Fall tornadoes?

Even though I was hoping Friday's bombogenesis chase day would pan out, it looks like Thursday is going to have the best daytime tornado potential with this monster trough.

Models have agreed on a squall line developing after dark Wednesday and track it to around a DFW-OKC-ICT line at 12z Thursday. Here's where it gets interesting. The deepening surface low will suck up the remnant frontal boundary from the previous system and pull it north as a warm front with a very moist airmass to the south. This frontal boundary is still deep in the gulf (and actually still moving south attm) and I want to be just south of wherever this boundary sets up Thursday afternoon. With the models now showing the trough breaking apart into two separate shortwaves, it looks like there is another surface low that tries to develop in front of the southern wave. Recent runs have shown this cyclogenesis clearly in the moisture fields with the best dp's being sucked back west into the subtle secondary low in OK along the front instead of being drawn up into the bombing low over NE. This should keep the effective warm front pretty far south, especially given early morning showers slowing its northward progress.

According to model precip forecasts, the squall line will be maintained and strengthen through the afternoon as it moves into AR. I've been watching this on the models for a few days and ALL of the runs of the GFS and NAM fired convection in the warm sector in front of the squall line and south of the warm front. Should this happen, the environment will be very favorable for supercells and tornadoes given the excellent shear making up for the meager instability... given a semi-discrete nature. Although this is a high shear/ low cape event, the storm speeds will not be outrageous because the storms should be well west of the strongest mid-level flow, 30-40 mph to the northeast is doable.

Right now I'm liking somewhere in southeast OK as a starting point. Probably end up deep in the heart of Arkansas before all is said and done.

Synoptically, this system is an absolute beast. And regardless of the time of year, throw 70's dewpoints under a jet like this and you've got trouble. Now we just have to nail down those pesky mesoscale details.

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Blowhard Bill and severe prospects

Tuesday August 18th, 2:27 pm: Hurricane Bill has strengthened to a Category 2 with max sustained winds of 105 mph as per the 10AM update. The current National Hurricane Center's forecast track takes the storm to the west of Bermuda and then curves to the north. This would keep the storm well away from the US but our forecast certainty for tropical systems outside of 3-4 days really drops off. A couple days ago the GFS had three consecutive models runs where it took Bill into the Gulf of Mexico, and now it has Nova Scotia as a possible target. Our best tool in forecasting the track of hurricanes has to be a spaghetti plot which shows the forecast track from multiple models. The smaller the spread, the higher the certainty. Take a look at the latest thinking : LINK


Tropics aside, tomorrow looks to be an active severe weather day around the Central US as a very potent shortwave trough digs south from Canada on the backside of a long wave trough that is drifting east. Forecasting for tornadoes with late-season events like this is exponentially harder than Spring events (as evidenced by the wording in the SPC's Day 2 outlooks, ha!) but I do see some tornado potential tomorrow. What makes these events so difficult to forecast is the widespread areas of elevated thunderstorms that seem to blow up and fade away seemingly without rhyme or reason. Our inability to forecast this early and mid-day precipitation with much confidence makes forecasting surface features a very difficult task, and without that, tornado forecasting is nearly impossible. Like Dr. Doswell says, "Chasing boils down to going out on synoptic possibilities and succeeding or failing based on unresolved mesoscale events." Tomorrow definitely has a favorable synoptic (large-scale) setup, but we likely won't know until the afternoon what the mesoscale (intermediate-scale) environment will be like.

Summertime and the chasin ain't easy

Friday July 10th, 11:43 am: Blue sky bust yesterday in Nebraska but today could make up for it if the cap goes. I'm looking at yesterday as a nice day trip to Lincoln, NE to see the sights. Pretty cool town, except for that ugly red color that's all over the place. Depending on whether or not these rain showers and clouds clear out soon, we could get some supercells to develop in the KC area later today. With these very high 700mb temps we will need a lot of sunshine cooking the ground to be able to break this cap.

The rain showers and t-storm complexes are laying down a lot of outflow boundaries (OFB's are the boundaries separating the rain cooled air from the warm, moist air) which are generally the focus for new thunderstorm development later on in days with a strong cap like this. You get increased convergence in the low-levels with these OFBs which means that the air piles up along them and has nowhere to go but up and this vertical motion coming from the surface promotes thunderstorm development. The problem is that these OFBs (seen as a fine line on radar) can stretch for hundreds of miles and guessing the location of the new development can often be tricky. What it usually comes down to is putting yourself somewhere along the OFB in the most favorable thermodynamic and kinematic environment for tornadoes and hoping that the convergence there is sufficient to break the cap. These setups can be quite the test in patience and intestinal fortitude and you have to be able to mentally deal with the blue sky busts like yesterday, but the days that the tornado potential is realized REALLY make up for all the other ones.



