969 
fxus63 keax 211022 
afdeax 


Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
422 am CST Sat Nov 21 2009 


Discussion... 


Dense fog will be the short term problem as much of northern MO is 
experiencing visibilities a quarter of a mile or less. Conditions 
will improve by late morning as the fog lifts to form a stratus 
deck. Satellite imagery also shows a low cloud deck tied to deeper 
moisture advecting north from TX/OK/AR. A weak west-east surface ridge 
cutting through the center of the County Warning Area divides dense fog to the north 
and the low clouds to the south. This ridge axis is expected to 
fall apart to day as surface troughing over the High Plains pushes 
east and displaces the ridge...thus allowing the low clouds to 
spread into northern MO. Special fog loop suggests the dense fog is 
rather shallow and likely to burn off by middle morning. By this time 
the low clouds should be working their way into northern MO. The net 
effect is sunshine could be in short supply today. Maximum temperatures 
reflect this idea. 


Latest sref surface visibility probability forecast which correctly 
forecast this mornings dense fog is signaling the potential for 
dense fog for tonight over the northwest 1/4 of the County Warning Area. This would fit 
with the stratus/drizzle now over central OK advecting north-northeast across Kansas 
and eventually northwest MO. 


A couple of shortwaves will pass through the plains and middle MO 
valley during the Sunday-Tuesday time frame. The initial shortwave 
moving into the Central High plains on Sunday will most likely 
weaken as it is caught in between a stronger upstream shortwave 
diving into The Rockies and the upper wave now over eastern Texas. This 
initial shortwave will likely only have some middle/high clouds with it 
so precipitation is not likely to fall in our County Warning Area. 


The second system looks like it will be a different animal as it 
dives southeast with a negative tilt. NAM/GFS/ECMWF/sref/Gem all 
close off the upper circulation Monday night. There is decent model 
consistency in the placement of the upper low and general depiction 
of the upper wave. Earlier GFS runs were too progressive with the 
surface cold front and the 06z model run is now more in line with 
the NAM/ECMWF. With increasing confidence on evolution of this 
system have increased probability of precipitation for Monday night/Tuesday. Another model 
run or two showing this same consistency should allow later shifts 
to raise probability of precipitation to likely. 


Mj 


&& 


Aviation... 


For the 06z tafs...overall...there were only minor changes made to 
the previous forecasts. Concern for overnight dense fog remains in 
play for kstj and to a lesser degree kmci. Terminal currently 
reports LIFR conditions and vlifr is certainly possible after 11z. A 
surface ridge axis from east central Kansas through kmci to south of 
Kirk will be the demarcation line between dense fog north of this 
axis and MVFR stratus/fog to the south. This surface ridge axis is 
expected to move little overnight so kmci will be on the borderline 
and hence could go either way with yea/nay on dense fog. Will likely 
be needing a few amendments for kmci. 


The dense fog should be slow to dissipate Saturday morning and could 
last for the entire morning. Once the fog lifts/dissipates am still 
expecting to see considerable MVFR ceilings for the rest of the day 
as low level warm air advection/isentropic lift pulls up the 
extensive low cloud field now covering OK/south central Kansas/southern 
MO. 


Mj 


&& 


Eax watches/warnings/advisories... 
MO...none. 
Kansas...none. 
&& 


$$