Severe Thunderstorm Warning 46, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
629 AM CDT Tue Oct 24 2023

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 239 AM CDT Tue Oct 24 2023

Key Messages:

- Thunderstorms expected this morning (80% chance) with heavy rain
  (60% chance) and small hail possible (5% chance).

- Marginal risk (5% chance) for severe weather this afternoon and
  this evening with damaging winds and large hail possible from
  additional thunderstorms (70-90% chance).

- Unseasonably warm temperatures expected today.

- Heavy rain expected at times with up to 1 inch of rain expected
  this morning across central and east-central Wisconsin (60%
  chance) and around 1 inch expected this afternoon and tonight
  (80% chance) with up to 2 inches possible (30% chance).

Forecast details:

Showers and thunderstorm developing along a warm front across
southern Minnesota and west-central Wisconsin will push east
through central and east-central Wisconsin this morning. These
storm will be elevated, with some small hail possible with the
stronger storms. In addition, heavy rain is possible at times,
which would being up to an inch of rain to central and east-
central Wisconsin this morning.

The warm front will lift north through the morning, which will
bring unseasonably warm temperatures to the region this afternoon.
Highs this afternoon are expected to rise into the lower to middle
60s across the north, with lows in the lower 70s across east-
central and portions of central Wisconsin. The warm front lifting
north will cause the shower and thunderstorm activity to lift
north, with the best chance for additional activity north and west
of the Fox Valley. In addition to the frontal boundary the area
will be in the right entrance region of an upper level jet,
frontogenesis, and a weak mid level shortwave tracking through the
area. There could be a break between the activity this morning
and the activity expected this afternoon and this evening. Storms
that develop this afternoon and this evening could be marginally
severe, with damaging winds and large hail possible as MUCAPEs
rise to around 500 J/kg with mid level lapse rates of 6-7 C/km. In
addition, heavy rain is likely as PWATs are near climatological
maximum for this time of year with values of 1.3 to 1.5 inches.
This second round of rain will likely bring an additional inch of
rain, with up to 2 inches possible.

Although the frontal boundary will remain across the western Great
Lakes, the dynamics will shift to the east on Wednesday. This will
keep a chance for additional showers and thunderstorms (20-40%
chance), with coverage and intensity much less than today and
tonight. Despite abundant cloud cover there will not be a push of
cold air; therefore, temperatures will remain mild on Wednesday.

.LONG TERM...Wednesday Night Through Monday
Issued at 239 AM CDT Tue Oct 24 2023

Main forecast focus to be on the Wednesday night through Thursday
night time frame as a second round of heavy rain is expected to
move through the region and raise the possibility of at least some
urban flooding. A secondary focus to be on temperatures this
weekend as much colder air is set to arrive.

.Wednesday night and Thursday...
Precipitation chances will be on the increase again later
Wednesday night as a 30 to 40 knot low-level jet interacts with a
nearly stationary front parked over central WI. Additional lift to
be provided by the right entrance region of the upper jet. PW
values around 1.5 inches to reside over the area which is about
300 percent of normal, thus another round of heavy rainfall is
anticipated to begin toward daybreak. Min temperatures to be in
the upper 40s to lower 50s north, middle to upper 50s south.
Models are in good agreement with the northeast movement of a
mid-level shortwave trough toward the western Great Lakes by
Thursday afternoon. The increased mid-level Q-G and FGEN forcing,
coupled with a surface wave riding along the stationary front,
will compensate for the loss of upper jet support and bring
additional heavy rain potential to northeast WI on Thursday. This
heavy rain would fall on saturated soils, thus leading WPC to
forecast a slight risk of excessive rain. The extent of any
flooding is conditional depending on how much rain fell earlier in
the week. The public should be alert to urban flooding with storm
drains that may be clogged with leaves. Mild conditions to persist
despite the rain with max temperatures in the middle to upper 50s
far north, lower to middle 60s south.

.Thursday night and Friday...
The surface wave and shortwave trough push across northeast WI
Thursday evening with a continued threat for heavy rain. The rain
chances will linger through the rest of Thursday night as the
frontal boundary to still be hanging over the area. By this time,
we will also have to watch rivers and streams as some flashier
rivers could go above bankfull or even reach minor flood stage.
Cooler air will begin to advect into the region with min
temperatures in the lower to middle 40s north-central WI, lower
50s east-central WI. Rain chances to persist through Friday as a
strong cold front sweeps into the Great Lakes. Low-level moisture
will not be nearly as deep compared to earlier in the week and the
cold front is progressive, thus any additional rainfall would be
light in nature. After morning temperatures in the lower 50s to
lower 60s, expect to see readings to slowly fall in the afternoon
as CAA sweeps across WI.

.Friday night and Saturday...
Any lingering light rain over far eastern WI would end Friday
evening, allowing for the area to dry out. There could be some
lake clouds or even a few lake effect flurries into Vilas County,
but will keep that area dry for now. Any breaks in the clouds
appear to be short-lived as the cold front stalls over the OH
Valley and some models already bring a chance of light
precipitation into northeast WI by Saturday afternoon.
Temperatures would support a rain/snow mix over north-central WI
with light rain elsewhere.

.Saturday night through Monday...
The bulk of any heavier rain will be to our south later this
weekend into early next week in the vicinity of the stalled
frontal boundary. The exact location of this boundary will
determine how far north to take pops Saturday night through
Sunday. Monday is looking dry at the moment. The bigger story for
Sunday and Monday will be the chilly conditions with max
temperatures both days well-below normal.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 628 AM CDT Tue Oct 24 2023

Showers and thunderstorms will continue for much of the morning,
with the most activity across central and east-central Wisconsin,
as a warm front lifts north across the region. This will cause
conditions to deteriorate to MVFR/IFR in the showers and
thunderstorms at times.

A lull in the precipitation is expected later this morning into
the early afternoon, before additional showers and thunderstorms
develop during the later afternoon and last into the evening
hours. This round of showers and thunderstorms could once again
reduce conditions to IFR/LIFR, especially once deeper moisture
arrives and ceilings lower across the region. These storms could
also be strong to severe, with large hail and damaging winds
possible.

Southwest winds will be gusty at times today as winds remain
strong aloft, highest south of the warm front. LLWS could again
develop mainly south of a Wausau to Marinette line this evening.
&&

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

SHORT TERM.....Kurimski
LONG TERM......Kallas
AVIATION.......Kurimski

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