861 
fxus63 karx 281939 
afdarx 


Area forecast discussion 
National Weather Service La Crosse WI 
239 PM CDT Thursday Aug 28 2008 


Short term...through Saturday night 


Main forecast concern is with rain chances this evening and then 
temperatures through the period. 


Surface analysis this afternoon shows the main cold front 
extending from about kimt across the eastern parts of the forecast 
area to kmci. Secondary cold front was just entering northwest 
Minnesota. 


Water vapor and RUC analysis indicate the main short wave trough 
extends from northern Wisconsin into eastern South Dakota. Secondary 
short wave trough was near the international border over extreme 
southwest Ontario. With the main short wave trough almost on top 
of the forecast area...all the significant synoptic scale forcing 
has moved downstream of the forecast area. The surface cold front 
should be very close to or out of the forecast area by 00z so not 
anticipating the need for any evening probability of precipitation across the far eastern 
or southern sections of the forecast area. Visible satellite 
showing an agitated cumulus field across northern Minnesota with 
kbde reporting a thunderstorm at 19z. This activity will likely 
build a little south along the cold front in the weak ml cape axis 
with values to around 1000 j/kg into far northern Wisconsin. The 
28.18z RUC keeps the cape axis north of the forecast area and then 
quickly dissipates it by 01z. The 28.15z arxrucwrf seems to have a 
good handle on this secondary front and short wave trough and only 
brings the convection as far south as Duluth and then moves it off 
into the u.P. Of Michigan. 


After this evening...high pressure at the surface with ridging 
aloft builds over the upper Midwest for the remainder of the 
period. Little in the way of cloud cover expected...except for the 
possibility of a little more clouds across the north Friday night 
into Saturday as a weak boundary zips by to the northeast. Dew 
points expected to remain in the 50s through the period which 
should allow for some pretty good diurnal ranges...especially 
later in the period when the high slips off the east and allows 
south winds to bring some warmer air back into the area. Highs 
expected to steadily climb each day reaching the middle 80s by 
Sunday with overnight lows mainly in the 50s. 


Long term...Sunday through Thursday 


Medium range models in decent agreement through the period with 
general synoptic scale flow/pattern. Ridging will build over the 
eastern Continental U.S. In response to the tropical systems coming across the 
Gulf and the Atlantic. Troughing will dig into the western Continental U.S. And 
remain until late in the period. This is where model differences 
start to show up in how fast this troughing will move east and start 
to ride up and over the eastern Continental U.S. Ridging. The 28.06z 
operational GFS and 28.00z GFS ensemble means are quicker to bring 
this trough northeast than the operational 28.00z European model (ecmwf). Will blend 
these two solutions and have probability of precipitation as the surface cold front comes 
through the area Tuesday or Tuesday night into Wednesday. 


&& 


Aviation... 


Latest 17z surface analysis indicating cold front extending from 
northeast Wisconsin into south central Iowa. Latest visible 
satellite imagery indicating low stratus deck along and ahead of 
cold front. Ceiling heights ahead of cold front were in the MVFR 
range. As the cold front passes this afternoon...winds will shift to 
the northwesterly direction at both taf sites. Cold front has passed 
through krst and will within the next hour or two at klse. High 
pressure building in from the northern plains states will bring a 
much drier airmass and skies will become clear by 00z Friday at both 
taf sites. With high pressure in control through the Labor Day 
weekend...may need to watch valley fog potential at klse into the 
weekend. 


&& 


Arx watches/warnings/advisories... 
WI...none. 
Minnesota...none. 
Iowa...none. 
&& 


$$ 


Short/long term...04 
aviation...dtj