May 10, 2010


Today looks to be a HUGE day for tornadoes across parts of south-central KS and north-central OK. A very potent shortwave trough will plow through the warm sector with the perfect timing to initiate supercells along the dryline. Seasonably high dew points (65+) are being advected northward and, with strong surface heating and steep mid-level lapse rates, should result in very strong instability along the I-35 corridor and eastward. The wind fields today are going to be outrageous... with a very strong westerly jet streak juxtaposed with a strong southerly low level jet you'll get rotating storms. When that happens in a very unstable and moist environment, like today, you have the perfect ingredients for a tornado outbreak. Hence the HIGH risk just issued from the SPC. The image below is the NAM's output for the Significant Tornado Index for 7pm tomorrow, as you can see it is completely maxed out!

My target is around Enid, OK. Storms should fire around 3pm and will move east rather quickly. The live stream will be up once we hit the road. Tune in for what promises to be a day to remember!

May 6, 2010

Triple Tornado Thursday

Thursday, May 6:
SHORT: I will be leaving Lawrence here soon for Ottawa, KS where I expect initiation in the next couple hours. Very large hail will be likely here in eastern KS, and there is an outside chance at tornadoes. If I do see one, it will be the third Thursday in a row. I will try to get the live stream up, but I've been having difficulties with that since switching to Blackberry and can't guarantee it will be without hiccups. My video of the tornado near Washington, KS and other fun stuff from last Thursday is on the Videos page.

LONG:Well the new Day 1 outted my favorite lesser-known forecast reflectivity model so I don't mind talking about it now... the HRRR has been absolutely stellar this season with predicting initiation (timing AND location). For each of the last 6 hourly runs (up to 18z) it has been initiating convection between 23z and 01z along the nose of the strengthening LLJ in essentially the same location in eastern KS. With +60kts of effective shear, supercells will be the dominant storm mode. The question is whether or not the storms will be able to form south of the warm front and root in the boundary layer, not atop the stable layer north of the warm front. If they do become surface based and then interact with the boundary, there is a good chance of tornadoes in the 7-9pm time frame, given the strong low-level turning. That's a big if, though. As of right now, I don't think the dynamic ascent and surface heating will be enough to break the cap, I think isentropic lift will be needed for that. Regardless, I'm expecting to see a few significant hail reports to the south and southwest of the KC metro area this evening.

Below is a composite map I threw together of the 17z HRRR's output for 7pm. The fcst composite reflectivity shows a nice blob southwest of Lawrence, right on the WF, and other updrafts further south, into the warm sector. The underlay is the sfc CAPE chart, showing +2000 j/kg south of the front. The white line is the 1500 j/kg isoline from the MUCAPE chart (not shown), which indicates ample elevated instability north of the warm front. LINK:

April 28, 2010

It's the most wonderful time of the year...

April 29th Forecast:
The placement of the secondary sfc low is going to be pivotal in whether or not tomorrow is a tornado day. Most of the recent model runs (including the new GFS) have developed it further down the front, in the Panhandles, but the new 0z NAM puts it in wcntrl KS. If this actually happens, it would really help out with low-level convergence, and also (hopefully) slow the forward speed of the cold front which would extend the tornado window.

This initial shortwave over the nrn Plains will pull moisture rapidly northward throughout the day but will also act to slightly veer the LL winds in KS/NE. If the secondary low does develop further north, as the 0z NAM suggests, hodograph shapes in the lowest 1km will be much more favorable for tornadoes before dark from cntrl KS northeastward into wrn IA.

Marginal low-level moisture will be a limiting factor for tornadoes but, regardless, there is going to be some WICKED structure out there somewhere. My initial target will be in southeast NE, but I will adjust west from there if initiation appears likely at the cold front/dryline intersection north of Salina. Storms will be moving east rather quickly so my options will be open if something fires to the west.

April 30th Forecast:
Feel free to call it a geographic bias and stay away, but I'm really liking the ern KS target for Friday. Some precip forecasts (including the 0z NAM) have been clearing the squall line out of this area by late morning, which combined with strong moisture advection will allow for rapid destabilization. Storms would fire first along the surface front in northeast KS into southern IA in late afternoon and then possibly southward, along the dryline as the cap erodes. +80 kts (!) of effective shear along with moderate instability will promote the rapid development of rapidly moving supercells. We've got climatology and synoptics pointing to a big tornado threat over a big area, we'll just have to wait and see how the mesoscale plays out.

Again, the placement of the secondary surface low along the front will dictate the amount of low-level turning and the overall tornado threat. If the track is similar to what the NAM is thinking, it could be a big tornado day in the KC area.

October 28, 2009

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.

August 18, 2009

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.

July 10, 2009

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 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