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fxus63 keax 231134 
afdeax 


Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
534 am CST Monday Nov 23 2009 


..updated aviation discussion... 


Discussion... 


In the short term favor the NAM mass fields as the GFS is too wet 
below 800mb. If one took the GFS at face value all of MO would be 
cloudy right now...and it isnt. Middle clouds have peeled off to the 
north as the better isentropic lift exits the northern County Warning Area. So 
expect to see at least morning sunshine. Low cloud loop does show 
quite a bit of stratus/fog over central Kansas which is trending slowly 
east. Expect some of this moisture to move east resulting in SC/cumulus 
development by late morning. One last day of above normal 
temperatures before reality sets in. Only made minor tweaks to 
previous maximum temperature forecast 


Primary attention will focus on the evolution of the much advertised 
upstream trough. Latest water vapor imagery shows upper trough 
digging into the central rockies. Drying in water vapor imagery 
occurring near the 4-corners suggests the upper level speed maximum of 
90 kts is dropping into the base of the trough and aiding in the 
strengthening/deepening process. 00z GFS/ECMWF/sref/Gem model runs 
continued their past trend of showing very good agreement between 
models and run-to-run consistency. The 00z NAM had continued to be 
the slow poke and outlier model with a more southern track. 
Interesting to see the 06z NAM has sped up and decided to jump on 
the band wagon and is much closer to the other models. This gives 
more confidence that the upper low will track close to the GFS/European model (ecmwf) 
path which will take it into central Kansas tonight before lifting 
northeast through northwest MO on Tuesday. 


Low level moisture continues to be a problem in the downstream 
environment and will likely be the primary reason for delaying the 
arrival of rain into the County Warning Area tonight. So have lowered evening probability of precipitation 
but hit them hard after midnight...in essence shifting the timing by 
3-6 hours. Did notice that the models are developing a southerly low 
level jet late tonight which will aid in transporting additional 
moisture from the Southern Plains as well as increasing the warm air 
advection. 00z GFS continues to steepen lapse rates tonight 
resulting in most unstable convective available potential energy of 100-200 j/kg. This may be enough 
for a few rumbles of thunder tonight. 


Expect a blustery day on Tuesday with a dry slot likely pushing the 
rain out of the southern County Warning Area early. Northern 1/2 of the forecast 
area should see off and on rain while wrap around clouds/patchy rain 
associated with the deformation zone spread back into the western 
County Warning Area in the afternoon. Will not mention any snow in the County Warning Area with this 
system as cold air will not be in place and dynamic cooling within 
the deformation cloud band may not be sufficient for a change over 
to snow. GFS/NAM wet bulb temperatures only drop into the upper 30s 
within the deformation zone. Better to hold off on any mention of 
snow for now. 


Backwash cloudiness and moderately strong cold air advection will 
limit warmup on Wednesday and then a clipper type system quickly 
dives southeast through the northern plains/Minnesota Wednesday night and 
displaces the aforementioned upper low and sends a shot of cold 
Canadian air into the region for Thursday. Have lowered maximum 
temperatures a bit for Wednesday and Thursday. Bulk of 
energy/lift/moisture with this clipper system will miss the County Warning Area and 
feel no need to go any higher than slight chance probability of precipitation for the 
northeast portion of the County Warning Area. 


Mj 




&& 


Aviation... 
for the 12 tafs...VFR conditions are expected through much of the 
valid period. A scattered VFR deck will expand eastward from Kansas 
this morning and persist and gradually thicken through the day. By 
this evening bases should lower and ceilings should eventually become 
overcast. Steep middle-level lapse rates should develop later this 
afternoon as an upper level system starts to influence the area. As 
atmosphere begins to saturate latitude this afternoon/this evening more 
vertical development is likely to clouds. However with lack of any 
focus until a cold front encroaches upon the area Tuesday morning 
thunderstorm chances at any particular point look small so will not 
mention anything with this issuance. As ceilings lower towards the 06z 
time frame some -ra or drizzle is expected. With decent depth to 
saturation felt it more likely to be -rain. Regardless...at this time 
will mention MVFR ceilings/visibilities until confidence increases that IFR 
conditions would prevail. 


Cdb 


&& 


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


$$