Chad Cowan's Severe Weather Blog

Tornado-geddon

2010-05-10T01:29:00.003-05:00

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!

Triple Tornado Thursday

2010-05-06T16:48:00.004-05:00

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: http://chasethestorms.smugmug.com/Weather/Radar-images-etc/compmap/858991709_DAoLR-XL.png

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

2010-04-28T23:45:00.003-05:00

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.

Fall tornadoes?

2009-10-28T02:01:00.000-05:00

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.

Blowhard Bill and severe prospects

2009-08-18T16:02:00.002-05:00

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

2009-07-10T13:14:00.003-05:00

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!?!

2009-06-07T01:23:00.002-05:00

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

2009-06-05T15:13:00.002-05:00

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...

2009-04-25T12:46:00.002-05:00

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!

March Madness!

2009-03-06T14:05:00.002-06:00

- Saturday March 7, 2009 Big day in Kansas' Flint Hills! -

ChaseTheStorms.com has just signed an agreement with TornadoVideos.net and Weather Decision Technologies to deliver live footage to their new state of the art streaming service! This new iMap technology will revolutionize severe weather streaming. We should be up and running tomorrow! More details shortly!

FORECAST SUMMARY: Compact but potent system over the western half of the US will eject into the Plains Saturday afternoon placing a strong jet stream (150mph @ 35k feet) over a moderately moist airmass. A surface low pressure system will strengthen over western KS in response to the approaching shortwave trough. Isolated supercells and tornadoes will be possible near the surface low, dryline, and warm front intersection (triple point) west of Wichita before the cold front comes through and mashes everything into a linear mess after dark.

TECHNICAL DISCUSSION: Depending on morning analysis, I might start the day playing the warm front in northeast Kansas and northern Missouri... getting some help from isentropic lift (air being forced to rise as it is slammed into denser cold air) to help punch through the cap. If this happens and a surface based supercell fires on the warm front, projected easterly storm motions would track the storm directly over the east-west oriented warm front and the enhanced low-level turning. Even a blob of elevated, left-over convection will have a chance to become surface based throughout the morning and early afternoon if it can remain on the warm side of the boundary. The NAM and the GFS have been showing a pool of the best surface moisture (~60F) well off to the east of the triple point which will give a big boost to any updrafts that track into it on the nose of the LLJ. Definitely want to stay on the southernmost cell in this scenario.

Regardless of if the warm front idea pans out, I'll be positioning myself 25-30 miles east of the deepening surface low around late afternoon, likely around Newton or Hutchinson, Kansas. There should be a window of opportunity for tornadoes within of a couple hours around sunset when the LCL's (cloud bases) diurnally lower to a more manageable level given the marginal surface moisture. Very steep mid-level lapse rates (850mb-500mb 8C) spreading above the warm sector will promote rapid convective development with any updrafts that can penetrate the cap. Low-level convergence and locally strong surface heating will be crucial to breaking the cap before sunset. Hopefully the only convergence won't come from the advancing cold front. As the afternoon progresses, I'll be keeping a close eye on the surface obs and visible satellite imagery looking for subtle boundaries and areas that are receiving strong insolation.

STAY TUNED!

- Chad

Forecasts from the past season

2009-01-09T01:33:00.001-06:00

Seeing as though I have thoroughly neglected this blog over the past year and want to change that for the upcoming severe weather season, I am going back through my personal forecasts and Stormtrack posts and posting them here.

Where applicable I will post the image of my forecast map drawn on my handy-dandy whiteboard. I will make a later post explaining the process behind this in depth, but it should be said that I complete it the night before a potential chase (or whenever I want to practice) before looking at the SPC Day 1. I draw the surface features for the initiation period and two areas; the first being a general tornado threat area (usually in green), and the second area within the first of the highest tornado risk (usually in red). I then pick my chase target (normally within this red area) based upon terrain, road network, forecast storm mode, and daylight. This target is marked with a black dot and is hopefully covered up in the verification stage where I overlay the SPC preliminary storm reports for that day onto the forecast map.

This first forecast is one I made on May 16th, 2008. Due to Stormtrack's restrictions for forecasting for only one day at a time, this forecast is geared specificaly for May 21st, though I was using this forecast as a jumping off point for my forecasts for the four days of tornado mayhem after the 21st:

May 21, 2008 Forecast:

"Confidence in a widespread severe outbreak next week has grown significantly over the past 36 hours with the GFS finally trending toward the ECMWF's consistent doomsday(s) solution. Although Wednesday will likely be the smallest day of the bunch in terms of areal coverage and probabilities, there is a slight prospect of late evening tornadic activity near the I-80 and I-70 corridors. Very warm mid-level temperatures will be in place due to the amplified trough just entering the picture from the West. This pattern will effectively cap most of the warm sector but will also result in a considerable amount of divergence aloft. Cyclogenesis will begin early Wednesday morning over the high plains and the sfc low will rapidly deepen throughout the day. Before nightfall, we could be looking at a sub-980mb low. When is the last time that happened in May? The LLJ will rapidly strengthen to over 60 knots after dark which will contribute to very favorable shear profiles for any updrafts that can break through the cap.

GFS Model Forecast

ECMWF (Euro) Forecast evolution"

June 10, 2008 Forecast:

"Epic battle tonight of NSSL 4km WRF vs NAM-WRF... who will fire the the loaded gun?

