BIG UPDATE

I haven't had enough time to update this blog. But here are the major severe wx events of April:

April 3 - big severe wx outbreak with a couple of tornadoes.
April 10-11 - small event with two very impressive supercells, one over OK, one over AL.
April 13-14 - really had potential with a high risk over TX on the 13th that did not verify.
April 20-21 - tornadoes over the Plains, specifically, NE and the TX Panhandle.
April 23-24 - started out with several discrete and powerful, but widely isolated, Plains supercells. Ended with a high risk bust just to the east over I-35.

Granted, I didn't post a lot on the last two events. But as one can see, it was an active month for severe wx, although not even close to last year.

The limiting factor for this year so far has been the stagnant pattern over Western Europe and the Atlantic, which has been crunching up a fast Pacific jet. The jet is a result of Indian Ocean convection and the associated IO subtropical jet/Siberia polar jet "phasation" (is that even a word, lol?). At any rate, the flow is not as progressive when it punches into the CONUS, so basically a big bowling ball closed low results as the jet energy is forced to crunch up. These big bowling balls tend to not be prolific tornado producers. Case in point: April 24.

WHY DID APRIL 24 BUST?
For those who don't know, April 24, 2007 was predicted to be potentially one of the biggest outbreaks in the Plains in recent years. A big 500mb low was progged to hit a very moist and unstable airmass (the GFS, for instance, had predicted -10 LI's in central OK about a week out, although it did not verify). Many of the ingredients were there. Dr. Greg Forbes of TWC, Larry Cosgrove, among other very good mets were predicting an outbreak on the scale of the intensity of May 3, 1999. An almost unprecedented Day 3 Moderate risk was hoisted by the Storm Prediction Center.

In the end though, it all went bust, as convection formed too early. But why?

IMO, the reason it busted is mainly because the bowling ball closed low which had already stacked by the time. It is fairly common knowledge that a stacked low tends to be less condusive for severe wx. In this case, the dry line pushed very far east as CAA behind it intensified and the low matured and began to stack. Convergence along the dry line intensified, and coupled with strong upper air support, a line formed early and hard.

I think, that perhaps with less instability in the morning, or with some type of earlier convection to stabilize, this could've still ended up being a notable event. Strong instability fostered big anvils, which stablized things, and the convection developed into a line quickly, preventing moist inflow to areas later.

Still though, one tornadic supercell did form along the dryline later that day, a testament to how much potential this setup really had. A high risk was hoisted for central TX later that afternoon, but it mainly busted with few reports in the area. The lack of juxtaposition between the instability axis, the location of initiation, and the low level shear axis probably prevented from supercells which formed there in the afternoon, from being tornadic.

Ironically, the one strong, classic supercell that formed, formed in northern MX and entered deep south TX near Eagle Pass, TX, killing 10 people, 3 in MX, 7 in TX. It had perhaps one of the most impressive radar signatures I've ever seen, along with a monster supercell in rural northwestern KS the night before.

Long-awaited update: 3 significant events including possibly a massive outbreak to come April 10-17

Sorry I have not updated this; been busy.

Regarding the last event in the previous blog, March 28 there was a big outbreak across the Plains. The second system failed to amplify significantly but spawned a big severe wx outbreak with minimal tornado activity on April 3.

If I had time to post, I would've said that there looked to be potential. Now it looks even more likely. Strong 150 kt Pacific Jet (PJ) is coming in. Reloading with record low temperatures across the east and snow all the way down to TX (in April!). Indeed, powerful polar vortex (PV) is right now parked over the Eastern 2/3 of the country. As the PJ moves in, it will kick the PV out, reasserting it near the North Pole. Pacific air will flood the country as several disturbances within the flow amplify over the Intermountain West.

The first threat looks to be from the 10th to the 11th. This one will be a phase of a piece of the PV and an impulse riding along the Pacific Jet. Right now, a lead disturbance that goes through in the morning is the question mark. Will it be weak enough to not cause too much an effect for the bigger stuff in the afternoon? Nevertheless, given my analysis of previous events, the fact that moisture might be limited will not allow this to be a historic outbreak, IMO.

Next threat: 13th thru 15th. This one could be the biggest depending on the third system (see belwo). Another disturbance will come in via the Pacific Jet Highway. This time there could be more moisture to work with. Details are sketchy right now, since it's a week away, but dynamics look incredible (just as they will for the first system), but there will be more moisture to work with - latest GFS paints 65° to 70°F dewpoints all the way north to Memphis, TN. Caveat may be if the first system doesn't move out quickly enough.

Final threat before I think things calm down again: 15th thru 18th. This one is a question mark. The full force of the PJ rolls in this time, so this certainly has the most potential with regards to dynamics. But the instability is the question mark. It looks like this might be the signal of another pattern change as the Pacific becomes extremely convoluted after this and the NAO tanks. In other words, another cold pattern for the east. (BTW, do want to remind everyone that the idea of the "reloading pattern" with the PV over Hudson Bay -- only works consistently for early season and cold season outbreaks. Not going to go further into that though). If the NAO tanks early, this system will not have moisture to work with as the second system gets caught up and trapped behind the building ridge/block. If the NAO does not tank early, or more specifically, the second system moves out of the way, this might be the biggest of the three events as it will have the full mass of the PJ helping it to amplify into a low-amplitude high-wavelength trough -- most ideal for big outbreaks. Won't get into too much detail here as well.

Most of the major global models that go to the 240 hr range - specifically the GFS, CMC, and EURO, show the progression of these three systems. So confidence is much higher than last time where I had the right idea initially but bombed it due to relying too much on the poor model performance.