As I mentioned a couple of days ago...I'm going to talk a bit about the severe weather season so far...that will have to wait a few minutes...

The good news is that skies are clearing out now...temperatures should pop...perhaps into the lower 60s before the afternoon is done...overall a nice evening is heading our way...

Our storm is continuing to pull away...and is creating quite a bit of rainfall off towards the east of the area...this continues to be a very slow moving storm...that in a sense has broken up into several pieces...here is the radar portrayal of the system...

Early this morning...on the back end of the sttorm..combined with some mid level convergence...a relatively long but very small (widthwise) band set up near the I-70 corridor in the KC area...between 1:30-7AM or so...the downtown airport had close to 1.85" of rain...while KCI had nothing and on Signal Hill we had about .5"...the radar portrayal (doppler indicated storm totals) shows the heaviest locations...and I'll post those images later this afternoon...it seems our server is down...

Click on the images and then "View Enlarged Image"

That bulleye just SW of the Riverside area represents 2-3" or so of rainfall...in part generated by an outflow boundry that pushed northwards from a bunch of convection earlier in the evening along the I-44 corridor.

Onto sensible weather...still expecting milder temperatures this week...60s are likely through TUE...then some more moderation on WED...followed by the real warm push to finish off the week...whether or not we can keep the real warm air next weekend reamins to be seen...the more than likely will be a cold front moving down from Canada...and while whatever we get from the front (IF) would be a glacing blow...it could certainly knock us down some 10+ degrees into next weekend...there is also the vERY real chance that the front bellies up towards the I-80 corridor...the EORO seems alone in pushing this front towards I-70...while other modeling, which I'm leaning towards right now, keeps the front farther north...keeping us in the warmer air...for MUCH longer...most of the ensembles are in the northern solution as well...but about a 1/3rd of them do have that front very close...it would make the difference between temps in the 80s...or perhaps the potential of temps in the 60s with a chance of more rainfall...again at this point I'm leaning warm...but it's certainly something to watch for the next several days...these fronts seem to want to come down this way regardless...so it's certainly concerning...the key will be to see how the northern stream energy interacts with an upper level low north of Hudson's Bay...

Yesterday there were a few tornados that produced some damage out in western KS...my good friend, severe weather researcher, Jon Davies wrote up a quick synopsis of the scenario...take a look...

Sunday, April 19, 2009

Prolific cold core tornado event in southwest KS on 4/18/09

Shawna and I have had quite a lot of difficult family stuff going on, so I haven't posted lately. But it has certainly been an early spring season of midlevel cut-off lows and cold core systems so far, most of which have failed to produce tornadoes.

For example, way back on 2/9/09, a large dynamic cold core system raced northeast through the plains, but overwhelmed any semblance of a surface pattern that might support tornadoes due to a dry slot that blasted northeast at 70 mph, a typical problem with very early season cold core systems. Then in early April, a fairly organized system on 4/4/09 lifted through Nebraska, but could only produce brief gustnado-like vortices with storms because of dew points only in the 40's F and rather high cloud bases (usually not supportive of cold core system tornadoes). A few days later on 4/9/09, a strong cold core system in northern Oklahoma and Kansas again was "too dynamic" when the surface low jumped and reformed farther east, destroying the surface pattern focus beneath and near the midlevel low. The resulting large area of convection that developed tended to overwhelm the surface pattern and effective boundary intersections that are often important for tornadic cells in cold core cases, though there were strong tornadoes later that night in Arkansas and Louisiana within the broader warm sector farther to the southeast.

Yesterday (Saturday 4/18/09) finally saw a cold core system that produced several tornadoes over a 90 minute period that were well photographed in southwest Kansas, northwest of Dodge City (see photos above). There was some damage east of the tiny town of Kalvesta, but thankfully no injuries. Being that this was a slow-moving system that was not overly "dynamic", surface features were able to focus near Dodge City, and an initial storm that developed was able to stay isolated for a long period near the midlevel low and cold air aloft and the surface boundary intersection, rather than being overwhelmed by a large area of convection.

I watched this event develop from Kansas City (I really miss living in central KS!), and noticed the surface pattern at late morning was focusing over southwest Kansas (see 2nd graphic above) near a surface low and boundary intersection west and south of Dodge City. The 500 mb closed low aloft was not far to the west-northwest, near the Colorado border (see positions marked on satellite image, 3rd image above), with plenty of cold air aloft and temperatures near -20 C at 500 mb, and -5 C at 700 mb. (See here for more on cold core tornado settings.) Put that cold air above surface dew points around 50 F advecting northwestward into the high plains, and you have a recipe for strong stretching in isolated storm updrafts below 10,000 ft or 3 km. The tight spin/vorticity/forcing of the nearby midlevel low probably helped as well.

Surface convergence at 1:00 p.m. CDT (see 18 UTC SPC maps, 4th graphic above) was maximized near the surface low and dryline/warm front intersection near Dodge City, Surface-based CAPE was also plentiful for a cold core setting (> 1000 J/kg, see SPC map). The supercell developed rapidly between Dodge City and Garden City between 12:30 p.m. and 1:00 p.m. CDT (not shown), and the first tornado developed barely 20 minutes into the storm's lifetime. Such rapid tornado development relative to storm initiation is not uncommon with cold core settings, probably due to the majority of CAPE being located below 500 mb (relatively close to the ground, see the final graphic above, a RUC analysis/estimation at Dodge City during the tornadoes).

It is interesting to note from the RUC profile above that there was very little if any low-level shear (storm-relative helicity or SRH) in the local environment, reiterating the fact that cold core tornado events near the midlevel low don't always require lots of helicity. Limited low-level shear and the surface focus near a reasonably well-defined boundary intersection seemed to suffice in this case.

- Jon Davies 4/19/09

His complete blog...with other case studies is located here...if you're into severe weather Jons' name is very recognizable...

I'll try and get another blog together this evening...assuming I can get access to our image/video server

Joe