The live stream will be up if there is anything to chase, to view it, click on my car icon on the radar map on my website http://ChaseTheStorms.com. In the meantime, check out my videos of my last two chases, both were quite memorable:



July 3rd tornado near Abilene, KS

June 20th INCREDIBLE supercell structure and maybe-nados near Ottawa, KS

Tornadoes in Kansas!?!

Tornado chances are looking stellar for tomorrow in eastern KS if we can get initiation to the south of the warm front. The forecast hodograph shapes are just about classic; unfortunately the second lobe of this potent EML will be over the target area tomorrow afternoon featuring 700mb temps likely 1-2C degrees higher than the cap bust we had today. BUT we will have a couple things working for us tomorrow that today lacked. First of all, low-level moisture may be of much higher quality given the trajectories coming from the western Gulf instead of northeast Mexico. This richer moisture may not make it far enough north in time to have a huge positive consequence but the extended period of low-level moisture pooling we've had along the surface front should be sufficient to weaken the cap and provide high instability. Now all we need is some lift to fire this loaded gun, which brings me to:



Above, from left to right, there is the 5z IR image, the NAM 500mb vorticity map for 18z and the GFS 500mb vorticity map for 18z. What you can see is a small piece of subtropical energy that was sucked up into this swrly flow from off the coast of the Baja. This subtle upper-level disturbance is forecast to be slightly upstream of the target area near initiation time which will hopefully provide lift with the help of upper-level diffluence and more significantly the strong, negatively-tilted shortwave ejecting across the Central Plains. This little piece of energy may not have a big roll in initiating convection on the warm front or triple point, but if I were targeting further south along the dryline I would be keeping a very close eye on it.

June is the new May

Friday June 5th, 1:15 pm: This darn ridge is finally breaking down as the cut-off low is forecast to be scooped up into the polar jet and eject across the Plains this weekend. Today has a decent shot for some daytime tor's around Cheyenne, WY and southeast along the surface boundary. I'll be chasing tomorrow somewhere between Omaha, NE and Great Bend, KS. Yep, the forecast is still that hazy. If I think the cap can be breached I'll head west to the dryline; if the cap looks too strong on morning soundings I'll head northwest to the surface front and maybe west from there to the triple point. One of those days where you have to hedge your bets and not take yourself out of position for a potentially better show, but that's going to be tough given such wide range of targets.

Sunday is looking good across eastern KS where strong moisture return will result in high instability beneath a powerful jet, the problem once again will be the seasonably high 700mb temps which could cap most of the warm sector. On both days, IF the cap is breached south of the surface front, along the dryline, tornadic supercells are a definite possibility. If the cap holds south of Nebraska and Iowa on Sunday, it will mean lots of sunburns but Monday's chances will look much better.

On Monday the cold front is forecast to finally drift through eastern KS, and given three days of substantial moisture return via 50kt nocturnal LLJ's and continuous southerly surface flow, the warm sector will be primed for a big day. This is especially true if the airmass isn't worked over by an MCS, which would likely happen if the cap is breached on Sunday. The increased surface dew points will make the high 700mb temps less of a hindrance on initiation away from the undercutting cold front.

Looking over this quick forecast, I'm leaning towards rolling the dice tomorrow (Saturday) and playing the dryline given the decent tornado chances on the next two days. If it were a one day event, I would be tempted to target the warm front for its higher chances of seeing a storm but with a risk-reward tossup like this it's nice to have two other days to make up for it.



Monday June 1st, 11:42am: Leaving for St. Joseph, MO here shortly where I'll have to make an east or west decision. There will be storms all over this east-west boundary, it's just a matter of finding the best low-level shear and getting on the storms verrrrry early in the life cycle before they gust out. Probably more of a structure day but I can't rule out a tornado. Live stream and chat room will be up shortly. To view the live stream, click on the green car icon on the radar map below.

Sunday May 24th, 11:42pm: I'm driving for Tempest Tours this week and should be able to update via Twitter semi-regularly on what we see and where we are. The stream won't be up until this tour is over on Saturday but I'll upload some pics and vids if I get anything worthwhile. The weather pattern this week looks just awful for severe weather across the Plains but it is May and anything can happen. The 0z GFS run tonight has officially re-sparked my interest in this season. It shows this death-ridge breaking down over the weekend and an extended period of western US troughing (ie May's tornado conveyor belt). There is hope yet!

First tornado day of many...

Saturday April 25th, 12:19 pm: I'm seeing tornado potential in eastern KS this afternoon, so much so that I couldn't justify a drive to the popular western OK target where storms could hold off until after dark. There is some cloud cover over my target area right now but instability will not be lacking given the highest dewpoints we've seen this year. There is a subtle and compact bit of energy moving across central KS toward my target area, which I'm hoping will set off a supercell or two this afternoon. The front that had been shown on previous models as a cold front (tornado killer) will likely remain stationary over this area and actually edge north as a warm front after 7pm in response to the deepening surface low west of here. Will be leaving Lawrence shortly and head south until we find some clearing/ insolation. Live stream will be up!