465
FXUS63 KGRB 190911
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
411 AM CDT Sun May 19 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Thunderstorms are likely Monday. A few storms may become strong
  to severe south of Highway 29. The main threats are strong
  winds and hail.

- Active weather is expected to continue through midweek, with
  confidence increasing in the potential for heavy rainfall and
  strong to severe storms on Tuesday.

&&

.DISCUSSION...
Issued at 410 AM CDT Sun May 19 2024

Short Term...Today...Tonight...and Monday

Very nice weather is expected today. A weak cold front moved across
the region this morning. While the air behind it is not very cold,
the air is much drier. Relative humidities of 20 to 25 percent
are expected this afternoon in the sandy soil areas, but the threat
of fires will be reduced by yesterdays rain and relatively light
winds. Highs today will be five to ten degrees above normal.

Clouds will increase tonight as an upper level disturbance and
surface low approach from the Central Plains states. Lows will be
close to normal.

Showers and elevated thunderstorms are likely Monday as the system
moves across Wisconsin. Very heavy rain is possible as precipitable
water values of 1.25" to 1.45" are close to the maximum recorded
for this time of the year. This will likely cause rivers and streams
to rise, but probably stay within their banks. Additional heavy
rain is expected Tuesday, which could then result in flooding. The
threat of severe storms Monday afternoon is mostly across southern
Wisconsin, but there is some chance of strong or severe storms south
of highway 29 if the warm front makes it that far north. Highs Monday
will be a few degrees below normal in the north and a few degrees
above normal in the south.

Long Term...Monday Night Through Saturday

Forecast continues to center around chances for rain and storms,
with the potential for some severe weather, with the passage of a
dynamic mid-week system. Main concerns with this system will be
heavy rainfall and potential for localized flooding, thus changes
in QPF will be something to look out for over the next few days.
As a result, the WPC has highlighted the forecast area to be in a
marginal to slight risk of receiving excessive rainfall Tuesday
through Wednesday. The threat for severe weather on Tuesday is
also becoming increasingly more prominent as we get closer to the
event.

Tuesday/Wednesday system... Details are beginning to come into
focus about the track of Tuesday`s system as medium-range models
now come into play. Models agree that the surface low is expected
to eject from the central Plains into the upper Mississippi
Valley by Tuesday evening, deepening to ~985 to 990 mb by the time
it reaches the western Great Lakes. Overall, main concern for the
time being will be increasing confidence in periods of heavy
rainfall Tuesday and Wednesday. There is still some model spread
regarding exact amounts, although the current target seems to be
northwest Wisconsin. Synoptic setup also appears favorable for
convective potential as a negatively tilted trough sets up to our
northwest and a 50 to 60 knot low-level jet builds into eastern
Wisconsin. Additionally, deep layer shear profiles and moisture
transport also look impressive. Biggest question regarding severe
threat will be how far north and east the warm front will make it.
Most instability looks to be trapped in the warm sector to our
south, which would inhibit storm development this far north.
Nonetheless, the SPC has included the entirety of the forecast
area in a slight risk for the Day 3 Convective Outlook. Confidence
is increasing in this scenario playing out, especially with how
robust the parent low appears to be. According to the NAEFS and
ECMWF ensembles, a low of this caliber climatologically occurs
only once every five to ten years during the spring. Regardless,
definitely something to keep an eye on.

Rest of the extended... The remainder of the extended sees the
current pattern quieting down slightly as mid-level flow begins to
flatten out toward the end of the week. Next chances for precip
look to arrive over the weekend, although models are still
struggling to hone in on timing this far out in the forecast
period. Otherwise, temperatures begin a steady decline through the
end of the work week before plateauing in the mid 60s to low 70s
over the weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1056 PM CDT Sat May 18 2024

Scattered showers and isolated thunderstorms will continue to
push east across eastern WI late this evening. Any storm could
bring brief erratic/gusty winds, small hail and plenty of
lightning. Once the storms exit by around 11pm, quiet weather and
VFR conditions return to the area overnight into Sunday.

&&

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

&&

$$

DISCUSSION.....RDM/Goodin
AVIATION.......Bersch