290
FXUS63 KGRB 170902
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
402 AM CDT Fri May 17 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Dense fog is likely in the Fox Valley, the lakeshore counties,
  and the area west of the bay early this morning.

- Dense fog is likely over the bay through mid morning, and over
  the nearshore waters of Lake Michigan through mid afternoon.

- There is a chance of thunderstorms in northcentral Wisconsin
  this afternoon.

- Isolated thunderstorms are possible Saturday afternoon and
  evening, although most of the area is expected to remain dry
  throughout the day.

&&

.DISCUSSION...
Issued at 400 AM CDT Fri May 17 2024

Short Term...Today...Tonight...and Saturday

AIr with low 50s dewpoints flowing over the 45 degree waters of
Lake Michigan was producing areas of dense fog over the lake, bay
and adjacent land areas early this morning. The fog over the land
should dissipate a couple hours after sunrise, while the fog over
the bay should dissipate by mid morning. The fog over the
nearshore waters of Lake Michigan could last through late
afternoon, or perhaps even later, as there will be a lake breeze.

Skies should become sunny once the fog has dissipated. 925mb
temperatures support high temperatures in the middle 70s to lower
80s this afternoon, but of course much cooler near the lake. An
upper trough moving across Upper Michigan could produce scattered
thunderstorms this afternoon and early evening in northcentral
Wisconsin.

Tonight will mild, with some clouds and a steady wind. Lows will
range from the middle 40s over northern Door county to the middle
50s in the Fox Valley. Summer like weather is expected Saturday,
as south winds increase. Highs will be mostly in the 80s, though
dewpoints in the 50s will keep it from being too humid. There is a
chance of thunderstorms in central and northcentral WIsconsin in
the afternoon ahead of a weak cold front.

Long Term...Saturday Night Through Thursday

As the weekend trends drier, main focus for the extended will turn
to another active pattern to set up early next week. A train of
shortwaves are expected to bring multiple rounds of rain/storms to
the forecast area beginning Sunday evening and lasting through
mid-week. This type of spring pattern can be volatile, so changes
to the forecast are possible over the next few days as models
come in to better agreement about the timing and track of two
driving systems.

Saturday evening... Models continue to be unimpressed with
rain/storm chances Saturday evening due to moisture inhibition. As
widespread subsidence behind the cold front places weak high
pressure across the western Great Lakes, dry air will make it
difficult for any rain or storms to get going. Thus, dewpoints
will need to be on the rise to saturate the profile enough to
warrant any precip. This being said, potential for isolated pulse
storms and light rain remains due to temperatures in the upper 70s
and low 80s resulting in sufficient surface-based instability
(approaching 1000 J/kg CAPE). Dry conditions will then persist
through Sunday as a dry airmass situates over Wisconsin.

Next week... On and off rain/storm chances will continue through
at least mid-week as large-scale ridging across the eastern CONUS
puts most of the Midwest under a southwest flow regime. Meanwhile,
a robust trough settled over the western US will eject several
shortwaves and accompanying precip chances up into the region. The
first round of precip is expected to move through the forecast
area Sunday night through Monday. In its wake, a more dynamic
system is expected to trek from the central Plains to the upper
Mississippi Valley by Tuesday evening. A first glance shows that
this system has the potential to bring heavy rain and
thunderstorms to the area, although it is too soon to make out any
details. Will continue to monitor convective potential and precip
amounts as we get closer to the event.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1046 PM CDT Thu May 16 2024

Areas of fog have started to develop across northern and east-
central WI as skies have clear out behind the departing showers and
storms and winds have become calm. Expect vsbys to become
LIFR/IFR at GRB, ATW, MTW, and RHI as fog expands in coverage
overnight. And area of high clouds that moved over central WI this
evening are slowing temperatures falls and thus preventing fog
formation at the moment. Do expect these clouds to clear out
overnight and create conditions conducive for fog and low clouds
at AUW and CWA after 09Z with IFR vsbys.

Fog across the region should burn off quickly after the sunrises
Friday morning with VFR conditions returning to all TAF sites. Much
of the region will stay dry Friday, however, a warm front may bring
a few showers to northern WI Friday afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 8 AM CDT this morning for WIZ022-
038>040-048>050-073-074.
&&

$$

DISCUSSION.....RDM/Goodin
AVIATION.......GK