229
FXUS63 KGRB 270029
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
729 PM CDT Sun May 26 2024

New Information added to update section

.UPDATE...
Issued at 717 PM CDT Sun May 26 2024

Widespread moderate to locally heavy rainfall covered all but the
far northwest part of the forecast area early this evening. To
this point, the heaviest rainfall amounts have been reported over
central WI, where 1-2 inches has already fallen. Think the heavy
rainfall threat has diminished in C WI, so not expecting any
major flooding concerns there, other than rising rivers. Farther
east, some elevated instability is working its way into the
southern Fox Valley, and should continue to spread northeast
through the valley and lakeshore areas this evening. A potent
negatively-tilted short-wave trough will also sweep through this
area, generating thunderstorms with periods of torrential
rainfall this evening. This, combined with the heavy rainfall
that moved through an hour or two ago, may lead to some urban
flooding. For now, we have issued a Special Weather Statement to
highlight the concern, but we will be monitoring for potential
urban flooding through the evening.

&&

.KEY MESSAGES...

- Showers will continue through late tonight. A few strong
  thunderstorms are possible in the Fox Valley and lakeshore areas
  through this evening. Around an inch of rain is expected across
  the area, with locally higher amounts approaching 2 inches
  possible. Flooding of streets and small streams will be
  possible, especially in the Fox Valley and lakeshore areas.

- A few rivers across central and eastern Wisconsin could surpass
  minor flood stage early this week.

- Areas of patchy frost are possible Wednesday night into early
  Thursday morning across far northern Wisconsin.

&&

.DISCUSSION...
Issued at 256 PM CDT Sun May 26 2024

Short Term...Tonight and Monday

Showers and a few elevated thunderstorms will
continue tonight as the surface low moves right across Wisconsin.
Rainfall amounts of .10" to .20" an hour have been reported at
2pm with the bright band echoes (35 to 45 Dbz) over central
Wisconsin. The heavier rain should move into Northeast Wisconsin
this evening.

An inch or two of rain could fall from central to northeast
Wisconsin, with less to the east and west. This amount could
produce some street flooding and maybe brief flooding of small
streams. The rain from tonight will make it into the larger
streams and rivers over the next day or two and will likely raise
some of the levels to bankfull, or perhaps minor flood stage.

The rain will likely end by daybreak across the lakeshore counties,
but there will be a chance of showers and thunderstorms again in
the afternoon as a weak short wave approaches. Highs will be a
couple of degrees below normal.

Long Term...Monday Night Through Sunday

Focus for the extended remains on rain chances early in the week
before the current pattern begins to quiet down mid-week.
Lingering wrap-around precip on the back end of Sunday`s system
is expected to be light. The remainder of the week then looks to
be mostly dry as a high amplitude blocking pattern sets up across
the CONUS. Next chances for precip are expected to arrive sometime
over the weekend, although models are struggling to hone in on
timing this far out in the forecast period.

Monday evening through Tuesday precip chances... Following the
passage of a weak shortwave on Monday, a more robust mid-level
disturbance is expected to trail across the Great Lakes region
early Tuesday. Synoptic support associated with Monday evening and
Tuesday precip is lacking due to the absence of surface features
or any convective elements. Thus, rain chances will be largely
dependent on mid-level forcing associated with the shortwave. This
being said, a rumble of thunder wouldn`t be out of the question
across east-central Wisconsin Tuesday afternoon during peak
heating. However, any thunderstorm activity would likely be short-
lived as already minimal instability declines with the loss of
daytime heating. There is still some model spread in exact
rainfall amounts through Tuesday, although most locations should
see between 0.1 to 0.2" of light rain. Locally higher amounts
approaching 0.4" QPF may be possible across east-central
Wisconsin, especially near the lakeshore.

Rest of the extended... Rest of the week looks relatively quiet as
an omega block centers itself over the CONUS. The combination of
upper-level ridging and dominant high pressure at the surface
will place most of the western Great Lakes under a south/southwest
flow regime, advecting up a warmer airmass from the south. As a
result, temperatures will gradually increase through the end of
the week before plateauing in the low to mid 70s Friday through
Sunday. Light winds and mostly clear skies may drop temperatures
down into the low to mid 30s across the far north, will thus be
monitoring potential for patchy frost. Next chances for precip
then enter the forecast area either Friday or Saturday as return
flow from departing high pressure tracks a plume of moisture
across the upper Midwest.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 641 PM CDT Sun May 26 2024

Widespread moderate showers covered most of the forecast area,
with the exception of north central WI. Thunderstorms will be
possible this evening in the Fox Valley/lakeshore areas, so have
included TEMPO groups in the TAFs. Flight conditions ranged from
VFR over NC/far NE WI to MVFR/IFR farther south. The showers will
gradually taper off from SW to NE overnight into early Monday,
but low clouds (IVF/MVFR) will linger into Monday morning before
lifting to VFR in the early afternoon. A short-wave trough will
bring a chance of showers and storms to central WI Monday
afternoon, but confidence is not high enough to mention storms at
the TAF sites.

LLWS will occur in parts of the CWA tonight. Gusty surface winds
from the NE will back to the NW late tonight into Monday.

&&

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

&&

$$

UPDATE.........Kieckbusch
DISCUSSION.....RDM/Goodin
AVIATION.......Kieckbusch