Weather

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fxus63 karx 280735 
afdarx 


Area forecast discussion 
National Weather Service La Crosse WI 
234 am CDT Thursday Aug 28 2008 


Short term...today through Saturday night 


Forecast challenge is in first 15 hours as northern flow short wave 
trough energy moves through today with convective threat. After that 
it looks like a quiet Holiday weekend on tap. 


Fairly potent short wave trough is moving along the Canadian and 
North Dakota border early this morning. Middle/upper level jet crashing 
out of the northern rockies into the Dakotas this morning has set up 
strong low level flow in response with 55 kts around 850 mb on oax 
VAD wind profile as of 06z. This has generated quite a bit of 
convection overnight with MUCAPES still in 500 to 1000 j/kg range 
mainly west of Mississippi River. Based on laps soundings appears 
elevated convection is developing around 800 mb so main threat is 
some hail and actually storms have been weakening as they shift 
east...even with decent dynamic forcing for late August. Much needed 
rainfall will probably stay under an inch for nearly everyone. 


As short wave energy continues east...stronger surface front over 
northern plains will likely merge with nearby quasi-stationary 
boundary and then move east this afternoon. Short term model 
guidance supports this and given progressive nature would agree that 
main rain threat will be this morning. Have already dropped rain 
threat for most areas this evening and left central and southwest 
Wisconsin counties in for just early evening hours before return to 
dry spell. 


After that heights start to rise and ridge builds across central 
U.S. For what looks like quiet several days. Surface ridge settles 
in for seasonal temperatures and dry airmass. Given this and 
climatological favored time of year...River Valley fog possible a 
few mornings in there as well. 


Long term...Sunday through Wednesday 


Upper trough that develops across Pacific northwest this weekend 
prognosticated to eject east early next week but subtle differences in 
medium range guidance on track of trough. General trend will be for 
the wave to open up and lift northeast passing mainly north of US 
for days 6 and 7. Active tropics and parade of tropical storms into 
the south may also stall pattern somewhat or keep trough even 
further northwest of the area so some uncertainty. Small probability of precipitation in 
later period seem reasonable for this scenario. 


&& 


Aviation... 


Line of storms to work east of the taf sites through 09z...with 
scattered rain showers/isolated storms likely to be a threat to aviation 
through the morning at krst...and into the afternoon at klse. 
Probably the biggest concern will lie in the morning hours at both 
sites with the low clouds/mist hanging around after the rain ends. 
Upstream observations and satellite data showing stratus developing 
with IFR capabilities. This ahead of the cold front where weak 
convergence and boundary layer moisture is maximized. Current tafs 
carry MVFR ceilings and/or visibilities through the morning...and will 
monitor the need for IFR conditions based on how expansive upstream 
stratus field becomes. Would expect any vigorous thunderstorm 
activity today to remain south/east of the taf sites. As the 
afternoon wears on...frontal passage will bring shift to northwesterly winds 
and much drier airmass...with ceilings lifting/scattering out 
quickly. VFR conditions expected through tonight into much of the 
rest of the weekend with high pressure building in. 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...Shea 
aviation..........seb