Tough forecast for tomorrow, as I'm sure everyone who is reading this knows. Deep-layer shear appears to be supportive of supercells across most of the warm sector in NE, KS, OK, and even down into TX. Also, as we've known for the past few days, low-level moisture quality will likely be the limiting reagent in our tornado-chase reaction. However, I have a few other concerns:
1. Cloud-cover and its impact on insolation -- Model forecast RH fields indicate that low-level cloud-cover may be a significant inhibitor of surface diabatic heating tomorrow afternoon. I do like that the NAM appears to have backed off a bit in terms of strong isentropic ascent that it had been forecasting across most of OK west of I35. As it stands now, it appears that there will be isentropic ascent across southern KS, though the strongest ascent will, not surpringly, be located north of the warm front across the upper MS River Valley. At least we'll have decent moisture advection (see the 305K isentrope forecast from the 12z NAM valid 36 hrs
HERE). Interestingly, both the GFS and NAM appear to forecast subsidence ahead of the cold front central KS -- yuck. This can also be inferred by the backing wind profile near 750mb seen on forecast soundings.
2. Hodograph shape / wind profiles -- Though the overall magnitude of deep-layer shear and orientation of the deep-layer shear vector seems to support supercell mode, I'm worried about some of the S-shaped hodographs being forecast by the models. I've had very bad experience with such hodographs -- supercells tend to have trouble sustaining cyclonic and anticyclonic mesocyclones IMO. As noted above, the models are forecast some backing-with-height / CAA occurring in the 600-800mb layer ahead of the cold front in KS and northwestern OK around 00z. For those locations that do not show this, they at least indicate a nicely-curved hodograph in the <2km AGL layer beneath a straight-line, SW-NE section on the hodograph. This, in turn, is going to create problems for low-level shear. For example, check out the
P28 forecast sounding/hodograph from the 12z NAM valid 36hrs. Unfortunately, for a northeast storm motion near 30-35 kts, that hodograph look to yield
negative 0-3km SRH, and it could be strongly negative for a left-mover. Yuck.
3. Thermodynamic environment -- forecast soundings indicate significant capping ahead of the dryline and cold front for much of tomorrow afternoon, even at 21 UTC. Between 21 UTC and 00 UTC, the GFS and NAM support rapid removal of the cap, presumably owing to strong ascent from DPVA as the leading edge of the vort max reaches the western edge of the warm sector. Of course, this cooling of the cap layer is also related to some of the above-noted CAA, which is creating less-than-ideal hodographs. The sun sets shortly after 00z tomorrow in most of the risk area, which means that timing may be an issue. If the above-PBL cooling doesn't reach the warm sector until 00z, we're going to be in big trouble for daytime convection.
4. Low-level convergence mechanism -- It appears that the triple point will be located somewhere in the vicinity of west-central OK or the EC TX PH by 00z. This means that forcing in most of KS through the afternoon will be caused by convergence along the cold front. Though the deep-layer shear vector has some component normal to the front, I generally strongly prefer chasing drylines than cold fronts. This helps substantiate my preference for staying OK tomorrow.
Overall, I'm favoring western OK. I expect storms to develop along the dryline and front by mid-afternoon, where the cap should weaken earliest (cooling aloft occurs and surface insolation is greatest -- see
21z sounding from 12z NAM valid at GAG). Unfortunately, the low-level shear immediately along the front and dryline is meager, so I don't think we'll see decent tornado threat until the storms can move deeper into the warm sector. Of course, if cloud cover blankets the warm sector for most of the day tomorrow, we can expect CAPE to be quite marginal, which may not allow supercells to thrive in this stonger-shear environment.
I also think that there may be a bimodal severe event tomorrow, with the most significant severe thread either along the dryline in western OK or to the northeast of the sfc low in northeastern KS and southcentral/southeastern NE (if the NAM verifies, I suppose).
