046
FXUS63 KGRB 201936
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
236 PM CDT Thu Jun 20 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- There is a chance of thunderstorms in central and east-central
  Wisconsin tonight. Severe storms are unlikely.

- Thunderstorms with gusty winds and locally heavy rain are
  possible Friday and Friday night. The rain could produce small
  stream and urban flooding.

- Strong to severe thunderstorms are possible Saturday with
  damaging winds the main threat. Heavy rains may cause rivers to
  rise rapidly.

- More showers and thunderstorms are expected Monday night into
  Tuesday.

&&

.DISCUSSION...
Issued at 236 PM CDT Thu Jun 20 2024

Short Term...Tonight and Friday

A weak mid level shortwave and upper jet will bring the chance for
some showers or thunderstorms across the region tonight; however,
most areas should remain dry as the forcing will be fairly weak.
Lows tonight will stay fairly close to normal ranging from the
lower 50s across the north to around 60 across east-central
Wisconsin.

A warm front will lift north on Friday over southern Wisconsin.
There will be abundant moisture along with a vigorous mid level
shortwave tracking through northern Wisconsin along with the right
entrance region of an upper level jet. Instability will be fairly
modest, with MUCAPEs of 500 to 1000 J/kg, and long skinny CAPE
profiles. Given the strong dynamics, moisture, and long skinny
CAPE profiles moderate to heavy rain is expected at times on
Friday. QPF amounts on Friday should generally be below an inch,
as probabilistic forecasts indicate there is only a 20 to 30
percent chance of getting more than in inch mainly across western
portions of central and north-central Wisconsin. Therefore,
flooding concerns are fairly low through Friday as most area
rivers and streams can handle this initial surge of moisture.

Highs on Friday should be below NBM values given the abundant
cloud cover and precipitation expected. Highs are only expected to
get into the middle 60s across the north, with lower 70s across
east-central Wisconsin and portions of central Wisconsin.

Long Term...Friday Night Through Thursday

Models are in good agreement with regards to a persistent upper-
level high pressure over the southern CONUS. The main band of
westerlies to run across the northern tier of states and bring a
series of shortwaves through the Great Lakes. In addition, a wavy
frontal boundary to be situated over the Great Lakes to act as a
focal point for periods of showers and thunderstorms through
Saturday night and again Monday night/Tuesday. Temperatures to be
at or above normal for much of next week.

Friday night and Saturday...
The warm front to stretch across central/east-central WI Friday
night. An increasing southwest low-level jet of 35-40 knots will
continue to draw gulf moisture into the region with PW values of
around 2 inches. This moisture transport, coupled with the passage
of a subtle mid-level shortwave and a diffluent flow aloft, will
bring the next round of showers and thunderstorms across northeast
WI. Exactly where the warm front sets up will determine who gets
the heavy rain as convection would tend to train west to east over
the same locations. Potential is there for over an inch of rain to
fall. Min temperatures to range from the middle to upper 50s
north, lower to middle 60s south. This warm front is forecast to
remain parked across central/east-central WI through Saturday and
continue to be the main focal point for additional showers and
thunderstorms. An unknown at this time is whether the remnants of
a MCS could be tracking across WI during the morning. If this MCS
does develop, a damaging wind event may occur. Otherwise, the air
mass south of the warm front will become more unstable in the
afternoon as MUCAPES rise to near 2K J/KG over southern WI and
with shear of 35-40 knots, will need to watch for stronger storms
over central/east-central WI. The main threat though for Saturday
will be the potential for more heavy rain with PW values in the
1.5 to 2.25 inch range. If the heavy rains fall over the same area
Friday night and Saturday, flooding would become a major concern,
along with rapid rises in area rivers. Max temperatures Saturday
will be tricky depending on where the warm front resides and any
breaks in the rain. For now, have readings in the lower 70s far
north to the lower 80s far south.

Saturday night and Sunday...
The threat for heavy rain will continue into Saturday night as a
surface low and cold front move through the region. The heavier
precipitation should shift to our south and east later Saturday
night once the cold front exits. While too early for specifics,
models are indicating the potential for anywhere from 1 to 4
inches of rain with flash flooding and river flooding a concern.
Even as we finally say good-bye to the initial system, models
indicate a mid-level shortwave trough to dig southeast into the
Great Lakes on Sunday. This trough, coupled with cooler air aloft
and daytime heating, will bring another chance of showers/slight
chance of thunderstorms to northeast WI with northern WI having a
higher chance. Max temperatures on Sunday to be in the lower to
middle 70s north-central WI, upper 70s to around 80 degrees
elsewhere.

Sunday night and Monday...
The departure of the shortwave trough and loss of daytime heating
will end any further precipitation by Sunday evening. An area of
high pressure will then move into the region for Sunday night
allowing for skies to become mostly clear with a light northwest
wind. Will have to watch for fog due to all the rain from the
previous few days. As the high pressure slides to our east on
Monday, a return flow develops over WI as dew points begin to rise
again. Max temperatures Monday to range from the middle to upper
70s near Lake MI, upper 70s to lower 80s inland.

Monday night and Tuesday...
The next shortwave trough/associated cold front are progged to
sweep into the Great Lakes Monday night into at least Tuesday
morning. Temperatures on Tuesday will be determined on the timing
of this system as models differ a bit. For now, have max
temperatures to range from the lower 80s near Lake MI and northern
WI, middle to upper 80s south.

Tuesday night through Thursday...
Toward the middle of next week, models are showing an upper ridge
to build across the Rockies into the Plains. This would bring a
northwest flow aloft into northeast WI which would then keep
temperatures around normal with less humidity and a chance to dry
out.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1254 PM CDT Thu Jun 20 2024

MVFR/IFR ceilings are expected roughly south of Highway 29 early
this afternoon, with scattered showers diminishing across east-
central Wisconsin.

VFR conditions are likely this afternoon and evening as slightly
drier air arrives thanks to a surface high over Lake Superior.
Rain and IFR conditions are likely over most of the region late
tonight and Friday as a warm front approaches from the central
Plains.

&&

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

&&

$$

DISCUSSION.....Kurimski/Kallas
AVIATION.......Kurimski