Weekly Severe Weather Discussion

Severe Weather Discussion for March 1 – 7, 2010.
Valid: 03/01/2010.

Highlights:

– Rain is likely across southern/central Oklahoma tonight into
Monday, although amounts will be on the low side. Snow is possible
early Monday in this same area and the panhandle. Amounts will be
highest in the panhandle of 2-4 inches with less than 2 inches in
southern Oklahoma.

– Thunderstorms are possible on Sunday across Oklahoma, but
confidence is very low.

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

Probabilities:

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

Discussion:

Atmospheric pattern will remain amplified early in the week, but
rapidly deamplify by mid-week. Overall sensible weather impacts for
Oklahoma appear to remain low at least through Saturday. There will
be at least two systems moving through the southern stream this week.

12z models are in good agreement through Wednesday with differences
appearing after the short-range period. The pattern through 84 hours
will feature a closed low moving eastward through Texas tonight into
Monday. This system then moves into the southeast U.S. and reloads
the eastern U.S. longwave trof late Tuesday. Impacts from this system
are expected to remain low as precipitation amounts should be below
0.50 inches and mainly rain. Cold air is lacking across the region,
as noted by upper 50s temperatures in Oklahoma today. Cooling
sufficient for snow will be cooler air on backside of upper system and
any lift associated on the north side. Amounts should be very low
with mainly a dusting expected. Temperatures will be near or slightly
above freezing, which should allow the snow to melt.

As the eastern U.S. longwave trof cranks up, a ridge will move into
the Gulf and displace 55F + dewpoints beyond the Yucatan and Cuba.
Models have been consistent with this forecast for the past several
runs. 12z NAM is also showing the same impacts. Longwave mid-level
ridging will develop across the central U.S., which should provide a
warming trend across Oklahoma. This week is likely to be the warmest
week Oklahoma has experienced since mid-January. A southern stream
shortwave trof will traverse eastward into the mean longwave position.
Models take it into KS/NE on Friday. Moisture should remain limited
and as such POPs are left out of the forecast for Friday.

Primary forecast problem appears at the end of the forecast period.
GFS and ECMWF diverge quite a bit relative to a SW U.S. system. The
GFS brings the system onshore and into Oklahoma by Sunday, keeping it
quite progressive. The ECMWF is about 24 hour slower, a pretty
significant difference. I'm used to 12 hour differences between these
models, but this is a little weird. Given that a major pattern shift
is about to occur, I'm really inclined to side with the ECMWF. I have
gone with some POPs on Sunday, along with svr/chasing probabilities,
only as a small nod to the GFS. The more likely outcome will be
thunderstorm potential on Tuesday/Wednesday March 9th/10th. The
positive side of this would be additional Gulf recovery after the
significant cold air intrusion this week. If the GFS is right, then
severe thunderstorm potential would be confined to eastern Oklahoma on
Monday. As such, the 10% severe probabilities seem warranted for
low-end impacts, even though the forecast confidence as a whole is low.

Temperature wise I went with the NAM through 84 hours and then my own
through Sunday. GFS MOS appears too cool and I modified temperatures
upward. Main issue is expected system on Sunday, which may play havoc
with temperatures.

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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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