Weekly Severe Weather Discussion

Severe Weather Discussion for December 7 – 13, 2009.
Valid: 12/06/2009.

Highlights:

– Light freezing rain is possible Monday evening into early Tuesday
for northwest Oklahoma. Significant impacts are not expected, but a
little of this stuff goes a long ways.

– Rain is likely Tuesday across much of Oklahoma. Snow is likely
north-central and northeast Oklahoma Tuesday evening. Currently 1-2
inches seems possible, with a trace to 1 inch the most likely totals.

– Slight chance of rain on Friday for central/eastern Oklahoma.

– Temperatures will be in the upper 30s on Monday, mid 40s on Tuesday,
mid 30s Wednesday – Thursday behind a cold front, low 40s Friday, mid
40s Saturday, and upper 40s Sunday.

Probabilities:

– Severe Thunderstorms in Oklahoma: < 5%
– Storm Chase: < 5%
– Winter Precip: 15%

Discussion:

Rapid southern stream flow will continue this week as an Omega Block
continues over the eastern Pacific. This feature, along with cross
polar flow will allow cold fronts to continue moving into the region.
Ensemble plots indicate this pattern will continue through much of the
upcoming week. However, by Friday models show the ridge decreasing as
the jet stream undercuts it. The southern jet will remain quite
progressive with three systems to impact the region this week. Due to
the rapid movement of the upper systems and limited moisture return,
significant precipitation is not expected.

The first system will move through Monday evening and is rather weak.
It should grab enough moisture to produce light precipitation across
northern Oklahoma. Temperatures will be below freezing, so light
freezing rain appears possible. Models are low on the QPF, but
doesn't take much to cause a problem. A stronger system will move
east and reach the area late Tuesday. This system will be stronger
and likely grab low-level moisture as it moves east. Models are
warming southern Oklahoma above freezing and lack of a cold/dense
Arctic high indicates this ia good forecast. Precipitation amounts
will be higher but temperatures warmer. Best chance of frozen stuff
will be Tuesday night, most likely snow as the 850mb low moves east.
Not much is expected given movement of the upper system, better
chances will be north and east. The final system is another weak one
expected on Friday. By this point the cold air tap is expected to be
closed off with temperature above freezing, as such light rain is the
main precipitation type.

Followed NAM pretty close through Wednesday on temperatures. Several
of the GFS ensembles keep us below normal through next weekend and so
does the 12z GFS. At this point I see no reason not to stick close to
it.

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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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