Determining exactly what type of precipitation will occur where and how much accumulation there will be is very difficult. If we look at the big picture, one way to be able to at least make an educated guess as to what type of precipitation will fall is to look at the Surface – 500 mb (About 17,000 feet) max temperature and the surface temperature predictions. These maps are for Saturday morning at 3 AM CST, which the GFS model is currently indicating has the highest probability to see both cold temperatures and precipitation. The thick black line marks approximately the freezing isotherm.

Sfc-500 mb Max Temp (°C)

Surface Temperature (°F)

If you are below freezing on both maps, you will more likely than not see snow. If you are above freezing on both maps, you will likely see rain. If you are above freezing on the Surface-500 mb max temperature map, but below freezing on the surface map, you will likely see either sleet or freezing rain. It is impossible to determine whether you will see sleet or freezing rain just by looking at these two maps.

The easiest way to get a better grip on whether you’ll get sleet or freezing rain is to look at soundings. The following are GFS Forecast soundings for Oklahoma City, OK and Amarillo, TX for 3 AM CST Saturday.

 

The first thing that really jumps out is the depth of the warm (above freezing) layer. At Oklahoma City, the warm layer is close to 200 mb (about 6,000 ft) deep, while at Amarillo, that same layer is only 75 mb (about 3,000 ft) deep. The other key ingredient is how high that warm layer is. Even when we take into account that the elevation of Amarillo is about 2,500 feet higher than Oklahoma City, the warm layer is much higher compared to the surface at Amarillo than it is at Oklahoma City. If these models verify, I would expect sleet in Amarillo with a shallow, elevated warm layer, while I would expect freezing rain in Oklahoma City with a deep and much lower warm layer.

In situations like this, a small change in temperature at any given height can mean a big change in what type of precipitation falls and its subsequent impacts. Forecast soundings for Guymon, OK (in the panhandle) show all layers below freezing, which means folks there are more likely to see snow, but again, it’s so close that if any of the lower levels are warmer than what the model says, they could easily end up with sleet or freezing rain. The good news is that since it has been in the 60s and 70s all week, the ground is so warm that nothing will stick, but I would expect to see some light ice/snow accumulations on elevated surfaces such as bridges/overpasses, trees, and powerlines.

Stay tuned for more info. Things change very fast with these types of storms. There’s a second round of precipitation coming in between Sunday and Tuesday, so I will be posting more as we get closer.

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Another powerful upper-level storm system is set to move across the United States later this week, and a cold front will sweep across parts of the central and northern plains between Thursday and Saturday. While it is still too early to say exactly what will happen, I would expect to see at least a few severe storms somewhere in that time frame.

Before we jump into the details, remember that to generate severe weather, you need four main ingredients: instability, moisture, lift, and shear. Let’s start by looking at the big picture forecast from the GFS for Thursday evening at 7 PM CDT. Below you will find the upper-level jet stream map, as well as a surface temperature/wind map, with the approximate location of the cold front labeled.

500 mb Wind and Height (GFS Forecast)

While I normally use CAPE (Convective Available Potential Energy) to assess instability, predicted CAPE values are expected to be between 1000 and 1500 J/kg. These are relatively low CAPE values for the plains, but is enough to generate thunderstorms, especially if the front is powerful and can provide large amounts of upward forcing (the lifting mechanism). I have also included a plot of Theta-E to show the axis of higher instability across western Kansas and Nebraksa, extending south into the Texas and Oklahoma Panhandles. The easiest way to describe Theta-E is that it combines temperature and moisture into one index, which is essentially what instability is. Higher Theta-E values indicate where the warmer and more humid air is located.

GFS Predicted CAPE for Thursday, Oct. 10th at 7 PM CDT 

One ingredient that is noticeably lacking in the latest model runs is moisture. Dewpoints ahead of the cold front will struggle to get to 60°F, if they can even get that high, which explains the low instability values. The cold front that swept through over the weekend left an extremely dry air mass over much of the plains, and this week’s storm system is coming in so close behind it that there is simply not enough time to get significant moisture return into Kansas and Nebraska from the Gulf of Mexico. A lack of moisture often results in LP (low-precipitation) or high-based storms, but it can prevent storms from forming altogether (which is unlikely to occur with this week’s system).

The final ingredient for severe weather is the wind shear. The axis of maximum shear contains shear values above 50 knots, which is plenty of shear to produce severe thunderstorms. The axis of maximum shear also aligns almost perfectly with the axis of maximum instability, which should set the stage for thunderstorms as the cold front sweeps through the area and provides lift.

