Weekly Severe Weather Discussion

Severe Weather Discussion for December 27, 2010 – January 2, 2011.
Valid: 12/26/2010.

Highlights:

– Rain is possible Wednesday and again Friday. Snow is possible on Saturday.

– Temperatures will be in the mid 40s Monday, upper 40s Tuesday, low
50s Wednesday, upper 60s Thursday, low 60s Friday, mid 30s Saturday,
low 40s Sunday.

– Fire danger is likely to be critical Thursday and Friday.

– Happy New Year!

Probabilities:

– Severe Thunderstorms in Oklahoma: 10%
– Storm Chase: < 5%
– Winter Precip: 30%

Discussion:

Tough forecast for the week and this one likely to end up in the
toilet before all is said and done. For the first part of the week,
models are in good agreement on a weak southern stream shortwave trof
moving through Texas. This system will draw moisture northward from
the Gulf, but the main impacts will be in Texas. Parts of eastern
Oklahoma, especially southeast may get some additional run. Friday's
rainfall was best only in a few counties of southern Oklahoma, so
overall drought improvement is not likely.

Next up is the development of a longwave trof across the western U.S.
This is where the models go funny. Model ensemble forecasts emphasize
this issue as the ensemble plot is unreadable at 144 hours. The
development of the western U.S. system seems likely, but subsequent
strength and movement are illusive. As sch, the forecast Friday and
beyond appears to be a WAG and a wash. The rather reliable ECMWF is
also flopping around like a dying fish. However, the 12z run may
deserve more credit than the other runs.

General idea is the longwave trof will develop on Thursday, developing
into a closed low by Friday. A surface low will develop on Thursday
in response to strengthening flow aloft. While moisture will be
near-by, it will take some time to return. As such, increasing flow
will likely cause fire weather concerns and above normal temperatures.
Cloud cover has been a serious thorn in my side recently, so I'm
taking a risk on Thursday. However, drought conditions and southerly
flow will help warm things up.

Things get interesting on Friday as the models want to lift out the
closed low. The difference between the models is holding some energy
west in the base of the trof. This is where I side with the ECMWF.
So, moisture will continue to advect northward but the surface low
will eject east with the closed low pushing a dryline and cold front
across the state. I think warm temperatures are likely again and
dewpoints will drop into the teens and single digits. GFS is cooler
with highs but maybe advancing the cold front a little fast. Another
consideration is the lack of an upstream kicker and the models may be
too fast with the lead low. Either way, appears Friday will be warm
and dry with best rain/storm chances in eastern Oklahoma. I have
added POPs for this and upped the severe weather chances for the just
in case. SPC has noted the ARLATEX as an area of concern for Friday
and this appears reasonable.

Saturday has the great bust potential of any part of this forecast.
Siding with the ECMWF means forecasting snow in Oklahoma, but I see no
reason not to go this direction. Again, models are typically too fast
in lifting these systems out and not always giving them enough credit.
For fear of boxing myself in to a corner, I'm going to be a little
vague at this point. I have increased snow potential to 30% and we
could actually see a medium-end event. However, given drought
reasoning above, I'm going to be careful on forecasting precipitation
in-general. I'll handle any issues with special discussions as
necessary.

I didn't use MOS this week, can't be any worse than last Thursday when
I got had by 15F. Most of the forecasting effort this week was on the
general pattern, I'll leave the temps to the TV weather guys.

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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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