Convective Addiction

FCST #2: 05/10/10 – KS/OK/TX

Posted on 09. May, 2010 by Jesse in Forecasts, Uncategorized

Now that the actual event is drawing closer, and previous model uncertainties are beginning to become clearer, it’s time once again to revisit Monday’s potential for some significant severe weather over a relatively narrow corridor from northern Texas into central Kansas.  It was decided to refer more to the NAM/WRF for today’s forecast, as we believe it has a firm grasp on the setup and its smaller resolution (4km or 12km) is much better than a 20 or 30km model.  Forecast models should come into excellent agreement on the 00z runs this evening as the system comes shorewards.

While not to minimize the serious nature of what could potentially unfold on Monday, especially given the strong dynamics,  it should be noted that a relatively compact, unpretentious warm sector will likely prevent this event from becoming the widespread areal outbreak that it has already been likened to in some circles based solely on its upper air dynamics being congruous to past events (e.g. April 26, 1991).  Not to vituperate or discount the convective dynamics that are certain to come into play, it should also be emphasized that this warm sector, albiet small, will be a volatile environment for supercellular development as the afternoon progresses on Monday.

The warm sector dynamics have been well-advertised in numerous locales, including the forecast that was released here at Convective Addiction yesterday, so there is no need to dwell fervidly over said dynamics in this forecast.  As a quick reiteration, a trough will eject out of the SW CONUS, with an attendant surface low moving across SC Kansas on Monday.  In the wake of overnight convection sparked by robust WAA associated with a strong LLJ, the atmosphere is expected to recover Monday afternoon, bolstering instability values as strong forcing in the wake of this aforementioned system collides with a thermodynamically primed atmosphere across the outlook region.  As thunderstorms develop on Monday afternoon, wind shear profiles are favorable for rotating updrafts, with the potential for some significant tornadoes across the region.

While many chasers, Vortex 2, the mass media, etc. will be focused in the SE KS/NC OK region, there are other viable chasing options which could yield a tornado for those able to find the needle in the haystack.

Taking a look at both the surface map and water vapor imagery across the southern Plains on Sunday afternoon, note that the dew points in the lower 70s have already reached the Gulf shore, indicating that more robust moisture advection into the target region has commenced.

————————————————————————————————————————————————

It should be noted that historically the triple point can be a locus where tornadoes can and often do indeed occur.  For a case that would serve as a referential example, see the May 08, 2003 outbreak across this region.  Not to get too befuddled, just when you thought the sweet spot was evident on all of those colorful, kaleidoscopic model bullseye charts, the cardinal reason for these tornadoes where the traditional ‘tornado indicies’ are not maximized is because of boundaries, which will only be discernible using mesoscale analysis techniques on the day of the event.

Per the latest WRF, forecast EHI indicies appear to be maximized in central Oklahoma, giving the illusion that a triple point target would be unfruitful due to more unfavorable helicity and thermodynamic parameters.

—————————————————————————————————————————————————-

An item that warrants some additional attention is the strong ‘cap’ that will exist across the region (see diagram below), which traditionally precludes much in the way of organized convection, yet with such strong forcing at play the shortwave will create relatively intense LI values as we can see being forecast below on the WRF.

Surface Based LI values at 00z Monday per the WRF

————————————————————————————————————————————————-

————————————————————————————————————————————————-

Storm motions Monday evening are poised to be on the order of 35-45 kts, with hodographs strongly favoring right moving storms.  Since some of these storms are likely to contain very large hail, this will be an issue that chasers will indubitably wish to account for.

Forecast Storm Motions per the NAM

A quick glimpse at the 850 mb heights/relative humidity/wind profile for late tomorrow appears below per Sunday’s 12z WRF run.  Note that mositure will continue advecting northward throughout the day tomorrow.

The graphic below shows the forecast K Index values at 21z on Monday.

Interested parties will want to monitor this situation very closely as clearing takes place ahead of this dry line, creating an environment ripe for intense thunderstorms tomorrow afternoon and evening, especially across central Oklahoma into far south-central Kansas.  It will certainly be meritorious to watch visible satellite imagery on Monday morning to try and discern the location of any leftover boundaries from overnight convection, as this will serve to enhance tornadic potential for any storm that can co-locate along those boundaries ahead of the dry line.

Jesse Risley and Ryan Wichman