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Saturday, May 8, 2010 - 10:31PM CDT

Plains forecast update V: May 9-12 system

By DAN ROBINSON
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Update 10:31PM Saturday: The 00z GFS doesn't come out for a while yet, but the new NAM run is out - and it hasn't tanked on the setup, aside from veering the low level wind fields a little more than before. By all indications this is a 'go' with a departure for Tulsa after church tomorrow, all Lord willing - with maybe some nice lightning photo opportunities Sunday night with an overnight MCS indicated for eastern OK/KS. After Monday's event, I may stay for Tuesday and Wednesday's potential expedition days in southern Oklahoma/north Texas.

Looking ahead in the medium range, according to the GFS, things should quiet down in the Plains by the end of the week as the upper support wanes. The Euro shows southwest flow remaining for a few more days, although the frontal boundary and associated storms may keep moisture too far south for the upper support to have any benefit. Afterward, the GFS and Euro show strong ridging over the Plains by the 7-10 day period. At this point, I don't see high chances of an additional round of Plains observing opportunities happening before the week of the 17th. If the two models are right about the period beyond that, then chase probabilities would remain low through at least the 23rd.

2010 Storm Expeditions - Probabilities as of May 8
May 9-1299%
May 13-1740%
May 18-2335%

Update 9:41AM Saturday: The 12Z NAM now shows an improved scenario with a weaker cap - with the area of interest this time moved into Oklahoma. Meteorologically speaking, there is no reason to expect to not chase a setup as currently shown. The positives of the setup are robust, with models consistent about the general configuration over the past few days (only varying its location slightly from run to run). While a catastrophic blunder of both the NAM and GFS is still possible, we're getting close enough now that a major flip-flop by both models is less likely. Still possible, just less of a concern at this point.

If I have any concern about an expedition on Monday, it's going to be about the number of storm observers out. With such a clearly evident strong tornado day, everyone who is a storm observer, or has ever thought about being a storm observer will be there. The fact that it's on Monday probably won't have much of an impact, as I see this event as the type that typically makes storm observers skip/cancel/reschedule work, school or any other prior commitments they might have. Add to that the fact that VORTEX 2 crews will be in operation. So I think the chances of seeing a tornado might be higher than usual Monday, but whether or not most will be able find a clear spot to pull of the road to get decent pictures or video remains to be seen.

Update 11:58PM Friday: Quick update per the 00z NAM and GFS. All parameters still look good. Differences are mainly NAM showing a SW Oklahoma target, GFS showing the OKC-Wichita corridor. Would like to see surface and 850mb winds backing a little more, but given the rest of the setup, I don't forsee that being a big detraction from tornado potential.

Update 12:12PM Friday: Monday is now within the NAM model's window as of the 12z runs. Some significant differences in details exist between the GFS and NAM, though both still give a good reason to head west on Sunday. Ratcheting up chase probabilities as a result.

Posted 11:46PM Thursday: Models appear to suggest that Monday the 10th in Kansas/Oklahoma will be the only good expedition day out of the upcoming system, but a potentially incredible one nonetheless. Every desirable tornado ingredient should be in place Monday, mainly in central Kansas - moisture, instability, low-level wind fields, upper support, you name it. In the following days however, storm setups generally deteriorate and/or move far to the south as a precip-laden frontal boundary pushes moisture away from the mid/upper level wind support. Sunday looks moisture-starved and capped in the Texas Panhandle, so I'm not liking the prospects for a Saturday departure for the 'day before the day'. Tuesday may have some potential in Missouri and Illinois.

So, absent any recovery of Plains tornado probabilities post-Monday, this is looking to be a one-day run to the Plains with an on-the-way-home (or at-home) event afterward. In a nutshell, my confidence in observing Kansas on Monday is a little higher - mitigated only by the models' ever-possible chance of a meltdown between now and Sunday.

In the extended range, the GFS and Euro are in disagreement, with the Euro showing a continued western trough poised to keep tornado chances higher across the Plains. In contrast, the GFS shows a deep eastern troughing pattern for the period beginning late next week, which would shut down the Plains tornado season for an extended time.

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The following comments were posted before this site switched to a new comment system on August 27, 2016:

I have a feeling the target area is going to end up along the I-35 corridor between KOKC and KICT. Looks like a pretty impressive setup.
- Posted by Jeff D. from STL
Jeff, I agree - that is, if the GFS is right. If theNAM is on to something, we could be anywhere from Childress to Wichita.
- Posted by Dan R. from New Baden, IL

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