FXUS63 KGRB 210257

AFDGRB



Area Forecast Discussion

National Weather Service Green Bay WI

957 PM CDT Mon Apr 20 2026



Updated aviation portion for 06Z TAF issuance



.KEY MESSAGES...



-Minor to moderate flooding continues on the Menominee and Wolf

 Rivers and associated tributaries, with major flooding expected

 on the Wolf River at New London through Tuesday night. Water 

 levels have crested in most areas, and due to an extended period 

 of dry weather, a gradually drop is anticipated through the week.



-Showers and thunderstorms are expected Thursday night into

 Friday. Heavy rainfall may accompany any thunderstorms. There is

 a 50-70% chance of rainfall in excess of 1/2 inch, but higher end

 amounts to 1-2 inches could occur.



-Temperatures will be much above normal from Tuesday through

 Friday, with highs in the 60s and 70s expected away from Lake

 Michigan.



&&



.DISCUSSION...

Issued at 304 PM CDT Mon Apr 20 2026



Partly sunny skies and gusty south to southwest winds were

observed across the region this afternoon. Temperatures were in 

the middle 40s to middle 50s, except upper 30s and lower 40s near 

Lake Michigan due to a pronounced lake breeze.



Quiet weather is expected tonight, with south winds keeping

low temperatures 15 to 20 degrees warmer than last night. A weak 

surface low/trough will move through the region with no 

precipitation on Tuesday. Much warmer gets drawn into the region 

ahead of the trough, with high temperatures rising into the 60s 

and lower 70s, except 50s and lower 60s due to a lake/bay breeze. 

High pressure returns Tuesday night into Wednesday, with continued

dry and mild conditions inland from Lake Michigan. Throughout 

this period, low afternoon humidity is anticipated, which may 

result in an uptick in wildfire potential.



South winds develop Wednesday night and gust to 25 to 35 mph on 

Thursday, resulting in an increase in Gulf moisture over the 

region. There is a 20 percent chance of showers in our far western

counties late Thursday afternoon, but showers and embedded storms

become more numerous Thursday night, as a cold front moves 

through. Models are a bit slower with the timing of the front, so 

precipitation is likely to linger into Friday. With PWATs 

increasing to 1.20-1.50 inches and marginal instability (MUCAPE of

500-1000 j/kg), would anticipate locally strong storms and 

potential for heavy rainfall. Current probabilistic forecasts call

for a 50-70% chance of rainfall amounts in excess of 0.50 inch. 

The 90th percentile forecasts show rainfall totals in the 1-2 inch

range, and offer a glimpse of the higher-end potential for this 

event. The frontal showers should taper off Friday afternoon or 

evening, with mainly dry conditions anticipated over the weekend.



Above normal temperatures are anticipated from Tuesday through

Friday, with the cold frontal passage only bringing modest 

cooling for the weekend.



&&



.AVIATION...for 06Z TAF Issuance

Issued at 950 PM CDT Mon Apr 20 2026



VFR conditions will continue through Tuesday evening. Mid and

highs will move across the region tonight, with mostly sunny

skies expected on Tuesday. Some fair weather cumulus will develop

across eastern WI during the mid to late afternoon. Low level 

wind shear from 220-240 degrees at 35-45 kts will end around 09z.

A weak cold front will move across the area Tuesday morning, 

shifting winds to the northwest. During the afternoon, a lake 

breeze boundary will develop around 18z at KMTW/KSUE, spreading 

westward to KGRB/KATW/KOSH between 21z Tue and 00z Wed. There also

could be a bay breeze that would impact the KGRB taf site. A

little uncertain in the wind direction tomorrow afternoon at 

KGRB, but current thinking the winds will swith to the northeasst 

and then probably east during the evening as lake breeze moves

inland. 



&&.HYDROLOGY...

Issued at 304 PM CDT Mon Apr 20 2026



Minor to moderate flooding continues on the Menominee and Wolf

Rivers and associated tributaries, with major flooding expected 

on the Wolf River at New London through Tuesday night. Water 

levels have crested in most areas, and due to an extended period 

of dry weather, a gradually drop is anticipated through the week.



Those living near rivers should continue to monitor the latest

Flood Warnings and statements from the National Weather Service

in Green Bay.



See the discussion section above for information pertaining to

precipitation forecasts for the Thursday night to Friday period.



&&



.GRB WATCHES/WARNINGS/ADVISORIES...

None.



&&



$$



DISCUSSION.....Kieckbusch

AVIATION.......Eckberg

HYDROLOGY......Kieckbusch