Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
1015 PM CDT Tuesday Jun 18 2013 


Update... 
issued at 902 PM CDT Tuesday Jun 18 2013 


Weak cold front has slowly pushed through the area this evening 
and is currently over far southern counties. Front will continue 
to sag south tonight. Trimmed probability of precipitation back as isolated showers/storms 
along front and previous outflow boundaries have dissipated in 
part due to loss of instability/daylight heating. Otherwise...only 
cosmetic changes made to tonight's forecast. 


Gosselin 


&& 


Short term...(through late tonight) 
issued at 243 PM CDT Tuesday Jun 18 2013 


Focus tonight will be probability of precipitation...again. 


This portion of the afd is beginning to sound like a broken record. 
Have increased probability of precipitation through early this evening. Expect ongoing thunderstorms and rain to 
dissipate and/or move southeastward out of the area by middle to late this 
evening. 


Models do depict an area of 850h convergence across portions of north 
central MO late tonight into Wednesday morning. The NAM is...so far...the 
only model that produces precipitation with this feature. Other models suggest 
middle level temperatures will be too warm to allow for convection. Will 
therefore keep the period after midnight dry for now. 


Very minor adjustments made to the previous forecast. Can not rule out 
some fog development late tonight...especially across central MO where drier 
air will struggle to advect into the region. 


Tilly 


Long term...(wednesday through next tuesday) 
issued at 243 PM CDT Tuesday Jun 18 2013 


Wednesday through Friday... 
dry and seasonal weather is expected for Wednesday with light winds 
from the east as the surface ridge dominates the region. Wednesday 
night a 50kt low level jet will intensify across the plains and 
interact with a shortwave topping the upper level ridge. The GFS 
depicts a deeper shortwave when compared to the NAM and therefore 
develops showers and thunderstorms across central Nebraska and east 
central Kansas. The question is how far east will the convection 
travel Wednesday night into Thursday morning as the low level jet 
veers. For now have maintained slight chance probability of precipitation across central and 
northeast Missouri late Wednesday night...but feel the better 
chances will remain west of the County Warning Area. 


Meanwhile...at the surface a warm front will be pushing northeast 
across the region on Thursday. Instability will increase throughout 
the day bringing a greater chance for thunderstorms to the area. 


The warm front should move northeast of the region as the upper 
ridge builds over the County Warning Area. Deep mixing and a southerly surface wind 
will allow temperatures to rise above normal into the lower 90s. 


Saturday through Tuesday... 
southwest to northeast orientated upper level ridge to dominate the 
center of the nation this weekend...with above normal temperatures 
and limited chances of precipitation. The pattern will begin to 
break down by early next week as the flow becomes more zonal and the 
upper level ridge reestablishes itself to our west. 


Grana 


&& 


Aviation...(for the 06z tafs through 06z Wednesday night) 
issued at 1010 PM CDT Tuesday Jun 18 2013 


VFR conditions are expected at most taf sites for the majority of 
the taf period with light winds becoming southeasterly tomorrow. The exception 
may be at kcou later tonight if the cirrus clouds clear out before 
a drier air mass arrives at low levels. The resulting radiational 
cooling conditions could produce a few hours of MVFR fog or 
stratus before conditions improve by mid-morning. 


Specifics for kstl...VFR through the period with light winds becoming 
southeasterly tomorrow. 


Kanofsky 


&& 


Lsx watches/warnings/advisories... 
MO...none. 
Illinois...none. 
&& 


$$ 


Weather forecast office lsx