May 22, 2013

May 22, 2013: Down Days Coming and Early Exit

Retrospective

Thom and I are in Wichita Falls after a day in north-central Texas.  This will be the last active log, and I will now concentrate on trying to get some pictures up for our productive days, mostly May 18 and 19.

I am impressed with the numercial models, particularly the ensembles, which suggested a pattern favorable for supercells in the central Plains almost 10 days in advance.

It turns out that several research projects on tornado formation and evolution were able to get excellent data sets during the last five days.  The Moore, Oklahoma tragedy casts a pall on this.  Nonetheless, we are going to learn much about tornadogenesis because of these couple of projects.  They were not on the Oklahoma City supercell, however, as they were south where most storm spotters and chasers were that day.

I just learned that the tornado we documented near Kinsley, KS has been rated an EF4.   There was no damage (as far as I know) to assess to determine this.  But the Doppler on Wheels (DOWs) were there, and they were able to estimate the wind speed associated with the funnel.  The map above shows the track for the first tornado.   The colors correspond to damage or DOW evidence for a rating.  The red tag shows the position of the tornado when the winds were 165-185 mph.  This corresponds to an EF4 rating.  The radar plot below right shows the DOW plotted radar images at the time the tornado was at maximum strength.   We have pictures and video corresponding to most of the 7 mile damage path for this tornado.

The damaging tornado that struck Moore is still making the news.   I was interviewed via cell phone by KTVU-Channel 2 in Oakland...but I declined other interviews (one from CNN, and directed them to my colleagues who are actually in the Oklahoma City area and who have done refereed research on the previous tornadoes that struck that area.

One reason I don't want to answer specific questions about the Moore tornado is that Thom and I were not there, nor have we assessed the damage.  Several of my colleagues have already been involved in that, and their results already are belying the hyperbole about that tornado (for example, it was not two miles wide, nor did it have a two mile wide damage path.  So far, I've only heard of documentation of damage consistent with an EF4 rating.   But I only get that information hours after the surveys take place.

I'm personally curious what meteorological parameters were in play in the Oklahoma City area that afternoon, that were not in play further south, where most researchers, spotters and chasers were placed.  It's not obvious from the weather data and charts I have for that hour.

Yesterday's Chase

The early runs of the models suggested a few isolated supercells forming around 1PM between Fort Worth and Abilene.  By the time we got into that area, the models were showing none of that, but more of a discontinuous line.  And that's what happened.  We played hopscotch with the rapidly progressing front, trying to stay in the rich moisture ahead of it.

When we got to Waco, several of the cells on the south end of the line became somewhat discrete.  They showed some signs of becoming supercells, but never did.  So, at around 6PM, we called it a chase, and drifted back to Wichita Falls.  Along the way, we changed our plane reservations from Sunday afternoon to tomorrow, Thursday, May 23.

This will be my earliest exit from a storm chase in all my years of chasing.  However, apart from the first day, we've had pretty intense chasing every day of the trip.  Of course, the best and most productive days for documenting tornadoes occurred on May 18 and 19 for us.

Once I have more time to examine our photography and videos for May 18, I will begin posting photo documentation of that day.


May 21, 2013

May 21, 2013: North Central TX

Another Round of Supercells Expected Today:  Risk of Strong Tornadoes Again

Not much time to post as we expect early initiation.  We are currently near Gainesville TX and then are heading southwest to the area just east of Abilene.

The morning weather map shows the low pressure area having drifted southward into central TX overnight.   The setup is a bit different today as 500 mb winds (see graphic) have slackened just a bit.

However, there is still the tap of high dew point air coming into central TX.   The surface flow is a bit weaker than yesterday.   Yet forecast hodographs indicate wind shear favorable for supercells, although the window for tornadoes appears short.

An additional factor is an outflow boundary that is shifting southward out of the thunderstorms we just left in Ardmore.  That also might provide a focus if storms forming to the west cross it later today.  Unfortunately, the Dallas-Fort Worth metroplex may be under the gun later today.

May 20, 2013

Moore Tornado

Just an awful coincidence that the tornado that devastated Oklahoma City's southern suburbs took basically the same path as the May 3, 1999 tornado, and very similar path to the tornado that struck the same area a couple of years later.

Most chasers were on the storms further south.  Thom and I passed that storm when it was developing and figured that more substantial storms would be further south...so we went on by, in fact around it, to get to the tornadic storm further south.  We did not get to any storm today that had a tornado.

Just as well that we didn't leave even later, as we came from Ponca City in the north....and would have probably chased that storm as our only option later in the day.

It looks like all my chase colleagues are safe, and most who are down here are choosing not to contribute to the confusion in Moore....as I35 passes right through that beleagured town.

The graphic is designed by Meredith Botnick to show support for the people of Oklahoma who have endured tragedy today and yesterday.

There is a plea for $10 donations, via a text number.

Text 32333
Subject:  FOOD

That will provide a $10 donation for victim relief.

May 20, 2013: S-Central Oklahoma

More Tornadic Supercells Today in Oklahoma:  Preliminary Target for Storm Intiation---Lawton, OK

(More complete discussion with illustrations later.  Also, still have not had time to fill in log with pictures.   Looks like we may have a down day soon, on which I can catch up).

We overnighted in Ponca City, Oklahoma.   Just returned from a nice run around Lake Ponca.

The morning weather map shows a surface low in sw Oklahoma, with a dry line extending southwestward into north Texas.  A cold front extends from that dry line, with the intersection near Altus OK, back northwestward.

A warm front extends from that intersection across Oklahoma to se KS.  That three way intersection is often referred to as a "triple point" by severe weather meteorologists.


Ahead of the dry line, an air mass rich in moisture is found to the warm front.  That air mass is projected to have surface based CAPE values (a measure of how warm ascending air parcels will be relative to their surroundings through the deep troposphere) of 4000-5000 J/kg (see graphic to right).   These really are values at the upper end of the sort we usually see with severe weather, and indicate (Metr 201 and 415/715 students will know this) updrafts that should support extremely large hail.  On the map above, the light green represents areas with 60F+ dew point, and the darker green 70+.

Once again a very strong jet stream  (see graphic at upper right) will produce wind shear values favorable for supercell convection and, in parts of Oklahoma, low level wind shear favorable for these supercells to develop tornadoes.

The issues center on two aspects of  the forecast storm motions.  First, the storms will be moving at an angle that's too close to the dry line, instead of at right angles.   This could mean that each storm will be running over a previous storm's cold pool....and we can end up with a big line of storms, as we did yesterday in northern Oklahoma.  If that happens, the time window for tornado formation will be small...before each storm runs into that cold pool.

Second, unless the surface winds cooperate, storm motions could be 40-50 mph, as they were yesterday, making for exceedingly difficult chasing....it's almost impossible to set in one location and take pictures, for example, when the storm rushes by like that.  Fortunately, the surface winds are forecast to be more southerly or south-southeasterly, rather than hard southeasterly.  In that case, we're likely to have storm motions of around 30 mph.

In any case, we are off to our target area, where the visible image above shows a low level cumulus field already bubbling.


May 19, 2013

Brief Elephant Trunk Tornado near South Haven KS

Tornado near Sourh Haven KS developed right over our heads.