Weather

441 
fxus63 kgrr 110818 
afdgrr 


Area forecast discussion 
National Weather Service Grand Rapids Michigan 
418 am EDT Sat Oct 11 2008 


Latest update...all sections except aviation... 


Synopsis...(418 am EDT Sat Oct 11 2008) 
high pressure will remain parked over the eastern Great Lakes into 
early next week. The weekend will feature mostly clear skies with 
daytime temperatures in the 70s today...and around 80 on Sunday. 
Clouds will return late Sunday night into Monday as a cold front 
approaches from the west. However...any rain will hold off until 
Monday night or Tuesday. 


&& 


Short term...(418 am EDT Sat Oct 11 2008) 
(today through monday) 
strong high pressure...at the surface and aloft...will control the 
weather through the short term. Mostly clear skies will continue 
today through Sunday. It appears the warmest day will be Sunday as 
we will have abundant sun and southerly winds. 


Will indicate more clouds Sunday night into Monday as a cold front 
approaches. However...these clouds will just largely be high level 
with the sun still coming through much of the day. The clouds 
will probably keep temperatures three or four degrees cooler than Sunday. 
Deeper moisture begins to arrive toward the evening hours Monday 
when clouds should begin to thicken up...but any precipitation should hold 
off until after dark. 


&& 


Long term...(418 am EDT Sat Oct 11 2008) 
(monday night through friday) 
during this time period the upper level flow transitions from highly 
meridional to more of a zonal flow. It seems a rather strong Pacific 
storm has just moved off of Asia...just north of Japan. This system 
strengthens impressively with the support of a 150 knot 300 mb jet 
core. From there it races across the North Pacific Ocean in the next 
few days. The system breaks through the upstream ridge and then 
through the next upstream storm over Alaska. All of this action is 
what seems to flatten the upper level flow over the northern 
hemisphere and shears out the upper level closed low over the SW 
U.S. 


Typically this sort of transition in the upper level flow results in 
a low confidence forecast. This time is no different. The first big 
issue is just how the closed upper low shears out. The models are 
typically too quick in breaking down features like that. That leads 
ME to believe that the cold front and it's associated convection 
would come later than we are currently forecasting it. Also...the 
European model (ecmwf) leaves some of the upper level energy behind which comes out 
the next day. That results in a wave on the front which could well 
stall near the southern Great Lakes. Meanwhile as the storm from 
Japan works it's way across the Pacific...numerous shortwaves will 
propagate out ahead of it to bring a series of quick moving systems 
across the Great Lakes. There is some indication subtropical wave 
energy could work it's way into all of this too. As a result I once 
again made few major changes to the on going forecast. 


As for the potential for strong thunderstorms with the cold front in 
the Tuesday time frame....it still looks questionable for southwest 
Michigan. Storm Prediction Center does not have any part of the U.S in the day 4 
outlook. First thing to note on this is the upper wave is quickly 
shearing northeast into Canada in this time frame. The low level jet 
is lifting northeast with it and will be lifting out of the area as 
the front comes through. The surface and middle level instability is 
marginal at best. After adjusting some model soundings I convinced 
myself unless we can get surface dew points about 65f into lower 
Michigan the cape for convection will be very limited. On the other 
hand the deep layer shear is over 60 knots over northern lower Michigan 
Tuesday afternoon. We will have to keep an eye on this as the time 
gets closer. 


&& 


Marine...(418 am EDT Sat Oct 11 2008) 
southeast winds will persist through Sunday night. As a result... 
wave heights will remain low through the weekend. 


&& 


Aviation...(232 am EDT Sat Oct 11 2008) 
VFR conditions expected at all terminals through 06z sun with 
east to southeast winds of less than 11 knots. At 06z the VAD wind 
profiler at GRR is showing 25 knots from 1000 above ground level up.... considering 
the surface wind is near calm... that would mean more than 20 knots 
of shear in 1000 feet. So I updated the tafs to reflect this. Likely 
we will see low level wind shear again after 03z tonight but I will 
put that in the 12z tafs. 


&& 


Hydrology...(418 am EDT Sat Oct 11 2008) 
the next chance for rain is not until Monday night and Tuesday when 
a cold front will be tracking through the region. No Hydro issues 
are expected until then. 


&& 


Fire weather...(418 am EDT Sat Oct 11 2008) 
with the lack of rain and with the dry air mass lingering over the 
region the fire danger will increase over the weekend. Temperatures will 
be in the middle 70s to around 80 each day with daytime relative humidity values 
dropping to 30-35 percent. Winds will generally be around 10 miles per hour. 
This isn/T red flag conditions...but it deems watching. We begin to 
advect higher dew points by Monday. With the higher relative humidity values the 
danger will lessen. 


&& 


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


&& 


$$ 


Synopsis: jk 
short term: jk 
long term: wdm 
marine: jk 
aviation: wdm 
hydrology: jk 
fire weather: jk