Severe Weather Discussion for November 22 – 28, 2010.
– Showers are possible in southeast Oklahoma Monday and Wednesday
evening. A low chance does exist for central sections on Wednesday.
– Temperatures will be in the mid-70s on Monday, mid 60s
Tuesday-Wednesday, near 40F Thursday, low 50s Friday, upper 50s
Saturday, and near 60F Sunday.
– Happy Thanksgiving!
– Severe Thunderstorms in Oklahoma: 5%
– Storm Chase: < 5%
– Winter Precip: 5%
Western U.S. longwave trof will persist through Wednesday, before
finally ejecting eastward across the U.S. The general idea is for
strong southerly flow to continue across Oklahoma with dewpoints in
the upper 50s/low 60s through Tuesday. A shortwave trof will eject
northeastward into South Dakota late Monday and this may give a decent
push on the frontal boundary across Kansas. Another small shortwave
trof will quickly follow it late Monday, however this one will be
farther south. Models had hinted at showers in southeast Oklahoma
with the passage of this shortwave trof, however the 18z NAM is dry.
I'll continue low POPs for southeast section late Monday.
Tuesday looks quiet as a western U.S. closed low takes shape. This
formation has been the subject of much discussion the past few days
and is vital to the forecast Wednesday and beyond. All models agree
that this closed low will develop by Tuesday morning, supported
in-part by a 80-90kt jet max on the backside of the low. By late
Wednesday the low starts to weaken with the strong winds on the
southeast side of the low at 500mb. This should move the system
eastward towards the central U.S. by Thursday. As this process takes
place, a strong Canadian cold front will plunge southward. There are
two issues regarding the arrival of said front. 1) models typically
under-forecast the movement of Canadian/Arctic air and 2) the movement
of the upper low, as the surface low will provide some resistance.
GFS forecasts the past few days had the cold front through Oklahoma by
Wednesday morning. 12z/18z runs of the NAM/12z GFS/ECMWF have the
front arriving Wednesday night. This appears to be the best solution
given the movement of the northwestern U.S. closed low and no other
features to dislodge the cold air. As such, currently thinking a
pleasant day is expected for Wednesday with above normal temperatures.
By late evening, say 10pm, the cold front should be blasting through
Oklahoma. This will end several days of above-normal temperatures,
with temperatures in the 30s and low 40s expected on Thursday. Due to
the overnight arrival of the cold air, I expect little diurnal
temperature climb on Thursday and I may be too high with 40F. The
wind will certainly make things feel quite cold, with the GFS showing
20-25kts on Thursday. The resulting windchill should be in the teens.
Closed low moves into the northeast U.S. by Friday and exits the U.S.
late in the weekend. Moisture is pushed past the Yucatan as the
surface high settles into south Texas. 500mb flow transitions to
short-wave ridging and eventually zonal by Sunday. Lack of moisture
precludes POPs beyond Wednesday/cold front passage.
I went with the NAM through Wednesday and generally undercut the GFS
through Friday. The GFS ensembles are way high on Thursday and I
agree with OUN on 40F, even though that may be too high. A hard
freeze will occur Thursday night, across much of the state, ending the
2010 growing season. Surface high moves off quickly by Saturday and a
robust warm-up to normal temperatures is likely by Saturday.
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