000
FXUS63 KGRB 131051
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
551 AM CDT Sat Apr 13 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- There is a chance of thunderstorms tonight across the north.
  Small hail is possible with some storms.

- Dry and very mild weather is expected today and Sunday, with
  relative humidities of 25 to 30 percent inland from Lake
  Michigan in the afternoon. This may create conditions conducive
  for grass fires.

- There is a good chance of showers and thunderstorms next Tuesday
  and Wednesday. A few strong storms are possible, mainly across
  central and east central Wisconsin.

&&

.DISCUSSION...
Issued at 432 AM CDT Sat Apr 13 2024

Short Term...Today...Tonight...and Sunday

A surface ridge will move east of Wisconsin today
allowing winds to shift to the south and bring somewhat warmer
air into the area. Highs will be about five degrees higher than
yesterday, though a lake breeze will make it turn cooler near
Lake Michigan in the afternoon.

A jet streak moving across southern Canada and an approaching weak
surface front could produce some elevated showers and thunderstorms
along the Michigan border tonight. Mid level lapse rates are pretty
decent, but the air below 700mb is very dry. So do not expect much
precipitation from any activity that materializes. Lows tonight
will be around ten degrees above normal.

Sunday should be mostly sunny and very mild, as air that warmed
from descending the eastern slopes of the Rockies moves into
Wisconsin on northwest winds. The air is quite dry as well, which
will make for relative humidities of 25 to 30 percent inland from
Lake Michigan in the afternoon.

Long Term...Sunday Night Through Friday

The primary focus of the extended period will be the potential for
active weather Tuesday and Wednesday as a strong low pressure
system develops on the lee side of the Rockies. This system is
expected to intensify fairly quickly, cross the Central Plains
late Monday through Monday night, and then lift towards the Great
Lakes Tuesday. Timing on the development of precipitation remains
variable as models like the GFS bring rainfall in with the initial
warm air advection overnight while the ECMWF and Canadian delay
the onset of rain until later in the day Tuesday. This timing will
be important for thunderstorm potential, as an overnight onset
would likely limit how much the area can destabilize by Tuesday
afternoon. Given the dynamics of the system, ample moisture, and
the potential for instability, some strong storms may be possible,
mainly focused across central to east-central Wisconsin as of now.
Better potential for severe weather will generally be south of our
area focused mainly across southern Wisconsin and southwards, but
this may change if the general track of this system shifts.
Outside of strong thunderstorms, this system will bring with it
ample Gulf moisture, pushing PWATs to around 1.25+ inches. With
convective weather in the forecast, this could make for some
fairly high rainfall amounts Tuesday into Wednesday. The area is
currently in the marginal risk for excessive rainfall for both
days.

Unsettled weather then shows some signs of sticking around behind
this stronger initial system, with a broad upper low remaining in
place over Manitoba. A couple of shortwaves rounding the low may
bring additional, albeit lighter rain amounts to the area. Colder
air coming around the low at the same time may even mean some of
the precipitation falls as snow or a brief mix overnight Thursday
night into Friday.

Temperature-wise, the warmest day in the extended will be Monday,
with highs in the 60s to low 70s. Tuesday will be slightly cooler
as the rain crosses the region, with highs in the 60s. Cooler air
then filters in behind the low, bringing highs back into the upper
40s to lower 50s for the rest of the week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 550 AM CDT Sat Apr 13 2024

VFR conditions are expected today, with some middle and high
clouds moving across northern Wisconsin.

An upper level disturbance moving across Lake Superior could
produce scattered showers or thunderstorms tonight near the
Michigan border, with clear skies further south. Low level wind
shear is possible tonight with light south winds at the surface
and southwest winds around 40 knots at 2000 ft.

VFR conditions are expected Sunday, with some high based cumulus
clouds in the afternoon.

&&

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

&&

$$

DISCUSSION.....RDM/Uhlmann
AVIATION.......RDM