Planning and Forecast for the Storm Chase Expedition

The start date for chasing is being finalized as I type this, but it looks like Jason, Ian (will be bio’ed later) and I will head out from Maryland on April 30th, with the plan to start actively chasing on May 2nd (so long as there are storms on that day). We be out chasing through the 13th, which will give us 12 full potential chase days before we have to start heading back to Maryland.

There’s a few things still left to buy, like a sleeping bag and duffel bag, but other than that there’s just prepping Jason’s car and finalizing the itinerary.

I will be posting a daily blog from start to finish for everyone to follow along and enjoy. It should be an interesting two weeks!

Looking at the climatological statistics and the teleconnection forecasts, it appears as though early May could be quite active in the Central Plains, Midwest and Tennessee Valley regions.

The NAO and PNA are forecast to be either negative or trending negative as we head into early May:


 
Below are the loading patterns (ridges/troughs) that correlate with the NAO and PNA in spring:


(The height anomaly maps are from the Climate Prediction Center)

 
The images are the positive phase correlations of the NAO and PNA. Warm colors indicate positive height anomalies, and the opposite is true for the cooler colors. If you invert the colors for the negative phase, you can see that the -NAO induces a trough over the Rockies and that the -PNA induces a ridge over the Southeast. Together, they help steer the storm track through the Central Plains and into the Midwest, as seen with the red arrows that are added to the images on the right-hand side. This track is quite favorable for severe weather.
 
Here is the latest U.S. Drought Monitor map:

 
It shows dry conditions over the Southern Plains and parts of the Southeast. I won’t go into it much, but I’ll quickly just say “drought breeds drought” in that the drier areas on the map will have a tendency to stay dry, which would indicate that most of the storms will form further north in the Central Plains and the Midwest/Tennessee Valley regions. In a hand-waiving manner, the drought conditions will help keep the storm tracks further north, which will help support the -PNA pattern.

We are also coming out of a strong La Niña winter into a weak Niña or neutral ENSO state, which is climatologically-favored to produce more active severe weather seasons.

The U.S. has been quite active with low pressure systems in recent months as pockets of upper-level energy that form these systems continually move onshore into the West every 2-4 days. All together, this should provide us with an active May pattern, with plenty of severe weather in the Central Plains and Midwest.


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