Tuesday, April 27, 2010

Mississippi Tornado Outbreak Update

I'm working on a more detailed track map of the deadly Mississippi tornado of this past Saturday but don't yet have it complete.

The National Weather Service in Jackson has upgraded its maximum EF-intensity rating from the "main" tornado to EF4 (which is what I had suspected would happen - see my last post).  They now believe that the tornado was on the ground continuously for 149 miles.  At times it was 1.75 miles wide!

Here is a link to the information on what the Jackson NWS has collected thus far.

Sunday, April 25, 2010

Mississippi Tornado Outbreak of 4-24-10 - Part III

The National Weather Service in Jackson is continuing to conduct ground surveys to ascertain the exact path lengths and intensities of the family of tornadoes that struck Mississippi on Saturday.

So far, they have estimated that the tornado that struck Yazoo City traveled at least 50 miles, from near Eagle Lake before finally lifting (or at least they preliminarily estimate that it lifted) near the Yazoo/Holmes county lines Northeast of Yazoo City.  (See map below).

We know that if the above track scenario turns out to be true, we had additional touchdowns and damage reported very shortly thereafter, in Ebenezer and Durant, including a cross-over I-55 where many cars were flipped and people were injured.

The report also stated that the damage path was 1.5 miles wide, but did not specify the location(s).  It also gave a "preliminary" estimate of EF3 (160mph) damage, but cautioned that this was only preliminary and may be revised upon completion of the survey.

I always hate to "arm chair quarterback" the damage estimates, especially when I can't see it first hand (having to rely on media images can leave much to be desired), however based on some of those images, I would expect to see a higher estimate when the Yazoo City survey is complete.  I'm going to sit back and watch for a few days, then I'll post a few images to illustrate what I'm talking about.

Mississippi Tornado Outbreak of 4-24-10 - Part II

Below are screenshots of Nexrad Level II data, corresponding as closely as possible to the damage reports that I highlighted on the Part I blog (map #3) concerning yesterdays tornado outbreak across Mississippi.

Unless otherwise noted, all images were taken from the Jackson, MS (DGX) radar and depict the 0.5 degree elevation scan.  

The first shots are from 16:09Z (11:09 a.m central time) when the first tornado damage report was received near Tallulah, LA:

16:09Z (11:09am) Reflectivity Image

Corresponding Storm-Relative Velocity Image

Now we'll jump ahead about 50 minutes, as the dangerous storm was approaching Yazoo City (where extensive damage, numerous deaths and injuries were about to take place) from the Southwest:

17:00Z (12 Noon) Reflectivity Image

Corresponding Storm-Relative Velocity Image

17:05Z (12:05pm) Reflectivity Image

Corresponding Storm-Relative Velocity Image

17:09Z (12:09pm) Reflectivity Image

Corresponding Storm-Relative Velocity Image

About this time (17:09Z/12:09pm central time) is when really interesting signatures began to appear on the radar imagery, unfortunately the result of the intense damage that was being done in the Yazoo City area.

When examining the above storm-relative (SR) velocity image with a slightly different color scale, you can actually begin to see a "donut-hole" that emerges immediately Southwest of the center of Yazoo City:

Another view of the 17:09Z Storm Relative Velocity Image

Shortly thereafter, on the 17:14Z (12:14pm) images, you can also begin to see the enormous debris field being carried by the circulation show up on the reflectivity imagery as well:

17:14Z (12:14pm) Reflectivity Image

Corresponding Storm-Relative Velocity Image

The 17:19Z (12:19pm) imagery shows the deadly storm exiting the immediate Yazoo City area.  So much debris has now been sucked up by the storm that it is even more evident on the reflectivity imagery: 

Corresponding Storm Relative Velocity Image.  Small white circle depicts approximate location of the debris field indicated on the corresponding reflectivity image.

17:50Z (12:50pm) Reflectivity Image.  Note small debris field still visible, noted by white circle.

Corresponding 17:50Z Storm Relative Velocity Image.  Small white circle shows approximately location of the debris field indicated on the corresponding reflectivity image.

With the storm now nearing the outer limits of the most effective range of the Jackson radar, the images as the beast nears the French Camp area are not quite as crisp and telling, though you can still clearly see a well-defined circulation center on the velocity image.

