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fxus63 kgrr 181757 
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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
200 PM EDT Friday Jul 18 2008 


Latest update...aviation... 


Synopsis...(408 am EDT Friday Jul 18 2008) 
a frontal system will slowly drop southeast across the area through 
tonight. This front will gradually increase the chance of rain 
across the area as it encounters a warm and moist air mass ahead of 
it. The best chance of rain is expected to move in across southwest 
lower Michigan late in the day on Saturday and Saturday night as a 
wave moves along it. Showers and storms will remain possible through 
Sunday...before ending early next week. Cooler air will move in 
behind the front early next week. 


&& 


Short term...(1145 am EDT Friday Jul 18 2008) 
(tonight through saturday) 
focus of the forecast through the short term remains on the frontal 
boundary that remains nearly stationary over the Great Lakes. 


Believe the best threat for thunderstorm development later today (assuming 
sunshine emerges) will be in far northern County warning forecast area closer to the surface front 
and better surface convergence. Will feature the highest probability of precipitation this 
afternoon in Osceola and Clare counties. Updated grids earlier to 
remove thunder through 18z with only scattered/isolated rain showers 
across the central and northern County warning forecast area. Then after 18z will carry 40-50 
probability of precipitation in the NE corner of the County warning forecast area... and only slight chance probability of precipitation 
elsewhere. Deep layer shear values are somewhat respectable up in 
that area... around 30-40 knots... although instability may be a big 
limiting factor especially if clouds hold in for several more hours. 
Latest RUC prognosticated mu convective available potential energy at 21z does show a bullseye of 1500-2000 
j/kg in northern lower Michigan including the NE County warning forecast area... but only a few hundred 
joules elsewhere in the County warning forecast area. 


A few storms will remain possible tonight with the front in the 
vicinity. However the better activity looks to move in late in the 
day on Sat and Sat night. The front will sink to just south of the 
region by late Sat. A fairly decent wave is expected to move along 
this front...and should help to fire a decent complex of storms via 
the strong convergence due to the 35-40 knots low level jet ahead of the wave. We 
do not expect that there will be a lot of sun to destabilize the 
atmosphere. Most of the instability should result from the warm and 
moist advection. This will limit severe potential some. If the 
storms come in late enough...the instability will be even less of a 
player. Some wind will be possible with these storms with some 
decent 0-3km shear. 


The complex of storms should move out by Sun morning...likely 
leaving the front just south of the area. It will remain close just 
enough on sun to keep a small threat of showers/storms in for the 
County warning forecast area. 


&& 


Long term...(408 am EDT Friday Jul 18 2008) 
(sunday night through thursday) 
00z European model (ecmwf) is quicker with the drying trend for early next week than 
the 00z GFS and GFS ensemble mean. European model (ecmwf) has surface high building in 
and precipitation departing by 12z Monday while the GFS lingers precipitation 
through Tuesday. Will split the difference here and keep the going 
forecast...which has low chance probability of precipitation for Monday but dry for Monday 
night and Tuesday. 


Looks like fair and seasonably cool weather for Tuesday into 
Wednesday as Canadian surface high builds in. Then a warm front 
approaches from the southwest with overrunning precipitation encroaching on 
lower Michigan near the end of the extended period. 


&& 


Marine...(408 am EDT Friday Jul 18 2008) 
we have cancelled the Small Craft Advisory a little early as winds 
at all of the coastal marine observation sites have remained below 
20 knots through the night. The low level jet will be moving 
east...and winds aloft will be diminishing slightly. Next potential 
of small craft criteria winds would come late Sat and Sat night as 
the next low level jet moves through. 




&& 


Aviation...(200 PM EDT Friday Jul 18 2008) 
radar shows some scattered rain showers developing across the region. At this time believe 
ceilings will remain VFR. Expect some fog to redevelop overnight 
due to high dewpoints. Higher chance of rain will arrive at the end 
of the taf period as a frontal boundary sags south through lower Michigan. 




&& 


Hydrology...(408 am EDT Friday Jul 18 2008) 
axis of moist air mass will move overhead during the day with 
precipitable waters increasing to over 1.5 inches. This moisture 
axis will remain in place through early Sunday before drying out by 
Sun afternoon. We do not expect widespread heavy rainfall 
amounts...but any storms will have the capability of producing 
locally heavy rainfall. The most widespread rain across the entire 
County warning forecast area should come late Sat and Sat night as the next significant wave 
moves along the front. 


&& 


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


&& 


$$ 


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