GFS Predicted Dewpoint for Thursday, Oct. 10th at 7 PM CDT 

So the bottom line at this point is that the most likely thing to happen would be for a squall line to form on the leading edge of the cold front, extending from western Nebraska back through western Kansas and into the Texas Panhandle. The most likely area to see severe weather is over western Kansas, where the four severe weather ingredients best come together. I am not anticipating a big outbreak with this system. Wind and hail will be the primary threats, but a few isolated tornadoes will certainly be possible. Vertical wind profiles will be very favorable for supercells, so if discrete cells can fire ahead of the main squall line, they could become supercellular despite the low instability. We are still a long ways out, and things will likely change, so stay tuned for more updates as we get closer.

The post Weekly Severe Weather Outlook: October 7, 2013 appeared first on Matthew Gove Blog.

The SPC had a Moderate Risk up for southeast Nebraska, extending down into central Kansas, with storms set to erupt on a dryline that was coming into Kansas and northwest Oklahoma. After I punched out from underneath a low cloud layer over west-central Oklahoma, there was nothing but blue skies. I didn’t think much of it, figuring it was still early and the dryline was still way west of where I was.

As I rolled through Woodward, Oklahoma, there was still not a cloud in the sky. I still wasn’t terribly concerned, and kept heading north. As I crossed the state line from Oklahoma into Kansas, I could see cumulus clouds starting to form on the dryline. A quick check of the radar showed there were no storms yet, I kept pushing north into Kansas.

As I pushed deeper into Kansas, I noticed that the cumulus clouds were not going up. They were instead just staying as fair-weather clouds. I drove around waiting for a while, and finally saw a target start to go up to my northwest. I started heading for it.

Further complicating the matter is that there is absolutely zero cell phone service in that part of Kansas, so I had no way of getting radar updates and statements about the storm. I had to go solely on what I saw visually, which is a lot harder than you’d think.

After chasing around for the better part of an hour trying to get a read on the storm, it fell apart. I pulled over and scanned the skies for any other possible development. There were some fair weather cumulus along the dryline to the north, and nothing but blue skies to the south. There was nothing I could do. The cap had held strong and won. I turned around and headed back towards Oklahoma to get back in cell phone range to get a last radar update, and I needed fuel too. Once back in cell phone range, the radar showed all the storms were up in Nebraska.

I spent the rest of the afternoon shooting Red Carpet Country of northwest Oklahoma for my Explore Oklahoma Series and took in a spectacular sunset at Glass Mountains State Park near Fairview. Even though the chase was a bust, I still got some great shots, so it was still a success.

The post Epic Clear Sky Bust in Southwest Kansas appeared first on Matthew Gove Blog.

I pulled off I-35 in Tonkawa, OK and had another look at the models and radar before making my final decision on a target. Supercells had fired in central Kansas and were beginning to backbuild to the south along the dryline, and more storms were beginning to initiate to the southwest of Woodward, OK. After a quick look at the radar, there was no doubt in my mind which storm to target. I headed north on US-81 into Kansas.

I had earlier identified two east-west roads to use as my main chase route. One was US-64 in Oklahoma, and the other was US-160 in Kansas. As I headed north out of Caldwell, KS, I had a spectacular view of the supercell developing to the west of Harper, KS, and could also see the storms starting to initiate in northwest Oklahoma. That visual alone made for a very simple reinforcement of which target to go to. No doubt, head to the supercell developing near Harper.

By the time I got to US-160 and turned west, the supercell had exploded into a monster (got some amazing shots of it on the approach). It had a Severe Thunderstorm Warning on it, and about five minutes later, when I found a strong enough cell phone signal to refresh the radar, the storm had gotten Tornado Warned. You could see the huge rain core to the north, so I just thought, “Okay, it’s probably wrapped up in the rain core. Just focus on the supercell shots.” No more than 30 seconds after I had that thought, I came over the top of a hill, and boom. Circulation on the ground (this was the landspout). I couldn’t tell at first if it was an actual tornado or whether it was just blowing dust (there was no funnel or connection to the cloud base), but it looked more and more like a tornado as time went on. Later analysis of pictures and storm reports confirmed it was likely a landspout.

