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fxus63 keax 072218 
afdeax 


Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
418 PM CST Wednesday Jan 7 2009 




Discussion... 


Short range (tonight-friday)... 


Satellite imagery this afternoon shows US that a long wave 
trough...and its axis...have shifted to the east of forecast 
area...leaving US under a cool northwest flow. Embedded in the 
northwest flow are the usual fast moving shortwave...currently 
heading southeast through central Iowa. Surface observations and 
radar indicate that some bands of light snow have developed across 
the southern tiers of Iowa this afternoon. The snow looks to be 
associated with where decent frontogenic forcing...along the 
southwest edge of the backdoor cold front that has settled through 
the County Warning Area today...is intersecting adequate 800 mb moisture. Latest 18z 
model run from the NAM-WRF seems to be picking up on the snow...it 
just has it a little too far west. Given the speed with which the 
shortwave is moving...have added some chance probability of precipitation along the Iowa 
border for the rest of the afternoon horus...then shifted chance 
snow probability of precipitation into central Missouri for the evening hours with flurries 
tailing back to the west. Additionally...given the speed of the 
event...accumulations should not be much. 


Otherwise for tonight...have cooled temperatures off across the 
forecast area based on observations up stream. Western reaches of 
the forecast area should range through the lower half of the 
twenties...but north central to central Missouri should see 
temperatures in the teens (or colder if the clear skies currently in 
Iowa really di make it down into missouri). 


Temperature gradient across the region will stay rather tight 
through Thursday as the cold surface high slides southeast through 
the Central Plains. However...latest runs of the short range 
models...and up stream observation...indicated the need to cool 
temperatures off for tomorrow...especially across northeast Missouri. 
However...by Thursday night the surface high will have slid off to 
the east allowing a southerly return flow to spread across the 
plains. Accompanying the return flow will be a shortwave ridge that 
will be traversing the plains in advance of a progressive 
shortwave...that will move through Missouri Friday. With the return 
flow...an advancing ridge...have continued the trend of using a 
non-diurnal temperature curve for Thursday night. Temperatures 
should drop off through about midnight...but then steady out or 
begin to rise before dawn Friday. 


For Friday...cold front will sweep in from the west during the 
afternoon...but not before the entire forecast area has a chance to 
warm to well above normal. Did back off high temperatures just a 
little as latest runs of the NAM-WRF have sped up the surface front 
a little...but like the previous forecast discounted the GFS as it 
still seems to aggressive with the speed of the surface feature. 
Going into Friday night...did add some chance probability of precipitation as the upper 
level features following the front sweep through the region and 
intersect some of the returning moisture from the Gulf. However... 
best potential for measurable precipitation still looks to be to our 
south and east Friday evening. 


Cutter 


Medium range (saturday-wednesday)... 


Cool high pressure will dominate the local area on Saturday...as upper 
level short wave pushes southeast of the area. Should skies clear on Saturday 
behind upper system...could see readings slightly warmer than 
currently forecast especially across the SW third of the County Warning Area. For 
Sunday...surface high will quickly drift off to the southeast ahead of next short wave 
in persistent northwest flow pattern. Expecting a quick warm up of temperatures 
as breezy westerly flow develops in the morning. Have adjusted 
temperatures slightly cooler than mex guidance which has shown a warm bias 
as of late. 


As we begin the week...models have been persistent in advertising a 
sustained period of colder than normal temperatures beginning 
Tuesday. Have trended temperatures significantly downward through 
the period...with the coldest air lurking just beyond this forecast 
towards the middle and end of next week. A high degree of 
uncertainty exists as to the degree and location of epac 
ridging...in which 12z models are well apart from each other as 
early as Tuesday morning. The evolution of this feature and downstream 
troughing could have large implications on our local forecast as a 
retrograding ridge as suggested by the European model (ecmwf) would allow a 
substantial amount of cold air to invade the country. The GFS on the 
other hand...maintains a less amplified ridge and also keeps this 
ridge locked over the western Continental U.S.. this solution would keep US on the 
fringes of the coldest air...however still below normal. No true 
preference at this point...however gefs guidance supports the less 
amplified ridge of the operational 12z GFS. 


As far as precipitation is concerned...see the potential for a few bouts 
with light snow as baroclinic zone gets shoved into the region. 
While location still remains a problem...time frame with the best 
potential would appear to be Tuesday night into Wednesday. 
Still...uncertainty much to high to introduce anything higher than 
slight chance probability of precipitation at this time. 


31 


&& 


Aviation... 


For the 18z tafs...mostly clear skies spread across the terminals 
this morning...but more clouds are poised to the northwest and will 
spread across the region this afternoon. Up stream observations 
provide good confidence that ceilings will should stay in the VFR 
range. However...will need to watch ceilings for the late afternoon 
hours as there are some scatted MVFR ceilings with some light 
snow/flurries tailing back across Nebraska. Overnight and morning 
hours of Thursday...ceilings should stay in the VFR range. 
Otherwise...look for the modest northwest winds to veer a little 
more to the north and stay there through middle morning hours of 
Thursday...but they should go light and variable late Thursday 
morning as a surface high slides across the region. 


Cutter 


&& 


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


$$ 

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