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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- 1035 Am Cdt Sun May 19 2024
This afternoon - S wind 5 to 10 kts. Partly Sunny. Waves 2 ft or less. Tonight - SE wind 5 to 10 kts. A slight chance of rain showers after midnight. Waves 2 ft or less. Monday - S wind 5 to 10 kts. A chance of Thunderstorms. Rain showers likely in the afternoon. Waves 2 ft or less. Monday night - N wind 5 to 10 kts. A chance of showers and Thunderstorms. Waves 2 ft or less.

LMZ500
No data

FXUS63 KGRB 191038 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 538 AM CDT Sun May 19 2024

Updated aviation portion for 12Z TAF issuance

KEY MESSAGES

- Thunderstorms are likely Monday. A few storms may become strong to severe south of Highway 29. The main threats are strong winds and hail.

- Active weather is expected to continue through midweek, with confidence increasing in the potential for heavy rainfall and strong to severe storms on Tuesday.

DISCUSSION
Issued at 410 AM CDT Sun May 19 2024

Short Term
Today
Tonight...and Monday

Very nice weather is expected today. A weak cold front moved across the region this morning. While the air behind it is not very cold, the air is much drier. Relative humidities of 20 to 25 percent are expected this afternoon in the sandy soil areas, but the threat of fires will be reduced by yesterdays rain and relatively light winds. Highs today will be five to ten degrees above normal.

Clouds will increase tonight as an upper level disturbance and surface low approach from the Central Plains states. Lows will be close to normal.

Showers and elevated thunderstorms are likely Monday as the system moves across Wisconsin. Very heavy rain is possible as precipitable water values of 1.25" to 1.45" are close to the maximum recorded for this time of the year. This will likely cause rivers and streams to rise, but probably stay within their banks. Additional heavy rain is expected Tuesday, which could then result in flooding. The threat of severe storms Monday afternoon is mostly across southern Wisconsin, but there is some chance of strong or severe storms south of highway 29 if the warm front makes it that far north. Highs Monday will be a few degrees below normal in the north and a few degrees above normal in the south.

Long Term...Monday Night Through Saturday

Forecast continues to center around chances for rain and storms, with the potential for some severe weather, with the passage of a dynamic mid-week system. Main concerns with this system will be heavy rainfall and potential for localized flooding, thus changes in QPF will be something to look out for over the next few days.
As a result, the WPC has highlighted the forecast area to be in a marginal to slight risk of receiving excessive rainfall Tuesday through Wednesday. The threat for severe weather on Tuesday is also becoming increasingly more prominent as we get closer to the event.

Tuesday/Wednesday system... Details are beginning to come into focus about the track of Tuesday's system as medium-range models now come into play. Models agree that the surface low is expected to eject from the central Plains into the upper Mississippi Valley by Tuesday evening, deepening to ~985 to 990 mb by the time it reaches the western Great Lakes. Overall, main concern for the time being will be increasing confidence in periods of heavy rainfall Tuesday and Wednesday. There is still some model spread regarding exact amounts, although the current target seems to be northwest Wisconsin. Synoptic setup also appears favorable for convective potential as a negatively tilted trough sets up to our northwest and a 50 to 60 knot low-level jet builds into eastern Wisconsin. Additionally, deep layer shear profiles and moisture transport also look impressive. Biggest question regarding severe threat will be how far north and east the warm front will make it.
Most instability looks to be trapped in the warm sector to our south, which would inhibit storm development this far north.
Nonetheless, the SPC has included the entirety of the forecast area in a slight risk for the Day 3 Convective Outlook. Confidence is increasing in this scenario playing out, especially with how robust the parent low appears to be. According to the NAEFS and ECMWF ensembles, a low of this caliber climatologically occurs only once every five to ten years during the spring. Regardless, definitely something to keep an eye on.

Rest of the extended... The remainder of the extended sees the current pattern quieting down slightly as mid-level flow begins to flatten out toward the end of the week. Next chances for precip look to arrive over the weekend, although models are still struggling to hone in on timing this far out in the forecast period. Otherwise, temperatures begin a steady decline through the end of the work week before plateauing in the mid 60s to low 70s over the weekend.

AVIATION
for 12Z TAF Issuance Issued at 538 AM CDT Sun May 19 2024

A surface high moving across Wisconsin today will bring mostly clear skies, light winds and excellent visibility.

Middle and high clouds will increase tonight as a weather system approaches from the Central Plains. Showers and thunderstorms will create IFR conditions across the region Monday. The rain will end from west to east during the late afternoon and early evening, with improving flight conditions.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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