Weather

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Area forecast discussion 
National Weather Service La Crosse WI 
342 PM CST Monday Jan 5 2009 


Short term...today through Friday 


Main forecast concerns this period involve precipitation chances 
for Tuesday night/Wednesday and then with precipitation moving in Thursday 
night/Friday. 


Upper level shortwave trough currently over the northern rockies 
will push southeast across the upper Midwest Tuesday 
night/Wednesday. Deep moisture is limited as soundings/cross sections 
in these areas show saturation only up to around 700mb during the day 
Wednesday. However...as much of that layer is in the dendritic 
zone and then along with some large scale lift associated with 
the shortwave...did opt to increase precipitation chances a bit on 
Wednesday. 


The next weather maker moves in Thursday night/Friday as another 
shortwave trough moves through the northwest flow across the area. 
Large area of low pressure develops over the plains Thursday night 
ahead of the shortwave. As the whole system progresses toward the 
upper Mississippi River valley region...warmer and more moist air 
will come northward and should bring about deep column saturation 
during the overnight hours. 05.12z operational European model (ecmwf)/GFS 
showing the strongest qg forcing across northern Minnesota/northern 
Wisconsin. These signals along with warm air advection and 
isentropic upglide on 280k surface indications that the 
precipitation should be focused from around central Minnesota into 
southern Wisconsin. Something to consider in upcoming shifts will be 
the strength of the warm layer as 05.12z operational GFS brings 
enough warm air north to around Interstate-90 that would suggest a 
mix of snow/sleet for a few hours Friday morning. As this was the 
first and only model run being this warm...did not have the 
confidence to add a mixture into the forecast and...decided to stick 
to just snow for now. 




Long term...Friday night through Monday 


Snow should move east of the area Friday night...leading to the next 
concern being temperatures for Saturday through Sunday. 05.06z mref 
plumes strongly indicating colder solution for Saturday/Sunday. All 
but 2 or 3 members showing little or no rise in surface temperatures 
through the day Saturday with mean high at lse Saturday of 5f. 
Operational 05.00z European model (ecmwf) showing cold air advection across the area 
behind the cold front that moves through Friday/Friday night. 
05.00z European model (ecmwf) indicates 925mb temperatures at or below -12c... 
while 05.12z operational GFS even colder with 925mb temperatures 
across the forecast area from -17c to -23c. Did start trending these 
days cooler but may need to go colder yet...which will need to be 
watched by upcoming shifts. 


Next feature that will come into play is shortwave energy moving 
across the upper Midwest for Sunday night/Monday. 05.00z European model (ecmwf) a bit 
weaker and more progressive than 05.00z/05.12z GFS with this 
feature...which did produce stronger forcing/more quantitative precipitation forecast for this time 
frame. As this is quite far out in the forecast and details are 
uncertain at this time just added light precipitation chances for 
Monday. 


&& 


Aviation...today and tonight 


High pressure over ill will continue to influence the region as it 
slips east overnight. 500 mb shortwave trough will spin across the 
northern plains tonight...moving over the upper Mississippi River 
valley on Tuesday. Krst/klse can expect an increase in middle/high level 
clouds starting Tuesday morning...with a thickening/lowering of the 
ceilings Tuesday night. MVFR conditions could result. -Sn with the 
shortwave looks to stay to the north. South winds will decrease some 
for tonight. 


&& 


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


$$ 


Short/long term...Brooks 
aviation..........rieck