As the landspout dissipated, I saw another rotating debris cloud on the ground just to the north of where the landspout was. This one had a funnel and vigorous rotation, so there was no doubt that this was a tornado. There was nowhere to pull over, so I continued slowly west on US-160, keeping a close eye on it and snapping a few pictures. It roped out and dissipated just before I got to Harper.

I knew that this storm likely wasn’t done producing tornadoes, so I turned around in Harper and headed back east on US-160 to find a place to stop and pull over to shoot more photos of the storm. The Tornado Warning was reissued as I was leaving Harper, and a few minutes later, I could look in the rear view mirror to see another tornado on the ground. This one was bigger and much more well-established than the first one.

I finally found a spot to pull over, got the big lens on the camera, and just went trigger happy shooting the tornado. That big telephoto lens is absolutely perfect for shooting tornadoes from a distance, and the pictures came out amazing. I was surprised I didn’t see very many other chasers out there, but I can’t complain at all about having the whole show to myself.

As far as the chase goes, it was mission accomplished both in terms of getting shots of tornadoes and in terms of my goal of topping the April 9th chase in Woodward. I likely got my picture of the year, too. It’s gonna be hard to top those shots with the chase season starting to wind down in a couple weeks, but I’m sure gonna try.

The post Gorgeous Tornadoes Touch Down in Kansas appeared first on Matthew Gove Blog.

The SPC had been forecasting the big outbreak on Saturday April 14th since the previous weekend, and had already gone High Risk by the morning Day 2 Outlook on Friday, which was the earliest it had ever issued a High Risk and was just the second time in its history that it issued a Day 2 High Risk. Since all forecasts pointed to the highest risk for severe weather to be in the late evening and overnight and I wanted to avoid the chase crowds, I opted to make my main chase day Friday, especially since the elevated tornado risk was very close to home and the chaser crowds would be much less.

A cluster of supercells formed in southwest Oklahoma early in the afternoon and began tracking northeast along Interstate 44. One cell in particular caught my eye, which was located to the southwest of Chickasha, which I was tracking on radar from my house. The projected storm track showed it going up into southwest Oklahoma City, so I grabbed my things and set off to chase it.

The initial chase plan was to head to Blanchard and document it from Highway 9 as it passed to the north and west. I didn’t even make it close to there. In the time it took me to drive from my house out to I-35 (less than 10 minutes), the storm had developed a vigorous mesocyclone on its southeast flank and was beginning to turn right, so I quickly adjusted my plan and set up to the north of Goldsby.

One of the interesting things about the dynamics of these big supercells is that as a mesocyclone develops, the storm’s rotation pulls the whole storm to the right. In general, the stronger the rotation, the more the storm pulls to the right. You will often hear chasers and meteorologists call this type of storm a “Right-Mover.” You can also have left-movers, but they usually occur when a supercell splits, like I saw on April 9th up in Woodward.

The mesocyclone on this supercell developed and strengthened so quickly, that it turned the storm pretty significantly to the east and pointed it straight at downtown Norman. I could see the storm turn to the right both from my location north of Goldsby and on radar, so it was time to reposition to the east. The only way across the Canadian River is on I-35, so I raced back north on I-35 to go east on Highway 9 and reposition on the east side of Norman. With a brand new windshield, I wanted absolutely no part of any hail core that was associated with the storm.

As I got off of I-35 and started heading east on Highway 9, you could see the beginnings of a tornado vortex signature start to form on radar. The storm was a huge HP (high-precipitation) mess, so all I could see to the west was absolutely black skies and a white wall of rain, coming straight at me.

By the time I had gotten over to the southeast side of Norman, it was becoming clearer and clearer that a tornado may be imminent. Realizing that this was an HP mess (so no good photo ops) and there were no really good options to the south as far as escape routes go (and I was only about 5 minutes from home), the best decision was to head for home to take shelter.

I pulled into the driveway and quickly began unloading my cameras and things out of the truck. As I was locking the truck up, the tornado sirens began blaring, so I went inside and turned the TV on to see what was going on. They said a tornado had been confirmed on the ground near the OU campus. It took me a couple seconds to put it all together, but this tornado was headed straight for the house. Time to gather a couple things and head for the safe room.

I had actually spent the morning prepping and stocking the safe room in anticipation of the High Risk day on Saturday, and boy was I glad I did so. It was a pretty tense several minutes sitting in the safe room listening to the wind and rain pound the house as the tornado passed. The main circulation/vortex passed between half a mile and a mile from the house, so I was probably in the outer fringes of the circulation. As soon as the main circulation was to my east, I grabbed the camera and headed back outside and did manage to get some nice shots of the back of the mesocyclone as it moved away. The storm continued to produce tornadoes as it moved northeast, and had a multi-vortex tornado on the ground as it crossed Interstate 40 near Shawnee. And this was only the beginning of the outbreak.

