Severe Weather Discussion 2007-12-2

Severe Weather Discussion for October 14, 2007.
Valid: 10/11/2007.

Highlights:

– Severe thunderstorms are possible across western and central Oklahoma on Sunday.

– Thunderstorms are possible Saturday evening across the panhandles and northwest Oklahoma.

Discussion:

Main change from yesterday was to emphasize Sunday more than Saturday for this area. Models in decent agreement, but are showing differences in the handling of the northern stream system…per AFDOUN. The GFS has done a good job handling the incoming system, so will stick with this model. The 18z NAM-WRF keeps the systems separate, maintaining a southern stream closed low while the 18z GFS shows some phasing Sunday night. Overall the GFS is preferred for this forecast period.

There is a little change to the forecast for Sunday as the system timing and associated dynamics are similar from yesterday's models. The primary issues come from the thermodynamics. The NAM-WRF continues to be on the low side of the instability parameters despite decent deep layer moisture and daytime heating. Earlier concerns about overnight convection have decreased and the NAM-WRF indicates not precip through the event. The GFS seems to be a better pick at this point and I do prefer its thermo fields. It develops isolated storms during the afternoon on Sunday and eventually develops a squall line as deep layer forcing moves across the region. Actual moisture return remains in question, but at this time there is enough confidence that sufficient moisture will return to support a moderate risk. Many parameters appear in-place for a moderate-end event. Additional moisture return could enhanced the moderate.

SPC has this well covered on the Day 4 and expected a slight risk with a 30% area on the new Day 3. The area will likely be similar to what is on the current Day 4. I doubt they'll do a moderate with the moisture questions we currently have.

Farther down the road there is potential for another event mid-next week. GFS isn't really that favorable at this point, but we'll see what happens. Wednesday would appear to be the better day. Moisture should be much better by t hen.

Probabilities:

Risk area for any part of OK/TX (valid: 10/12 Day 3):

Slight: 100%
Moderate: 5%
High: N/A

Chase Status:

Level 1 – Normal

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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of Hook-Echo.com. For his day job, Putnam works in emergency management for information technology.
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