960
FXUS63 KGRB 161111
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
611 AM CDT Wed Sep 16 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Light rain chances (40 to 60%) return tonight into Thursday
  morning, though rainfall totals will remain light at under one
  tenth of an inch.

- Confidence is increasing for a significant heavy rainfall event
  Friday afternoon into Saturday, focused across central and east-central
  Wisconsin.

- Another round of showers and potential thunderstorms towards early
  next week.

&&

.DISCUSSION...
Issued at 119 AM CDT Wed Sep 16 2026

The latest RAP analysis and satellite/radar imagery show high
pressure centered across the northern Plains early this morning,
steadily shifting eastward into the western Great Lakes. Latest
radar imagery depicts an active thunderstorm belt along a cold
front extending from eastern Kansas into southern Lower Michigan,
with cirrus streaming northward across central and northeast
Wisconsin. Satellite imagery shows clearing skies across north-
central Wisconsin where patchy ground fog has developed. Further
west, shortwave energy moving east across southern Canada will be
the primary upper- level driver influencing weather across the
Great Lakes over the next 24 to 36 hours.

Light rain tonight into Thursday morning:
In the near term, patchy ground fog early this morning over
north-central Wisconsin will lower visibilities to one- quarter to
one-half mile before lifting after 8 AM. High pressure sliding
quickly across the region today will keep conditions dry,
accompanied by scattered shallow fair- weather cumulus. Cloud
cover will increase this evening as weak overrunning moisture
moves in ahead of a shortwave moving east across southern Canada.
Rain chances tonight generally range from 40 to 60 percent, but
precipitation will be light with 90th percentile amounts only up
to 0.10 inches. Spotty light showers or drizzle will linger into
Thursday morning before clearing develops Thursday afternoon.
Seasonable high temperatures ranging from the upper 60s to middle
70s are expected today and Thursday.

Heavy rainfall potential Friday through Saturday:
Heavy rainfall late Friday into Saturday represents the most
significant weather hazard during the 7-day forecast period, with
increasing potential for localized flooding across central and
east-central Wisconsin. Shortwave energy advancing across the
Rockies will trigger a 30 to 40 knot low-level jet directed into
central Wisconsin Friday afternoon into Friday night. Strong
dynamic forcing will overspread the region, characterized by
upper-level divergence in the right rear quadrant of an upper jet
streak, robust mid-level frontogenesis, and strong moisture
convergence above the returning warm front. Precipitable water
values are forecast to climb to around 1.70 inches, which sits
near the 96th percentile for mid- September. Warm cloud depths in
excess of 12,000 feet will favor efficient rainfall processes.
Model guidance has trended slightly southward over the past 24
hours, concentrating the heaviest precipitation swath over central
and east-central Wisconsin. Probability of 1 inch or more of rain
has increased to 60 to 75 percent in these areas, while the
probability of 2 inches or more has increased to 20 to 45 percent.
Because these same locations received heavy rainfall earlier in
the week, antecedent soil moisture remains high, elevating the
threat of localized urban and small stream flooding. Severe
weather risk remains low due to meager instability, with
most unstable capes generally under 500 J/kg.

Additional rain chances early next week:
Following the departure of the Friday night and Saturday system,
a brief break in precipitation is expected Saturday night into
Sunday as weak surface ridging passes over the Great Lakes.
However, the progressive mid-level flow will keep the region in an
unsettled regime heading into early next week. Another upper
shortwave trough and associated surface system will approach from
the Great Plains toward Sunday night and Monday, bringing
additional chances for rain showers and scattered thunderstorms
through Tuesday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 611 AM CDT Wed Sep 16 2026

Through 00Z Thu:
Patchy ground fog is occurring over north-central WI but low
confidence of impacts at RHI through 13Z. Otherwise, VFR
conditions will prevail today. Few to scattered fair weather
clouds with VFR bases are expected this afternoon. Winds will
remain light under 10 kts.

After 00Z Thu Thru 12Z Thu:
Clouds increase and lower tonight as a shortwave approaches. Light
rain chances increase after 04Z Thu over central and north-
central WI (KAUW, KCWA, KRHI) and after 07Z Thu over eastern WI
(KGRB, KATW, KMTW). Handled with PROB30 groups. CIGS will
deteriorate to MVFR across central and east-central WI overnight.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC

NWS GRB Office Area Forecast Discussion