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Area forecast discussion 
National Weather Service Norman OK 
326 am CST Sat Nov 22 2008 


Discussion... 
forecast over the next several days remains pretty much unchanged. 
Returning S winds and gradual modification of the cold air mass will 
lead to a gradual warming trend. Low probability of precipitation are maintained Sunday and 
Sunday night for some -ra/-shra ahead of Pacific cold front... 
mainly over east/southeast OK. Drier and somewhat cooler air moves in by 
Monday followed by another slow warmup as upper ridge axis moves 
from The Rockies into the plains by around midweek. Met guidance 
temperatures have been followed closely through Monday. It is 
notable that the next cooler/drier air mass is not forecast to go 
very far into the western Gulf. This has implications for the 
speed and quality of expected low-level moisture return late in 
the week. 


Our attention is turning more and more to the system forecast to 
affect the area late next week. This system appears destined to be a 
significant player in one way or another over Thanksgiving. The good 
news is that it easily looks to remain warm enough to keep all 
precipitation rain /barring any T-storms with hail/. We will trend the probability of precipitation 
upward a bit more from Thursday into Friday... but keep them in the 
chance range due to a number of inherent uncertainties in details. 


General longwave pattern evolution for next week remains the same - 
big upper low closing off over the northeast and a Pacific system 
dropping into the SW. Latter will nudge the upper ridge axis east of 
the area by Thanksgiving... opening the way for moisture return and 
increasing rain/T-storm chances beginning as early as Wednesday night. 
While the models are on the same general Page with the big 
picture... devil is in the details. European model (ecmwf) is among the slowest to 
move the SW system east into the plains... which makes sense to US 
given the overall blocky character of the pattern. However we are a 
bit concerned that the European model (ecmwf) essentially has lost most of the 
upstream kicker. Most of the models drop a good chunk of it into the 
SW... while the European model (ecmwf) now takes most of it into British Columbia. 
That and the ecmwf's somewhat suspect handling of the low over the 
northeast - moving it northwest/north to James Bay and building a ridge over 
the southeast states - lowers our confidence in the European model (ecmwf) toward the end of 
next week. Thus we are leaning a little more toward the GFS... which 
brings strongest kinematic forcing across the area Thursday and Thursday night 
before shutting down any lingering precipitation by late Friday. GFS has 
backed off on surface moisture return Wednesday into Thursday... keeping 
trajectories initially from the Gulf Coast states and thus keeping 
surface dewpoints in the 30s/40s over most of OK/ntx. European model (ecmwf) may be 
overdone with 60+ dewpoints to the Red River by Friday morning. What 
verifies is apt to be somewhere in between the two models. That 
still would be enough to support a potential for some embedded 
convection... but instability is likely to be limited this far north. 
Increasing dewpoints and clouds will act to keep nighttime temperatures 
up... while precipitation and the same clouds keep daytime temperatures down. 
GFS has mean-layer relative humidity over 90 percent by late Thursday... suggesting 
a cloudy cool and occasionally rainy Thanksgiving. Behind this 
system... GFS builds another 1040 Canadian high down through the 
plains by next Saturday as a double-vortex block sets up near the 
West Coast. Or... if the European model (ecmwf) is right... there will be a 590 upper 
high off the West Coast with ridging into west Canada. Either way... 
looks colder again by the end of next week. Temperatures next weekend may 
well be similar to - or lower than - what we've had the past 
couple days. 24 


&& 


Preliminary point temps/pops... 
Oklahoma City OK 54 35 59 37 / 0 0 10 10 
Hobart OK 54 37 64 38 / 0 0 0 0 
Wichita Falls Texas 60 42 65 38 / 0 0 10 0 
gage OK 58 29 66 28 / 0 0 0 0 
Ponca City OK 53 34 60 35 / 0 0 10 10 
Durant OK 54 40 60 52 / 0 10 20 30 


&& 


Oun watches/warnings/advisories... 
OK...none. 
Texas...none. 
&& 


$$ 


22/24