Weekly Severe Weather Discussion

Severe Weather Discussion for March 9 – 15, 2009.
Valid: 03/08/2009.

Highlights:

– Severe thunderstorms are possible on Monday for much of central and
eastern Oklahoma. Primary threat is large hail, though an isolated
tornado or two is also possible.

– Fire danger will be very high to extreme Monday and Tuesday for the
western 1/2 of Oklahoma.

– Arctic cold front will move through the state Tuesday evening.

– Temperatures will be in the upper 70s on Monday, near 80F Tuesday,
upper 30s Wednesday, mid 40s Thursday – Friday, low 50s Saturday, and
upper 50s Sunday.

– Precipitation is possible Thursday – Friday, with mainly light rain
expected.

Probabilities:

– Severe Thunderstorms in Oklahoma: 30%
– Storm Chase: 15%
– Winter Precip: 10%

Discussion:

Sensible weather will be rather high this week but overall impacts
should remain on the low end of the scale. Hence, special discussions
are not anticipated right now.

After nearly a week long taste of spring and a little summer, winter
will make a big come back by the middle of the week. 12z models are
in decent agreement and BUFKIT data supports the map outputs.
Overall, the ECMWF's 500mb pattern was favored, but really fits nicely
with the GFS. The 12z NAM BUFKIT temperatures and 12z GFS are blended
through Tuesday with the NAM favored on Wednesday. GFS numbers are
used with some adjustment after the fact, giving a lot of credit to
the incoming Arctic air. While ground temperatures are in the upper
50s statewide and there is no snow pack to our north, the incoming
airmass is truly Arctic and will use appropriate SOP for the
Wednesday-Friday time period.

500mb pattern will be dominated by a southern stream shortwave trof
ejecting northeast on Tuesday. As this feature moves into eastern
Canada, it merges with a northern stream shortwave trof as the pattern
across the lower 48 deamplifies. The latter system will help dislodge
an Arctic airmass, with impacts across the eastern 2/3rds of the U.S.
likely. The center of the high will follow the base of the trof
through the northeast U.S. and impacts on the Gulf will be limited.
However, Gulf moisture will be pushed to the coastline as indicated by
the NAM/GFS runs.

Beyond Wednesday the main influence on Oklahoma with be a weak
southern stream system, progged to lumber eastward across the southern
U.S. The 12z GFS/ECMWF are in good agreement regarding this feature.
By this time Gulf moisture will be along the coastline, so better
precipitation chances will be south of the region. There is some
opportunity Thursday and Friday with good 925/850mb moisture. 850mb
moisture remains in-place next weekend and I wonder if this will cause
skies to be a little more cloudy than currently progged. Since we do
remain in a drought, I'll bump up temperatures a little more than I
planned on earlier. Additionally, the GFS wants to hit at winter
precipitation and while it can't be ruled out, doesn't seem likely.

Monday's severe weather threat looks to be on the low-end of the scale
right now. However, it will have to be monitored given the impressive
wind fields aloft. Models continue to have major problems resolving
the rather active southern jet and the current placement of the
subtropical jet. A warm front is progged by all models to surge
northward across the state early Monday with low 60s dewpoints
in-place east of the dryline (expected in western Oklahoma). Model
soundings show deep layer moisture with dewpoints greater than 10C up
to 830mb. BUFKIT plots indicate little to no CIN Monday afternoon and
this appears to be the possible limitation to a more robust event.
Widespread showers and thunderstorms may occur and when combined with
expected cirrus, may limit surface heating. Monday afternoon will be
a high shear, low CAPE time period and after what happened in Kansas
yesterday; low topped supercells are certainly a possibility.
Therefore, will go with large hail as the primary threat and add in
the chance of isolated tornadoes in Oklahoma. As always, discrete
supercells will have tornado potential, especially those anchored on
surface boundaries.

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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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