122
FXUS63 KGRB 181737
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1237 PM CDT Sat May 18 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Thunderstorms are likely late this afternoon across central and
  north-central Wisconsin. There is a chance of thunderstorms in
  east central and far northeast Wisconsin this evening. Some
  storms may become strong to severe with damaging winds and hail
  the main threat.

- Chances for showers and thunderstorms continue through mid-week.
  While too early to determine severe potential, confidence is
  increasing in locally heavy rain on Tuesday.

&&

.DISCUSSION...
Issued at 420 AM CDT Sat May 18 2024

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

Scattered light showers and sprinkles are possible in far north
central Wisconsin early this morning due to elevated instability.
They should end shortly after sunrise.

It will be a summer like day today as gusty southerly winds
provide good mixing of the lower atmosphere. Mixing to 900mb or so
will result in highs in the 80s in the forecast area, though it
will be cooler near Lake Michigan. A scattered to broken line of
thunderstorms is expected to develop ahead of a cold front that
will move into central and north central Wisconsin in the late
afternoon. 1000 J/KG of CAPE and an inverted V sounding could make
for a few strong or severe storms with damaging winds and hail.
The activity should should diminish as it moves into the Fox
Valley and lakeshore counties in the early evening and encounters
lake stabilized air in the low levels and loss of surface heating
as the sun sets.

Whatever convection makes it to the lakeshore should move out over
the lake by midnight, with clearing skies and slightly cooler and
drier air arriving overnight. Lows will be near normal. Sunday
should be very pleasant, with light winds, mostly sunny skies and
low humidity. Highs will be about 5 to 8 degrees above normal.

Long Term...Sunday Night Through Friday

As previously mentioned, focus for the extended remains on
rain/storm chances through mid-week brought on by an active
synoptic pattern. Large-scale ridging across the eastern CONUS
is expected to put much of the Midwest under a southwest flow
regime through mid-week, which is conducive to warm air advection
and moisture transport up from the south. Hence, periods of
moderate to heavy rainfall with potentially high QPF will be
something to look out for.

Monday precip chances... A robust trough situated across the
western CONUS will eject a shortwave up into the western Great
Lakes, bringing a fast-moving round of rain to the forecast area
Monday morning. During this time, a warm front will stall to our
south, providing some lift via isentropic ascent and a surge of
warm air advection. Additionally, an open Gulf will bring a swath
of deep moisture up into portions of central and east-central
Wisconsin Monday afternoon, placing a corridor of 1.5+" of PWAT
across the Fox Valley. Models seem to be targeting central
Wisconsin to receive the bulk of the precip with this system (~0.6"
to 0.8" QPF) due to showers being more prolonged over that area.
Most convective elements look to remain to our south along the
warm front, but cannot rule out a rumble of thunder along/south of
Highway 29.

Tuesday/Wednesday precip chances... As Monday`s system departs to
the east, attention then turns to a more dynamic system that
treks from the central Plains to the upper Mississippi Valley by
Tuesday evening. Current model guidance suggests that this system
has the potential to bring heavy rain to much of the forecast
area Tuesday through Wednesday morning, although it is still too
soon to discern exact amounts given significant model spread this
far out. With plentiful Gulf moisture and dewpoints in the low to
mid 60s, suspect that QPF will trend on the higher end of what
ensembles are currently showing. This being said, forecast
confidence is high enough to warrant a day 4 marginal to slight
risk of excessive rainfall across the CWA. A first glance also shows
that thunderstorms may be possible across our southern counties.
However, instability in the warm sector will struggle to make it
this far north and east, hindering severe potential for the time
being. Will continue to monitor convective elements as medium-
range models come into play. Overall, biggest things to look out
for will be changes in QPF and risk for flooding/flash flooding.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1237 PM CDT Sat May 18 2024

A broken line of thunderstorms are expected to move
across the region during the late afternoon and evening hours
ahead of a cold front. The activity should be along a line from
RHI to ISW around 22z, IMT to DLL around 01z, and ESC to OSH by
02z. The activity will like weaken as it moves towards Lake
Michigan. Strong wind gusts, hail and brief IFR conditions may
accompany the stronger thunderstorms. VFR conditions are expected
outside of the thunderstorm activity. After the convective
activity exits the area by late evening, there will be clearing
overnight and good flying weather Sunday.

&&

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

&&

$$

DISCUSSION.....RDM/Goodin
AVIATION.......Kallas