Severe Weather Discussion for January 19 – 25, 2009.
– Monday mid 50s, Tuesday 50F, Wednesday mid 60s, Thursday upper 60s,
Friday 40F, Saturday low 30s, Sunday mid 30s.
– Light freezing drizzle/rain is possible Friday night into Saturday
morning, impacts appear limited to isolated travel problems. Main
area will be southern Oklahoma with some possible light stuff in
– Fire weather concerns will be present much of the week, but
especially Wednesday and Thursday.
– Severe Thunderstorms in Oklahoma: < 5%
– Storm Chase: < 5%
– Winter Precip: 10%
12z GFS/NAM/ECMWF are in remarkable agreement through 84 hours and the
GFS/ECMWF through the remainder of the week. There is one detail that
is different, the southern stream shortwave trof expected
Friday/Saturday. The GFS is now 18 hours slower than the ECMWF.
Persistent and seemingly long-term 588dm longwave ridge will weaken
this week resulting in a pattern deamplification across the CONUS.
The models are actually handling this quite well, given the GFS's
propensity to crash western U.S. ridges. However, this transition
will take some time and currently is expected to happen by Thursday.
As this occurs, split flow develops across the CONUS with a weak
southern stream shortwave trof moving eastward to the region. Most of
the time this type of system could make for some decent rainfall
across the region, however the Gulf has been whacked several times the
past few weeks. The net result is 70F dewpoints are past Cuba with a
small area of 65F in the Gulf today. As such some recovery will be
necessary, especially given another cold air intrusion on Tuesday.
The timing of the southern stream system and Gulf moisture are
problematic for this forecast since there is a cold front expected
Friday morning. GFS BUFKIT data hits on light freezing rain Saturday
morning due to WAA over the cold dome. Going with forecast GFS
dewpoints, temperature, and ECMWF 500mb field yields a chance for the
freezing drizzle and rain to occur. With the cold front in north
Texas, the moisture doesn't have too far to go. OUN noted a few days
ago that we have seen the best the Arctic has to offer and this is
certainly true. The high building in is only 1033mb, a wimp compared
to what we have seen. We'll also have to see if the cold air loads in
Canada as fast as the GFS indicates. Either way, there is enough of a
chance to include low POPs Friday night into Saturday for freezing
drizzle/rain. The main area will be southern Oklahoma as it is closer
to the progged shortwave track and moisture source.
In the dailies, I followed the model BUFKIT output pretty closely,
with some minor changes. Winds will remain generally from the
northwest through early Wednesday as the eastern U.S. surface low
remains close enough to influence the region. Despite the northerly
winds, Monday will be much like today with temperatures in the mid
50's as the 800mb level cools a little. Tuesday appears colder and
more wind as a western Canadian high moves into the region early
Tuesday. I'm going with a high of 50F as compromise between the
NAM/GFS which are about 6 degrees apart. I'm giving a little more
credit to the NAM as we're in a drought and can warm quickly.
Midlevel flow becomes westerly on Wednesday with weak southwesterly
flow at the surface. Winds appear calm as surface ridge to the south
and weak low to the north keep Oklahoma in a reduced pressure
gradient. Either way, temperatures aloft will warm and support mid
60s. Thursday will be similar with temperatures in the upper 60s.
I'm going above model guidance as they have been too low on days like
these the past few weeks. 850mb temps certainly support at least mid
60s both days. The only thing keeping Wed/Thu from being critical
fire weather days will be relatively light surface winds. However,
dewpoints in the 20s and temperatures in the 60s will still make for
high fire danger.
Cold front moves in Friday morning and appears to have a little more
bite, assuming the GFS is correct with the cold air loading in Canada.
As such, temperatures may not recover as much on Friday as the GFS
indicates. Although, initially CAA may be a little weak as the high
settles into the area. I'll compromise with a high near 40F on
Friday. Saturday looks cold as WAA increases clouds across the
region. A high in the low 30s looks good and Sunday will be in the
mid 30s, both along with the 12z GFS BUFKIT data as the models tend to
move Arctic air out too fast. I'm building in a cold bias at Days 6
and 7 since people rarely complain when it is warmer than forecast
this time of year. I'd rather it not be the other way around.
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