May 17, 2012

May 17, 2012: Refining our targets...

Meteorological Synopsis:  The blog below contains a lot of meteorological reasoning for our targets.   I realize that will be obscure to some of the readers of the blog.  As we get into the Plains and actually have some pictures and weather maps to show, the blog will get more entertaining for the  non-meteorologists who are following along.

Friday May 18:  sw Nebraska

The dew point "surge" from the Gulf of Mexico doesn't look like it will bring the moisture values up sufficiently for low LCLs/LFCs under the area of best shear in SD.  This means that it will be difficult to get surface air parcels up to the level at which they will be spontaneously buoyant. Sure, there still appears to be potentially 2000 J/kg in spots north of the Black Hills. But since the mesocyclone-induced tornado risk appears low to nil up north, Thom and I are shifting our target to an area of less impressive CAPE values, but with no convective inhibition. (CIN)..further south so that the dew point field will likely develop reasonable values.

That would be sw Nebraska. I've plotted soundings for Imperial, McCook and North Platte....and they all have decent values of CAPE (~1500-1700 J/kg) albeit with very high LCLs...and little CIN. The hodographs look best in sw Nebraska, with some great veer of the wind shear vector through the lowest 3 km in several spots.

In short, "risk/reward" issues, plus our target in KS for Saturday, suggest getting nearly a sure thing, a nicely sculpted high based supercell...maybe even a non-mesocyclone tornado as an outside hope....has redefined our target as the area between North Platte and Imperial. An added plus to this is the much shorter drive. 

Saturday May 19:  central Kansas

Our target, provisionally, will be the area around Pratt to Great Bend to between Russell and Salina for Saturday afternoon. I've plotted the soundings from the WRF-NAM and get lots of CAPE, with hardly any CIN. 

There are issues with respect to how air streams will move relative to the slowly sagging frontal boundary.  This could mean that storm motions will be such that they move over the shallow cold frontal air mass.  However, I get storm motions for right movers slightly east of northeast, which would keep storms in the "CIN-less" area of high CAPE, until the front catches I am not too worried about the front, really.

But even when you look at the front itself... and the temperatures and dew points there show still a lot of surface based CAPE...and, you know, with northeasterly winds, the hodographs have some dramatic loops. The deep layer shear looks good, and the low level shear issues look to be the main concern... 0-3 km shear as evidenced by the SREH values look best on the cold air side of the front and around Pratt. 0-1 km shear is marginal throughout....but who knows what boundaries might be around left over from previous convection...and/or nature has a hiccup and we end up with better low level shear.

Sunday May 20:  north-central Oklahoma

Posted ImagePosted ImageI think this is potentially a "stealth" pattern.

The dragging frontal boundary inches into Oklahoma...stretching from Lawton to Tulsa by late afternoon. The WRF-NAM has adequate sbCAPE in and along the area on either side of that front, as is the case the day before, even in the northeasterly flow on the cold air side of the boundary. I am getting sbCAPE around 2300 J/kg and a nice loop in the hodograph (shown here below) for the region between Stillwater and Tulsa, with virtually no CIN.

Now, looking at that hodograph meteorologists might really conclude that the loop is nice, but the deep layer shear is too weak for any sustained organized convection. However, just on the cold air side of the boundary, the surface winds are northeasterly, and there is much longer length to the 0-6 km AGL shear vector....and with southeastward motions for extreme right movers.... hmmmm....