516
FXUS63 KGRB 172144
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
444 PM CDT Mon Jun 17 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- There is a slight risk of severe storms across the region
  through this evening. The best chance of severe storms will be
  across parts of central and east-central WI, with large hail
  being the main threat.

- There is a slight risk of excessive rainfall through this
  evening. There is a continued risk of excessive rainfall from
  Wednesday through Friday.

- Well above average temperatures and humid conditions are
  expected Tuesday, with heat indices climbing into the 90s. Some
  locations in east-central and far northeast WI may see heat
  index values approaching 100.

- Periodic thunderstorm chances will continue throughout much of
  the week. Strong storms and locally heavy rainfall may be
  possible.

&&

.DISCUSSION...
Issued at 444 PM CDT Mon Jun 17 2024

Short Term...Tonight and Tuesday

Precipitation/Thunderstorm Potential:

This afternoon`s surface analysis had a stalled cold front/outflow
boundary situated east-west from Clintonville to Kewaunee.
Thunderstorms developed along and southwest of the front in east-
central WI where a healthy 2000-3000 J/kg of SBCAPE and dew points
in the low 70s prevailed. This will leave a severe threat in east-
central WI for the remainder of this afternoon with hail being the
main threat. Torrential rainfall is also expected with these storms
due to PWATs of 1.75 inches.

The cold front is expected to gradually pivot and lift north as a
warm front late this afternoon into this evening. This will allow
the pool of instability to increase across central and east-central
WI. While thunderstorms are expected to develop and spread into
central WI and continue in east-central WI, the severe potential
will gradually decrease as the evening goes on due to a lack in deep-
layer shear and instability becoming elevated. A marginal hail
threat will remain in place for the evening as a result.

The showers and thunderstorms will shift north into north-central
and far northeast WI late this evening and overnight before exiting
WI into Upper MI by early Tuesday morning.

With the front well to the north of the area, dry conditions are
expected for the remainder of Tuesday. However, some guidance is
indicating an embedded shortwave/MCV will lift north into
southeastern WI and produce some light showers or thunderstorms in
far eastern WI. Included some slight chance PoPs for thunderstorms
in east-central WI for now.

Temperatures/Winds:

Warm and humid conditions are expected to continue overnight as the
frontal boundary lifts north and low-level southerly flow continues.
This will result in well above normal low temperatures ranging from
the middle 60s to low 70s. The hot and muggy conditions will
continue into Tuesday with high temperatures rising into the upper
80s and low 90s. With dew points expected to be in the low 70s, heat
indices will soar into the 90s to near 100. The highest heat indices
are expected in east-central and far northeast WI. Decided to hold
off on a Heat Advisory with this forecast issuance, as there is some
uncertainty with temperatures and dew points. Forecast soundings
indicate afternoon mixing will occur and bring gusty south winds to
the surface, with gusts to 30 to 35 mph.

Long Term...Tuesday Night Through Monday

An active pattern will persist through the majority of the
extended with several rounds of rain and storms possible through
mid-week. Some strong to severe storms will be possible across
north-central Wisconsin Tuesday evening and overnight. Main
threats with stronger storms would be gusty winds, hail, and
locally heavy rainfall. Mid-level flow will then flatten out
toward the end of the week, resulting in an active westerly flow
regime across much of the Midwest.

Tuesday evening storm chances... As a surface low passes across
Ontario, additional storm chances will enter the forecast area
Tuesday evening along a trailing cold front. Most medium-range
model guidance keeps decent instability (between 2,500 and 3,000
J/kg CAPE) out ahead of the cold front through 00Z Wednesday.
This would be enough to sustain convection into early Tuesday
night due to lingering heat and humidity before storm activity
gradually decreases overnight. Heavy rainfall and localized
flooding will once again be a concern given a strong signal for
1.75" to 2" PWATs from central to north-central Wisconsin.

Rest of the extended... Expect a brief dry period on Thursday as
the cold front departs to the southeast, leaving an area of
large-scale subsidence and weak high pressure in its wake. A more
robust system will then trek across the upper Mississippi Valley
to start the weekend, bringing another round of potentially strong
storms Saturday into Sunday. It is too soon to determine severe
potential. Additionally, models are struggling to handle how long
the high pressure will stick around, and are thus disagreeing
about precip timing this far out. Will continue to monitor as we
get closer to the event.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 118 PM CDT Mon Jun 17 2024

A cold front has progressed eastward towards the east-central WI
TAF sites this afternoon. The front has triggered a few showers
and thunderstorms to develop, but have opted to only include VCSH
at the ATW and GRB TAF sites for this afternoon due to their
isolated nature. Will amend as needed. Further west, scattered
showers and isolated thunderstorms were moving into the central
and north-central WI TAF sites. Anticipate the front to gradually
lift north later this afternoon into this evening and bring
additional showers and thunderstorms mainly to the central and
north-central WI TAF sites. Showers will linger the longest at the
RHI TAF site tonight before lifting north early Tuesday morning.
MVFR conditions will only be associated with the heavier showers
and thunderstorms throughout this TAF period, otherwise, VFR
conditions are expected. Dry conditions are anticipated for
Tuesday. LLWS is also expected to develop this evening and
continue overnight.

&&

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

&&

$$

DISCUSSION.....Kruk/Goodin
AVIATION.......Kruk