NSSL 4km WRF: 10pm forecast sounding for DDC and simulated reflexivity (no precip, -158 MLCINH):

http://img517.imageshack.us/img517/7517/061008ddcfcstsdgnsslzu3.jpg

NAM-WRF: 10pm forecast sounding for DDC and NCEP derived simulated reflexivity (-76 MLCINH):

http://img515.imageshack.us/img515/1962/061008ddcfcstsndgnammf6.jpg"

November 5, 2008 Forecast:

"http://img87.imageshack.us/img87/6989/115otlkhp9.jpg

This is my preliminary target map, using the 03/12z model suite and 21z SREF as main guidance and refined with the 0z runs. Note that this map is my forecast for tornadoes only and not general severe weather which will extend well east into the night. The GFS has been unsurprisingly more progressive with the trough and subsequent sfc features. A quick glance at the ensemble members shows the Operational GFS as the progressive outlier (Black line), so this fcst will lean towards a blend of the slower NAM and Euro.

I am not convinced the moisture return will be anything near what the 0z NAM is advertising, with 60 dews up into NE. In fact, I wouldn't be surprised to see the 60 degree isodrosotherm not make it into OK on Wednesday. The SW low level flow prior to the event will not favor deep, quality moisture return- but given a narrow tongue of mid-upper 50 dps, the seasonably cold temps aloft and unseasonably warm temps at the sfc, instability will be sufficient for supercells and tornadoes as far north as the sfc low in SD. Hodographs will enlarge throughout the afternoon as the LLJ backs and strengthens with time across the warm sector. This will be vital to the low-level turning in an otherwise unidirectional flow. I agree with Brian Stertz that we could see some LEWPs/embedded sups after everything goes linear.

I am favoring the southern target ATTM for a few reasons. First of all there is the potential for early-mid day convection in nrn-KS and NE as the strong forcing arrives a tad early. This could kill any instability, but the screaming storm motions up there would quickly take this convection away from the initiating boundary. Secondly there is the issue of the cold front and how much it will push east during daylight potentially mashing potential supercells into a congealed mess. Depending on which model to believe, the CF won't undercut the dryline until after dark in the southern target. Lastly, storm motions in the northern target under the 70+kt H5 jet streak will not be fun to chase. I miss spring."

November 10, 2008 Forecast:

"http://img185.imageshack.us/img185/9839/p1050638yq1.jpg

Target: Brownwood, TX (100 mi sw DFW) @ noon

Compact shortwave trough currently over AZ will take on a slightly negative tilt and phase with the sub-tropical jet early in the fcst period. Lift/divergence will be enhanced downstream of the phasing. This will result in elevated convection during the overnight hours into early morning over the target area. Even with the possibly remnant overcast skies, instability will be sufficient for supercells owing largely to a very moist airmass. Main concern right now is too much forcing and not enough cap to hold off convection until peak heating and to also keep cells discrete. H5 speed max is currently rounding the base of the shortwave and will be over the target area around noon when sfc based convection will develop along the dryline. Slightly veered H85 winds should not be a problem due to the se'rly sfc windfield which will enlarge low-level hodographs. Tornadoes are possible in the Texas target area and an isolated strong tornado cannot be ruled out in the northern half near the baroclinic zone due to the low LCL's, high shear, and moderate instability in this area especially if low clouds can mix out early. Early-mid day elevated convection ne of the sfc low will be capable of large hail. Climatology and pattern recognition suggest that a significant severe event is possible tomorrow, but mesoscale features need to be nailed down before where and if this will be realized."

4/25 Forecast

2008-04-29T11:08:00.000-05:00

Full thread can be viewed here: http://stormtrack.org/forum/showthread.php?t=16164

4/23/08 - 12:17 PM
Potent shortwave trough with attendant surface low and cold front will slowly eject into the upper MS valley on Friday. Moderate instability will be present as far north as central WI owing largely to a very moist air mass. The triple point should be in eastern IA around 18z and lift ne into WI as the day progresses and the cold front should drift into the Chicago area by 00z/26. Amount of shear in the northern target should be sufficient for supercell structures if (as usual) we can get some cloud breaks and insolation after the morning convection moves out. My second concern is the 85ht LLJ veering progressively as the day goes on, so I'll be hoping for early clearing and initiation, which isn't unlikely given the meager forecast CINH.

4/24/08 - 5:05 PM
I'm losing hope in the potential tomorrow. Recent model runs have the sfc low screaming into northern WI in the mid-afternoon, taking the best shear profiles with it- far away from the best thermodynamics. My current thinking is that there will be a brief window of opportunity where tornadoes will be possible in the early afternoon near the MS river (Davenport, Dubuque area), and I can't rule out a rouge tornado in central WI before 00z, but that isn't exactly chaseable terrain. If we get enough sfc heating, the cap could be overcome out away from the cold front and produce a discrete storm before the cold front mashes it into a messy line, but that's very conditional.

4/25/08 - 11:41 AM
Decided to scrap the chase yesterday at 5 and it's looking like I might regret that decision. Things are looking up for eastern IA into northwestern IL with the MCS/ overnight convection moving out rapidly and the mid-level dry punch mixing out the low clouds behind that. I still believe there will be a brief window from 2-5pm where tornadoes will be possible in the e IA/nw IL/sw WI area. If I were chasing right now, I would be sitting in Davenport with the 77/70 surface ob.