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2018-03-26 EVENT: OK/TX

I'm not overly thrilled by chase prospects later today, but there is now a day 1 slight risk across parts of Oklahoma and Texas, so why not?

The surface map becomes increasingly lackluster through the day on Monday. An area of low pressure over the Oklahoma panhandle Monday morning ejects into central Kansas, becoming more diffuse/elongated with time. By afternoon, around peak heating, a frontal boundary is projected to be draped from southeastern Kansas, across central Oklahoma and into northwest Texas. To the west and southwest of that region, a dryline, and/or composite cold front will arc from the Rolling Plains into the Edwards Plateau vicinity.

In the upper levels, a positively tilted trough will continue to slowly migrate east across the Desert Southwest. An attendant 500mb speed max will eject from northern Mexico into the southern High Plains and eventually parts of Oklahoma and Kansas by late in the day.

The upper level synoptic map looks good, but the main issues with this setup are really in the lowest 2km above ground level. The 850mb low Monday afternoon will be centered over the middle Missouri Valley, with less than 20 knots of flow at 850mb across the risk area in Texas. There are several red flags with this event already, but whenever I see relatively weak winds in the low levels, I become concerned. The strongest low level jet will be displaced well to the northeast of the risk area, across Missouri and areas east over the Midwest. The 850mb winds over Oklahoma and eastern Kansas should be in the 20-40 knot range, but ongoing convection, cloud-cover and limited boundary layer heating suggest that this stronger low-level shear will be accompanied by only marginal instability.

Convective regimes:
1. Early day convection is forecast to blossom over Oklahoma from early to mid morning, over a stable boundary layer, ahead of a surface low and associated low level jet. This elevated convection may pose some hail risk, although given skinny CAPE profiles, the threat for any large hail seems marginal at best. This convection may continue through the day across northern Oklahoma, southeastern Kansas and perhaps southwestern Missouri, but limited boundary layer heating suggests that the only notable threat may be some small to marginally severe hail.

2. Late morning to midday convection is modeled to develop across the North Texas/Rolling Plains vicinity, driven by moderate boundary layer heating, convergence along a frontal boundary and glancing influences of upper level impulses. Convection allowing model (CAM) solutions are quite varied, as some allow for discrete/semi-discrete storm development, while others show a messy or at least clustered storm mode. Even the 3km NAM vs. the 3km TTU WRF show significantly differing convective evolutions. Forecast soundings near and downstream of this activity show a plume of favorable CAPE in the 1500-2500 J/kg range, even up into central Oklahoma, but wind profiles are not what you want to see for organized severe weather. Weak flow in the lowest 2km was mentioned earlier, but backing winds around 700mb and westerly winds at 850mb (southwest at 500mb!) create some hideous looking hodographs with very little SRH in both the 0-1km and 0-3km layers. With time, wind fields do notably improve by mid to late afternoon over North Texas, so it is possible that activity on the southern flank of earlier convection may better organize, while a mass of convection moves into Oklahoma, posing little to no organized severe risk. The continued issue with weak low level flow does not give much confidence to any progs of long-lived severe convection, so the ultimate evolution may lead to sporadic severe hail and perhaps some strong wind gusts. One cannot rule out a cell or two having some modest longevity, especially if earlier convection leaves any outflow boundaries to locally improve low-level wind fields. If that were to happen, then we could talk about the odds of an isolated tornado increasing, but the environment, as advertised, does not look all that favorable for tornadoes, given weak low-level shear.

3. Farther southwest, the warm sector appears to be more open, in the vicinity of the dryline and potentially dryline/cold front intersection, depending on how surface boundaries evolve. There seems to be better model consensus with isolated storm development between roughly Midland and Abilene by late afternoon. Again, low-level wind fields look weak here and deep layer shear vectors aren't exactly ideal either (only making small angles with the initiating boundaries), so there is some uncertainty with any sustained, robust convection. While hail may be a better bet with these storms, as well as strong to locally severe wind gusts given steep low-level lapse rates, weak flow in the lowest levels precludes a greater tornado threat. As mesoscale details become more clear, any boundary intersections (probably dryline/cold front in this region) would be the most apparent focus for a marginal tornado threat.

Some things could change, but for those hoping for tornadoes, this looks like far from an ideal setup. The weakening surface low is one issue, while the weak low-level flow is probably the most glaring red flag, in terms of tornado potential. Where low-level flow should be stronger, instability fields look less impressive, along with sub-optimal directional shear.

For those who don't have to see a tornado for a successful chase, then it's probably a setup to give a shot. I would like to think that a large number of chasers will be within a few hours of the threat areas outlined above, so it's not like we're talking about driving all day for a messy setup. If you're hoping for tornadoes, or have a long drive to get into the threat area, then this is probably n event to pass up. It is still March after all and we have several more weeks before we reach prime chasing season in the Plains...
 
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