794
FXUS63 KGRB 072321
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
621 PM CDT Fri Jun 7 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Showers are expected overnight into early Saturday afternoon.

- There is a slight chance of thunderstorms Saturday afternoon,
  mainly across northern Wisconsin. Severe weather is not
  expected.

- Below normal temperatures are forecast through early next week,
  then go above normal latter half of the week.

&&

.DISCUSSION...
Issued at 333 PM CDT Fri Jun 7 2024

Short Term...Tonight and Saturday

Main forecast challenge to be timing of precipitation onset late
tonight, ending Saturday afternoon and whether additional showers
and storms can redevelop later Saturday afternoon.

The 19Z MSAS surface analysis showed a weak area of high pressure
that extended from ND to the Upper Midwest. Otherwise, surface
features were rather diffuse which is typical of summer. Visible
satellite imagery indicated fair weather cu over northeast WI with
middle and high clouds to our west. across the Plains.

Clouds will be on the increase this evening as a weak surface
boundary and mid-level shortwave trough move across the Upper MS
Valley. An uptick in both moisture transport and mid-level Q-G
forcing will bring a swath of showers toward central WI after
midnight and perhaps reach eastern WI toward sunrise. Instability
is essentially nil, thus no mention of thunder for later tonight.
Min temperatures to be in the upper 40s to around 50 degrees
north, lower to middle 50s south.

This band of showers will continue to move across the forecast
area Saturday morning before forcing shifts east with the
shortwave trough. Exactly how has this precipitation (and its
associated clouds) moves will set the stage for additional
precipitation chances Saturday afternoon. A faster exit would
allow for some clearing to occur and bring a minor increase in
instability (200-400 J/KG) mainly to northern WI (maybe into parts
of central and east-central WI). Shear is forecast to be in the
30-50 knot range north, so despite the weak instability, cannot
rule out a slight chance of thunderstorms to pop-up in the
afternoon. Severe weather is not expected. All of this would be
mute if we cannot clear out the clouds, thus there is still some
doubt to the forecast overall for Saturday afternoon. Max
temperatures to continue running below normal with readings in the
lower 60s along Lake MI, mainly upper 60s inland.

Long Term...Saturday Night Through Friday

The main focus for the forecast period is resolving the
precipitation trends for the late weekend and early next week.

Saturday night through Sunday...A few lingering showers are
possible Saturday evening before dry conditions return to the
region overnight. Sunday, another weak shortwave will round the
upper low to our northeast, bringing some brief stronger CAA in
the afternoon. Short term models do develop a couple showers as a
result, relying mainly on some meager instability from the
surface. While the instability may suffice for a brief rumble of
thunder, would still expect that overall and rain will be light,
brief, and fairly small in areal coverage.

Rest of the extended...The precipitation trends for early next
week will rely heavily on the evolution of the upper pattern over
the weekend. Previous model runs featured a shortwave riding
across the Northern Plains, leading to the development of a closed
low south of Wisconsin and light precipitation on Monday. More
recent trends now go the other way however, keeping the
aforementioned shortwave closed off in Canada while upper ridging
builds eastwards behind the cold air advection. This will keep us
dry Monday until the shortwave finally arrives behind the ridging
sometime on Tuesday. It`s important to note that regardless of
which way the precipitation comes through, the overall impact
will be low as neither solution has potential for any severe
weather in our area. Additionally, both still see some more modest
return flow beyond Tuesday, which would see the return of some
warmer temperatures to the region.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 621 PM CDT Fri Jun 7 2024

VFR cumulus clouds from 4K-5K ft will dissipate early this evening.
Mid and high clouds are forecast to quickly overspread the region
this evening into the overnight period as a frontal boundary and
shortwave trough approach from the west. Chance of showers to
reach central WI toward daybreak with cigs/vsbys lowering into the
MVFR category. These MVFR conditions would then spread east into
eastern WI Saturday morning, along with the rain showers. Cigs
could briefly dip to IFR under any of the heavier showers in the
morning. Some improvement is expected Saturday afternoon with cigs
returning to VFR. Depending on amount of clearing, a few
showers/storms could pop up mainly over northern WI in the
afternoon.

West/northwest winds gusting to 30 kts will dissipate early this
evening around sunset.

&&

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

&&

$$

DISCUSSION.....Kallas/Uhlmann
AVIATION.......Kurimski