textproduct: Green Bay

KEY MESSAGES

- Showers and thunderstorms are possible at times through Saturday. Heavy downpours are possible within any thunderstorms. A few strong to severe storms will also be possible on Saturday.

- Next round of active weather arrives during the middle of next week.

DISCUSSION

Issued at 428 PM CDT Thu Jul 10 2025

A mid-level shortwave over eastern MN/western WI producing scattered showers and thunderstorms is progged to make eastward progress through this evening before weakening with time overnight. This will allow the scattered showers and thunderstorms to move into portions of central, north-central, and east-central WI this afternoon through this evening. The potential for strong or severe storms is low, but PWATs will be nearing 2 inches leaving the potential for heavy downpours within any thunderstorm. Later this evening, the weakening of the shortwave and loss of daytime heating will cause the coverage to decrease or remain mainly across southern WI.

Meanwhile, another shortwave will be on its tail that is progged to phase/overcome the leading shortwave overnight. However, the evolution of this second shortwave has much uncertainty revolving around it. Models are still not in agreement with the timing, placement, or intensity of the shortwave/precip axis for Friday, but there is decent agreement Friday morning will be dry under some cloud cover. Overall, there appears to be a southern trend with the shortwave/precip axis for Friday afternoon and evening, but there are still indications that portions of eastern WI could see some of the main precip swath. If the latter is correct, these areas would be more likely to see higher rainfall totals (1-2+ inches), especially with a juicy atmosphere in place (PWATs around 2 inches). Otherwise, if the more southern solution occurs, much of the forecast area could see much lower rainfall amounts (less than 0.75 inches) for Friday/Friday night. Given the low confidence and much uncertainty, the potential for strong or severe storms has also decreased.

Additional showers and thunderstorms are possible on Saturday with the main upper-level trough and leading surface cold front sweeping across the region. The severe potential Saturday afternoon and evening will depend on what happens Friday afternoon/night and how much cloud cover sticks around. Cannot rule it out at the moment given a tongue of 1000-2000 J/kg of MUCAPE ahead of the cold front, deep layer shear around 35-40 kts, and steeper mid-level lapse rates. SPC has included almost the entire forecast area in a Marginal Risk for severe storms, which reflects these features.

The remainder of the weekend will be dry, but there are subtle indications of a weak boundary sweeping across the area on Monday, which could bring light rain and a chance of thunderstorms. A higher chance for widespread showers and thunderstorms is shaping up for midweek with an upper-level trough moving across the northern CONUS.

AVIATION

for 06Z TAF Issuance Issued at 1058 PM CDT Thu Jul 10 2025

Showers from the evening will give way to clearing skies and some fog over central WI overnight. Also could see patchy fog over north-central WI. Have continued to carry MVFR VSBY with TEMPO groups for IFR VSBY at AUW/CWA and RHI. Though fog will lift around daybreak, IFR stratus could linger into mid morning. Over east-central WI, no fog is expected, but a small chance of some showers may arrive after 07-08z as steadier showers over southern WI graze the area while lifting across south half of Lake Michigan. The showers will be done shortly after daybreak. In wake of any showers, expect MVFR CIGS to prevail much of the day as easterly flow keeps stratus persistent, except over far north- central WI with only scattered to broken mid and high clouds are expected.

Based on recent model trends for Friday, have refreshed TAFs to keep all sites dry through early afternoon. Did intro PROB30 for some thunderstorms over central WI terminals (AUW/CWA) late in the day as next wave arrives with increasing instability. By Friday evening, most of the area will see scattered showers with small chance of thunder. Conditions on Friday evening will mainly be VFR central WI to north-central WI, while MVFR will grudgingly hold over east-central WI sites (GRB/ATW/MTW).

GRB WATCHES/WARNINGS/ADVISORIES

None.