Winter Weather Discussion 2010-1-5

Winter Weather Discussion for January 27-29, 2010.
Valid: 2010-01-27

*Significant Winter Storm to Impact Oklahoma*
*Preparations should be rushed to completion*

Highlights:

– Winter Storm Warning for much of Oklahoma, north of a line from
Lawton to Muskogee. Excessive snowfall is expected in northwest
Oklahoma and the panhandle with 8-12 inches total accumulations
likely. Along the I-44 corridor, a cold rain will start off Thursday
and turn to freezing rain during the midday hours. A quick transition
to sleet and eventually snow will occur by Friday morning. Total ice
accumulations may exceed one inch in some areas with sleet of 2-3
inches and snow 2-5 inches.

– Winter Storm Watch for much of south-central and southeast Oklahoma.
In southeast Oklahoma a cold rain is likely much of the day Thursday
changing to freezing rain and sleet during the overnight hours. The
event should end with snow.

– Timing of this event is particularly problematic in Oklahoma City,
since the general public will venture out Thursday morning only to be
caught in the transition to freezing rain during the late morning
hours. This may lead to widespread wrecks, stranded motorists, and
difficulty for emergency vehicles to move around. A situation similar
to December 24th is quite possible.

– Strong winds will occur with this system and after it leaves late
Friday. This will likely aggravate the situation and widespread power
outages are becoming a likely result.

– The forecast continues to call for a high-end event across much of
Oklahoma. Additionally, after the system passes, temperatures will
plunge into the single digits and teens. This will create a
life-threatening situation for those unable to move to warm shelters.

Discussion:

18z NAM did not change things much, still starts freezing around 10am
– 12pm on Thursday. Issues become at what point the freezing rain
starts to accumulate on exposed surfaces. Conventional thinking in
this matter revolves around already subfreezing temperatures prior to
the event. In this situation the rain is expected to change over to
freezing rain as the cold air deepens and temperatures drop. There
will likely be a period of time where the temperature is technically
below 32F/0C but exposed surfaces remain warm enough to prevent ice
accumulations. There is little confidence and accuracy as to when ice
will start to accumulate and ultimately how much. Another serious
consideration is the impacts on Oklahoma City and Tulsa as now both
are under the gun for freezing rain. The duration and expected amount
of freezing rain certainly points to accumulations of at least 0.25
inches and most likely up to 1 inch along the I-44 corridor. Farther
northwest excessive snow continues to be the primary type in the
panhandle and far northwest Oklahoma with 8-12 inches likely. Just
southeast of that area a zone of freezing rain and then sleet will
occur, transitioning to snow later Thursday. Oklahoma City may remain
freezing rain/sleet during the night and only briefly switch over to
snow on Friday. This is predicated on the 700mb dry slot and subject
to change without notice. Points south and east of I-35/I-40 will
stay warm longer and likely only experience a freezing rain threat.
This threat won't be transient and still likely to cause problems for
this area. The strong winds expected with this system continue to be
of concern as even 0.25 inches of ice driven by 20-30mph will cause
power problems.

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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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