498 
fxus63 kmkx 182045 
afdmkx 


Area forecast discussion 
National Weather Service Milwaukee/Sullivan WI 
345 PM CDT Thursday Mar 18 2010 


Forecast focus on amount and type of precipitation for late Friday 
into Saturday. 


Short term/tonight through Sunday... 


Tonight and Friday...high confidence. 


Clear skies through the early evening...with clouds increasing northwest to 
southeast after 01z. Surface trough/cold front to sag into southern WI overnight 
..but precipitation will hold off until better moistening and isentropic 
lift/frontogenetic forcing move in late Friday afternoon/evening. 
Temperatures tonight will not drop off as SW/west winds and increasing 
clouds prevent strong radiational cooling so followed a consensus of 
MOS guidance. Early afternoon highs Friday then falling with surface 
cold air advection. 


Friday night and Saturday...medium confidence. 


Models honing in on a narrow band of precipitation developing and moving up 
along tight baroclinic zone over southern WI/northern Illinois. Temperature profiles and 
forecast soundings indicate precipitation will fall initially as 
rain...possibly starting in the far west as early as late 
morning...then spreading east in the afternoon. The rain will mix 
with snow in the evening...and turn over to all snow after midnight 
Friday. Though models are bringing 0.25 inch quantitative precipitation forecast very close to the 
southern WI border...along with strong frontogenetic forcing brushing the 
far south...slope of frontogenesis is shallow and little sign of 
instability aloft. Omega maximum is below dendritic growth zone which is 
slow to moisten. Expect the heavier snows to stay south of the 
border...with 1 to 3 inches over southern WI...mainly along and south of 
a Lone Rock to Watertown line...with the higher snow amounts over 
the SW portion of the County Warning Area which cools early enough to capture some 
of the stronger forcing before it slides southeast out of the state. 


Warmth of paved surfaces will prevent much accumulation on roads and 
sidewalks...with grassy surfaces collecting some snow. Friday night 
temperatures will hold up above freezing prior to midnight...allowing for 
the mainly rain...then falling from northwest to southeast leading to near sunrise 
lows in the upper 20s to lower 30s. 


Light snow ends by 18z Saturday across the northwest half of the 
County Warning Area...lingering in the southeast until late in the afternoon. Little 
additional accumulation is expected...though the far southeast could see 
1/2 to 1 inch before snow ends...again mainly on grassy areas. 


Some late day sun may get northern locations that receive little to 
no snow accumulation may reach low 40s Saturday afternoon...with 
upper 30s in the south. .. 


Long term /Sunday night through Thursday/...low confidence. 


Models agree that Sunday night through Tuesday will be dry with 
short wave ridging between strong closed low to the south and open 
wave over southern Canada...then stray with remainder of extended. Will 
follow the HPC European model (ecmwf)/European model (ecmwf) ensemble blend which keeps Tuesday short 
wave and weaker surface reflection...as well as better chance for 
precipitation to the north of the County Warning Area. Will recognize frontal passage...and 
potential of GFS stronger short wave...and have slight chances for 
Tuesday night and Wednesday. Dry Wednesday night and Thursday as 
high noses in. 


Cool easterly flow holds temperatures down in the eastern 1/3 of County Warning Area 
Monday...and a chance at upper 40s/50 before a lake breeze limits 
highs Tuesday along the lake. Went optimistic on Wednesday 
highs...but more clouds and precipitation than expected will hold them back. 
+4 925mb temperatures will battle north to northeast winds with a struggle 
to reach 50 inland and 40s along the lake. ... 




&& 


Aviation...VFR conditions expected through Friday. Gusty west 
southwest winds will subside by sunset...with loss of daytime 
heating. Light southwest winds are then expected until cold frontal 
passage between 14z Friday at kmsn...and 17z at the eastern taf 
sites...when they shift northwest. Scattered middle level clouds 
expected through 06z...before becoming broken to overcast. 5000 foot 
overcast deck should then develop by 21z across all sites. 




&& 


Marine...Small Craft Advisory level winds and waves are expected at 
times Friday night through Saturday evening. Brisk north to 
northeast winds to 25 knots are possible Friday night and 
Saturday...in the wake of a cold front. High waves are expected with 
the onshore winds through Saturday night. 




&& 


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


$$ 


Short/long term...09/rem 
aviation/marine...08/wood