Update: 4/7/2015
Most of what we saw yesterday looking at Wednesday 4/8/15 remains unchanged. The outlook for a possible chase day in the central plains is still likely. One interesting change was that the NAM, previously the most bullish, looks slightly less favorable for tornadic storms whereas the GFS looks a little stronger.
Both models still depict strong instability, over 3,000 J/KG CAPE, developing across central Oklahoma and eastern Kansas.
With the capping inversion expected to erode in midafternoon, storms will likely become severe across portions of Kansas and Oklahoma.
While the forecast remains mostly unchanged, a few caveats need to be made. Most models have significantly reduced the amount of surface backing of the winds and have the winds through the boundary layer becoming somewhat veered during the day, even near the warm front. This would serve to reduce the potential for tornadic storms. However, given the presence of significant instability, sufficient speed shear, and probable mesoscale boundary interaction, this should be negated to a degree.
As a final note, it is important to remind ourselves of the current trough position:
While satellite derived analyses are much improved, it cannot replace real observations to date. That said, with the core of the trough still offshore, significant forecast changes will be possible (if not likely) between today and tomorrow.
For now, look for scattered severe storms, a few of which will produce tornadoes.
Wednesday 4/8/15 in particular holds a lot of potential for a storm chase across the central plains. While the phrase “outbreak” has been used by some, that is not always what chasers looking to see a tornado are interested in. What’s important to a chaser isn’t that widespread destruction and dozens of tornadoes form, but that the storms are photogenic, in terrain that offers a good vantage point, that of course some storms produce tornadoes, that the storm motions aren’t ridiculously fast, that the storms produce in the day time, and that the target area is definable.
That’s a lofty list and one that hasn’t been fully checked off often in recent years. Wednesday has the potential to change that.
Models are in general agreement that a large trough will move onshore the west coast and begin to move into the plains through next week. This will provide synoptic lift to help storms get going. The high winds aloft and potential presence of embedded shortwaves will further perturb the atmosphere and aid in the generation of storms.
Beneath 500 mb, at 700 mb, the NAM depicts a dry punch moving into northern Oklahoma and southern Kansas. Should this verify, this could aid in increasing instability as the layer is lifted as well as reducing the amount of moisture in the column which can increase the strength of an updraft as well aid in both keeping storms discrete and possibly keep storms more photogenic for a longer period of time.
At the surface, ample moisture and high temperatures will allow instability to climb. While the NAM (bottom) , Euro, and GFS (top) disagree a bit on the exact placement and how far north the warm front will get ….
You can see how despite the disagreements, both models bring surface dewpoints to near 19 C, have a favorable wind profile, and are largely uncapped. Certainly the NAM is more bullish, but the GFS isn’t too shabby either. (Skew-Ts at 00z in SE Kansas)
Taking a look at the NAM sounding at 21z further west, near Pratt, KS it’s clear that the cap does not wait to break until dark like in most recent events, and instead a convective event could be well underway even in the early afternoon hours across central Kansas and down into northern Oklahoma.
This is further pointed out in the 0-1km Energy-Helicity Index plot. A bullseye appears right along the warm front and into central Kansas. This index measures the combined effects of instability and shear and can be a good indicator of where rotating severe storms may form.
Finally, looking at the precipitation projection from the GFS, it’s clear that the model certainly shows no capping along the warm front and also breaks out storms along the dry line in Kansas, Oklahoma, and into northern Texas. Though this model doesn’t actually mathematically solve for individual thunderstorms, it does show that overall the environment should allow storms and not be capped and dry.
Should these models verify or come close to verification, all this together should yield storm motions under 45 mph, chaseable terrain, good timing during the day, photogenic storms and possibly tornadoes through the early evening, and a well-defined chase area. While this may not be a record breaking day, it will probably be one to remember. And almost certainly will feature some excellent photography from the chasers out in the field.
Side note: Thursday will feature severe storms as well, perhaps more numerous than Wednesday. But from a chaser’s perspective is less than ideal and thus was not covered in this article.
Logan Poole
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