I once again decided to target the area close to home on Saturday (since I wanted to avoid the chaser crowds and be close to home in case anything happened. I focused mainly on the extreme southern part of the High Risk area and the part of the Moderate Risk area to the southwest of that.

As the day went on, models and forecasts showed tornadic supercells exploding in West-Central Oklahoma around dinnertime, so that became my primary target. It was amazing watching the tornado outbreak unfold over Kansas and northern Oklahoma on TV throughout the day.

As the dinnertime hours rolled around, severe weather and tornado parameters were maxed out across much of northwestern Oklahoma and were still extremely high over West-Central Oklahoma, but the area had remained under cloud cover nearly all day, significantly reducing surface heating and allowing what little bit of a cap that was there to still hold. With no boundary around either, there was simply no way to initiate the upward motion required to form thunderstorms. The focus then shifted to a dangerous and explosive squall line that was supposed to come ripping across Oklahoma overnight.

In the meantime, I tracked a very powerful, long-track tornadic supercell that came out of the Texas panhandle and began producing tornadoes near Waynoka, OK right at sunset. The shots from the news helicopters of the tornadoes forming are just breathtaking (see photos). The storm produced strong tornadoes for over two hours, prompting a Tornado Emergency in Wichita, Kansas shortly before 10 PM.

After a short lull in the action after the tornado passed just south and east of Wichita, the explosive squall line very quickly formed in the Texas panhandle around 10:30 PM as the cold front overtook the dryline and nearly instantly became severe and came plowing into western Oklahoma during the 11:00 hour.

When the squall line came ripping into western Oklahoma, the tornado parameters were absolutely maxed out (quite a bit more than they were on May 24th last year), particularly north of I-40. There was so much spin and wind shear in the atmosphere it would cause the squall line to wiggle. If a cell was able to break out in front it would instantly become supercellular and tornadic. Unfortunately one cell was able to do that at about 12:15 AM, which struck the northwest side of Woodward with a deadly tornado with less than 3 minutes of warning.

My original plan was to get a couple hours of sleep while this line tracked across western Oklahoma, but after watching the disaster unfold in Woodward, I decided that was probably not the wisest thing to do. A PDS (Particularly Dangerous Situation) Tornado Watch was still in effect for pretty much the entire northwest quadrant of Oklahoma, and tornado parameters were still extremely high right through the I-35 corridor and the Oklahoma City metro.

The squall line was at its peak strength between about 12:30 AM and 2:30 AM. At one point the squall line was over 800 miles long (no that’s not a type-o), stretching from north of Topeka, Kansas all the way down to just north of the Mexican border in southwest Texas. A good portion of the line had Severe Thunderstorm Warnings on it.

Between 2:30 and 3:00 AM, the very potent squall line was beginning to encroach on the Oklahoma City metro, with the Tornado Watch extended to include the metro. There was still so much spin in the atmosphere that even the small updrafts had pretty good rotation in them. You could see the cells on radar really trying to break out ahead of the line, but this time it was south of I-40, which really peaked my interest, since strong tornadoes could still easily form in any cell that could break out ahead of the line. Fortunately, as we closed in on 3:00 AM, the line was able to hold together strong.

I don’t know whether to call it luck or irony or what, but the feature that really helped Central Oklahoma was actually the same feature that caused this massive tornado outbreak: the potent low pressure system coming out of the southwest. As system came roaring out of the southwest, it accelerated the westerly winds behind the cold front, which ended up being strong enough to undercut the squall line with cold air, choking off its fuel supply and both significantly weakening the whole line and eliminating any remaining tornado threat. By 3:45 AM, as the line was beginning to come into the western Oklahoma City metro, it had been undercut so much it had come back down below severe parameters and was weakening, so there were no warnings as it came into the metro.

The line came through Norman around 4:15 AM, giving us a pretty good lightning display and some gusty winds and heavy rain, but that was about it. Cool stable air settled in behind the front, closing the book on another memorable Great Plains Tornado Outbreak. It has been one heck of a start to storm season here in Tornado Alley. Quiet weather over the southern plains the next week will be a nice little break, but I’m already looking forward to the next chase.

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