144
FXUS63 KGRB 012052
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
352 PM CDT Mon Jul 1 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

 - Periods of heavy rain will be possible early Tuesday morning
   through Tuesday night. In general, 0.5 to 1.5 inches of rain
   will be possible across the entire area, highest in central
   Wisconsin, which could lead to minor river and stream
   flooding, along with urban flooding.

 - There is a high risk of rip currents on Lake Michigan beaches
   on Tuesday and Tuesday night due to high wave action. Beach
   goers are advised to remain out of the water when waves are
   high.

 - The next chance of widespread rain will arrive late on July 4
   into July 5.

&&

.DISCUSSION...
Issued at 352 PM CDT Mon Jul 1 2024

Short Term...Tonight and Tuesday

20Z surface analysis shows the high pressure center over northern
Lake Michigan. The region will remain dry through this evening as
the high departs, however, with the tightening pressure gradient
on the backside of the high southerly winds will increase with
gusts reaching 20-25 mph across central and northern WI tonight.

A pattern shift then comes Tuesday as an upper-level trough and
surface low pressure system are forecast to track north of the
region. Expecting rain to push into central and northern WI just
after midnight and into the Fox Valley early Tuesday morning.
There may be periods moderate to heavy rainfall through Tuesday
morning, especially across central WI where the isentropic ascent
and vorticity advection is expected to be maximized, along with
PWATS approaching 2 inches. Not expected any severe weather with
this first round of rain, however, won`t rule out a few rumbles
of thunder late Tuesday morning. In addition to the rain,
southerly winds will be breezy Tuesday morning with gusts
reaching 25-35 mph. Most of the hi-res models are showing a lull
in the precipitation Tuesday afternoon ahead of a second short-
wave progged to bring another round of rain Tuesday evening (see
long-term discussion). Total QPF amounts have come down a touch
from earlier forecast with much of the region now looking at
around 0.5-1 inch of rain, with locally higher amounts of 1.5-
2 inches possible across central WI. Even with the lower QPF
amounts several area rivers will likely return to or near
bankfull, and low laying areas may see minor flooding.
Temperatures Tuesday will continue to be a few degrees below
normal with highs forecast to reach the upper 60s to middle 70s
across the region.

Long Term...Tuesday Night Through Monday

Main focus from this forecast period revolves around another round
of potentially heavy rainfall Tuesday evening/night, thunderstorm
potential for the Fourth of July, and additional rain chances for
the weekend.

Tuesday night through Wednesday morning...Rain chances will increase
into Tuesday evening/night as a cold front, supported by the RRQ of
an upper-level jet, moves across the region. With the Gulf open,
impressive PWATs of 1.75 to 2 inches will lift into the area and
support moderate to heavy rainfall at times. Rainfall amounts have
decreased some due to deterministic guidance indicating the
convective axis being further south of the forecast area. However,
ensemble guidance is still showing signs of higher amounts across
central and east-central WI with probabilities of 1 inch or more
between 10-20%. Given the uncertainty of the convective axis,
decided to lower rainfall amounts slightly during this time frame,
with most locations seeing at least a couple tenths of a inch in far
north-central WI to about 0.50" in far eastern WI. Isolated higher
amounts are expected if the convective axis shifts slightly further
north. Severe weather is not expected with this frontal passage due
to limited instability around 200 J/kg, but non-severe thunderstorms
will be possible at times.

Independence Day through Friday...A low pressure system will track
across the Northern Plains into MN on Thursday, across WI on Friday,
and exit the region Saturday morning. The onset of the precip has
changed very little, leading to portions of central and north-
central WI seeing the greatest chance for thunderstorms late
Thursday evening, when firework displays are likely to occur. The
remainder of the forecast area would see the arrival of shower and
thunderstorm chances early Friday. Rain and thunderstorms will
continue across the region for the remainder of Friday through early
Saturday morning. Will continue to monitor the timing of this system
given the holiday festivities on Thursday and busy holiday
weekend.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1226 PM CDT Mon Jul 1 2024

VFR flying conditions are expected for the remainder of the
afternoon and evening as a high pressure system slowly shifts off
to the east. High based cirrus clouds will start to spread over
central WI this afternoon and into eastern WI this evening ahead of
an approaching low pressure system. Currently have rain arriving to
the central and northern WI TAF sites (AUW, CWA, and RHI) during the
06-07Z hour and the eastern WI TAF sites (AUW, GRB, and MTW)) during
the 08-09Z hour. Cigs will likely lower into the MVFR range as rain
begins to fall and will continue to lower toward IFR as rainfall
intensifies, mainly across central WI Tuesday morning. May also see
periods of borderline MVFR/IFR vsbys with the heaviest showers
Tuesday morning. Left any mention of thunder out of the 18Z TAFs as
instability is forecast to be quite weak and confidence is low, but
won`t rule out a few rumbles of thunder just yet. Lastly, did
include LLWS at all TAF sites, except MTW, early Tuesday morning
with 10-15kt southerly winds at the surface, and 35-40kt
southwesterly winds at around 2km above ground.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from Tuesday morning through Wednesday
morning for WIZ022-040-050.
&&

$$

DISCUSSION.....GK/Kruk
AVIATION.......GK