FXUS63 KGRB 210810

AFDGRB



Area Forecast Discussion

National Weather Service Green Bay WI

310 AM CDT Tue Apr 21 2026



Updated aviation portion for 12Z TAF issuance



.KEY MESSAGES...



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

  period of dry weather, a gradually drop is anticipated with

  flooding expected to continue through the week.



- Showers and thunderstorms are expected Thursday night into

  Friday. Heavy rainfall may accompany any thunderstorms, with a

  20-30% chance of exceeding an inch of rain. 



- Temperatures will well above normal through Friday, with highs 

  in the 60s and 70s expected away from Lake Michigan.



&&



.DISCUSSION...

Issued at 1243 AM CDT Tue Apr 21 2026



Dry weather is expected through the middle of the week, which

will allow area rivers to continue to slowly subside. A weak 

surface low/trough will move through the region with no 

precipitation today. 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 tonight into Wednesday, with continued dry and 

mild conditions inland from Lake Michigan. Throughout this period,

low afternoon humidity is anticipated (20-30 percent range), 

which may result in an uptick in wildfire potential.



South winds develop Wednesday night and gusts to 20 to 30 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 the region. Rain will continue into Friday as the front

slowly moves through the region. PWATs increase to 1.2 to 1.5

inches during this period with modest instability (MUCAPEs of

500-1000 J/kg). The long, skinny CAPE profiles and increased

moisture will mean locally heavy rainfall will be possible. NBM

probabilities of exceeding an inch are currently 20-30% with a

less than 10% chance of exceeding 2 inches, which appears to be 

the high end amount for this event. Once the rain ends Friday

afternoon/evening a period of dry weather is then anticipated for

the upcoming weekend. 



A low pressure system lifting north from the Plains is then 

expected to bring another round of rain to the region during the 

early part of next week. This system looks similar to the late

week system with modest MUCAPE values of 500-1000 J/kg with the 

90th percentile for rainfall amounts around 2 inches.



Above normal temperatures are anticipated through Friday, with 

the cold frontal passage only bringing modest cooling for the 

weekend into early next week.



&&



.AVIATION...for 12Z TAF Issuance

Issued at 310 AM CDT Tue Apr 21 2026



VFR conditions are expected through the TAF period. Mid and high

clouds will move through the area early this morning, with mostly

sunny skies expected later this morning and through the afternoon.

Some fair weather cumulus will develop across eastern Wisconsin 

during the mid to late afternoon. Mostly clear skies are then

expected across all TAF sites tonight.



A weak cold front will move across the area this 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 KGRB. Given the lake and 

bay breezed, there is uncertainty regarding wind direction at 

KGRB; however, current thinking is winds will switch to the 

northeast this afternoon then east during the evening as the lake 

breeze moves inland.



&&



.HYDROLOGY...

Issued at 1243 AM CDT Tue Apr 21 2026



Minor to moderate flooding continues on many rivers, with majorflooding expected to persist on parts of the Wolf River through 

tonight. Most of the river levels have crested, and with a 

prolonged stretch of dry weather anticipated through Thursday, 

water levels should gradually subside 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 to Friday period.



&&



.GRB WATCHES/WARNINGS/ADVISORIES...

None.



&&



$$



DISCUSSION.....Kurimski

AVIATION.......Kurimski

HYDROLOGY......Kurimski