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fxus63 kgrr 051835 
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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
230 PM EDT Sat Jul 5 2008 


Latest update...all sections... 


Synopsis...(230 PM EDT Sat Jul 5 2008) 
high pressure overhead will move slowly east through Sunday. Warm 
and dry weather will continue into Sunday. A low pressure system 
will move 
into the region on Monday and persist through Tuesday. Warm humid 
air and numerous showers and thunderstorms will likely occur Monday 
night into Tuesday. Canadian high pressure will bring cooler and 
drier air for Wednesday into Thursday. 
&& 


Short term...(230 PM EDT Sat Jul 5 2008) 
(today through sunday) 
forecast concerns are minimal today but deal with convective 
potential late Monday. 


Expect tonight will be similar to last night except about 3 to 5 
degrees warmer. Good radiational cooling...light winds...and wet 
ground should produce patchy fog again. Sunday...warming trend 
continues with high reaching lower 80s. Dewpoints start an upward 
trend with S flow on back side of exiting high pressure. 


Kept chance probability of precipitation for early Monday morning - expectation is for 
weakening convection moving across lake associated with warm front. 
Trend has been slower so probability of precipitation a bit lower than previous package. 


&& 


Long term...(336 am EDT Sat Jul 5 2008) 
(monday through friday) 
few showers and thunderstorms are anticipated Monday and it will 
continue to become much more humid as dew points climb through the 
60s to near 70 degrees by Monday evening. Convection will become 
more likely Monday night as elevated instability continues to 
increase along with the continued influx of Richer low level 
moisture in continued SW flow. We are also concerned that a 30-40 knots 
low level jet will trigger mesoscale convective system development off to our west which could roll 
into our County warning forecast area late Monday night. 


Our best chance for convection will come Tuesday. Forecast soundings become 
nearly saturated by late Tuesday and precipitable water values will ramp up 
significantly to 2-2.5 inches out ahead of the approaching and 
intensifying low pressure system. This system will certainly need to 
be monitored closely for severe weather potential Tuesday. Potential for 
heavy rain is also quite high... which will likely result in some 
Hydro issues. 


High pressure will build in behind that system for middle to late 
week... resulting in fair and cool weather. Based on latest medium range 
guidance and trends... we lowered the forecast maximum/min temperatures somewhat 
for Wed-thur. Dry weather and a moderating trend of temperatures is anticipated 
late in the week into next weekend as the 500 mb ridge axis builds in. 
In fact temperatures should average 5 to 10 degrees above normal by Saturday. 


&& 


Marine...(230 PM EDT Sat Jul 5 2008) 
no concerns through Sunday. Waves increase with S flow Sunday night 
into Monday. Threat of showers and thunderstorms beginning Monday 
through Tuesday evening. Areas of fog as well Monday night. 


&& 


Aviation...(230 PM EDT Sat Jul 5 2008) 
VFR conditions except for patchy fog between 09z and 12z Sunday 
morning. Some light chop for small aircraft along lake breeze front 
this afternoon. The front will be roughly 10 inland and parallel the 
coast. Outlook - VFR on Sunday with increasing S winds. 


&& 


Hydrology...(230 PM EDT Sat Jul 5 2008) 
rivers slowly receeding from last weeks event. New concern for heavy 
rainfall Monday into Tuesday with next frontal systems. Precipitable waters  of 
above 2 inches for 24-36 hour period and a low level jet of 30 to 40 
kts will intersect a frontal boundary resulting in a potential 
rainfall of locally several inches. Still plenty of spread in nwp 
guidance as to where the frontal boundary will be Monday night into 
Tuesday morning. 


&& 


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


&& 


$$ 


Synopsis: Cobb 
short term: Cobb 
long term: Laurens 
marine: Cobb 
aviation: Cobb 
hydrology: Cobb