783
FXUS63 KGRB 010323
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1023 PM CDT Fri May 31 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Showers and isolated thunder over north-central Wisconsin
  tonight through Saturday (60-70 percent chance of rain). Lower
  chances for showers and isolated thunder northeast to east-
  central Wisconsin (remaining dry until 30-50 percent chances
  arrive Saturday afternoon).

- Watching Monday for a chance of strong thunderstorms and
  locally heavy rainfall as a cold front crosses the region.

- Strong thunderstorms may again be possible Tuesday afternoon
  and evening as another cold front moves across the region.

&&

.DISCUSSION...
Issued at 233 PM CDT Fri May 31 2024

Short Term...Tonight and Saturday

Doppler radar shows a line of broken showers associated with a
cold front stretching from the western UP to southern Minnesota.
The front and associated showers will move very slowly tonight and
only make minimal progress during the overnight hours. The
scattered to isolated nature of the showers is expected to
continue overnight as the forcing will be rather weak and spread
out over a large area. Some modest MUCAPEs of a few hundred J/kg
will mean some rumbles of thunder will be possible at times, but
should not be ubiquitous. The abundant cloud cover across the
region will keep temperatures mild tonight as lows range from the
middle 50s across the north, with around 60 across the Fox Valley.

The front will make progress east on Saturday; however, there are
signs the front will wash out as it heads east as the main mid
level forcing lifts north over southern Canada and a modest mid
level trough tracks to the south. This will create two areas of
precipitation that will affect north-central and central Wisconsin
with the northern stream system and possibly the Fox Valley and
lakeshore with the southern stream system. There are some models
that keep the Fox Valley and lakeshore dry on Saturday, which is
entirely possible given the weak southern stream system. However,
there are signs that this system will at least provide a glancing
blow to the lakeshore, if not affect the rest of east-central
Wisconsin. Once again some modest MUCAPEs of a few hundred J/kg
will keep the chance for a few thunderstorms possible across the
area.

The precipitation forecast will play a role in high temperatures
on Saturday as more precipitation would hold down high
temperatures while less showers would mean warmer temperatures.
The coolest temperatures will be across north- central Wisconsin
and the lakeshore given the higher chances for rain (40-60
percent) with highs around 70. The warmest temperatures will
likely be across the Fox Valley and portions of central Wisconsin
given the lower rain chances (30-40 percent) with highs in the
lower 70s.

Long Term...Saturday Night Through Friday

 Main focus of the long term forecast period revolves around a
couple chances for showers and thunderstorms beginning Sunday
night through Wednesday.

Saturday Night through Sunday...As a weak mid-level ridge
develops over the region most areas will become dry Saturday
night, with the exception possibly being a few lingering showers
and storms behind a departing short-wave. Model trends over the
past 24-hour have slowed the onset of precipitation Sunday and it
now looks like the daylight hours should stay dry. This drier
trend also helped boost high temperatures a few degrees Sunday
afternoon with inland areas forecast to reach the upper 70s to
low 80s, while lakeside areas peak in the upper 60s.

Sunday Night through Monday night...Ensemble guidance has come
into better agreement with respect to an upper-level shortwave
and surface low pressure system ejecting out of the northern
Plains into the western Great Lakes Sunday night through Monday.
An initial northward surge of warm moist air with a developing
low-level jet may initiate scattered showers and storms late
Sunday night into Monday, however, this showers and storms may
remain spotty as there is a lack of stronger forcing. With
diurnal stabilization no severe storms are expected with this
initial round of precipitation, however, isolated storms may
produce some gusty winds, especially across central and northern
WI there the 850 mb winds in the low- level jet are forecast to
reach 35-40kts.

The better chance for a few stronger to possible severe storms
comes later Monday morning into the afternoon with the passage of
the attendant cold front. Models are showing a wedge of 600-
1200 J/kg of SBCAPE extending into central and northern WI during
this period. However, the instability during this period will
depend on how the atmosphere destabilizes after the expected
initial round of showers and overcast skies. Temperatures Monday
are forecast to be slightly warmer than normal with highs in the
middle 70s to low 80s away from Lake Michigan and about 5-
10 degrees cooler lakeside.

Tuesday through the end of the extended...The unsettled pattern
is expected to continue through the middle of next week. Ensemble
guidance is in broad agreement with a system propagating across
the northern Plains and dragging a cold front across Wisconsin
sometime Tuesday into Wednesday morning. Both the GFS and ECMWF
are showing abundant SBCAPE Tuesday afternoon and slightly above
normal PWAT values. While the details and timing of this system
need to be refined over the coming days, this time period does
bear watching, especially for those with outdoor or travel plans
Tuesday afternoon. Temperatures are expected to peak next Tuesday
before beginning a slightly downward trend to normal or just
slightly cooler than normal.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1023 PM CDT Fri May 31 2024

A very slow moving cold front across northwest Wisconsin will
produce scattered showers and isolated thunderstorms north of a
SAW to RHI to EAU line tonight.

This front should move slowly east Saturday, probably producing
scattered showers and isolated thunderstorms west of a IMT to STE
line by early afternoon. There could also be scattered showers or
thunderstorms near the bay and Lake Michigan in the late afternoon
or early evening as an upper level disturbance moves across
southern Wisconsin. VFR conditions are likely Sunday.

&&

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

&&

$$

DISCUSSION.....Kurimski/GK
AVIATION.......RDM