930 
fxus63 kmkx 172022 
afdmkx 


Area forecast discussion 
National Weather Service Milwaukee/Sullivan WI 
322 PM CDT Wednesday Mar 17 2010 


Short term... 


Tonight and Thursday...forecast confidence...high 


Upper low exiting southwest Missouri area then phasing with the 
southeast upper low on Thursday. Northern stream short wave from 
the northern rockies to north of Lake Superior...with west 
southwest flow over the upper Midwest. Weak pressure gradient at 
the surface tonight. Dew points have dropped with afternoon 
heating and mixing. Lake breeze has reached around 25 miles inland 
bringing dew points up and temperatures down with lake air. 


With low dew points...not expecting much in the way of 
fog...except in the river valleys. However winds will start to 
increase out of the west-southwest Thursday morning. West winds will inhibit lake 
breeze development...so expecting another mild day. 


Model soundings show decent mixing once again...and dew points will 
drop again. Fire weather conditions will be more of a concern 
with the winds picking up. 


Friday through Sunday...forecast confidence...medium 


Friday...upper trough swinging across southern Canada to the 
Central Plains...aided by right entrance region of polar jet. 
Meanwhile...western portion of polar jet diving south and meeting 
up with zonal subtropical jet producing potent shortwave that will 
head northeast towards the Ohio Valley region by Sunday morning. 
Model trends on the European model (ecmwf) have been more southward and slower. NAM 
also trends more toward European model (ecmwf). 


Elongated frontogenetic zone over the Midwest stretching from Kansas 
to WI will set up by Friday night and Sat on NAM...sinking a bit 
farther south on GFS by Saturday. 


European model (ecmwf) diverges from GFS...keeping the closed upper low farther 
south over western Kentucky/Tennessee Sunday. GFS has more of a 
trough axis. Resultant stronger surface low spreads more precipitation 
into the southeast. 


Precipitation type suggests rain initially...then cooling temperatures brings 
rain snow mixture then mainly snow. Will lower snow amounts since 
quantitative precipitation forecast in the colder areas of south central Wisconsin appears to be 
less than earlier expected. Also boundary layer temperatures will be 
rather warm. Snow will be wet and melt somewhat on roads unless 
convection occurs. 


Long term... 


Monday and Tuesday...forecast confidence...medium 


Zonal flow over the upper Midwest. Surface low moves across 
southern Canada later Sunday. Prefer the European model (ecmwf) more northern track on 
this. Then high builds over the western Great Lakes Monday...and 
over the eastern Great Lakes by Tuesday. 


Wednesday...forecast confidence...medium 


Both GFS and European model (ecmwf) similar in bringing shortwave into the Central 
Plains late Wednesday. Resultant surface low develops over the 
Southern Plains. Some warm air advection clouds and light 
precipitation possible by Tuesday night and Wednesday. 


&& 


Aviation... 
Fr conditions expected through Thursday. High pressure 
moving south through the plains will continue to bring quiet 
weather. Light winds early tonight will gradually increase as they 
shift from the southwest to west later tonight into Thursday. West 
southwest wind gusts to 22 knots possible Thursday afternoon...with 
daytime heating and robust mixing of low level winds to the surface. 
Scattered cirrus clouds early on Thursday become broken by late in 
the day. 


&& 


Marine... 
the cooler nearshore waters of Lake Michigan...with 
surface temperatures in the upper 30s...should support an inversion 
over this area on Thursday. This should suppress any 22 to 25 knot 
gusts trying to mix down to the surface. Thus...am not anticipating 
Small Craft Advisory level winds for Thursday. 


Small Craft Advisory level winds and waves are expected at times 
Friday night through Monday...as two separate low pressure systems 
move through the region. For now...will just mention potential in 
hazardous weather outlook. 


&& 


Fire weather... 
higher dew points in the lower to middle 30s should 
shift into the area later tonight and Thursday. This...combined with 
highs on Thursday in the lower to middle 60s...should yield minimum 
relative humidities in the middle 30 percent range. Breezy west 
southwest winds of 10 to 20 miles per hour are expected during the afternoon. 
Further mixing out of the dew points are possible...though not as 
much as this afternoon given the higher values expected. 


&& 


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


$$ 


Short/long term...06/hentz 
aviation/marine...08/wood