333 
FXUS63 KGRB 060349
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1049 PM CDT Tue Oct 5 2021

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 249 PM CDT Tue Oct 5 2021

High pressure over the region will preclude any risk of
precipitation over then next 24 hours. The main forecast issue to
be on the extent of fog tonight with locally dense fog possible.

The 19Z MSAS surface analysis showed this high pressure situated
over northern sections of the Great Lakes. Anticyclonic flow
around this high had brought an east-northeast wind into the
forecast area with lake moisture and daytime heating aiding in low
clouds over all but far northeast WI.

The high pressure and an upper-level ridge to remain parked over
the Great Lakes region tonight, bringing light winds and an
easterly fetch off of Lake MI. Time sections show plenty of low-
level moisture across WI, thus the favorable scenario of more low
clouds and fog can be expected mainly during the overnight hours.
Based on the positioning of the high pressure, anticipate northern
WI to have thicker fog compared to central/east-central WI. This
would include dense fog and the eventual need of an advisory.
Prefer to let next shift see the fog develops this evening, thus
no headlines right now. Min temperatures to range from the middle
40s to around 50 degrees north, lower to middle 50s south.

The fog is expected to linger through mid-morning Wednesday before
slowly lifting into a stratocu deck. The high pressure and upper
ridge both slowly shift east during the day, but the light wind
field may take mixing a while to shake these low clouds. Look for
skies to eventually become partly to mostly sunny with max
temperatures in the middle to upper 60s near Lake MI, upper 60s to
lower 70s inland.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 249 PM CDT Tue Oct 5 2021

Focus in this part of the forecast mainly revolves around precip 
chances in the Thursday-Friday and Sunday-Monday time frames. Models 
have strength/timing differences regarding the system for Sunday and 
Monday, but are in reasonable agreement into early this weekend.  

Wednesday night through Thursday night...Upper level low pressure 
will be shifting north across the mid-Mississippi Valley on 
Wednesday night.  Will see increasing clouds through the night. But 
high pressure will remain across the Great Lakes though and dry air 
should slow the northward push of light showers.  Will keep the 
forecast dry.  The upper low makes slow northward progress on 
Thursday and Thursday night.  Scattered showers seem like a decent 
bet to slide in from the south at times.  A few thunderstorms cannot 
be ruled out since instability of 200-400 j/kg shifts into central 
to northeast WI.  But instability this low is too low for severe 
weather chances given the poor dynamics.  Mild temperatures over 
this period.

Rest of the forecast...The upper low/trough will lift northeast 
across the region on Friday, and showers and spotty storms will 
continue until the trough exits on Friday night.  Broad southwest 
flow will remain aloft on Saturday as low pressure organizes over 
the central plains.  Some clouds and/or fog may linger over far 
northern WI on Saturday morning, but then should see clearing 
through the day.  Saturday looks like the warmest day over the next 
7 days with highs in the low to mid 70s.  By Saturday night into 
Sunday, low pressure will be lifting northeast across the northern 
Plains while a cold front moves east across Wisconsin on Sunday. A 
ribbon of instability could arrive ahead of the front on Sunday, but 
timing of the front will help determine how widespread thunderstorm 
potential will be.  Some rap around showers could linger into Monday 
behind the system.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1049 PM CDT Tue Oct 5 2021

Conditions were mainly VFR across the region this evening, with
some remaining cloud cover across portions of central and east-
central Wisconsin and an area of stratus coming onshore across
Door County. High pressure overhead along with light winds and 
sufficient low-level moisture is forecast to allow for fog to 
develop once again during the overnight hours. There are already
signs of fog forming across portions of north-central and central
Wisconsin at issuance. This fog may again become locally dense, 
especially at the RHI TAF site which would persist into early 
Wednesday morning. Much like today, it may take some time for the 
fog to dissipate and low clouds to mix out, thus lingering MVFR 
cigs may persist through most of the morning hours before lifting 
to VFR cigs in the afternoon and continuing into Wednesday 
evening.
&&

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

$$

SHORT TERM.....AK
LONG TERM......MPC
AVIATION.......Kurimski