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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
625 PM EST Sat Nov 21 2009 


Latest update...aviation... 


Synopsis...(304 PM EST Sat Nov 21 2009) 
a large high pressure system...centered over Michigan early this 
afternoon will slowly move east to the coast by Monday morning. That 
will put southwest lower Michigan in a southerly flow of air that 
will keep temperatures well above normal for this time of year. 
Light winds and mostly clear skies during this evening and Sunday 
evening will allow for fog to form after midnight tonight and Sunday 
night. A cold front and associated storm system will bring rain and 
cooler weather toward midweek. Some wet snow may mix in by Wednesday. 


&& 


Short term...(304 PM EST Sat Nov 21 2009) 
(tonight through Monday night) 


The main issue with this forecast package is the potential for fog 
tonight and Sunday night. 


With the high pressure system overhead this afternoon and the 
shortwave of last night to our east...skies were mostly sunny at 2 
PM. The combination of light winds tonight and mostly clear skies 
will allow for a considerable amount of fog by morning. Our fog plot 
procedure indicates dense fog across the area overnight. I could see 
a stratus deck forming by sunrise. 


The high moves to our east Sunday so a southerly flow will become 
a little stronger (mean wind surface to 1000 feet above ground level 240/04 knots at 
200 PM today compared to 150/08kt Sunday at 2 pm). Once the low 
clouds and fog burn off it should be a sunny day on Sunday. 


Winds will be stronger in the boundary layer Sunday night...still it 
would seem with the low level moisture increasing and nearly clear 
skies during the evening...fog and stratus would be a good bet 
again. 


Monday into Monday night a system will be passing to our southeast. 
That will bring in some middle clouds but not much else. 




&& 


Long term...(304 PM EST Sat Nov 21 2009) 
(tuesday through saturday) 
we didn/T change the forecast too much. European model (ecmwf)/GFS continue to show 
an intrusion of colder air into the Great Lakes next week. But the 
trend has been to wrap the cold air around the departing low with 
the result being the coldest air flowing southwest of the County Warning Area. Even 
so we still may see some wet snow during the end of the period. 


Rain should develop Tuesday in advance of an occluding low that will 
move from the plains toward Lake Michigan. Those showers will linger 
into Wednesday. A second stronger wave will kick the first one out 
and bring down the colder air from Canada. 800 mb temperatures will slowly fall 
from -2c to perhaps -5c from Wednesday through late Friday. The 
coldest air looks like it will be on Friday as the the upper low 
moves away so that is when we/ll have the greatest chance of seeing 
some snow. We/ll see a warming trend begin Saturday as the low pulls 
away. 


&& 


Aviation...(625 PM EST Sat Nov 21 2009) 
high pressure overhead tonight and clear skies and calm winds will 
result in fog forming. Expect visibilities will be falling to less than a 
mile late tonight. The fog will lift during the morning hours with 
VFR expected by Sunday afternoon. 


&& 


Marine...(304 PM EST Sat Nov 21 2009) 
even with the surface high moving east of the area by Sunday winds 
are not expected to become strong enough for small craft advisories 
to be issues (wave heights will stay below 4 feet). Area of fog 
are expected during the morning hours of Sunday and Monday. 


&& 


Hydrology...(304 PM EST Sat Nov 21 2009) 
no precipitation expected through Monday. No Hydro issues are 
expected. 


&& 


GRR watches/warnings/advisories... 
Michigan...none. 
Lm...none. 


&& 


$$ 


Synopsis: wdm 
short term: wdm 
long term: 93 
aviation: ostuno 
marine: wdm 
hydrology: wdm