303 
FXUS63 KGRB 062312
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
612 PM CDT Wed Oct 6 2021

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 236 PM CDT Wed Oct 6 2021

Quiet and mild weather is expected tonight with surface high 
pressure still centered over the Great Lakes. Some low cloud and 
patchy fog is likely once again late tonight with light winds and 
initially clear skies. An upper low over central Missouri will 
begin to lift northeast Thursday, and produce low and mid level 
convergence and upper diffluent flow. This should be enough to 
produce light rain showers. An isolated thunderstorm is not out of
the question south of highway 10. Easterly flow over Lake Michigan
will make for low clouds near the lake and bay but probably not 
much fog due to the mild lake water temperature for this time of 
the year.

.LONG TERM...Thursday Night Through Wednesday
Issued at 236 PM CDT Wed Oct 6 2021

Focus in this part of the forecast is timing occasional precip 
chances as the region will be under southwest flow aloft. 
Temperatures will likely remain above normal in this pattern, while 
precipitation will also be near to above normal depending upon 
thunderstorm coverage.  

Thursday night through Friday night...Upper level low pressure will 
be slowly shifting northeast from the mid-Mississippi Valley to the 
central Great Lakes on Thursday night into Friday.  The low will 
bring scattered showers at times, which will likely see a diurnal 
uptick with the heat of the day on Friday afternoon.  Looking at 
instability parameters, instability looks less than what models were 
depicting yesterday, and will keep thunder chances low on Thursday 
night. Thunderstorm chances will be higher on Friday afternoon, most 
particularly over east-central WI where most unstable cape values 
range from 400-600 j/kg. As the upper trough moves east across lower 
Michigan on Friday night, showers should gradually diminish. There 
should be plenty of cloud cover, but if any clearing were to occur, 
dense fog could become a hazard.

Rest of the forecast...Shortwave ridging will build across the 
region on Saturday ahead of low pressure traveling northeast across 
the central Plains.  After some morning clouds, the area should see 
a period of sunshine before clouds return again ahead of the low. 
The strongest dynamics will pass northeast of the region on Saturday 
night and Sunday.  But a weakening cold front will still provide a 
chance of showers and a few storms on late Saturday night into 
Sunday.  Instability is meager, so severe weather is not expected 
despite decent wind fields.  A new wrinkle to the forecast occurs on 
Monday and Monday night when a southern stream low lifts northeast 
into the region.   Showers and a few storms appear possible with 
this feature.  Then will be watching the possibility of a strong 
cyclone during the middle of next week. Like the previous systems, 
strong dynamics look to remain well west of the region. Temperatures 
to remain above normal for the period.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 611 PM CDT Wed Oct 6 2021

Surface high pressure over the Great Lakes will keep mostly VFR 
conditions across the area at least through the evening hours. Low
clouds will likely form late tonight or early Thursday. These low
clouds and an area of showers moving from south to north during 
the day Thursday will bring IFR conditions to much of the region. 

An upper level low over Missouri will move into Illinois Thursday
and to Lower Michigan Saturday. It will produce periods of
showers and IFR conditions as it does.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....RDM
LONG TERM......MPC
AVIATION.......Kurimski