204 
fxus63 kgrb 062000 
afdgrb 


Area forecast discussion 
National Weather Service Green Bay WI 
300 PM CDT Monday Oct 6 2008 


Short term...tonight and Tuesday. Main forecast concern remains timing of 
next precipitation event due to arrive Tuesday morning (central) and Tuesday 
afternoon (east). 


The 19z msas surface analysis indicated an area of high pressure over the 
Quebec/Ontario border...low pressure over southeast North Dakota and 
central Kansas...and a cold front connecting the two areas of low pressure. There 
was also a warm front which stretched from central Minnesota to southern WI. Band of 
warm air advection precipitation had lifted north and cleared almost all of NE WI. 


Models are consistent in bringing a longwv trough across the plains 
tonight while both an upper ridge and surface hi pressure reside over the eastern 
Great Lakes. A steady southerly 30 to 40 knots low level jet will continue to 
Pump Gulf moisture northward into the upper Midwest/western Great Lakes...although some 
of this moisture influx may be disrupted by thunderstorms over the deep south. 
Focus for precipitation tonight will be in the vicinity of the cold front which is 
prognosticated to reach central Minnesota/western Iowa by 12z Tuesday. Lack of forcing and a 
slight drying of the atmosphere from the hi pressure to our east...should keep 
precipitation away from NE WI. Combination of a 30 knots boundary layer wind and 
middle/hi clouds streaming ovrhd will help keep temperatures up once again tonight. 


The longwv trough slowly creeps eastward on Tuesday as the eastern Great Lakes upper 
ridge hold firm. The cold front is forecast to only reach extreme western WI by 
00z Wednesday...however persistent warm air advection and upper diffluent flow aloft 
should bring a band of showers/isolated thunderstorms along and ahead of the 
fnt. There are some model timing differences with the faster 
GFS/UKMET versus the slower NAM/Gem. Pretty much split the 
difference which turned out to be close to the European model (ecmwf) solution. Previous 
forecast already had likely probability of precipitation for central WI and chance probability of precipitation in the east 
which still looks good. Despite clouds and approaching precipitation...mild 
start to the day will allow temperatures to reach into the lower to middle 60s. 


Long term...Tuesday night through next Monday...the main forecast 
concerns are precipitation trends and probability of precipitation for the midweek period...and 
for the weekend/early part of next week. 


Cold front and associated upper trough will move through the forecast area 
Tuesday night into early Wednesday. Although the front and upper 
system are both expected to weaken as they shift east...the 
impressive slug of Gulf moisture that has advected north in 
advance of the front supports an increase in probability of precipitation for Tuesday 
night. Based on the location of the cold front and upper trough 
axis...any lingering precipitation should be confined to NE/ec WI on Wednesday 
morning. 


Pacific high pressure will bring mild and dry conditions to the 
region from Wednesday afternoon through at least Friday. 


Have continued the trend of delaying precipitation arrival and increasing 
temperatures over the weekend...as the medium range model trends 
offer support for the more amplified pattern depicted by the 
European model (ecmwf). The European model (ecmwf) has been very consistent over the past several 
days...so despite hpc's concern that it's solution is a bit extreme... 
they have trended the extended forecast more in that direction. The 
GFS continues to be inconsistent with the timing of a significant 
low pressure system and cold frontal passage over the weekend. 
Have opted to focus our highest probability of precipitation on Sunday night and Monday... 
which is consistent with the frontal timing on the European model (ecmwf). 
&& 


Aviation...lingering MVFR ceilings over northern WI will lift by early 
evening...with VFR conditions expected over the region for the overnight 
hours. Have added some wind shear later tonight and surface winds weaken...but 
boundary layer winds remain in the 30 to 40kt range. VFR conditions to 
persist into Tuesday morning...however the approach of a cold front and its 
associated showers will bring MVFR ceilings back to central WI by early 
afternoon...and eastern WI by late afternoon. 
&& 


Marine...a Small Craft Advisory for the Lake Michigan zones remains 
in effect until 06z Wednesday. Persistent southeast winds of 10 to 20 kts 
with higher gusts will increase waves along the coast to 3 to 6 feet. 
&& 


Grb watches/warnings/advisories... 
none. 
&& 


$$ 
Kallas/kieckbusch