event. On the two sides, we find two very mature low pressure centers. These areas are the cooler, wetter zones. For us though, we're in between -- underneath that Jet Stream in a transition zone. As you probably could guess, these are the "tricky" spots to forecast.
Underneath that Jet Stream, we find a stationary front at the surface where the cooler and warmer air masses collide. This front serves a couple of purposes. First of all, it serves as a firing point for thunderstorms during the heating of the day. In addition to that, it can act as a highway, sending whatever storms form right down the front from west to east. So -- for us, we need to watch some potent storms here along the front in our backyard, but we ALSO need to look at storm formation up in the Great Lakes since they can travel all the way into the Southeast along this boundary.
If that weren't enough variables to account for, this boundary is meandering slowly back and forth throughout the process - meaning it's exact position will determine exactly who sees thunder, and who sees nothing. The end result? Varying degrees of thunderstorm chances almost each day in the forecast - frustrating!
Mighty Mississippi Rages On
As you've certainly seen in the wall-to-wall news cycle, the Mississippi is at record levels, and continues to assualt Memphis and the surrounding areas. Up next, cities to the south - including Baton Rouge and New Orleans. This is something we've been looking at for a while though through both the winter and the Spring, as Mother Nature typically gives plenty of warning for these events.
Looking at this graphic, it was almost a perfect storm of sorts setting up this flooding. To the north, a record snowy winter in parts of Minnesota, the Dakotas, and Illinois created huge pools of snow just waiting to melt. Add on to that a late season blizzard in Minneapolis followed by some big warm-ups, and huge amounts of water were sent into the river in a short period of time.
But it's more than just the Mississippi. The Ohio River is an enormous river and the largest tributary of the Mississippi. This river has been swelled to the brink this year with record breaking April rains in places like Louisville, Cincinnati, and Tennessee. It's this combination of the flooding Upper Mississippi and the flooding Ohio River that is creating the devastating river crests in the Memphis area.
Thankfully for folks in Tennessee, the waters will slowly but surely begin to recede over the next 4 days. BUT, the real trouble is still to come for folks in Baton Rouge - and of course New Orleans. This will be another test of engineering to ensure that the city is not flooded in a major way like it was during Hurricane Katrina.
Carolina Fire Still Burning
The major fire in Dare County which brought smoke all the way to Wilmington Monday continues to burn. As of Tuesday afternoon - it's only 40 percent contained, and has consumed around 21,000 acres. Thankfully, most of this is uninhabited gameland. Hopefully it stays this way.
I do want to point out though how we can track these fires as meteorologists using the same data you see on your morning forecasts. The first is a visible satellite image - which shows the path of the smoke.
You can see the smoke originating right on the Pamlico Sound side of the Outer Banks, with this plume of smoke carrying all the way south to Morehead City and even into the Cape Fear area. That's why the faint smell of smoke hung in the air Monday morning.
The next image is an infrared image, which actually shows the heat signature of the blaze.
If you look REALLY CLOSELY in the same spot you see the smoke starting on the visible image, you'll see a dark black dot. This dot IS the fire itself on the ground. Infrared satellites actually image heat, showing you cooler cloud tops in white and the warmer land in dark colors. This black dot really stands out.
Phew! That's enough weather talk for one day! Let's hope this Omega block treats our forecast nicely. Hopefully the thunderstorm chances will subside by next week.
By: Tim Buckley