Weekly Severe Weather Discussion

Severe Weather Discussion for January 3 – 9, 2011.
Valid: 01/03/2011.

Highlights:

– Light rain is possible Tuesday evening into Wednesday morning.
Rain is likely on Saturday night into Sunday. A mix bag is possible
in northern Oklahoma/panhandle Sunday night. No impacts are expected.

– Temperatures will be in the upper 50s today, mid 40s Tuesday, low
50s Wednesday, mid 50s Thursday, near 50F Friday, upper 40s Saturday,
and near 40F Sunday.

– A significant and prolonged cold period is possible starting
1/10-1/11, luckily that is beyond this forecast period.

Probabilities:

– Severe Thunderstorms in Oklahoma: < 5%
– Storm Chase: < 5%
– Winter Precip: 10%

Discussion:

Forecast pattern for this week is a continuation of the split flow
across the western U.S. This leads to a longwave trof/closed low
across the eastern U.S. with a the weaker southern jet stream across
Texas. ECMWF/GFS are in good agreement through the period with the
usual minor differences. At this juncture, two systems are expected
to impact the state through D7. System one will split off from a
closed low over the eastern Pacific and translate eastward across
Oklahoma late Tuesday into Wednesday. Models tend to briefly
strengthen this system and then weaken it as the system moves into
confluent flow over the eastern U.S. Given lack of moisture and quick
movement, do not expect much out of it. However, there may be enough
lift for some light precipitation across the state.

The next system moves into the region late Saturday and is expected
pass through Texas. This should limit impacts on Oklahoma other than
some needed rain, however models consistently show Arctic air
approaching the region on Sunday as the upper system is moving
eastward. This would tend to allow a changeover to frozen/mix
precipitation late Sunday. The overall potential appears to be low at
this time, but a northward shift in the storm track would increase
chances.

Temperatures this week will be typical of early January and I see no
reason to go against MOS.

Real story appears to be a potentially significant intrusion of Arctic
air early next week. GFS/ECMWF are consistent with prior runs and
there is good intra-model run (per dProg/dt) analyses of the GFS. The
main disagreement is at which point the Arctic air arrives. GFS from
Saturday evening was about 12-18 hours slower than current runs.
There is little reason to get picky on how this setup might evolve.
Seemingly the main players are in-place, which includes a longwave
eastern Pacific ridge resulting in cross polar flow. Cold air loads
up in western/central Canada and then spills southward into the
region. ECMWF 192 hr sfc prog shows a ridge anchored in western
Canada with isobars from Oklahoma due north to the Arctic. This is a
classic Arctic air intrusion pattern and the GFS is similar.

All that being said, GFS shows the Arctic front moving through
Oklahoma City around noon on Monday, with temperatures going from the
mid 40s to the low 20s by 6pm. Note that this is significant as it
occurs during the diurnal temperature max. After that period, the GFS
shows the entire state below freezing through the end of next week and
the end of the model run (384 hours/01/19/2010). There are seemingly
very serious and potentially deadly considerations with this forecast.
There is potential for frozen precipitation next Tuesday (1/11) but
not seemingly as bad as some OKC media stations would have you
believe. A stronger system may approach around the 14th and that
needs to be watch but is at D10 for me.

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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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