Chase Discussion for April 6, 2010.
Target: Kingfisher to Enid
Departure Time: 14:30 CDT
Expected Risk Area: Slight risk for much of central/eastern Oklahoma,
with possibly a moderate in north-central.
00z NAM is similar to prior runs in handling of the western U.S.
medium wavelength trof. The model has oscillated between a closed low
and trof, but overall that seems to have limited impact at this point.
It has gotten a handle on the surface moisture as 65F dewpoints are
common across Oklahoma. Primary item of interest is the strong
veering of the 850mb flow on Tuesday, removing much of said moisture.
The GFS does not do this and tough call which model is correct. The
NAM may be too aggressive with the lead shortwave trof and influence
at 850mb. Despite the veered flow, the NAM backs the flow during the
afternoon and brings 850mb dewpoints of 12C back into the region.
This yields CAPE values at least 1500 J/Kg. Clouds would seemingly be
an issue, but won't be around if the veered flow occurs. So,
temperature wise it is anyone's guess. NAM does show deep layer UVV's
moving over the dryline with a 90kt 200mb jet max during the 4-6pm
time period. This should be sufficient to initiate convection along
this feature. Both the NAM and GFS have been very consistent with
their dryline locations and for now, will just have to monitor where
this feature sets up on Tuesday. I do think a shift east is possible.
I'm not inclined to go south this time as the better action should
be farther north. Instability will be about the same across the
state. NAM does not develop QPF across Oklahoma, but not sure that's
a bad thing. High resolution models do create QPF across central and
eastern Oklahoma tomorrow late afternoon into the evening hours.
Expected hazards remain rather conditional given the 850mb moisture
issue noted earlier. However, discrete activity will certainly rotate
with a tornado threat in northern Oklahoma do to stronger speeds aloft
and back flow. Sfc-500mb crossover is roughly 45 degrees. 0-3km
helicity values are around 250m^2/s^2 as 0-1km is around 200m^2/s^2,
which increases dramatically after sunset. Storms should eventually
form a squall line and race eastward across Oklahoma during the night
time hours. Primary threat with the squall line will be damaging winds.
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