18:27Z (1:27pm) Reflectivity Image

Corresponding Storm Relative Velocity Image

Shortly after 2pm, the storm passed about 5 miles North of Starkville.  We've had to switch to the Columbus AFB radar (GWX) for the following images.  Keep in mind there are thunderstorms ongoing over and near the radar site, so at least some minor distortion of the imagery is likely.

19:06Z (2:06pm) Reflectivity Image from the Columbus AFB (GWX) Radar

Corresponding Storm-Relative Velocity Image

I'll probably make at least one more radar-specific post after more of the ground-truth reports and survey data are in...


Mississippi Tornado Outbreak of 4-24-10 - Part I

Everyone is obviously aware by now of the horrible (but very well forecast and warned) events of yesterday in Mississippi, among other states.  Our thoughts and prayers certainly are with those victims, their families, and all of those that will be involved in the recovery effort.  Media reports indicate there are still potential victims unaccounted for in some harder to reach areas, particularly near Yazoo City and vicinity, and we especially think of those folks at this time.

I am still in the process of gathering information and looking at everything on this event, but wanted to put up a quick post of at least preliminary storm report and track information.  The NWS in Jackson will be performing surveys beginning today, and obviously more detailed information will be forthcoming.

First, below is a "wide-view" image of storm reports yesterday from within the Jackson NWS area of responsibility in Mississippi:

Below is a closer-view of what appears to be the long-track supercell and associated tornado family that began in extreme Northeast Louisiana and tracked across west-central through central and northeast Mississippi:

Finally, here is a map with my own notations of some of the more significant events and the approximate time they occurred, based on local storm reports issued by the Jackson office (you'll probably need to click on the image and enlarge it in order to be able to read all of the notations):

I'm still in the process of examining all of the radar imagery, (and there are some fascinating things to point out).  I hope to get several images and some comments posted later today.

Saturday, April 24, 2010

What Could Have Been .... Wasn't

Conditions were literally ripe for a significant severe weather episode along the I-35 corridor from San Antonio to Austin late yesterday evening/early this morning.  Though there were several severe reports (including a swath from San Antonio through Seguin from stronger cells that rolled through after 1am) what could have been a widespread, damaging episode simply wasn't.  As the old saying goes, we "dodged a bullet" last night/this morning - for sure!

The most interesting storms during the entire event occurred within a consistent band from near Eagle Pass to north of Crystal City.  Several of the cells that developed within this area showed rotation on numerous occasions.  I suspect there were tornado touchdowns in these areas, but due to the very rural and "spotterless" nature of the area, nothing was reported.

These same storms exhibited other classic signs of supercellular organization, including a couple of splits and a tendency to move to the right of the prevailing motion in the area (i.e., they originally started moving Northeast then turned into more of a due East motion over time).

Here is a reflectivity screenshot from the Laughlin AFB (Brackettville, TX) radar shortly after 11pm last night.  The cell immediately Northeast of Eagle Pass was in the process of splitting at the time, while the cell North of Crystal City was showing rotation on the Southwest flank.  (Sorry about the text box, that was a shot I used for a Twitter posting).

Meanwhile, numerous clusters of strong thunderstorms moved Northeast across areas West of I-35 to the West and Northwest of the San Antonio-Austin corridor throughout the late evening.  Between 12 and 1am Saturday morning, much of this activity collapsed and a strong gust front blew Southeast into the Austin-San Antonio areas.  At 12:35 a.m. I measured a 57 knot wind gust here at my home near Kyle (just South of Austin on I-35, at mile marker 217).

I attempted to upload reflectivity and velocity images of the above gust front, but I'm having technical problems right now.  I'll try again later and update this post...have to run right now.

Friday, April 23, 2010

Tornado Watch for Austin-San Antonio corridor until 6am Saturday

Thunderstorms are developing rapidly North of the Big Bend into west-central Texas now that intense upper level energy is moving deeper into the area (see last blog post for satellite image).  San Antonio is located at the right-most center part of the image below, taken at 9:59pm from the Laughlin AFB radar:

For the next 2 hours, the greatest threats will be increasingly large hail and gusty straight-line winds.  Toward and after Midnight, as the activity moves toward the I-35 corridor, conditions will become more supportive for possible rotation and tornado development.

