277 
fxus63 kgrr 211758 
afdgrr 


Area forecast discussion 
National Weather Service Grand Rapids Michigan 
1258 PM EST Sat Nov 21 2009 


Latest update...aviation... 


Synopsis...(400 am EST Sat Nov 21 2009) 
high pressure will produce dry weather and partly cloudy skies 
through the weekend. Patchy fog is anticipated during the early to 
middle morning hours of Saturday... Sunday and Monday. Temperatures 
will remain above normal into middle week before it turns a little 
cooler late in the week. 


&& 


Short term...(400 am EST Sat Nov 21 2009) 
(today through Monday afternoon) 


Short term forecast concerns remain fairly minimal. High pressure will 
produce dry weather through the weekend. Surface observation early this morning show 
patchy fog continues to develop which will linger through the early 
to middle morning hours before dissipating. Lingering morning cloud 
cover will give way to partial sunshine that will help to boost maximum 
temperatures into the low to middle 50s. 


00z model relative humidity forecasts and numerical guidance suggests more clearing 
will occur tonight as compared to early this morning. This in 
conjunction with light and variable winds will once again set the 
stage for patchy fog development during the early morning hours 
Sunday and then again on Monday. High temperatures Sunday and Monday will 
reach the low to middle 50s with min temperatures mainly in the upper 30s to 
lower 40s. 


&& 


Long term...(400 am EST Sat Nov 21 2009) 
(monday night through friday) 


The 00z/21 runs of the GFS and European model (ecmwf) are still not in very good 
agreement regarding the middle week system and have tried to 
incorporate both solutions into the forecast grids. A low pressure 
system will be tracking from the central/northern plains on Tuesday... east 
northeast through the Great Lakes region on Wednesday and Thursday. 


The faster GFS solution supports warm air advection rain moving into the region on 
Tuesday while slower European model (ecmwf) keeps it dry and holds the rain off until 
Wednesday. The compromise is to carry chance probability of precipitation both days... 
although believe Wednesday offers the better precipitation potential and will 
carry scattered vs chance wording on that day. 


Precipitation type becomes quite problematic by Thanksgiving day as the surface 
low moves by and cooler air is drawn down on the back side of the 
system. GFS solution is still colder than the European model (ecmwf)... although it 
is a common bias of the GFS to be colder beyond day 4. Even if one 
were to run with the cooler GFS solution... the 00z forecast soundings 
look just a tad too warm in the boundary layer to support snow. Will 
therefore go with with rain or snow shower wording. 


The current forecast for Thursday night and Friday currently has all 
snow for precipitation type and left that unchanged... although the speed of 
the system departure will dictate precipitation chances and the degree of 
cold air on the back side will dictate precipitation type. That/S still a big 
uncertainty at this time. 


&& 


Aviation...(1258 PM EST Sat Nov 21 2009) 
skies have basically cleared across the taf sites but some cumulus is 
beginning to develop. Water vapor loop shows abundant high moisture 
which is contributing to the hazy sky. Light winds during the next 
24 hours and generally clear skies tonight will result in visibilities 
falling to less than a mile late tonight. 


&& 


Marine...(400 am EST Sat Nov 21 2009) 
high pressure and light winds will result in minimal wind/wave 
action through the weekend. Some patchy early to middle morning fog 
through the weekend could pose a hazard to mariners. 


&& 


Hydrology...(400 am EST Sat Nov 21 2009) 
dry weather is expected through Monday. No Hydro issues. 


&& 


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


&& 


$$ 


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