128 
fxus63 kgrr 062017 
afdgrr 


Area forecast discussion 
National Weather Service Grand Rapids Michigan 
400 PM EDT Sat Sep 6 2008 


Latest update...all sections but aviation... 


Synopsis...(400 PM EDT Sat Sep 6 2008) 
an upper level disturbance over the Central Plains will move 
northeast and cross Southern Lower Michigan late tonight. This 
feature will bring an increased chance of rain after midnight and 
early Sunday morning... particularly south of Interstate 96. 


A frontal boundary will approach from the west Sunday night then 
stall from Southern Lower Michigan to the Central Plains on Monday. 
A low pressure system will form and intensify along this front 
Monday night... bringing another increased chance of rain to 
southern and central lower Michigan. 


&& 


Short term...(1150 am EDT Sat Sep 6 2008) 
(tonight through Monday night) 
recent model runs have been converging on a solution of a higher 
probability of rain showers late tonight and Sunday morning over the 
southern County warning forecast area. This is in response to strong upper level divergence and middle 
level fgen within a coupled jet structure aloft. This rain appears 
to move out of the area by 18z Sunday with dry weather likely 
thereafter. 


The next big weather maker appears to take aim on the area Monday 
afternoon and night. A frontal boundary will be situated from lower 
Michigan into the Central Plains during this time and will sharpen 
as 500 mb trough digs upstream. Models are not in great agreement on the 
timing... track... and strength of surface wave moving NE along the 
front. At this time prefer the European model (ecmwf) solution which has been very consistent. 


Temperatures/clouds/pops are very tricky on Monday since sharpening frontal 
boundary will probably be right over the County warning forecast area. This may lead to cool 
and showery conditions in the northern County warning forecast area and much warmer and dry 
conditions in the south. Will have probability of precipitation ranging from 30 percent in the 
southeast County warning forecast area to 50 percent in the northwest Monday... increasing to likely /60 percent/ 
over the entire County warning forecast area Monday night. Could be another good soaking 
rain although not nearly the quantitative precipitation forecast amounts we saw from Gustav. 


&& 


Long term...(400 PM EDT Sat Sep 6 2008) 
Tuesday through saturday) 
cooler air will be moving into the County Warning Area as the extended period begins 
Tuesday. Showers will end over the eastern County Warning Area Tuesday morning...then 
we/ll have a couple of dry days before the surface high moves east and 
another low heads toward lower Michigan. The south flow ahead of it 
will boost temperatures back into the middle 70s. We/ll keep thunderstorms and rain/rain showers in the 
grids Thursday and Friday as the front moves through and then the 
impressive closed low follows. Instability doesn/T look all that 
impressive...but some of the juice for convective development will 
be made up by the strong moisture convergence along the front. Dry 
weather expected Saturday. 


&& 


Marine...(400 PM EDT Sat Sep 6 2008) 
winds/waves should stay below Small Craft Advisory criteria through 
Monday. Monday night and Tuesday may turn very rough on Lake 
Michigan depending on intensity... timing... and track of 
developing/deepening low pressure system along the stall frontal 
boundary. 


&& 


Aviation...(131 PM EDT Sat Sep 6 2008) 
showers will diminish across the northern County Warning Area this afternoon. Much of the 
County Warning Area will see scattered cumulus this afternoon. An upper low will move across 
the region late tonight and early Sunday. This may generate showers 
across the County Warning Area. Taf sites should remain VFR. 


&& 


Hydrology...(400 PM EDT Sat Sep 6 2008) 
quantitative precipitation forecast amounts tonight are prognosticated to be a quarter inch or less... with 
maximum amounts expected to be south of a line from South Haven to 
Lansing. This will have little or no impact on Hydro. The system on 
Monday night looks to have the potential of producing widespread 
amounts of around one half inch... with local amounts of up to one 
inch possible. 


&& 


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


&& 


$$ 


Synopsis: Meade 
short term: Meade 
long term: 93 
marine: Meade 
aviation: 93 
hydrology: Meade