SPC has gone with a broad area of enhanced severe risk for Wednesday, also highlighting the possibility for significant (EF-2+) tornadoes and significant (2" or larger) hail. Most of the eastern 2/3 of Kansas is included.
The low pressure system that's to credit for the severe weather is forecast to come through a little slower than originally thought. That means winds at or near the same direction throughout the atmosphere much of the day, and several lines or clusters of storms possible. If a bunch of things come together right, we would see a higher risk for large hail and tornadoes around and after sunset. There will be any number of subtle, un-forecastable boundaries in the air mass, too, which may enhance things or get in the way.
The D2/Wednesday convective outlook presents a challenging forecast scenario, owing to the subtle nature of multiple impulses advancing across the Plains within a corridor of weakly anticyclonic flow. Most guidance indicates this evolution will result from continued digging of the western US trough on Tuesday, with subsequent closed low development within the broader trough. In turn, rising heights over the Plains should yield weak ridging aloft by Wednesday morning. At the surface, a front is forecast to extend from western Kansas east/northeastward to Wisconsin, while a dry line will be positioned from the front in Kansas south/southwestward into west Texas.
…Southern Kansas to the Missouri Valley… A weakening/veering low-level jet is expected to extend across eastern Kansas Wednesday morning. Through the late morning and afternoon, though, low-level flow should back slightly ahead of a triple point over southern Kansas. In turn, increasing warm advection and convergence is expected to support convective initiation over parts of southern/central Kansas. Meanwhile, southerly flow will transport dew points in the mid 60s over the area, supporting moderate mixed-layer buoyancy by afternoon. Organized by southwesterly mid-level flow around 45-55 kt, several cells should become severe, initially capable of large hail and damaging winds.
Mode evolution (i.e., discrete cell potential) remains questionable with this earlier convection, as the orientation of the larger-scale pattern and resultant veered 700mb flow may encourage straight hodographs, or perhaps some counter-clockwise curvature in mid levels. Therefore, storms may grow upscale into eastward-advancing linear segments, with damaging winds as the primary threat over parts of central/eastern Kansas. Concurrently, any higher tornado potential may not increase until late evening, as the low-level jet increases, and convective bands potentially acquire embedded rotating elements.
Wednesday looks like a very active weather day in the state. However, since we’ll have 2 days of prior storm activity, I’m not very confident on where the important surface boundaries (cold front, dryline) will be located by then.
Two computer model solutions (GFS/NAM) depict some upper level support moving out into Kansas Wednesday afternoon/evening so that will provide the lift we’ll need to get storms going. Strong winds veering with height support rotating storms and all storm modes. Boundary placement will be key to where those towers start to blossom first.
My two cents worth here. I used to work with a wise meteorologist named Ken Smith. I was a young, gung-ho meteorologist who was just sure that every one was THE big one! He taught me over the years to first look for all of the reasons an event WOULDN’T happen, then try to prove why he would. So, taking that approach:
What could go wrong? I am worried firstly about unidirectional shear and secondly about cloud debris garbage. We certainly saw on Monday how much a shield of cirrus can ruin a perfectly good severe weather forecast. Will the Tuesday storms put up so much grunge that surface heating won’t be maximized? As to the shear, that will be all in the timing. The latest model runs have REALLY slowed down the progress of the 500mb trof and kept it somewhat positively tilted (hence the unidirectionality). Our old “rule of thumb” used to be that if the center of the low was at the 4 corners at 12Z with the jet streak coming over Guadalupe Pass, TX, watch out! The latest model runs (for what they’re worth) still have the low WEST of the 4 corners by the END of the day with the left, front, exit region of the jet streak well to our west over southern Colorado. This opens some big questions on timing and makes this meteorologist wonder if Thursday might be a bigger day than Wednesday. Time will tell.
What could go right? Well, and this is no small thing, the models could be flat out WRONG. They ARE just models after all and models have a very hard time with cut-off lows over the southwestern CONUS. Moisture shouldn’t be a problem, and that is usually a big question mark on the early storm sequences of the season. Perhaps the thing this outbreak has going for it the MOST is climatology. I have seen setups that were MARGINAL at BEST this time of the year turn into huge outbreaks that few saw coming.
If I was able to chase on Wednesday, would I? You bet! Will I have my shelter ready to go? You bet! Will I be surprised if it is a later outbreak than it has been looking for about a week now. Yeah…that too. It is the time of year when just about ANY day can produce severe weather, so no need to focus on one day or another. ALWAYS be prepared in May!
One final thing, and I think this bears to be said because I think SPC made a huge mistake going with the “Enhanced” level a few years ago. Keep in mind that this would “only” be a slight risk day before a few years ago. I remember when those used to make people (other than us weather geeks, of course) yawn. Now it is treated almost like a moderate (or even high) risk used to be. The old adage of “be prepared, not scared” should certainly be applied to a slight and an enhanced risk. At “moderate,” your stomach should feel a little hollow, but wait for a “high” to make the hair stand up on the back of your neck and start taking your anti-anxiety medicine.
Disclaimer: I wrote this before going to bed Monday night, so things could have changed drastically in both the models and the SPC outlooks by the time you read this. Remember, a forecast is only as good as its latest update with the latest information.
Mark makes some substantial points above. One of the trends I’ve seen since Mark and Rodney threw their hats in the ring on this event is a push later in the day with the conditions which would bring about tornadoes and large hail. The SPC outlook acknowledges to an extent what Mark noted about the position and timing of the low, now indicating things may involve linear storms in the daytime while the tornado risk would be higher around and after sunset.
This forecast model (NAM Nest) simulates the storms like this (this is an hourly simulation starting at 4pm CDT and ending at 1am CDT):
The image below is from a composite I rarely show in my public discussions. I do now more to show that it is pegging enhanced tornado parameters even as late as 1am CDT.
The thought of night time tornadoes is unsettling to me partly because the closest scrape I’ve had from a tornado happened at night. Social science research has shown we need to hear or see the warning message from three separate sources before we take action. Unless we have a decent amount of lightning, one of the sources many are prone to use to confirm a warning — their sight — is no longer valuable. And nearly all of us are inside and many are bedded down for the night, making tornado sirens much less useful (they aren’t designed to be heard indoors). So the we had no warning factor goes way up and warning lead times shorten dramatically (that’s my opinion, I haven’t seen research to back it up).
All that said,
the difficulty in forecasting tomorrow because of the unknown effect of today and of storms earlier in the day tomorrow combine to make this a far-from-sure bet. The low may slow down. The daytime storms may not be ongoing at nightfall, or might be at the wrong angle to the low level jet. A mazillion (technical term) outflow boundaries may spin something up and kill it off before a warning can be issued. There’s so much that could go wrong.
So keep in the loop about the weather — from multiple sources.