Day 137: Upcoming Pattern Analogs

Posted by pmarsh on 17 May 2010 | 3 comments

Today is day 18 of VORTEX II and the armada once again deployed on thunderstorms in eastern New Mexico. These thunderstorms posed a low risk of tornadoes, but did give the armada a chance to practice deployment strategies in preparation for what appears to be another active pattern. More on this below.

How did the VORTEX II armada fair today? Well, at least five separate vehicles will need to replace windshields after today’s adventures. We probably won’t have a final count until sometime late tonight or tomorrow morning. The broken windshields were the result of hail up to the size of baseballs falling repeatedly on portions of the armada. If you are curious as to what this might look or sound like, then take a look at this video of the Oklahoma City hail storm that occurred yesterday. Warning, while the hail sound is loud, if you listen close enough you may hear some foul language.

So, above I mentioned the fact that we appear to be heading into a fairly active severe weather pattern. Above is a temperature forecast for the next 6-10 day. Instead of actually predicting what the high temperatures might be, this is a probability that a given location will experience a high temperature greater than normal for this time of year. In general, cool temperature indicates upper-level troughing and warmer temperatures indicate upper-level ridging.

If one were to translate the temperature forecast above into a forecast for mid-troposphere trough/ridge forecasts (below), we see that a trough is forecast for most of the western United States and a ridge is forecast for the eastern United States. This kind of pattern is conducive for extremely warm, moist air originating over the Caribbean Sea to move northwestward into the central United States. (For the more technical readers, this occurs because the persistent southwest flow at mid-levels results in a lee trough on the eastern slopes of the mountains that allows southeasterly winds to develop from the western Caribbean Sea into the northern plains.)

The warm, moist air is just one of the necessarily ingredients for severe thunderstorm development. We still need something to lift this warm, moist air into the troposphere to develop thunderstorms.

Typically on the east side of a large trough (such as the one forecast to develop over the western United States), minor shortwave troughs “eject” northeastward from the base of the trough to the crest of the ridge to the east. Ahead of each of these shortwave troughs rising motion is found. Without going into all the details, this rising motion that can act to lift the warm, moist air into the troposphere. Now, it is almost impossible to predict the exact timing of these shortwave troughs, but it is almost a sure bet to they will be there.

Like I discussed on 8 May 2010 (Day 128) for model forecasts, it is possible to construct analogs to previous events based on the forecasts above produced by the Climate Prediction Center (CPC). In the bottom right of the image below, analogs for this predicted pattern can be found. For convenience, I’ll post them below the image.

The analogs (click on the red ones to see the storm reports) are:

11 June 2005
17 May 1962
04 June 2005
27 May 1978
15 May 1999
23 May 1975
21 May 1991
07 June 2004
08 June 1984
14 May 1998

Most of these dates are either severe weather outbreaks themselves or are dates very near severe weather outbreaks. Like I said previously about analogs, you can’t take an analog as a specific forecast of what is going to happen. It should be used as a piece of guidance; it is merely one piece of information regarding a particular pattern’s potential. It’s a form of pattern recognition, and in this case the pattern appears to be an active one.

Day 136: Oklahoma City, OK Hailstorm

Posted by pmarsh on 16 May 2010 | 0 comments

Mother Nature must have it in for the residents of central Oklahoma. Mere days after a violent tornado outbreak affected residents of central Oklahoma, a very powerful thunderstorm tore through the Oklahoma City, OK metropolitan area this afternoon. In the wake of this storm area residents are left to deal with damaged roofs and broken windshields.

The storm (shown above) was a classic supercell with a rotating updraft, heavy rain, and a lot of hail. I’ve seen at least one report of softball sized hail (4.75″ diameter) falling across portions of the area. Several people reported picking up hail stones measuring nearly 2″ in diameter almost 2 hours after they fell! The hailfall was so intense that photographs after the fact looked as if they were taken during the Christmas Eve blizzard last winter.

So what did I do during all this? I slept on the couch. The last 20 days of preparing for and then execution of VORTEX II activities left me exhausted. Since today was a VORTEX II travel day, I did not have to worry about V2 operations. Thus, I came home early, saw the hail storm would miss us to the north, and promptly took a nap. Tomorrow starts the Experimental Forecast Program at the National Severe Storms Laboratory and Storm Prediction Center. So in addition to worry about VORTEX II operations, I’ll also be working this program as well.

It’s going to be a long five weeks…

Day 135: The “Death Ridge” is Forecast…

Posted by pmarsh on 15 May 2010 | 0 comments

Today was Day 15 of VORTEX II, and the atmosphere showed signs of being “overworked”. Several days of thunderstorms over the same areas has used almost all of the available instability and thus VORTEX II was struggling to find a storm to target. They drove all the way into southeast New Mexico to target something. There were no tornadoes, but there were storms with hail. All in all, today was a good “practice” day with real thunderstorms.

