777
FXUS63 KGRB 192355
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
655 PM CDT Tue Aug 19 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Patchy dense fog overnight tonight through daybreak on
  Wednesday, especially central and north-central Wisconsin.

- Isolated showers are possible at times through Wednesday. The
  rest of the week will be dry with the next chance for showers
  and thunderstorms Friday into Friday night. Severe storms are
  not expected.

- Temperatures will be around normal for much of the upcoming week,
  with the potential for well below normal temperatures late in
  the weekend into early next week.

&&

.DISCUSSION...
Issued at 211 PM CDT Tue Aug 19 2025

Low amplitude shortwave trough in northwest flow along with
ongoing cold air advection will result in small chances for
showers through Wednesday. High pressure centered over northern
MN and western Lake Superior through Wednesday with low pressure
crossing the lower Great Lakes will lead to general northeast
low-level winds, with convergence maximized near bay of Green Bay
and Lake Michigan. It will be in this zone, where the shower
chances will be maximized on Wednesday. Rainfall amounts will be
very light, well under 0.25 inch through Wednesday. Given the
cooler air flowing across the lakes (+12c at 850mb/5kft), took a
glace at potential lake effect processes aiding in the showers,
but even with water temps on the lake and the bay around 68-72f
(20-21c), delta t/s stay below threshold of 13c which is typically
what is needed to see even a weaker lake response. This also keeps
us out of any range for potential waterspouts, for now.

Other issue through Wednesday will be patchy dense fog late tonight
into early Wednesday. Using the HREF data, highest risk of visibility
less than 1 mile (30-60%) is located over central and north-central
WI. Added mention of patchy dense fog to the HWO. Temps tonight
will drop into the 50s north-central into far northeast WI. Highs
on Tuesday will mostly rise to the middle to upper 70s.

Looking ahead, after a couple days of dry weather later Wed through
Thu thanks to Canadian high pressure, approaching cold front brings
next chance of showers and storms across the region on Friday.
Instability and shear shown by LREF could support isolated strong
storm if this fropa occurs during max heating on Friday afternoon,
but severe storms are not expected. Behind the front, next weekend
looks more fall-like with highs by next Sunday perhaps not even
reaching 70. Skies will partly to mostly cloudy with cu and
stratocu and it may be breezy at times. Forecast currently will
carry small chance of showers on Sunday, especially north and
northeast. Pattern would suggest that later forecasts may end up
showing higher chance for showers especially Saturday over the
north and on Sunday for all areas, along with an increase in
cloud cover. Further increase in the showers may be due to lake
effect as 850mb temps bottom out at 5-6c. The taste of fall will
last through early next week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 654 PM CDT Tue Aug 19 2025

A few MVFR lingered across parts of north central and far
northeast WI during the late afternoon hours; otherwise, VFR
clouds were found over parts of the area. These high-end MVFR and
low-end VFR clouds will persist through the early evening hours.
Then look for lower LIFR/IFR clouds to spread southwest across
the area later this evening and overnight, with some MVFR ceilings
likely prevailing over eastern WI. Fog is also expected to
develop tonight as winds decrease and enough low-level moisture
will remain in place. Mainly IFR/MVFR VSBYs are expected, with
some LIFR VSBYs possible in central to north-central WI.

Some sprinkles or light showers will be possible at times
overnight into Wednesday, but should not create any worse flying
conditions than the lower clouds and fog. A stray storm can`t be
ruled out over central WI this evening, where instability is
greatest, but threat is too low to include in the AUW/CWA TAF.

On Wednesday, once the fog lifts, expect lower ceilings to
persist early in the day, with a slow improvement through the day
as conditions improve to MVFR/VFR.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....JLA
AVIATION.......Bersch