Weather

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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
345 am EDT Tuesday Oct 7 2008 


Latest update...all except aviation... 


Synopsis...(345 am EDT Tuesday Oct 7 2008) 
fair weather will prevail through this afternoon before a low 
pressure system brings showers tonight and Wednesday. Pleasant 
weather will return Wednesday night and Thursday as a surface high 
pressure ridge builds in. 


&& 


Short term...(345 am EDT Tuesday Oct 7 2008) 
(today through Thursday afternoon) 


Fair and dry weather is anticipated today. However middle and high 
level cloud cover will gradually thicken in advance of the next 
system... as suggested by rgnl infrared Sat trends and model time height 
relative humidity forecasts. We undercut guidance maximum temperatures slightly today given the 
strong low level east-southeast flow and increasing cloud cover... as well as 
the cool maximum temperatures noted in easterly flow across our County warning forecast area 
yesterday. 


Showers will develop late this evening and overnight in advance of 
the frontal boundary that will move through on Wednesday. This will 
be a slow moving frontal boundary... so showers will linger 
Wednesday. 


We noticed the prognosticated strength of the low level jet by 06z Wednesday. This 
potentially could trigger isolated convective development. However 
convective potential considering additional factors like instability 
is minimal and best elevated instability stays south of our County warning forecast area. 


Therefore we will continue to only mention showers for tonight into 
Wednesday. Future shifts may need to consider thunderstorm mention 
given 12z guidance trends on orientation and strength of low level jet and 
moisture/lift/instability considerations. 


Showers will come to an end Wednesday evening followed by decreasing 
cloud cover late Wednesday night. Very pleasant and mild weather is 
anticipated Thursday with a good deal of sun as a surface ridge builds 
in. 


&& 


Long term...(345 am EDT Tuesday Oct 7 2008) 
(thursday night through monday) 


My first thoughts are it looks like a rather dramatic change from 
the cool weather we have had the first 6 days of October. Warm and 
for the most part dry weather should prevail until the primary cold 
front comes through later on Tuesday (outside the long term period). 


The GFS and European model (ecmwf) are in better agreement tonight as the GFS is 
slower to bring the closed upper low from the SW US eastward into 
the Great Lakes. The problem seems to be related to how the models 
are handling the Pacific shortwave behind the one that closes the 
upper low off in the SW US Saturday. While the models all agree 
with the wave behind the one closing off on Saturday on Saturday... 
by Monday the GFS was to quick to shear out the system that is 
forecast at that time (monday) to be over the Gulf of Alaska. Which 
in turn brought the southwest upper level system east to fast(gfs). 
However the 00z run seems to have developed a better clue here. 


What all this means is the primary polar jet will be well north in 
central Canada (north of the great lakes) this weekend into early 
next week. An impressive 591 dam high is forecast south of lower 
Michigan by 12z Sunday. That sort of pattern will mean well above 
normal temperatures through the weekend into early next week. I did 
leave the weather grids as they were (bringing chance showers by 
sunday)but I could see it being dry until Tuesday (beyond our 
current forecast grids). 


&& 


Marine...(345 am EDT Tuesday Oct 7 2008) 
a rather strong east-southeast gradient will result in wind speeds of at least 
10 to 20 kts today. This will cause wave heights to increase to 2 to 
4 feet. We have some concern that we could flirt with Small Craft Advisory criteria 
later today. However it seems wave heights higher than 2 to 4 feet 
should not impact our nearshore waters due to the east-southeast wind 
orientation. 


&& 


Aviation...(1142 PM EDT Monday Oct 6 2008) 
upstream surface trough will gradually approach the next 24 hours. A 
thickening and lowering cloud deck can be expected. Conditions will 
be VFR for the remainder of tonight...with high cirrus level clouds 
in place. On Monday...the cirrus will lower gradually into an 
altocumulus deck...dropping from 20000ft to 8000ft. Between 03z-06z 
tomorrow evening it is possible some rain showers will be spreading 
in with slightly lower ceilings in the 3500-5000ft range. 
Decided...given the dry air in place...not to introduce 
precipitation and lower clouds just yet. So...a VFR forecast...with 
easterly winds throughout. 


&& 


Hydrology...(345 am EDT Tuesday Oct 7 2008) 
no Hydro issues expected this week. 


&& 


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


&& 


$$ 


Synopsis: Laurens 
short term: Laurens 
long term: wdm 
marine: Laurens 
aviation: Duke 
hydrology: Laurens