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fxus63 keax 180458 
afdeax 


Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
1157 PM CDT Wednesday Mar 17 2010 


..updated aviation discussion... 


Discussion... 
/400 PM CDT Wednesday Mar 17 2010/ 
tonight through Friday... 


By early this afternoon...drier air began to erode away the cloud 
cover over western Iowa. With a northerly flow present...this drier 
air will continue to work its way further south into northwest MO late this 
afternoon and evening. Will have to keep an eye on how quickly the 
clouds begin to break up. Once the cloud cover becomes broken...it 
should not take long before skies clear. Skies will clear out across 
the entire County Warning Area by late this evening and overnight...dropping temperatures 
to near seasonable normals. Bufr soundings suggest a slight chance 
for some patchy fog development over the eastern portions of the 
County Warning Area...stretching from Kirksville to Sedalia. However...low level 
moisture in the soundings is quite shallow...so still uncertain as 
to how much of this region will be affected by fog during the pre 
dawn hours. 


Thursday is looking to be a gorgeous day as an upper level ridge 
progresses eastward across the region. With this approaching 
ridge...winds will shift from northwest to SW Thursday morning...which will 
advect warmer air into the area. As a result of this southwesterly 
flow...temperatures will reach into the middle 60s...several degrees above 
seasonable normals. But this Spring-like weather will be 
short-lived...as an upper level trough begins to dig southward into 
the northern plains Friday morning. As the associated cold front 
approaches the region from the northwest...precipitation will begin to enter the 
northwest corner of the County Warning Area by around late Friday morning. Models are in 
fairly good agreement with the initiation of precipitation over the 
County Warning Area...with the exception of the NAM which is the least progressive 
of the models with respect to fri's precipitation. Bufr soundings show 
precipitation remaining in the form of rain through the day on Friday...with a 
few isolated thunderstorms possible. The cold front will likely cross into 
the northwest corner of the County Warning Area by early Friday evening. With this frontal 
passage...winds will shift from SW to northwest...leading to a drastic drop 
in temperatures Friday evening. With temperatures dropping first over the extreme northwest 
corner of MO...rain may begin to mix with or change over to snow by 
Friday evening before continuing to spread southeast through the overnight 
hours. 


Ach 




Main challenge for the extended focuses on a weekend storm system 
that will bring a mix of rain and snow to the region. 


Saturday and sunday: 
models are fairly consistent depicting a tight baroclinic area 
setting up Friday night/Saturday morning over the forecast 
area...within a coupled jet structure. With very strong upward 
motions and strong frontogenesis...widespread precipitation is 
expected to move into/develop over the region. Forecast soundings 
show a small amount of instability and this coupled with the strong 
vertical motions should be able to get a few thunderstorms going 
across the southern portions of the forecast as well. With the area 
still saturated and mainstem rivers still either in flood or running 
high additional river flooding is a distinct possibility. Across far 
northwest Missouri thickness values and colder low level 
temperatures will be supportive of snow. 


Beyond Saturday morning forecast confidence decreases significantly 
as models remain quite variable from run to run and model to model. 
The 00z/17 run of the European model (ecmwf) and the Gem dig the low deeper and move 
a closed low across the the Southern Plains with the European model (ecmwf) the more 
southerly of the two. By contrast the 06z and 12z GFS keep an open 
and progressive wave going through the central portions of Continental U.S.. 
this notion now has support from the 12z Gem which is quite a 
departure from the previous version. Several of the GFS ensemble 
members dig the upper low deeper Saturday evening but none really to 
the extent the European model (ecmwf) does. Several of the Gem ensemble members 
indicate this as well. With the large variability in the models the 
forecast tries to represent a blend of the various models with a bit 
more weight toward the European model (ecmwf). With this in mind...as the system 
deepens to the south colder air will work its way into the region 
and by middle Saturday rain/snow will have worked its way into the 
metropolitan area with rain across our southern zones. By Saturday 
evening/night a transition to all snow is expected throughout the 
forecast area. With the system likely to track to the south 
precipitation chances should diminish Saturday night over northwest 
Missouri but remain likely for central Missouri. Depending on what 
model is closer to verifying snow may linger across our far eastern 
zones into Sunday afternoon. Confidence is not high enough to 
warrant anything greater than slight chance probability of precipitation at this time. 


Monday through tuesday: 
despite the differences in the handling of the weekend storm models 
do agree in moving a ridge over the western Continental U.S.. with increasing 
heights and warmer air aloft it looks like the impacts of the 
weekend system will be short lived as a very nice warm up is 
expected by the middle of next week ahead of another system that 
may impact the area Wednesday into Thursday. 


Cdb 


&& 


Aviation... 


For the 06z tafs...biggest concern remains the fog chances tonight. 
Have been seeing ground fog developing in some locations to the 
south and east of Kansas City under the lobe of the surface ridge 
sitting in the region. RUC shows this axis getting shifted further 
south and east overnight...with a weak westerly surface wind setting 
up across the terminals advecting in slightly drier dewpoints...so 
thinking this should keep the threat of denser ground fog from 
forming. However...still a concern that in the River Valley at 
kstj...the site is sheltered enough to keep winds quite 
light...supporting at least light fog formation...so will keep a 
light fog mentioned in the terminal. Otherwise...looking for VFR 
conditions through the rest of the forecast period. 


Pc 


&& 


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


$$