234 
fxus63 kapx 061702 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
102 PM EDT Sat Sep 6 2008 


Synopsis.../issued at 724 am/ 


A weak upper Midwest storm system...will move over Upper Michigan 
today...before quickly exiting into Ontario this evening. This 
feature will generate a few light rain showers over northern 
Michigan through the afternoon. Swr 


&& 


Short term.../issued at 1037 am/...this afternoon 


Weak surface low over western Upper Michigan is getting 
left behind parent shortwave trough lifting across southern 
Ontario. Area of scattered showers is mostly confined to eastern 
Upper Michigan where better isentropic ascent on the 295-300k 
surfaces is located. Farther south...weak cool front/surface trough 
is extending over Northern Lake Michigan and south along the Eastern 
Shore of Lake Michigan to southeast Wisconsin...and is kicking off isolated 
showers/sprinkles from Leelanau Peninsula to Lake County. 
Aforementioned weak surface low will slowly shift to the NE towards 
Lake Superior during the afternoon while its cool front/trough will 
shift slowly east. Expect scattered shower activity over northern 
portions of the forecast area to exit/diminish by middle-afternoon when 
area of isentropic ascent lifts NE into Ontario. Think we will 
continue to see isolated light showers/sprinkles pop up along the 
cool front as it shifts east into north-central and NE lower with a 
loose low level thetae axis in place. Adjusted pop grids to reflect 
these trends as well as some clearing over northwest lower late in the 
afternoon as drier middle-level air works in. Otherwise...very few 
changes made elsewhere. 


Mpc 


&& 


Long term.../issued at 330 am/...tonight Onward 


Models still struggle resolving the individual waves within the 
broader upper trough over the north central US. They do however agree 
on when the best forcing for precipitation will be...Sunday night and again 
Monday night. 


Tonight...a somewhat weak shortwave will quickly lift east-northeast across far 
northern lower Michigan in the evening. In its wake...the weak surface low 
in central Upper Michigan will drift eastward and eventually fill. The 
best chance for any precipitation will be in the evening in eastern 
upper...once again where middle level forcing and low/middle level SW 
flow/isentropic ascent match up. Both of these fall apart late 
tonight. Will have scattered showers north of the bridge in the evening/ 
early overnight...diminishing to isolated by dawn. Extreme northern 
lower will have isolated rain showers early on...with little precipitation south of 
M-68. Mostly cloudy north...partly cloudy south (where some bog fog 
is again possible). Min temperatures low/middle 50s coasts to middle 40s in the 
interior cool spots. 


Sunday...main action should be to our south. A pair of reasonably 
vigorous shortwaves will race east-northeast into far Southern Lower Michigan. A 
ill-defined east-west surface boundary will result...also well downstate. 
Deeper moisture will eventually get drawn northward into our 
southern zones late in the day. Will have isolated showers in the 
morning in the south...expanding across the area in the afternoon 
with Chancy (30-40) probability of precipitation in the south. Instability is still meager 
(up to 300j/kg mucape)...and will not mention thunder. Maximum temperatures a 
couple degrees warmer than today...upper 60s to lower 70s. 


Sunday night/Monday...best shot of rain for the event thus far looks 
to be Sunday night...as vorticity ribbon lifts north from downstate. A 
surface cold front will also move through the forecast area from the 
northwest. And not quite willing to go with likely probability of precipitation just yet...but will 
boost to 50 across the entire area Sunday night. Monday may see a 
relative lull...with middle level subsidence for at least part of the 
day as vorticity ribbon pulls out. Reduced probability of precipitation a smidge to the 30-40 
range. Low temperatures mainly around 50. Cold advection Monday will keep 
highs mainly in the 60s. 


Rest of the forecast...one last middle-level trough in the episode will 
go through Monday night...with a resulting increase in precipitation chances. 
Still looks like we dry out mid-week...before return flow gets going 
Wednesday night. Tuesday will be cool like Monday...with some recovery in 
temperatures into Wednesday. 


Jz 


&& 


Marine.../issued at 330 am/ 


No marine headlines. Disorganized pattern will keep surface winds 
light until Sunday night...ahead of a cold front approaching from 
the northwest. 


Jz 


&& 


Aviation.../issued at 100 PM/...valid for 18z tafs 


Challenging forecast over the next 24 hours. Weak 
surface low over central Upper Michigan will track NE over Lake 
Superior with its trailing cool front/surface trough crossing 
northern lower through the afternoon. Showers will remain spotty 
with limited chances of impact on the taf sites. Secondary surface 
trough will pass across the area early tomorrow morning. Hard to 
say if any low clouds/fog will accompany this trough. Certainly is 
possible...judging by what occurred upstream this morning. Best 
chances would appear to be at pln and will trend towards lower visibilities 
and ceilings...but will refrain from going lock/stock/and barrel due to 
poor model guidance. So...will keep VFR going through the taf period 
except at pln. 


Mpc 


&& 


Apx watches/warnings/advisories... 
Michigan...none. 
Lm...none. 
LH...none. 
Ls...none. 


&& 


$$