Weekly Severe Weather Discussion

Severe Weather Discussion for January 12 – 18, 2009.
Valid: 01/11/2009.

Highlights:

– All POPs zero this week. Temperatures will be in the mid 50s on
Monday prior to a cold front early afternoon, cooling off during the
afternoon hours. Tuesday will be cooler with highs in the low 40s and
then a brief return to mid 50s on Wednesday before the bottom falls
out that afternoon. Thursday will be quite cold with temperatures in
the low 20s. Friday will also be cold with highs in the mid 30s. A
warm-up is expected Saturday-Sunday with temperatures in the upper
40s. This forecast is for Oklahoma City due to the variety of
temperatures expected this week.

– Drought conditions continue for parts of the state and the rain
forecast is not looking good.

Probabilities:

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

Discussion:

While sensible weather as a whole will be limited this week, there
will be three cold front passages in Oklahoma that will keep life
somewhat interesting. These cold fronts are in response to shortwave
trofs moving southeast into the mean longwave trof position over the
eastern CONUS. The amplifying ridge just off the west coast provides
confidence in the overall pattern this week. The resulting northerly
midlevel flow aloft will provide a conduit for cold air as cold
surface highs are dislodged from Canada.

The models have been jumping all over the place the past few days with
the forecast this week. Finally, the 18z GFS/NAM and 12z ECMWF are in
agreement regarding the surface pattern evolution and resultant
temperatures. BUFKIT was quite helpful in analyzing expected timing
of said cold fronts and comparison of run to run variations in the
models. This was especially problematic regarding the Tuesday
afternoon time period as I had extension discussions with Andy
regarding the expected max temperatures.

As noted above, I'm going all POPs zero this week. BUFKIT for the 18z
GFS has 0.000 inches of rain for the entire 180 hour period. That
would point towards continued drought conditions for the region and
most likely some worsening. As noted a few weeks ago, the NWS 30 day
outlook valid for January 2009 had us in above normal rainfall. Well,
I'd like to see that happen…really, I would. 18z GFS time series
this week for OKC shows RH values AOB 70% all week except for a period
Thursday morning into the afternoon at 5Kft (NAM has a little more
moisture). However, the surface is very dry and only expect clouds at
this point. Indeed, Thursday looks quite cloudy per BUFKIT cloud chart.

In the dailies, I used the 18z NAM through Tuesday for forecast
temperatures and frontal passages. On Monday we'll see a rapid warm
up into the mid 50s prior to a cold front arriving between noon and
1pm. After that we cool off into the mid 40s by late afternoon. 18z
NAM RH shows enough saturation in the low/mid levels for clouds.
Tuesday was a great discussion day as noted earlier. Since my
conversations with Andy, the models have significantly cooled the high
and I'm going with the 18z GFS at low 40s for Oklahoma City.
Wednesday will be in the mid 50s as we warm ahead of the next cold
front. It is this cold front that will bring the most significant
changes of the week. The front is expected Wednesday afternoon. As
the models typically do not forecast Arctic cold front well, I may get
hosed on my forecast high. I have brought the high down a few degrees
from what I wanted to go (59F). This is an area where the GFS appears
the best model as it is a few hours ahead of the NAM with the initial
windshift and arrival of cold air. I'm not going as low as GFS BUFKIT
data of 51F.

After the front, temperatures rapidly drop and stay in the teens on
Thursday as cold air advection and clouds keep temperatures from
recovering. The GFS showed this several times last week and I believe
this is a good forecast. The ECMWF also shows a decent chunk of the
cold air making it into Oklahoma, so confidence is decent on this
forecast. My forecast high for Thursday is 20F and this is going
below 18z GFS BUFKIT data. Models are way off on the warming for
Friday and I agree with NWS OUN on going in the mid 30s. Saturday may
see a recovery into the upper 40s ahead of the next scheduled cold
front on Sunday. Confidence on Sunday is below normal and the bust
potential is pretty high at D7. I'm going with climo at upper 40s,
which is what OUN has.

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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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