907 
fxus63 kgrr 282345 
afdgrr 


Area forecast discussion 
National Weather Service Grand Rapids Michigan 
745 PM EDT Thursday Aug 28 2008 


Latest update...aviation... 


Synopsis...(328 PM EDT Thursday Aug 28 2008) 
a weak cold front will come through southwest lower Michigan tonight 
with scattered showers and isolated thunderstorms. Most locations 
will likely not see significant rainfall from this event. Once the 
front is through high pressure from the Central Plains will move 
into the area and influence the weather through Labor Day. A weak 
cold front from Canada will try to come south Saturday but have 
little Success reaching lower Michigan. 


&& 


Short term...(328 PM EDT Thursday Aug 28 2008) 
(tonight through Saturday night) 
the cold front continues to push east across Wisconsin toward lower 
Michigan. However the upper level jet core is passing well north of 
lower Michigan through southern Ontario tonight. That puts southwest 
Michigan in the right front quadrant of the jet... and implies upper 
level convergence. That by itself would suppress convection on the 
front. Beside that... there is the old mesoscale convective system that has pushed south 
toward stl at 18z. That is blocking the inflow over lower 
Michigan...ahead of the front. Beside all of that there is really no 
low level jet tonight to fuel the storms. Given all of that negative 
forcing for convection and the weak lapse rates and marginal Li 
support... I am less than excited about the threat for convection 
tonight. Still there is a front with surface convergence and over 
the southern County Warning Area there is even some shallow warm advection... plus 
on top of all that the precipitable water values are near 1.8 inches... more than 
enough for a decent rain event. Bottom line I have put 40 to 50 percent 
probability of precipitation over most of the County Warning Area tonight. 




Once the front is through...before 12z Friday... high pressure 
builds in from the plains in conjunction with rising heights. So for 
the most part mostly clear skies... dew points in the 50s will lead 
to large diurnal temperature ranges. That is warm days and cool 
nights through Saturday night. A northern stream short wave 
trailing the one with the cold front tonight will push yet another 
cold front toward Michigan on Saturday but the rising upper level 
heights will kill any chance of that having any impact on southwest 
Michigan weather. 


&& 


Long term...(251 PM EDT Thursday Aug 28 2008) 
(sunday through thursday) 
building upper ridge is still poised to gradually move directly over 
the state by Monday with Gustav in the Gulf of Mexico and strong upper 
system moving onshore over the Pacific northwest. This ridge will only 
slowly slip east of the area by the middle of the week. 500 mb heights 
of 595 dm along with h850 temperatures approaching 20 c will allow for 
temperatures to approach 90f...with the best shot Monday through Wednesday. GFS has 
been consistent in bringing the next front through during the day on 
Wednesday. The GFS just looks like it is breaking down the ridge too 
quickly...and we have kept Wednesday dry for now. The Euro looks more 
realistic in bringing the front through Wednesday night and Thursday. 


&& 


Marine...(328 PM EDT Thursday Aug 28 2008) 
due to the weak nature of the cold front crossing the region 
tonight...there will not be enough cold air advection or pressure 
gradient behind the front to create strong enough winds for Small Craft Advisory 
criteria. Thus winds and waves will remain below Small Craft Advisory criteria. 


&& 


Aviation...(745 PM EDT Thursday Aug 28 2008) 
the combination of light winds and high relative humidity values 
should lead to increasing fog and haze through the night. Some IFR 
appears possible mainly for kazo and kjxn. Will need to monitor 
other taf sites closely. The convection developing in Wisconsin is 
forecast to weaken as it tries to move into Michigan overnight. I 
did keep the cumulonimbus wording in some of the tafs. Drying is forecast 
for Friday with conditions improving to VFR by noon. 


&& 


Hydrology...(328 PM EDT Thursday Aug 28 2008) 
given the more than feeble nature of the cold front convection over 
lower Michigan tonight...little question there are no Hydro issues 
in the near term. We may have to start being concerned with drought 
issues if this pattern persists. 


&& 


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


&& 


$$ 


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