Now, this leads me into displaying a forecast of what every chaser dreads: The Death Ridge. The Death Ridge is a high the develops in the middle of the troposphere, bringing with it sinking air and warmer temperatures. All lows (and subsequently, stronger mid-level winds) are pushed far to the north, leaving much of the central plains devoid of thunderstorms. A “Death Ridge” means that all chasing in the central United States comes to a screeching halt for an in-determined amount of time. In the figure above (and annotated below) a Death Ridge is forecast by the Global Forecast System (GFS) model for late next week. You can watch a short youtube video about the “Death Ridge” here; it accurately depicts the “fear” forecasts of the Death Ridge strikes into the heart of chasers.

I should add that this is not “my” forecast. I’ve been too busy with VORTEX II to think too much about the Death Ridge. However, it is a bad sign that the numerical forecast models are now beginning to forecast this feature. It’s still a long way off, but this would be bad news for VORTEX II and all the research needing to be done on tornadoes. I’m sure I’ll discuss this more in coming blog posts.

Day 134: VORTEX II TORNADO(ES)!!

Posted by pmarsh on 14 May 2010 | 0 comments

A weak upper-level shortwave trough ejected northeast from the southwest United States this morning into eastern New Mexico. This trough aided the development of showers and thunderstorms in eastern New Mexico through much of the morning. However, by late morning / early afternoon, the thunderstorms in far southwest Texas began to strengthen. Around 18 UTC (1 PM CDT) a thunderstorm southwest of Midland, TX began to exhibit rotation aloft and VORTEX II decided it was time to act. All assets converged on the storm to collect data, and it’s a good thing that they did. While VORTEX II was getting into position, the thunderstorm produced a tornado.

The meteorological setup for this tornado was pretty classic. A stationary front (black line in the image above) was positions across far southwest Texas and extended to the north along the front-range of the Rocky Mountains and to the east-northeast into Oklahoma. To the north of this boundary, east, northeast winds were advecting in cool, dry air at the surface. To the south of this boundary, southeast winds were advecting warm, moist air northward. Along the boundary, these two air masses collided and began to develop thunderstorms.

As these thunderstorms moved north of the boundary, the easterly winds at the surface combined with the southwesterly winds aloft to produce spin in the updraft. As the updraft began to strengthen, this spin being ingested into the updraft tightened. And like a ice skater pulling her arms in close in the midst of a spin, the rotation of the spin increased. Ultimately, this led to a tornado. This process, which is more complex than I described here, was one of the results from the original VORTEX project (mid 1990s). The storm that VORTEX II intercepted was not the only storm that did this process – several did, including two thunderstorms in far southeast New Mexico.

Casey Letkewicz, a member of one of the sounding (balloon) teams, snapped a picture of the tornado. You can follow her adventures by following her on Twitter.  You can also read about her adventures via her blog, which is linked on the right side of this blog in the blog links section.

The continued advection of warm, moist air into this boundary resulted in repeated thunderstorm development in the same locations. This led to a lot of flash flooding in the Midland-Odessa, TX areas today. Many roads were flooded and reports of cars being submerged on city streets was common. These thunderstorms continued to “train” over the same areas until the stationary boundary began to surge south late in the afternoon.

Day 133: OU Commencement Inside or Outside?

Posted by pmarsh on 13 May 2010 | 1 comment

Today, VORTEX II traveled to a new target location in hopes that tomorrow would be a day for operations. Since nothing exciting happened with them, I thought I’d discuss a high-pressure forecast event taking place here in Norman, OK.

Tomorrow night is the University of Oklahoma’s Commencement.  This event typically takes place in the football stadium so that everyone who wishes to attend can do so.  In the event of rain, it is moved into the basketball stadium and students must receive “tickets” for family members.  Unfortunately, due to limited space inside the basketball stadium, each student is only allowed a fixed number of tickets, meaning some family members might be left outside in the rain.

The official forecast for OU’s commencement (and winter weather) comes from Associate Dean of the College of Atmospheric and Geographic Sciences, Dr. Kevin Kloesel. He provides daily weather briefings to OU’s administration the week of commencement preparing them for whatever Mother Nature might be preparing to dish out on Friday night. Many of the last several years Dr. Kloesel has provided pin-point forecasts that the rain would hold off until after commencement finished. Last year he was so accurate that Norman, OK was walloped by severe thunderstorms a mere 30-45 minutes after commencement concluded. (In fact, I could watch lightning off in the distance at the same time the fireworks were going off at the football stadium!)

The image above is the forecast total precipitation for Friday, the day of commencement. That’s an awful lot of rain forecast for central Oklahoma, and even more rain is forecast overnight into the next day. Dr. Kloesel will be pouring over model guidance and observations tonight and tomorrow, looking (err, praying) for a three hour rain-free window from 6:30 PM CDT to 9:30 PM CDT.

