044 
fxus63 kmkx 200826 
afdmkx 


Area forecast discussion 
National Weather Service Milwaukee/Sullivan WI 
326 am CDT Wednesday Aug 20 2008 


Forecast focus on fog this morning...precipitation chances 
Thursday through Saturday. 


Latest water vapor imagery indicated the axis of an upper level 
ridge over western Ontario Canada. The ridge was bounded by two 
upper level troughs...one upstream approaching the Pacific 
northwest...and another downstream over far eastern Canada. A 
cutoff upper level low was located over northern Texas. At the 
surface...high pressure was located over Lake Huron...with low 
pressure over the northern rockies. 


Short term...today and tonight... 


Patchy fog has developed over portions of the forecast area 
overnight...with light winds and dew points in the upper 50s to 
lower 60s. Will continue to mention patchy fog in the early 
morning hours...with areas of fog in the Wisconsin River Valley. 
The fog and any low stratus clouds should then dissipate with 
daytime heating by middle morning. 


High pressure will slowly move away from the region today and 
tonight. Area forecast soundings show some weak instability below 
700mb developing with peak heating this afternoon across the 
western counties. Local high resolution 4km WRF model with GFS 
boundary layer initial conditions does generate some light 
scattered reflectivity across this area. 


Weak vorticity maximum moves northward today...keeping the area 
out of any appreciable upward vertical motion. An isolated rain 
shower may develop within expected cumulus field this afternoon 
across the western counties...but given low confidence will not 
mention in forecast. 


Onshore winds will continue to keep Lakeshore locations somewhat 
cooler than inland today...with 70s near the lake versus lower to 
middle 80s inland. 


Long term...Thursday through Tuesday... 


Short term models in good agreement with bringing cutoff low over 
northern Texas northeast as a open shortwave late Thursday through 
Friday. 30 knot plus low level jet points into the area late 
Thursday and Thursday night. Surface winds then shift southward on 
Friday...allowing for higher dew points in the upper 60s to spread 
across the area. So...have increased probability of precipitation a bit on Thursday 
afternoon...and kept them similar for Thursday night and Friday. 


Models also in pretty good agreement for cold frontal passage late 
Friday night and Saturday. Decent cape values of at least 1500 
j/kg seen at kmsn around 18z Saturday...with modest deep layer 
0-6km shear of around 30 knots. Will continue the probability of precipitation for Friday 
night and Saturday. 


European model (ecmwf) and GFS both then bring Canadian high pressure into the area 
for Sunday and into early next week. This feature should bring 
quiet weather back to the area. 


&& 


Aviation... 


88-d vwp appear to be overdoing amount of wind in the low levels 
below 1k. Blue River profiler showing light winds less than 8 
knots through 10k feet. Tamdar sounding from late evening vicinity of 
kmke had light winds up to 1k with stronger winds above this layer. 
Slight boundary layer mixing and lack of precipitation over past several 
days counter balancing lingering high dewpoints around 60 to 
produce patchy fog with visibilities mostly in the 1 to 3 mile 
range...however a few locations have been dropping to vlifr visibilities. 
Best chance for IFR or lower visibilities at kmsn/kenw with lighter surface 
winds. Also need to watch for potential low stratus redevelopment 
in slight mixing. Best threat for St redevelopment in south and 
west near better late night low level convergence...however St having 
difficulty expanding to the west perhaps due to dry air intrusion 
in low levels from east. Few-scattered SC likely later this morning and afternoon 
with increase cirrus from the south later tonight. 


&& 


Mkx watches/warnings/advisories... 
WI...none. 
Lm...none. 
&& 


$$ 


Short/long term...08/wood 
aviation/marine...11/mbk