Please stay alert as this potentially dangerous situation is made worse by the fact that it will reach the more populated areas well after most folks head off to bed.

Severe Weather For the TX I-35 Corridor This Evening & Tonight

Thunderstorms are beginning to fire in West-Central Texas along the main frontal boundary and immediately ahead of a strong upper level weather disturbance approaching from the West/Southwest:

Initially, large hail and damaging straight-line wind gusts will be the primary threats.  However, as the activity becomes more organized and the upper level forcing and stronger wind shear overspreads the I-35 corridor area later tonight, the threat of tornadoes will increase as well.

Nighttime severe weather situations are particularly dangerous.  Especially given this scenario where a large population area (i.e., the I-35 corridor from San Antonio to Austin) will potentially be affected after Midnight.  It is critical that all residents across the area stay alert tonight and be prepared to seek shelter should severe weather threaten their area.

It's not too late to buy a NOAA Weather Radio, which can alert you to severe storms 24-hours per day.  You can even program many newer models to only sound the alarm when severe weather threatens your immediate area.  Radio Shack, Wal-Mart, Target and other major retailers sell a variety of these devices.

Tuesday, April 20, 2010

Severe Weather Preview in the TX Panhandle This Evening!

Awesome shot of a tornado on the ground near Bushland, TX earlier this evening:

Snapshot of the Amarillo radar, Storm Relative Velocity mode, showing strong rotation just Southwest of Canyon, TX at about 8:10 pm CDT this evening:

The brighter orange and near yellow color shows wind blowing away from the radar (upper right corner of the shot) at approximately 65 mph.  Brigher green immediately adjacent shows wind blowing toward the radar at approximately 30-35 mph.

This should be just a preview of what's to come later this week....if current model trends verify.  More to come...

Ask and Ye Shall Receive

Yesterday I wrote a post remarking about how the Storm Prediction Center (SPC) had suddenly removed the extended period severe weather outlook areas later this week.  On today's early morning update the risk areas appeared once again.  The forecaster cited greater confidence in model data/consistency, among other things. 

It was a very busy day at work so I'm going to take a minute to gather my thoughts, examine all available data and then I'll post more on my opinion of the greatest threat area(s) later this evening or tomorrow morning.

Monday, April 19, 2010

Awesome Photo

Take a look at the latest spectacular volcanic eruption photo...with CG lightning no less!

Awesome shot by Marco Fulle!  (per UK Telegraph online).

SPC Day 4-8 Outlook

Don't get me wrong - I'm a huge fan of the SPC.  I'm just wondering why they removed the "extended range" severe outlook areas for later this week.  My understanding of the day 4-8 outlook is that it was designed to alert users to potential "large scale" events.  Model data continues to support widespread strong to severe weather later this week, over a large part of the country, so I'm perplexed as to why the risk areas that were up over the weekend have disappeared in the last 24 hours.  I strongly disagree that, as noted in the last discussion, the "predictability is too low" for the day 4-8 period this week.

Large Storm System Continues to Aim for Thursday-Weekend

It still looks like things are shaping up for several days of severe weather toward the end of this week, beginning on the High Plains Thursday.  Here are the latest GFS model screenshots at 500mb for Thursday and Friday of this week:

If the model trends of the past 24-hours continue, much of the Central Plains and Midwest could be in for several days  and several rounds of severe weather.

Dust-off the chase gear and stay tuned!

Sunday, April 18, 2010

Medium Range Outlook

Will a strong upper-level disturbance bring an end to the "severe weather drought" on the High Plains toward the end of this week?  The following snapshot form the GFS looks promising for the end of this week:

Beyond this week, the GFS is suggesting a potentially more active pattern may develop into the early part of the last week of April:

Stay tuned (and keep your fingers crossed)!!!

Saturday, April 17, 2010

What will spring bring?

So far it's been a wet start to spring here in Central and East Texas - as well as much of the Southern U.S.  It's also been one of the slowest starts of the "traditional" severe weather season in recent memory.  No surprise really, considering the continuing El Nino pattern in the Pacific...and much to the disappointment of the global warming alarmists, I'm sure...
Slowest "Tornado Start" since 1950!

Thursday, April 15, 2010

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