318 
fxus63 keax 201146 
afdeax 


Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
646 am CDT Sat Mar 20 2010 


..updated aviation discussion... 


Discussion... 
/427 am CDT Sat Mar 20 2010/ 
vigorous winter storm ongoing across portions of the plains and 
Midwest early this morning. Latest radar trends depicting warm air advection precipitation 
shield across the forecast area steadily moving east with time. Cold 
air has been a bit slow to advect across the entire County Warning Area but appears 
areas along and north of a Macon to Butler line has now transitioned 
to all snow. Ahead of this line...the transition area has produced a 
decent dose of rain...freezing rain and sleet as it propagated across 
the forecast area. With cold air steadily progressing southward 
now...appears most locations should be cold enough for snow by 
sunrise. However...biggest concern is whether there will be much snow 
around by the morning hours. 


Isentropic ascent...which is most prominent on the 290k surface...shifts 
east with neutral lift developing by the morning hours with the 
northern and western portions of the County Warning Area under isentropic downglide. 
Latest radar trends support this idea with decreasing activity 
across northwestern Missouri and northeastern Kansas as the more 
concentrated area of precipitation shifts east. Believe highest probability of precipitation 
through the morning hours will remain across the eastern portions of 
the County Warning Area before this area shift east. 


New area of precipitation has recently blossomed across central 
Oklahoma and this will be the next round to affect the area later 
today. Vigorous 100+ knots h25 jet will begin rounding the base of 
deepening upper trough today as it shifts into the Southern Plains. 
As this occurs...precipitation will likely become more widespread 
from central Oklahoma northward into central Missouri...likely 
somewhere along and south of a Kansas City to Kirksville 
line...although exact position is still uncertain. As the system 
strengthens...dynamical lift along with increasing isentropic ascent 
should lead to enhanced precipitation by the middle to late afternoon 
hours...into the evening. This precipitation swath is expected to develop 
into the main deformation band during this time frame bringing 
another dose of snowfall to the area. Current thinking is this round 
will align across the southern County Warning Area...mainly south of the Missouri 
River...although main snow swath may extent further north across 
portions of central Missouri..towards the Macon and Moberly area. 


System becomes better organized by overnight tonight and into the 
early morning hours as surge of rich Theta-E air mass is ingested 
into the system. This should lead to a decent trowal feature 
developing by Sunday morning. As this occurs...deformation band is 
expected to gradually weaken and any precipitation may even transition to a 
mix of rain/snow/sleet during the day Sunday as warm air noses into 
the atmospheric column. Precipitation is expected to wind down by Sunday 
afternoon as the system departs to the east. 


As far as headlines go...will cancel the advisory for the far 
northwest corner of Missouri as snowfall has lightened or ended 
across most areas. Also...added Howard and Cooper counties into the 
advisory with snow expected to increase through the day across those 
areas. Otherwise...regrouped the counties a bit for better timing. 


Deroche 




&& 


Aviation... 


For the 12z tafs...first wave of accumulating snow has moved out 
leaving behind a narrow band of very light snow and MVFR ceilings. A 
second wave of snow is surging northeast out of OK/south central Kansas 
and will define the new deformation zone with accumulating snow. 
Favor the last 2 runs of the NAM mass fields. This paints a picture 
of little if any additional accumulating snow at kstj with kmci 
likely on the northern edge and kmkc having a better chance of 
seeing another inch or two of snow this afternoon/evening. MVFR 
ceilings will last into this evening before the stratus departs to 
the east and VFR conditions return. 


Mj 




&& 


Eax watches/warnings/advisories... 
MO...Winter Weather Advisory until 1 PM CDT Sunday for 
moz025-031>033- 038>040-046. 


Winter Storm Warning until 1 PM CDT Sunday for moz043>045-053- 
054. 


Winter Weather Advisory until 7 PM CDT this evening for 
moz003>006-012-013-020. 


Winter Weather Advisory until 7 am CDT Sunday for moz007-008- 
014>017-021>024-028>030-037. 


Kansas...Winter Storm Warning until 1 PM CDT Sunday for ksz057-060. 


Winter Weather Advisory until 7 PM CDT this evening for ksz025- 
102. 


Winter Weather Advisory until 7 am CDT Sunday for ksz103>105. 


&& 


$$