979
FXUS63 KGRB 021144
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
644 AM CDT Tue Jul 2 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

 - Periods of rain may be heavy at times through late tonight. In general,
   0.5 to 1.5 inches of rain is expected across the entire area,
   highest in central Wisconsin, which could lead to minor river
   and stream flooding, along with urban flooding.

 - Conditions will be hazardous to mariners and beachgoers on the
   bay and Lake Michigan through tonight due to gusty winds and high
   waves.

 - The next round of widespread rain arrives late on the 4th of
   July and will last through Friday.

&&

.DISCUSSION...
Issued at 358 AM CDT Tue Jul 2 2024

Rounds of showers and some thunderstorms expected through tonight.
Moderate to heavy rainfall is likely, especially over central WI.
It then turns mainly dry Wednesday and Wednesday night, before more
showers return later on the 4th, continuing through Friday. First
full weekend of July will be unsettled with chances for showers
and thunder both days.

Today...Showers with moderate to heavy rain ahead of a shortwave
trough and well to the north of main warm front are shifting
across the state early this morning. Decaying area of lightning
strikes is present over southwest cwa on edge of MUCAPE of 1-2k/kg
well to the west and southwest over IA. As shortwave and low-
level jet translate east this morning, expect widespread showers
early to be followed by additional showers through midday. Maybe a
brief lull after that over parts of the area, but there will
already be another sharp H7 shortwave (generating showers and
storms over west central IA at current) and resurgent low-level
jet taking aim into central WI as early as early to mid afternoon.
This should keep at least scattered showers going. As has been
highlighted, PWATS nearing 2 inches are well above the 90th
percentile and closer to max values for early July. Thus the
threat for heavy rain will be across the region all day. With
multiple rounds of showers at the worst and patchy drizzle and
cloud cover at the best, went lower for high temps today. 70 will
be a stretch for any spot in the cwa today and northwoods will
have tough time reaching mid 60s.

Tonight into Wednesday...Another round of moderate to heavy rain
likely as primary shortwave trough edges closer and stronger
shortwave within the trough rotates through. Right entrance jet
forcing will only enhance lift as warm front approaches.
Sfc based instability (and associated severe threat) will be
maximized along and south of the warm front and approaching low
pressure wave, but sufficient MUCAPE just upstream of our area
along with PWATs still around 2 inches suggest moderate to heavy
rain showers especially during the evening into the early
overnight hours scntral to east-central WI along increasing low-
level jet. To the west of the LLJ axis, appears showers shut down
quickly after midnight especially after weak cold front/drier air
moves through. All areas should be in the process of drying out
by daybreak as the boundary shifts east of WI. Most areas will be
dry rest of Wednesday, but a few isolated showers out of some high
based stratocu may fall across northern WI. Rebound day for temps
with readings pushing into the 80s. Soundings and MOS guidance
point to it turning breezy from the west (gusts 25-30 mph) midday
into the afternoon.

4th of July and Friday...Signals in models and ensemble guidance
remain persistent that as shortwave trough digs across the
northern Plains and sfc low spins up over the upper mississippi
river valley by Friday morning, showers will spread west to east
across WI late Thursday afternoon into Thursday night. Heavier
rain likely holds off til late Thursday night into Friday, but
sufficient forcing ahead of the trough and some elevated MUCAPE
justify pops increasing to likely for central WI Thursday evening
while there is still a bit of uncertainty on whether the more
widespread showers reach the Fox Valley and lakeshore areas by
late evening or more so overnight. Looking like widespread showers
are in store for Friday (possible heavy rain again) and with sfc
low tracking across or south of our area, it likely will be another
cooler early July day with highs probably ending up below normal.

Sat-Mon...Pattern remains active with multiple shortwave troughs
and frontal boundaries dropping across the region. There will be a
lot of dry time, but the forecast carries chances of showers
throughout. At this time, Sunday looks like the day with better
chance of more widespread showers. Temps will be at or slightly
below normal.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 642 AM CDT Tue Jul 2 2024

Periods of showers and some thunderstorms will continue to impact
the area through late tonight. There will be some breaks in the
rain at times this morning is already showing up on the regional
radar. Another round of more significant rain is expected to
arrive from late afternoon into the evening hours as a shortwave
trough and resurgent low-level jet impact the region. There may
be a small chance of thunderstorms during the late afternoon and
evening, but confidence is not high enough to mention any storms
in the TAFs.

Flight conditions of mainly MVFR will deteriorate to LIFR/IFR from
west to east this afternoon into tonight. The passage of a boundary
with drier air will lift cigs to MVFR/VFR around daybreak on Tuesday.

LLWS will continue this morning at most of the terminals. LLWS
returns tonight at GRB/ATW/MTW. SE-S surface winds will prevail
through the TAF period, with winds becoming quite gusty later this
morning into this afternoon.

&&

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

$$

DISCUSSION.....JLA
AVIATION.......JLA