May 16, 2012

Preliminary Destinations---Friday-Sunday, May 18-20

May 18

According to the 0000 UTC run of the WRF-NAM, 50-55 F dew points curl into western South Dakota, but it also looks like the dew point field is partially "locally grown" via evapotranspiration (local sources of evaporation from fields and plants). The model has an elongated area of surface low pressure from ne CO through the Nebraska Panhandle into sw SD. There is a quasi stationary frontal boundary in that low, with stoutly capped air not too far south of the boundary.

However, this is the second run of the WRF-NAM that suggests decent CAPE (now up to 2000 J/kg) in the vicinity of the eastern portion of the Black HIlls and adjacent plains Friday afternoon. However, the LCLs will be quite high southeast of the boundary, ~2000 m.

In the area east of the Black Hills, we find the best low level shear and there is adequate deep layer shear, with a large circumference anticyclonic loop in the forecast hodographs I plotted. But it looks like the anvil level storm relative flow is pretty anemic.  Metr 535 students will appreciate the "potential" shown for this hodograph.

Hence, I'd guess there are going to be a few rotating storms in that area, though the bases are suggested as being quite high and, therefore, unlikely to be tornadic. 

Anyway, I think that's our target three days in advance....the sw portion of SD. 

May 19

The segmented wave in the middle and upper troposphere will drag its heels a bit for Saturday. The WRF-NAM shows a sort of triple point in north central KS, with backed winds on its north-east side. The WRF-NAM is struggling to show us 60F dew points....but whatever....shows 2000-2300 J/kg in the late afternoon. That will have to happen to have manageable LCLs. Interesting that the best hodograph loops show up for regions with surface northeasterly winds....but there are nice loops, adequate deep layer shear, and some pockets of strong low level shear in that area.

On the other hand there is quite a cap. Yet the WRF-NAM does break out precipitation in that area.

On balance, there may be a better chance for decent storms on this day in that narrow area. Hence, that will be our preliminary target.

May 20

Models are forecasting lots of buoyancy, with 3800 J/kg north of Tulsa. 35 knots of deep layer shear.

Issue will be the low level shear, which is less than 10 knots.   But 0-3 km SREH is super cellular.