290
FXUS63 KGRB 221146
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
646 AM CDT Sat Jun 22 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Occasional thunderstorms with heavy rain are likely today. The
   heavy rain could result in flash flooding of urban areas and
   small streams. A Flood Watch is in effect through early this
   evening along and south of Highway 29.

- Strong to severe thunderstorms are possible during the late
  afternoon and early evening, mainly south of highway 10. a few
  storms could produce damaging winds, and possibly tornadoes.

- Many rivers and streams will continue to rise into early next
  week due to runoff from todays rainfall.

- Additional strong to severe thunderstorms are possible Monday
night into Tuesday evening.

&&

.DISCUSSION...
Issued at 359 AM CDT Sat Jun 22 2024

Short Term...Today...Tonight...and Sunday

The potential for flooding rain is the main concern
for this forecast period. Forecast soundings have precipitable
water values of as much as 2.15", which is close to the all time
record for June. Some upstream sites in southern Minnesota and
northern Iowa had an inch to an inch and a half of rain in an hour
early this morning, and this will likely happen here today.

The computer models have very different forecasts for the axis of
heaviest precipitation. Some of them even have two axes, one
across northern Wisconsin and one across the central part of the
state, with a relative minimum in between. This is plausible given
split jet streaks moving across the area today. We will keep the
flood watch going for the area south of highway 29, as one and
three hour flash flood guidance is lowest there.

In addition to the heavy rain, there is some chance of severe
storms along and just north of the warm front, which will be
moving north through the Fox Valley during the late afternoon.
Storms with damaging winds are possible, and low LCL heights would
suggest some tornado potential if we can get rotating storms.

The rain will end from west to east this evening, with skies
remaining cloudy overnight. A strong jet moving through the
cyclonic flow aloft will likely produce some showers and low top
thunderstorms Sunday. The atmosphere will be much drier than
today, so additional rain will be modest.

Rain from today will produce rising streams and small rivers,
which will empty into the larger rivers in the next couple of
days. So there is some flood potential early next week as well as
today.

Long Term...Sunday Night Through Friday

A few showers and thunderstorms may linger into Sunday night as a
transient short-wave departs the region. Monday should trend
mostly dry as a brief period of high pressure develops over the
region. Southerly winds Monday afternoon will help bring
temperatures back up into the upper 70s to middle 80s.

The main period to watch for potential impactful weather during
the long-term is Monday night through Tuesday. Medium range
models are in decent agreement with a low pressure system
traveling across central Canada lifting a warm front across
northern WI Monday night with an area of mid-level convergence
developing along the noise of a low-level jet. Forecast soundings
show robust elevated instability and strong effective layer shear
during this time creating an environment that could conditionally
support stronger to possible severe elevated storms. However,
with nocturnal stabilization and a cap likely over much of the
region the best chance for stronger storms will be in close
proximity to the warm front. If thunderstorms are able to develop
large hail and strong winds gusts look like the primary hazards.
A second wave of thunderstorms may then be possible Tuesday
afternoon/evening as a cold front comes across the region,
however, the timing of these feature is still uncertain.
Additionally, Tuesday looks like the hottest and most humid day
next week with highs forecast to reach the middle 80s to around
90 degrees.

Once the cold front is through the region Tuesday night a period
of quieter weather is expected as a high pressure system takes
control of the region during the middle of next week.
Temperatures should trend closer to normal next Wednesday and
Thursday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 646 AM CDT Sat Jun 22 2024

IFR conditions will continue through around 15z Sunday. There
will be periods of showers and thunderstorms today, as a warm
front lifts north to near a AUW to GRB line by late afternoon. The
activity will end from west to east this evening, as a cold front
moves across the area. Improving flying conditions are expected
Sunday, though there could be scattered thunderstorms in the
afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for WIZ030-031-035>040-045-
048>050.
&&

$$

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