822
FXUS63 KGRB 012332
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
632 PM CDT Wed May 1 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Another round of showers and storms is expected Thursday
  afternoon through Friday morning. Best chance for thunderstorms
  will be Thursday afternoon and evening with small hail and gusty
  winds the main impacts with any storms that develop.

- Due to recent and upcoming rainfall, rivers and streams will be
  on the rise late this week. Some rivers are forecast to reach
  bankfull stage by Friday or Saturday.

- Additional showers are possible Saturday into Saturday night
  with more showers and thunderstorms Monday night through
  Wednesday. This will keep river levels elevated well into next
  week with some rivers remaining at or above bankfull.

&&

.DISCUSSION...
Issued at 228 PM CDT Wed May 1 2024

Short Term...Tonight and Thursday

As decaying low pressure continued to exit to the north this
afternoon, weak high pressure building in its wake began to erode
a lingering mid-level cloud deck across central and east-central
Wisconsin. West winds continued to ramp up behind the cold front
this afternoon with some assistance from daytime mixing and 850
mb cold air advection, with widespread gusts between 30 and 35 mph
observed across the forecast area.

Main concerns for the short-term will be pinpointing rain/storm
chances for tomorrow as well as potential for patchy fog across
the north tomorrow morning. A surface low currently over New
Mexico is progged to make its way into the upper Mississippi
Valley by Thursday evening, bringing rain chances to the forecast
area beginning Thursday morning. Warm air advection precip is
expected to arrive from the southwest out ahead of a warm front
Thursday morning before lifting northeast across the forecast area
and becoming more widespread Thursday afternoon. Most short-range
models are showing a strong signal (~60 to 70% probability) for
at least half an inch of storm total QPF across our western
counties, decreasing further east. Locally higher amounts
(between 0.75 and 1") may be possible in areas that receive
heavier rainfall, especially given strong poleward moisture
transport and an open Gulf. For this reason, can expect
river/stream levels to be on the rise through the end of the week
with a marginal/slight risk of excessive rainfall through Friday
morning. Localized flooding may also be possible in low-lying or
urban areas.

Thunder chances... Thunder potential for tomorrow doesn`t look
too impressive, with most convective elements looking to remain to
our south. However, an elevated thunderstorm with some gusty
winds cannot be ruled out Thursday evening with MUCAPE values in
the 300 to 400 J/kg range across east-central Wisconsin.
Additionally, any storms that do get going would have to contend
with a robust surface inversion due to easterly flow advecting a
stable lake airmass onshore.

Fog potential... Some radiation fog is possible tomorrow morning
across the far north, although confidence is currently low. Light
and variable winds overnight combined with brief windows for
partial clearing tomorrow morning may be favorable for development
of patchy ground fog, although its southern extent is still
uncertain. Moreover, low temperatures tonight in north-central
Wisconsin are expected to dip down between a favorable four to
five degrees below this afternoon`s lowest dewpoint temperature.

Long Term...Thursday Night Through Wednesday

An active weather pattern to continue as a series of systems moves
across the CONUS into next week. The first system to exit
northeast WI Friday morning. A weaker system may bring showers on
Saturday, but models disagree on the extent of precipitation. A
stronger system is forecast to arrive Monday night and may linger
over the area through Wednesday. Depending on rain amounts, hydro
concerns will remain an issue as a number of rivers in northeast
WI are already near bankfull. Temperatures will be at or above
normal through the period.

Thursday night and Friday...
Showers/isolated thunderstorms to already be underway across
northeast WI at the beginning of Thursday night as a cold front
pushes across the area. Instability appears meager at best, but
0-6km shear is 50 kts or greater, thus cannot rule out some
thunderstorms to persist through much of the night. Severe
potential does remain minimal due to the lack of instability.
Additional rainfall amounts of one-quarter to one-half inch can be
expected which would keep river levels elevated or even past
bankfull. Min temperatures to be in the lower to middle 40s north,
upper 40s to lower 50s south. Other than a few light showers
holding on to far eastern WI early in the morning, the rest of
Friday will be dry as weak high pressure moves into western
sections of the Great Lakes. Clouds will be on the decrease with
mostly sunny skies by the afternoon. The return of sun is forecast
to bump max temperatures up into the middle 60s to lower 70s.

Friday night and Saturday...
Quiet conditions to prevail Friday night as the high pressure
moves across the Great Lakes. Mostly clear skies through the
evening will gradually give way to increasing clouds later at
night as a modest mid-level shortwave trough pushes across the
northern Plains. The initial lack of clouds in conjunction with
relatively light winds, will send min temperatures down into the
upper 30s to lower 40s north, middle to upper 40s south. This
shortwave trough shifts into the Upper MS Valley on Saturday with
the main embedded shortwave moving into northern MN. Stronger
forcing to be focused over northern sections of the Great Lakes,
but instability is essentially nil. There is also less moisture
available compared to Thursday night, thus will have chance pops
in the forecast for Saturday with no thunder and less QPF amounts.
Max temperatures Saturday to range from the lower 60s north-
central WI/near Lake MI, middle 60s to around 70 degrees
elsewhere.

Saturday night and Sunday...
Any light shower activity would end Saturday evening over eastern
WI with the next high pressure building southeast across the Upper
Midwest. Look for clouds to gradually decrease from west to east
later Saturday night with mostly clear skies everywhere by
daybreak. This high pressure moves into the Great Lakes region on
Sunday providing for mostly sunny skies and warm temperatures.
Readings to range from the lower 60s near Lake MI, middle 60s to
around 70 degrees inland.

Sunday night and Monday...
Quiet conditions to persist through Monday as the high pressure
shifts into the eastern Great Lakes. It appears enough dry air to
remain in place to keep any precipitation from the next system to
our west and south. There will be an increase in clouds on Monday,
but enough filtered sun to keep max temperatures in the lower 60s
lakeside, upper 60s to lower 70s inland.

Monday night through Wednesday...
Models continue to struggle with the eventual movement of a
nearly-vertically system over the northern Plains and various
frontal boundaries toward the middle of next week. Trying to time
precipitation chances this far out in time is futile due to vast
model solutions. Therefore, have followed the blended solution
which keeps chance pops in the forecast all the way through
Wednesday. Max temperatures for both Tuesday and Wednesday would
be tricky depending on precipitation trends. For now, anticipate
readings at or above normal.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 631 PM CDT Wed May 1 2024

VFR conditions are expected overnight, but showers and thunderstorms
will produce IFR/MVFR conditions as they arrive during the late
morning and early afternoon hours Thursday. Poor flying conditions
are likely Thursday night as showers and scattered thunderstorms
continue.

&&

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

&&

$$

DISCUSSION.....Goodin/Kallas
AVIATION.......RDM