Severe Weather Discussion – 2008-16-1

Severe Weather Discussion for December 26, 2008.
Valid: 12/26/2008.

Highlights:

– Active severe weather day is possible across the eastern 1/3rd of
Oklahoma with isolated severe thunderstorms possible westward to
Oklahoma City. The most intense severe thunderstorms may occur east
of a line from Ada to Miami. In this area there is a threat for
tornadoes, some possibly large, along with damaging winds. The lower
threat area is west of a line from Walters to El Reno to Ponca City.
In this area damaging winds are the main concern.

– Timing – initial severe threat and the most potent may occur around
6pm or just after. A secondary threat and less potent will likely
occur around 4am Saturday.

Discussion:

Near medium end event/impact is likely later today and during the
overnight hours as a seasonably strong trof taps unseasonable Gulf
moisture. Oklahoma Mesonet at 7:20am indicated impressive moisture
surge with low 60's dewpoints in the southern part of Oklahoma and mid
50's in northern sections. This moisture return will continue
throughout the day. A dryline, currently located in the Texas
panhandle will mix eastward today as strong heating occurs in the warm
sector. By late this afternoon the surface low will be in South
Dakota with the associated dryline extending southward through central
Oklahoma. 00z NAM indicates CAPE values 500-1000 J/Kg, which we may
see some slightly higher values than models indicate.

Upper system will approach the region this evening but the southern
stream system may take a little longer as the northern stream
shortwave trof ejects northeast. This is what takes the surface low
into South Dakota. Wind fields at all levels will increase during the
day with NAM progged helicity around 300 m^2/s^2 to 400. Quite
impressive and also seasonable. Models point to the eastern 1/3rd of
Oklahoma for a heightened severe weather threat as the combination of
dryline location, best CAPE, and wind fields colocate over this
region. During the early Saturday morning hours the cold front will
catch the dryline over central Oklahoma. This should cause a squall
line to develop and race eastward. Severe weather threat may be
limited due to time of night and of course year. However, some
marginally severe thunderstorms are likely with the associated threat
of damaging winds.

Given the above, storms are expected to develop along the dryline
shortly after 6pm and race eastward into eastern Oklahoma. Marginal
instability fields would argue for a hybrid supercell/multicell event.
Any storms that can remain discrete will have tornado potential.
How the enhanced tornado threat develops will continued to be
monitored throughout the day. If anything, I hope this event provides
some much needed rain for the state.

What irritates me is I saw this potential last week in the ECMWF and
to some extend the GFS, then ignored it. Sigh. Goes to show that
Oklahoma can have severe weather all 12 months.

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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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