Weekly Severe Weather Discussion

Severe Weather Discussion for October 12 – 18, 2009.
Valid: 10/11/2009.


– Showers and thunderstorms are likely late Monday – Wednesday.
Severe thunderstorms are not expected, but can't rule out an isolated
hailer. Temperatures will be in the mid 50s Monday, low 50s Tuesday,
upper 50s Wednesday, mid 60s Thursday, 60F Friday, upper 60s


– Severe Thunderstorms in Oklahoma: 5%
– Storm Chase: < 5%
– Winter Precip: < 5%
– Tropical Development: 5%


Oh boy what an exciting forecast this week. Nice round of freezing
drizzle in the Oklahoma panhandle this morning, locked up several
Mesonet site anemometers. Not sure I would have forecasted that last
week, but alas it did happen. This week looks pretty exciting
although minus the freezing rain potential.

12z models are in general agreement on the 500mb pattern through
Thursday. There are big differences among the GFS and ECMWF regarding
the weekend. A northern stream shortwave trof will move eastward
across south-central Canada on Monday. This will dislodge a chunk of
Canadian air into the eastern U.S. Oklahoma only gets a glancing
blow, but it will be enough to keep temperatures well below
mid-October normals.

By Tuesday the southern jet stream amplifies a little along the west
coast as part of the prior western Canada northern stream low
retrogrades west. Two weak southern stream shortwave trofs will eject
eastward into the central U.S. Tuesday into Thursday. The 12z NAM is
quite bullish with precipitation on Tuesday and the 18z NAM is close.
I agree with OUN and will go high on POPs. SPC is low on severe
chances and I tend to agree. Lift isn't very strong this far south
and only general thunderstorms are expected.

Models have consistently progged the southern stream shortwave trof
phasing with the northern stream over the eastern U.S. to carve out a
longwave trof. This should result in a cold air dump for Oklahoma as
we'll be in northerly flow aloft. It will also dry us out in the low
levels and send deep moisture well off the Gulf coast. I'm not sure
how strong of a connection the east coast system will have to the
Canadian air and it appears much of the energy may be in the southern
stream. OUN commented on a Canadian/Pacific air mix and I do tend to
agree. So, while we'll get a cold front on Thursday, clearing skies
will actually warm us up from early in the week.

I have gone with the 12z NAM on temperatures through Wednesday, with
some modifications for WAA on Wednesday. This is in best agreement
with OUN. Thursday – Sunday is GFS/ECMWF/Climo blend as there
shouldn't be a lot of cold air with the front on Thursday.

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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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