10/1/05: FCST: OK

[nickgrillo]

I'd think that there should be some concern for convective debries/low-level cloud cover associated with the ongoing MCS across western OK, but if enough instability can develop tomorrow - the threat for a few supercells across central/eastern OK appears to be pretty good. Ahead of the trough, a strong >40kt southwesterly LLJ will enter the region. Deep moisture advection associated with the strong southwesterly low-level flow and any potential insolation will aid to boundary layer destabilization. Thunderstorms initiating across central OK shortly after 21z may attain supercell characteristics before cells/anvils merge and activity attains more linear character shortly before/at sunset. Given the relatively strong directional/speed shear through the <3km layer, a tornado or two could be possible with initital storm formation, but large hail should be of the greatest concern... The threat should slowly become hail/wind as activity enters eastern OK by sunset. This is all based off of the possibility of we can get some insolation tomorrow afternoon. The MCS will certainly lay down some OFBs for tomorrow's stuff, which will certainly enhance low-level shear/surface moisture pooling -- to help aid a higher tornado threat.

 

[Andrew Khan]

This 'once' supercell in TX, has now drifted NE, and has turned into a cluster/MCS storm. Supercells might be allowed to develop in SW OK. There are some very strong backing/veering winds, along the OK/TX Panhandle, which will aid in Possible supercell development. Tornado threat as of now looks pretty poor, but I assume it will ascend later in the day.

 

[Bill Schintler]

Chase target for October 1

Chase target:
Muskogee, OK. Note, this is generally poor chasing terrain with numerous hills and trees.

Timing:
Ongoing convection will strengthen and reach the target between 1 and 2 PM CDT.

Storm type:
Marginally severe storms capable of hail to 1â€￾.

Discussion:
Upper-low in SRN stream branch, currently centered just S of DDC, will lift slowly NEWRD today as it opens up into a wave. This feature was responsible for an outbreak of severe WX in the TX panhandle and OK yesterday. 12Z UA analysis indicates 50kt H3 steak with attendant diffluent SWRLY flow lifting through OK and NERN TX. A 40-50 kt LLJ has transported a plume of moisture through much of NRN and NERN TX, as well as most of OK E of I-35, as evidenced by 18C H85 dewpoints and ST fields on visible satellites imagery. SFC dewpoints at 14Z ranged from 60F to 70F from NE to SW as bands of elevated convection in association with the upper-low spiraled through OK. A significant outflow boundary is noted along an HRO to FSM to PRX line. A favorable shear environment exists, with significant hodograph curves below 700mb in the FWD sounding, and this environment will lift towards the target area later while deep-layer shear increases to 30-40 kts.

Today, renewed convection should take place along the outflow boundary and in association with the ongoing convection in NERN TX, SERN OK, into WRN AR. A vorticity lobe rotating around the upper-low should enhance lift in NERN OK in a region where general subsidence will exist in the wake of the mid-level streak.

- bill

 

[Andrew Khan]

There is not-so-good CAPE going on in OK, so far SBCAPE is only 1000 J/KG, and in N TX, we've got 2500 JK/G. That said, activity (right now) would have to be limited to the SC OK area, but should change later, during the main insolation time. There is pretty good 0-1 KM Helicity going on throught out all of Central OK.

 

[nickgrillo]

Strong 0-1KM SRH in excess of 400 M2/S2 is spread across central OK. A pronounced OFB across central OK is evident in VIS imagery... There shouldn't be much of a problem to get storms to develop - given surface-temperatures in the mid 70s are already developing across central OK, supported by cloud breaks/insolation. A moist/unstable boundary layer mixed with a southerly 40kt low-level jet and a 45kt mid-level jet above that will support supercells to form later in the afternoon, given CINH completely burns off.

 

[Andrew Khan]

There is still some really awsome 0-1 KM SRH along all of central OK. There are some very good Mid-Level Lapse Rates 7 C/KM. Based on this I would say Supercell Thunderstorms are extremely Likely along all of central OK. Further models show a steep slope in instability, and only further back up Tornado Development....tornadoes are a good possibility today. Large hail looks like could even be possible...looks like a good setup. Wow, I just saw there is CAPE of 3000 J/KG...

 

[Gabe Garfield]

I must say, the 18z mesoanalyis from SPC looks mighty tasty. I'm really liking the 2000+ CAPE running from SW OK to NC OK, which is juxtaposed nicely with >300 m2/s2 helicity values. Unfortunately, the vorticity maximum is ill-timed leaving us with subsidence in its wake. If storms can form, I would imagine a few supercells would be in order, and maybe a few tornadoes. But, at this time, that is a big "if." I'm almost half-way considering skipping the OU football game to go chasing, but I'm still not sure. Hopefully, OUN released an 18z baloon.

Gabe

 

[Dan Dawson]

I really like the setup today, at least as far as instability and low-level shear is concerned. The main concerns I have have mostly been stated already, that is subsidence in the wake of the departing upper-level system, and less-than-perfect deep layer shear. However, there appears to be enough of a lee surface trough left behind to keep the surface winds from veering too much. This is improving low-level shear. The 18Z LMN sounding is in, showing an apparent subsidence inversion just below 750 mb, almost 1000 J/kg of CAPE, and excellent turning and speed shear in the low-levels. Areas to the SW of LMN have had more sun, so the CAPE shouldn't be a problem there. If winds can keep from veering at the surface too much, and storms aren't completely killed by subsidence/capping, it could be interesting.

 

[nickgrillo]

There is a nice moist axis evident at the surface layer from northwest to southeast OK. This, in combination with strong insolation has aided to a relatively unstable boundary layer - with SFC-based instability between 2000-3000 across southern/central OK. Given the relatively unstable parcels that should be ingested by the updrafts, mixed with 200-300M2/S2 SRH and 30-40kts of deep-layer shear... Should be an sufficiant situation for a few supercells, if surface-based convection develops. The gradual decaying of cloud cover has allowed for enough daytime heating to occur to help weaken the inhibitation.

 

[Brett Adair]

60kt of Bulk Effective Shear is moving NWD across South Central OK attm with 3500J/kg of CAPE. Things are going to get quite nasty along this ULL interacts with this juicy environment. The ongoing convection should begin to rotate within an hour as it strengthens and EHI's rise. Already 6-7 nearing OKC. :shock:

 

[Jeff Snyder]

I was burned many times in 2002 when we saw numerous "departing shortwave/low" situations. I do think that, if storms can develop, we should see supercells and an attendant tornado threat. LCLs are pretty low (at least not high), and moderately strong flow immediately above the surface is helping to yield moderate low-level shear. Upper level flow is pretty bad in northern OK, near the axis of the trough/low, as evidenced by the 15-20kts flow on the Lamont profiler. Deep layer shear profiles look better near I40 and southward owing to stronger upper-level flow. Tds of 70 (+/- a degree or two) and temps rising into the low-mid 80s are yielding >3000 CAPE per SPC mesoanalysis (which is important to note since I've seen many instances of the SPC/RUC mesosanalysis greatly overanalyzing CAPE). So, I'm not overly optimistic about chances, since there are some factors discouraging convective development. There is a nice area of convergence that can be seen on KVNX radar and vis sat in nothern OK, but again, upper-level flow is pretty weak up there.