136 
fxus63 kgrb 230920 
afdgrb 


Area forecast discussion 
National Weather Service Green Bay WI 
320 am CST sun Nov 23 2008 


Synopsis...large scale flow across noam has become relatively flat. 
Reamplification of the old eastern trough will occur early in the forecast...but 
more important to the weather across the area will be the increasingly split 
nature of the flow that develops during the rest of the forecast period. 
Such a pattern favors temperatures near or maybe even a little above normal. 
Best chance of precipitation will be with system crossing the forecast area 
early...with little chance of widespread sig precipitation once the forecast area 
gets caught between the main branches of the developing split flow 
regime. Starting to get indications of that reconsolidation of the 
flow and a major amplification will occur beyond the end of the forecast 
period. && 


Short term...tda/tngt/Mon. Various cloud decks scattered across the region this 
morning. Of most significance will be the lower clouds that will probably 
hang on in the north much of the day. For that reason...stuck with 
colder temperatures there despite southwesterly low-level flow. Traj supported 
getting maximum temperatures near 40 over the southeast part of the forecast area...but that 
will only happen if we Don/T get stuck with too many clouds there as 
well. 


Shortwave moving in from the west will start to sharpen tonight as second shortwave 
digs southeast from Canada and begins to phase with the lead system. Models 
pretty consistent in generating precipitation...focused over the southeastern part of 
the forecast area. The GFS and European model (ecmwf) were faster with the forcing... 
while the NAM was the slowest. The sref mean was a bit slower than 
the European model (ecmwf)/GFS but quite a bit faster than the NAM and looked like a 
good compromise. Precipitation type could also be an issue. Although the 
GFS/European model (ecmwf) would suggest almost all snow...the sref products gave 
considerable support to warmer NAM solution. That also made sense 
given the warmer forecast maximum temperatures over the southeast part of the forecast area 
today...climatology...and the fact that we will have southwesterly low-level 
flow as the system approaches. Adjusted grids to delay the onset 
of precipitation a bit...and carry more of a mix later into the night over 
the southeast part of the area. Also bled precipitation a bit longer into Monday 
morning. 


Second shortwave looks very impressive on satellite...and will be digging southeast 
and should reach the northwest part of the forecast area by Monday afternoon. Upped 
probability of precipitation and went with scattered shsn there. 


Long term (mon night through fri)...main forecast concerns appear 
fairly minor at this point in the game...and revolve around lake 
effect snow accumulations Monday night into Tuesday. Models continue to 
advertise the departure of a deep occluded low early to middle of 
next week from the central to eastern Great Lakes. 
However...agreement breaks down rapidly Thursday Onward with 
amplification of split flow across North America. Although medium 
range operations models each offer their own set of 
discrepancies...the 12z ecwmf looks to have the most support from 
the 12z NCEP ensemble members (for whatever thats worth). 
Confidence is low on Friday. 


Monday night and Tuesday...northern and southern stream waves phase 
together and become vertically stacked Monday night across the 
south-central Great Lakes. Nearly all of the middle-level forcing will 
have exited NE Wisconsin at the start of the evening with the -divq 
to the east...and fgen along the shear axis to the west. 
However...will still have lingering diurnal instability initially 
for a chance of flurries and light snow showers before they diminish 
by mid-evening. Better chances of snow will reside across far 
northern Wisconsin in the snow belt. Over-lake instability is not 
the best (but sufficient)...with enough moisture poking into the 
dendritic growth zone and favorable low level wind trajectories for 
up to a couple inches during the evening over Vilas County. Moisture 
thins out overnight as the upper low pulls away and subsidence 
increases...all pointing to a diminishing trend in the snow showers 
with another half inch possible. Outside of a few lingering snow 
showers or flurries in Vilas County on Tuesday...will see the clouds 
gradually break apart with the incoming surface ridge axis and drier 
low level air. Clouds will hang on the longest over the NE forecast 
area where thermal troughing is most persistent. Highs in the lower 
to middle 30s. 


Tuesday night Onward...upper low pivots around the eastern Great 
Lakes through Thursday before finally lifting into Quebec on 
Friday. This will leave northeast Wisconsin within northwest flow without 
any significant clippers to impact the region. Additionally...850mb 
temperatures will also moderate through Thursday as warmer air 
invades from the west. Things get a little more interesting heading 
into Friday when a potent clipper dives into the northern Great 
Lakes sending a cold front our direction. Models do not have a good 
handle on this wave so will make very little changes until a better 
game plan is developed. All in all though..traveling across the 
upper Midwest looks fine Wednesday and Thursday unless you're 
heading east towards the upper low into Michigan. Highs near normal 
Tuesday through Friday. 
&& 


Aviation...MVFR ceilings should persist across the north for much of the day. 
Need to watch area of IFR ceilings to the northwest...but right now expect that 
to lift around the forecast area to the north. 
&& 


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


$$ 
Skowronski/mpc