5/22/05 FCST: Most of Central US

Dec 9, 2003
Since the day doesn't seem like a tornado blockbuster, we'll just try to fit all FCSTs under this umbrella "Central US" thread. Should there become more defined areas of signficant severe threat, we can break this up...

At any rate, the cold front will slowly slide south (nice alliteration, eh?) and into a JUICY airmass, particularly from OK to AR/MO. While absolute flow is pretty weak at all levels, strong directional shear is yielding moderate deep-layer shear (45kts across northern OK per 0z NAM). This evening's NAM run is shwoing Tds from 70-78 from northern OK, east-northeastward, resulting in extreme instability of 4000 to possibly 5000 from northern OK into southern MO/norhtern AR, and decreasing northeastward from there.

The nice directional shear is present in the low-levels as well, though relatively weak speeds are resulting in only 200-250 0-3km SRH across northern OK by 0z (per 0z NAM). The strong deeplayer shear and extreme instability will likely prove sufficient for strong supercells, and the low-level shear may well be sufficient for a tornado threat as well. With Tds into the "juicy" range (that's a meteorological term...), LCLs should be considerably lower than they were yesterday (5-21), particuarly across northeastern OK.

Right now, I'm probably going to head up I35 towards Perry and go from there. The 0z NAM is breaking out convection across the I35 corridor north of OKC and eastward from there. If anything else, some nice supercells seem to be a very real possibility.
The 06Z NAM doesn't look good for Southeast Michigan. MLCAPE around the time storms should arrive will not exceed 350, with SBCAPE ranging from 400 to 800. Low-level lapse rates will remain rather low (5.7 C/km), but mid-level lapse rates will be much better (around 7.5 C/km). 3km Helicity is looking impressive, around 260 m2/s2. BRN shear is within tolerance for supercell activity, so maybe there is hope for today. However, looking at the NAM, I just don't see a very good severe storm forming, let alone a tornado.
It looks like anything that forms today will have much better moisture to work with:

Chanute, KS @ 10AM is reporting T 77 / Td 72
Winfield, KS @ 10AM is reporting T 81 / Td 70

Looks like NE Oklahoma/SE Kansas/SW Missouri/NW Arkansas will make good targets today. Best upper level support will be in this area (not that much, though, ranging in the low to mid 30 knot range), and also best surface based instability. I am still at a thought process if I want to go or not, because this setup has "yesterday" written all over it. KSGF has conv. temperature of 97.9 degrees at their 12Z sounding, and KOUN has 103.9 degrees for the conv. temperature at their 12Z sounding, so modest cap is in place. SBCAPE of up to 5000 J/Kg and dewpoints at or higher than 75 degrees is entirely possible today. According to the 12Z RUC data, KSGF may reach pretty close to the conv. temperature this afternoon, so that will be worth watching. NAM also shows precip breaking out in all of E Oklahoma, so I am going to wait and see...
The boundary at 17Z extends from Cheyenne, OK to Bartlesville, OK. Vertical mixing has reduced dewpoints west of I-35 along the boundary, but upper 60s - near 70 dewpoints have held in to the east. Judging the strength of the capping inversion is very difficult today given the sparse data aloft, but it generally decreases to the east. Supercell shear is not present on the large scale and is not expected to develop. However, if locally backed winds can develop, or the shear zone remains strong along the boundary, a brief spinup might occur before the cold pools take over.

I will wait to see the 18Z Lamont sounding before making a final decision, but I might make the short trip from Norman. Like yesterday in Kansas, the first cumulus will mark initiation, so can't wait on satellite trends. Hopefully things will manage to go farther east along the boundary (toward Tulsa) where dewpoints will be higher, but this chase is more for photo ops than tornadoes anyway.