03/20/06 DISC: Oklahoma (cold core)

[Shawna Davies]

First of all, I hope I'm posting this correctly. If not, then Mods please move it or do whatever you need to do for this post to be in compliance with the rules of the board. (I did read the special rules sections, but am still not sure.)

Following is some information about yesterday's cold-core event in OK that Jon Davies asked me to post for the people who chased yesterday, or for anyone that might have an interest.

Shawna

Here's a few graphics from yesterday's setup in w-c OK...

surface map 22z:
http://members.cox.net/jondavies6/032006sfc2243anno.gif
satellite 2215z:
http://members.cox.net/jondavies6/032006sa2215anno.gif
NIDS radar image 2215z w/suggested boundaries:
http://members.cox.net/jondavies6/032006rd2215tlx_anno.gif

SPC meso graphics (0-3 km lapse rate, 0-3 km cape, sbcape):
http://members.cox.net/jondavies6/032006spcllr21.gif
http://members.cox.net/jondavies6/032006spccp321.gif
http://members.cox.net/jondavies6/032006spcsbcpe22.gif

Looks like the Dewey county cell was at the intersection of a N-S wind shift and the occluded section of the Pacific front/dryline just east of the surface low. Nice focus with lots of cold air aloft at this location, the 500 mb low over sw KS. Note the surface thermal axis and the steep low-level lapse rates "pointing" into the general area where the tornadic storm occurred. This seems to emphasize that sunshine and sfc heating is needed for these type of events. Thankfully, they are usually weak, but fun to chase and study.

I looked at a RUC20 profile for Watonga at 22z. Even with a sfc Td in the mid 40s F, there was 600-700 J/kg CAPE for low-level ML parcels (-26 C at 500 mb, -7 C at 700 mb), with the fattest CAPE centered at only 600 mb, and the EL near 400 mb. MLLCL around 1000-1200 m, MLLFC not far above that.

Neat to see snow being reported at GAG (22z) not that far away from the tornado location (!).

 

[Justin Walker]

Following is some information about yesterday's cold-core event in OK that Jon Davies asked me to post for the people who chased yesterday, or for anyone that might have an interest.
[/b]

I had success yesterday due in large part to Davies research. Myself, Gabe and Jeff all read through some of the papers Davies and other have written up the morning of, as well as while we were chasing. Very helpful stuff, especially the graphics. Definitely was a classic cold-core setup. Here is the paper that I found useful. Thanks for the info Shawna and Jon.

 

[John Farley]

Neat to see snow being reported at GAG (22z) not that far away from the tornado location (!).
[/b]

In light of Jeff Snyder's report (in the REPORTS thread) about the "snowballs" that he encountered with this storm, I am wondering if this might qualify as a rare tornado associated with snow. (I know the frozen precip with this storm was hard to classify, but Jeff said it was definitely not what you could call hail.) Any thoughts from anyone that was on this storm?

 

[Tony Laubach]

Jeff, how big were these snowballs? I imagine by his reference to grouple, it was probably just that, in which case, they were no bigger than peas.

However, I can vouch for the snow and tornadoes bit. Last April 20, the Colorado Gang and I had a possible (we can't confirm what it was) nighttime tornado, the on the backside of the MCS, got into winter precip (grouple mainly). This was within an hour and 40 miles east to west.

While this wasn't a cold core setup directly, the temps were certainly cool enough at the time we witnessed the possible tornado (in the mid to upper 40s) to warrent heavier jackets in the wind. Within an hour of witnessing this possible tornado, we got on the backside of the system returning home and found ourselves in the grouple (snowballs).

 

[Jeff Snyder]

In light of Jeff Snyder's report (in the REPORTS thread) about the "snowballs" that he encountered with this storm, I am wondering if this might qualify as a rare tornado associated with snow. (I know the frozen precip with this storm was hard to classify, but Jeff said it was definitely not what you could call hail.) Any thoughts from anyone that was on this storm?
[/b]

It was a very odd experience. I think we were only a several 10s of miles southeast of where snow was falling, and temps certainly felt cool enough to support snow. However, I'd still probably call it graupel or extremely soft, spongy hail. I can't really say that I'd associate what we saw with "hail", since it literally looked more like small snowballs and hit the road/windshield/grass/etc just like huge snowflakes (that "look" of ice+water mixture that you see sometimes with large, wet snowflakes when they hit your windshield). Actually, when this stuff fell, it splattered like snowcones or finely smashed ice. I've seen soft hail, but even the soft hail I've seen still looked like balls of ice when it fell in the grass (which is would "smash" into something hard enough to lost it's shape). I imagine that most of the vertical column (or depth of the updraft) was below freezing, so there was probably a larger-than-normal proportion of snow in the updraft (relative to liquid water)... With differential fall speeds, graupel may have been preferred since there may have been relatively little liquid water, so you'd get huge snow aggregates which slowly melted as it fell. These "snowballs" that we experienced were right where you would expect hail in a typical supercell -- on the periphery of the updraft along a relatively nice reflectivity gradient.

EDIT: I don't remember exactly, but I'd say the graupel/hail/iceballs/snowballs were 1/4-1/2" in diameter. It's really tough to measure since the they would lose their spherical shapes as soon as they hit anything (ground, car, etc). We did see video of actual hail associated with this storm and other storms to its east, but that actually looked like hail -- hard ice that maintained its shape in the grass, road, etc. The stuff we experienced seemed much softer than that, particularly when we were immediately north and northwest of the RFD (so, when we were along the northwest periphery of the updraft). I'd think that if any accumulated, it would look more like wet slush on the road than the 2-3" of pea-size hail that we saw video of from farther east.

 

[Justin Walker]

Jeff, how big were these snowballs? I imagine by his reference to grouple, it was probably just that, in which case, they were no bigger than peas.
[/b]

Here are a couple of video grabs as a ducked into my car as the "graupel" was falling. They are not of the best quality, but you couldn't get any other pics of them because they exploded as they landed. In the first image you can see that there is no accumulation. The second one was when the camera was tilting down and you can see the size compared to the frame on the car door.

 

[Simon Brewer]

I was northeast of the tornado and had pea-size hail on the ground around me, but as the tornado lifted the updraft crossed the road within hundreds of yards of my position and I experience these "hail/snow balls".

They seemed to be incredibly soft hail to me, but I keep thinking about the temperatures throughout the vertical profile of the updraft of that supercell and maybe they were a very large form of graupel; with collections of large snowflakes, which didn't cycle through the updraft, but instead, fell through the updraft and through the process of accretion a protective coating of ice prevented the snowflakes from melting in the relatively shallow layer of above freezing temps....... Hence, the snowballs! But this might not be the case, there was, however, classic pea-size hail falling from this particular storm to the northeast of the updraft, but the strange form of hail next to the updraft was very interesting.

I hope someone continues this quest to discover possible answers to this strange occurence. I might actually do a research paper on the subject when I have time over the summer, but I'm much too busy during the spring.