537
FXUS63 KGRB 132349
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
649 PM CDT Thu Aug 13 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- 50-80% chance for showers and storms Friday night into
  Saturday but the severe weather risk is low. Any storms may
  produce localized heavy rainfall.

- Seasonable temperatures expected over the next week.

&&

.DISCUSSION...
Issued at 122 PM CDT Thu Aug 13 2026

More widespread rainfall has occurred from southern Wisconsin
southward in association with a well-developed MCV. Locally,
there are small (20-30%) chances for a shower this afternoon,
but limited instability above the -10C level should keep any
lightning fairly isolated.

The period of most interest remains Friday night into Saturday.
Anomalous moisture lifts northward with precipitable water values
exceeding the 95th percentile relative to climo. A few
shortwave troughs will interact with the moist, unstable airmass
and low-level baroclinic zone to produce periods of
showers/storms. Confidence in timing/placement of convection
tends to be in low in these set-ups, especially beyond a day or
two. The greater instability will generally remain south of the
area with mean low-level jet placement also focused south. Thus,
the risk for severe storms is low and the higher odds of
heavier rain remain just to the south. However, if there is
sufficient instability, given the moisture present, any storms
may pose a heavy rain threat with NBM 90th percentile rain
amounts in the 2 to 2.5 inches across central into east-central
Wisconsin on Saturday. These details will be fine-tuned over the
next day.

Beyond this time frame, high pressure will build south to start next
week. A shortwave trough will drive a cold front south across the
area toward Tuesday. Although the greatest instability looks to
remain southwest of the area, there is some overlap in
CAPE/shear evident in global ensembles, owing to the continued
presence of seasonably strong mid-level flow. Thus, although
confidence in severe weather is low, the risk for showers and
storms increases to 50-70% later Tuesday into Tuesday night.

Fairly seasonable temperatures will persist over the coming week
with highs in the 70s and 80s.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 649 PM CDT Thu Aug 13 2026

Low status has finally cleared out across the Fox Valley leaving VFR
conditions across the region for the his evening. There are still a
few isolated showers in central WI, however, have pulled any mention
of precip from the TAFs given the higher uncertainty that any of
these will impact a terminal. Overnight there is another chance for
fog to develop across east-central WI, mainly between 7-11Z. Fog is
expected to be more patchy than the past few nights, however, IFR
vsbys are possible along the lakeshore, including MTW. Once the fog
clears VFR conditions are expected for the rest of Friday.

Winds will be light through the TAF period.

&&

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

&&

$$

DISCUSSION.....JM
AVIATION.......GK

NWS GRB Office Area Forecast Discussion