Weather

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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
1146 PM EDT sun Sep 7 2008 


Latest update...aviation... 


Synopsis...(400 PM EDT sun Sep 7 2008) 
a cold front will move into lower Michigan from the west tonight 
then stall from Southeast Michigan to Missouri on Monday. A low 
pressure system will develop along the front in the Central Plains 
Monday then intensify as it moves northeast. Widespread rain can be 
expected from this system Monday afternoon and night with cool 
conditions following Tuesday. 


&& 


Short term...(1055 PM EDT sun Sep 7 2008) 
(tonight through Tuesday night) 
a cold front continues to March across Wisconsin this evening. It 
will pass across western lower Michigan between 06-12z and be accompanied 
by a few showers. Will tweak the forecast to include the showers 
reaching a bit further inland...however it still appears most areas 
south of i96 will remain dry. Will also remove the mention of 
thunder as the instability was quickly waning this evening. The 
front and most of the showers will be out of the County Warning Area by 12z. 


The more southern track of the surface low and maximum quantitative precipitation forecast axis shown by both the 
European model (ecmwf) and GFS is being favored over the more northern NAM solution. Will 
bring likely/categorical probability of precipitation into much of the County warning forecast area after 18z 
Monday... with categorical probability of precipitation for all areas Monday night. Have 
included a chance for thunder Monday night due to strong upper 
divergence and middle level fgen forcing... but not much concern for 
severe weather considering the favored southern track of the surface low. This 
should keep US in low level NE flow for most of the event and keep 
any severe weather threat south. 


System is very quick to lift out to the NE on Tuesday. There may be 
some lingering cold air advection/lake enhanced showers early Tuesday... but 
surface ridging is quick to move in and decreasing cloudiness should 
follow in the afternoon. Tuesday night looks very chilly as the 
center of the high builds in. Wouldn't even rule out some patchy 
frost in the far northern and NE portion of the County warning forecast area. 


&& 


Long term...(400 PM EDT sun Sep 7 2008) 
(wednesday through sunday) 
long term portion of the forecast will begin on Wednesday morning with high 
pressure almost directly overhead. This ridge will gradually build 
east of the state by Thursday morning...and allow return flow to set up. 


Upper trough expected to dig southeast from western Canada in the Tuesday/Wednesday time 
frame will be the next feature of note for SW lower Michigan. Prior 
to the 12z run...all models except the GFS were quite progressive 
with the trough. They were bringing the trough through late 
Thursday/early Friday while the GFS was amplifying it a bit more and 
bringing it in later. The 12z GFS now has come into line with the 
others. We will maintain the chance of precipitation Thursday through Friday morning. 


A break in the precipitation will then be found late Friday as ridging slips in 
for a short stay. 00z Euro was bringing in the next wave the for the 
day on Sat and into sun...allowing for a chance of precipitation. New GFS is 
coming into line with this...just bringing the precipitation in on sun. We 
will go with a chance pop for next weekend for now and fine tune as 
agreement develops in the models. If the 12z GFS is correct...we 
will have a shot at some remnant moisture from Ike late next 
sun/Mon. 


&& 


Marine...(400 PM EDT sun Sep 7 2008) 
latest model guidance is increasing the winds with the passage of 
the cold front tonight... and it looks like waves will build to 
Small Craft Advisory criteria later tonight lingering into early 
Monday morning. 


The more southern track of the deepening surface low should keep the low 
level flow more northerly on Monday night. This should limit the 
highest waves to areas south of Holland Monday night into Tuesday... 
although small craft advisories may still be needed for all areas. 


&& 


Aviation...(1146 PM EDT sun Sep 6 2008) 
the weak cold front will cross southwest lower Michigan during the 
early morning hours of Monday. The best dynamical support is north 
of the GRR County Warning Area...where the jet dynamics are best. The most middle level 
instability stays north of the County Warning Area too. Thus I see mostly middle clouds 
cross the County Warning Area with the front. The 850 mb temperatures are cold enough for 
marginal lake instability... we will have to watch for that but the 
moisture was much better last night at middle levels then it is 
tonight. So expect a mostly dry night. 


The rain from the fgen / isentropic lift event Monday night will 
bring IFR conditions across the County Warning Area by 03z. 




&& 


Hydrology...(400 PM EDT sun Sep 7 2008) 
am using HPC quantitative precipitation forecast guidance in the grids which has total amounts for 
this evening ranging from 0.30 around Ludington to around 1.00 along 
the I-94 corridor. If it plays out like this there should not be too 
many Hydro concerns since the heaviest rain would fall south of 
where the Gustav heavy rain fell. A few urban and small stream type 
Hydro issues could develop Monday night and linger into Tuesday 
morning. 


&& 


GRR watches/warnings/advisories... 
Michigan...none. 
Lm...Small Craft Advisory St Joe to Manistee from 10 PM tonight 
through Monday morning. 


&& 


$$ 


Synopsis: Meade 
short term: Meade 
long term: njj 
marine: Meade 
aviation: wdm 
hydrology: Meade