NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 160007
AFDGRB

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

Updated aviation portion for 00Z TAF 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 00Z TAF Issuance
Issued at 707 PM CDT Tue Jul 15 2025

VFR conditions will continue early this evening, then flying
conditions will deteriorate (to mainly MVFR and IFR) across north
central WI, impacting RHI, as an area of showers and storms
spread into the area. The storms could bring brief gusty winds,
small hail and heavy rain. Locations to the south look to stay
VFR through the night.

On Wednesday, lingering low clouds and rain showers, with some
embedded storms also possible, will continue across parts of
central and northern WI during the morning. Then an area of
showers and storms is expected to move east across most of the
area. The showers/storms will bring MVFR CIGs (possibly IFR at
times), along with a threat for gusty winds and hail. The
strongest storms look to exit into Lake MI by 01-02z, with
lingering showers possible and low ceilings Wednesday evening.
Will carry prevailing thunder groups when/where the storms look
most likely, with TEMPO groups for the stronger storms with higher
winds gusts. Timing could need to be adjusted as the models hone
in on the timing.

&&

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

&&

$$

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