Winter Weather Discussion 2009-1-3

Winter Weather Discussion for January 26 – 28, 2009.
Valid: 01/26/2009.

Highlights:

– Ice Storm Warning is posted for seven counties in southeast
Oklahoma, ice accumulations of ½ to 1 inch are possible. Moderate
impacts are expected to critical infrastructure, including power
facilities. Travel will be highly impacted.

– Winter Storm Warning is posted north of a line from Ardmore to
Muskogee to Stillwell and south of a line from Snyder to Ponca City.
A mixture of sleet and freezing rain is expected in this area with
total accumulations of ½ inches appear likely. Low impacts are
expected to critical infrastructure, but travel will be highly impacted.

– Far western Oklahoma is under a Winter Weather Advisory, only minor
impacts from sleet are expected in this area.

Discussion:

Current RADAR loops and Mesonet observations indicate the event is
underway in southern Oklahoma. NWS Norman just modified their warning
time to start now and continue through Tuesday afternoon. The NAM
consistently showed this earlier start time. The 12z NAM is a little
wetter this morning, although I'm still reluctant to completely bite
into the model as it has been all over the place on precip amounts.
The cold air remained in-place yesterday and freezing temperatures are
now from Ardmore to south of McAlester to Poteau. This line may hold
steady during the day, but will move south during the night time
hours. Due to the colder start, areas in southeast Oklahoma are now
expected to receive freezing rain during this event. The axis of
highest probability of significant freezing rain (greater than 0.50
inches) is from Ardmore to McAlester to Poteau. Farther north in
Oklahoma City and Tulsa, there will be a combination of freezing rain
and sleet. The event should start off as freezing drizzle and
eventually turn into freezing rain. By Monday night sleet is expected
to become the dominate precipitation type.

Much of the state has been cold for a few days and this means that
exposed objects are also at or below freezing. Freezing rain will
rapidly stick to bridges and overpasses. Ground temperatures are in
the upper 30s in Oklahoma City and Tulsa, so little melting due to
warm ground will occur. Farther southeast ground temperatures are in
the mid 40s and surface roads may resist icing at first, but at some
point they'll most likely ice over.

No other changes to the forecast is currently expected. Updates will
be issued during the day to handle microscale modifications to the
sleet/freezing rain/rain areas in Oklahoma. Currently 74 of the 77
counties are under advisories/watches/warnings.

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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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