He has his work cut out for him…

Day 132: Thunderstorms Persist Across Central U.S.

Posted by pmarsh on 12 May 2010 | 0 comments

The last 72 hours have been a whirlwind for me. It all began with my blog post on Sunday night discussing the uncertainty in where the significant tornado outbreak would occur on Monday. It continued on Monday when a developing tornado nearly hit the VORTEX II Operations Center where I’ve been working for the last two weeks. It persisted on Tuesday with press conferences and interviews regarding VORTEX II’s research on the day before’s tornado outbreak and the work entailed in helping coordinate at least six different damage survey crews. Today, it didn’t let up as I briefed Congressman Tom Cole about VORTEX II’s research and goals. Throughout all of this, I’ve spent at least 12 hours a day running the VORTEX II operation’s center.

As you can probably imagine, I need a break. I could use a day or two of quiet weather to let me get caught up on everything I haven’t been able to get to the last few days. However, the atmosphere has different plans for me.

A large mid-level low is currently located over the central Rocky mountains (easternmost yellow circle). Associated with this mid-level low is a strong mid-level jet streak (northern most blue color fill) that is making its way into the central United States. On the “nose” (i.e., the leading edge) of the mid-level, cyclonically curved jet streak, rising motion is often observed (red circle). It just so happens that there are two separate jet streaks “nosing” into the central United States that are aiding “lift”.

This lift is assisting in the development, and persistence, of thunderstorms in the central United States. These persistent thunderstorms provide VORTEX II ample “targets” for data collection. Thus, VORTEX II was once again attempting data collection tonight. And once again, the atmosphere has toyed with VORTEX II.

Thunderstorms in southwest Oklahoma that were targeted by VORTEX II frequently showed signs of rotation, but tended to produce brief tornadoes in places that VORTEX II could not actually observe them. The armada “chased” these storms all the way from the Texas panhandle-Oklahoma border to the Clinton, OK area. It was shortly before dark, as the storm was racing away for VORTEX II, that the last observed tornado developed. I was able to watch this last tornado develop live on the Internet via storm chaser David Drummond’s live chase feed.

Although I could use a break to get some rest, it doesn’t appear that the opportunity will present itself for the next few days. A second shortwave trough (westernmost yellow circle) is currently just off the California coast, poised to race toward and into the central US over the next few days. Although this is bad news for me, it is extremely good news for VORTEX II as it should provide additional chances to collect badly needed data.

Day 131: Norman, OK Tornado (continued)

Posted by pmarsh on 11 May 2010 | 2 comments

Today is Day 11 of VORTEX II. Although operations were attempted today, it appears to have been an uneventful data for the armada when compared to the devastation that occurred the day before.

As I mentioned yesterday, Norman, OK was struck by a tornado during the late afternoon hours on 10 May 2010. This tornado was part of a larger outbreak of tornadoes that affected a large portion of central Oklahoma. The first four images below were collected by the University of Oklahoma’s (OU) PRIME radar. The OU-PRIME radar is located just east of the National Weather Center building. The tornado missed the radar by several hundred yards.

The image above depicts the developing Moore, OK tornado after crossing I-35 near Hillsdale Baptist College at 5:23 PM CDT. Just north of this tornado several homes received extensive damage from extremely large hailstones falling. I heard at least one report of hail stones crashing through the roof and through the second story floor to land on the first floor. Hail stones were most likely in the 5″ range. This is large than a softball…

The next image depicts the Moore, OK tornado as it nears I-40 and the Love’s Truck Stop. This is ten minutes after the tornado crossed I-35. Noticed how the reflectivity signature around the tornado appears to look like a hurricane.

While a tornado was raging through Moore, OK, a second tornado was developing to its south in Norman, OK. The image above depicts the tornado as it moves across Lake Thunderbird at 5:44 PM CDT. Notice the lighter colors in the middle of ball-shaped signature south of the main precipitation shield. These light colors look very similar to what you would see as an “eye” of a hurricane.

Eight minutes after the images above, the Norman and Moore, OK tornadoes appears in close proximity. It isn’t very often that a radar is able to sample two very strong (possibly violent) tornadoes at such close proximity like this.

The last image is from the National Weather Service’s Doppler radar (Twin Lakes; KTLX). Notice the velocity signatures that go along with the reflectivity signatures in the previous image. These are very impressive. Especially when I consider the southernmost signature tracked extremely close to where I live. As a meteorologists this is something you never want to see headed toward any populated area, let alone your own residence.

Although a lot of damage was done and a yet-to-be finalized number of fatalities occurred, the residents in the Oklahoma City metro area are extremely lucky. If these thunderstorms had developed 15 minutes earlier, they would have matured 15 minutes earlier and the potentially violent tornadoes would have moved directly through even more densely populated areas than they did. This is not meant to lessen the impact of those who were directly affected. It’s intended to say that as bad as it was (and it was very bad), it could have been much worse.