May 15, 2013

Preliminary Target...Western Nebraska

Our preliminary target for tomorrow is western Nebraska.  We're also keeping an eye on the TX Panhandle.   Either area is reachable from Denver, as we are due in 1230 PM MDT/

The main issue (and it's actually a good one to have) is the exact evolution of the trough that is coming into the West tomorrow.   In some years, we'd have no troughs to talk that's good news.

The complication is that this trough (shown on the morning's WRF-NAM 36 hour 500 mb forecas (see graphic)  for tomorrow afternoon at 5PM PDT/7PM MDT) is been consistently deeper and further south than previous runs of the models had it.  This then has the result of throwing the jet stream further north in a ridge over the eastern Plains, but keeping the stronger winds aloft further west.

As a result, we'll be struggling to get 30 knots out of the 500 mb flow over Nebraska.  The good news is that the flow impinging the Rockies is already generating a lee-side surface low that is pretty strong and bringing moist air from the Gulf of Mexico surging into the southern and central Plains.

Right now the surface warm front is on the KS-Nebraska border and it's expected to move only slightly northward over the next 36 hours (see graphic).   Along and just south of that front will be dew points in the middle to upper 50s, perhaps even 60F in moderately strong southeast winds.

This surface flow in combination with the winds in the middle and upper troposphere produce some interesting looking wind profiles tomorrow afternoon in Nebraska (and it seems the next afternoon in northern KS).  These profiles (shown below on the forecast sounding and hodograph  for North Platte Nebraska)would support rotating storms...although it could be that these storms, if they do occur, will be in the supercellular mode called "High Precipitation" (HP).

HP storms can be beasts...and the WRF-NAM model appears to generate one near North Platte tomorrow afternoon.  They can also be tornadic, though usually too much precipitation wraps around the updraft to allow the storm to proceed through the supercell cascade to produce a tornado.

You can see our preliminary target shown as a red box.  

We are also keeping our eye on the TX Panhandle, as conditions look reasonably good there too...but there is an awful lot of Convective Inhibition (a region of warm air through which lofting surface air parcels would need to be "forced" in order for them to become buoyant.

Beyond tomorrow, the evolution of the incoming western trough will have the final say in where we go.  With its increased amplitude, this trough appears to be aiming much further south than the current SPC outlooks suggest.