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LMZ521 Green Bay South Of Line From Cedar River To Rock Island Passage And North Of A Line From Oconto Wi To Little Sturgeon Bay Wi- Green Bay South Of Line From Oconto Wi To Little Sturgeon Bay Wi- 930 Am Cdt Sat May 18 2024
Today - S wind 10 to 15 kts. Patchy fog in the morning. Waves 2 ft or less. Tonight - S wind 10 to 15 kts veering W 5 to 10 kts after midnight. A chance of rain showers and a slight chance of Thunderstorms in the evening. Waves 2 ft or less. Sunday - W wind 5 to 10 kts backing S in the afternoon. Mostly Sunny. Waves 2 ft or less. Sunday night - SE wind 5 to 10 kts. A chance of rain showers after midnight. Waves 2 ft or less.

LMZ500
No data

FXUS63 KGRB 181053 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 553 AM CDT Sat May 18 2024

Updated aviation portion for 12Z TAF issuance

KEY MESSAGES

- Thunderstorms are likely late this afternoon across central and north-central Wisconsin. There is a chance of thunderstorms in east central and far northeast Wisconsin this evening. Some storms may become strong to severe with damaging winds and hail the main threat.

- Chances for showers and thunderstorms continue through mid-week.
While too early to determine severe potential, confidence is increasing in locally heavy rain on Tuesday.

DISCUSSION
Issued at 420 AM CDT Sat May 18 2024

Short Term
Today
Tonight...and Sunday

Scattered light showers and sprinkles are possible in far north central Wisconsin early this morning due to elevated instability.
They should end shortly after sunrise.

It will be a summer like day today as gusty southerly winds provide good mixing of the lower atmosphere. Mixing to 900mb or so will result in highs in the 80s in the forecast area, though it will be cooler near Lake Michigan. A scattered to broken line of thunderstorms is expected to develop ahead of a cold front that will move into central and north central Wisconsin in the late afternoon. 1000 J/KG of CAPE and an inverted V sounding could make for a few strong or severe storms with damaging winds and hail.
The activity should should diminish as it moves into the Fox Valley and lakeshore counties in the early evening and encounters lake stabilized air in the low levels and loss of surface heating as the sun sets.

Whatever convection makes it to the lakeshore should move out over the lake by midnight, with clearing skies and slightly cooler and drier air arriving overnight. Lows will be near normal. Sunday should be very pleasant, with light winds, mostly sunny skies and low humidity. Highs will be about 5 to 8 degrees above normal.

Long Term...Sunday Night Through Friday

As previously mentioned, focus for the extended remains on rain/storm chances through mid-week brought on by an active synoptic pattern. Large-scale ridging across the eastern CONUS is expected to put much of the Midwest under a southwest flow regime through mid-week, which is conducive to warm air advection and moisture transport up from the south. Hence, periods of moderate to heavy rainfall with potentially high QPF will be something to look out for.

Monday precip chances... A robust trough situated across the western CONUS will eject a shortwave up into the western Great Lakes, bringing a fast-moving round of rain to the forecast area Monday morning. During this time, a warm front will stall to our south, providing some lift via isentropic ascent and a surge of warm air advection. Additionally, an open Gulf will bring a swath of deep moisture up into portions of central and east-central Wisconsin Monday afternoon, placing a corridor of 1.5+" of PWAT across the Fox Valley. Models seem to be targeting central Wisconsin to receive the bulk of the precip with this system (~0.6" to 0.8" QPF) due to showers being more prolonged over that area.
Most convective elements look to remain to our south along the warm front, but cannot rule out a rumble of thunder along/south of Highway 29.

Tuesday/Wednesday precip chances... As Monday's system departs to the east, attention then turns to a more dynamic system that treks from the central Plains to the upper Mississippi Valley by Tuesday evening. Current model guidance suggests that this system has the potential to bring heavy rain to much of the forecast area Tuesday through Wednesday morning, although it is still too soon to discern exact amounts given significant model spread this far out. With plentiful Gulf moisture and dewpoints in the low to mid 60s, suspect that QPF will trend on the higher end of what ensembles are currently showing. This being said, forecast confidence is high enough to warrant a day 4 marginal to slight risk of excessive rainfall across the CWA A first glance also shows that thunderstorms may be possible across our southern counties.
However, instability in the warm sector will struggle to make it this far north and east, hindering severe potential for the time being. Will continue to monitor convective elements as medium- range models come into play. Overall, biggest things to look out for will be changes in QPF and risk for flooding/flash flooding.

AVIATION
for 12Z TAF Issuance Issued at 552 AM CDT Sat May 18 2024

A scattered to broken line of thunderstorms is expected to move across the region during the late afternoon and evening hours ahead of a cold front. The activity should be along a line from RHI to ISW around 22z, IMT to DLL around 01z, and ESC to OSH by 02z. The activity will like weaken as it moves towards Lake Michigan. Strong wind gusts and brief IFR conditions will accompany the thunderstorms. VFR conditions are expected outside of the thunderstorm activity. After the convective activity exits the area by late evening, there will be clearing overnight and good flying weather Sunday.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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