672
FXUS63 KGRB 152045
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
345 PM CDT Tue Jul 15 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Isolated severe storms over far north-central WI this evening.
  Severe Thunderstorm Watch is in effect until 10 pm. Heavy rain
  is also a potential, especially with training storms.

- Scattered severe storms expected Wednesday into Wednesday
  evening. Main hazards will be damaging winds and heavy rain. At
  the least, the severe risk and flooding risk will be more
  extensive than today.

- Very warm and humid through Wednesday. Cooler and less humid
  late this week.

&&

.DISCUSSION...
Issued at 345 PM CDT Tue Jul 15 2025

Main focus is on active period of storms with possible severe
weather and heavy rain through Wednesday evening.

Near Term Trends: Main cold front is over central MN with storms
starting to develop from northeast SD into west central MN, but
showers and storms have been developing most of the day along
outflow from morning storms that crossed Lake Superior and northern
Upper Michigan. These storms have not been handled well by majority
of models, but thus far they also have not moved much to the east.
Eventually, given effective shear around 30 kts and MLCAPES
1000-2000J/kg isolated severe risk could move into Vilas County
this evening. Severe Thunderstorm Watch mainly west and north, but
Vilas County is included as severe storms could clip far north-
central Wisconsin. Main risk will be damaging wind gusts and
smaller hail. PWATs up to 1.8 are well above 90th percentile and
warm cloud depths above 12kft will support locally heavy rainfall
especially within training storms. Showers and some storms will
continue through rest of the night at times over northern WI,
though capping will keep rest of area free of showers and storms.
Will be warm and humid night ahead of the approaching front.

Thunderstorm chances and severity Wednesday/Wednesday Evening:
Active, potentially high impact, weather in store for Wednesday as
MCV approaches and interacts with building instability of MLCAPES
of 1500-2000J/kg late morning to early afternoon. Effective shear
of 30-40 kts will result in organized storms will all hazards
possible. Enhanced 0-1km and 0-3km SRH along and north of the
northern edge of the MCV lead to at least a small potential of a
tornado. Heavy rain is a concern with robust moisture laden
convection as PWATs increase to over 2 inches and possibly as high
as 2.25 inches which would be a maximum for the day. Warm cloud
depths are forecast to be over 13kft which will lead to very
efficient rainfall. Higher-end HREF QPF forecasts of 3+ inches are
probably reasonable in this setup, but it is just not clear where
exactly the heaviest rain will occur with the MCV. Thought about
issuing a Flood Watch, but uncertainty in the heaviest rain
precludes it at this time.

Outlook: Frontal boundary shifts east by Thursday. Trend is for a
drier day now as main bulk of showers are well to the east by
daybreak. High pressure still forecast to settle over the western
Great Lakes for the end of the week. The high will bring cooler
and less humid, more comfortable conditions to the region. Dry
weather will be brief. West-northwest flow will bring the next
chance of showers and storms to the state as early as Friday
night. Currently it looks like greatest chances for rain will last
into Saturday evening, with Sunday mainly dry. Temperatures look
seasonable with highs upper 70s to lower 80s and lows in the mid
50s to lower 60s.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 103 PM CDT Tue Jul 15 2025

Primary risk of showers and storms through tonight will be over
north-central WI, including RHI, late this afternoon through this
evening. Scattered showers could linger most of the night.
Continued to include mention of gusty winds at RHI when greatest
risk of thunder occurs this evening. Otherwise, sct-bkn VFR CIGS
will become bkn and lower to IFR and MVFR late tonight through
end of the TAF period central to north-central WI as cold front
approaches from the west. VFR CIGS will prevail farther east at
GRB/ATW/MTW. Southerly gradient winds will remain gusty to 15-20
kts through 00z-01z this evening.

Looking ahead, showers and storms, some strong to severe with
gusty winds and heavy rainfall, are expected to impact majority of
the TAF sites just beyond the TAF period Wednesday afternoon into
Wednesday evening.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......JLA