Strong thunderstorms produced gusty winds as they tracked over the Lake Michigan nearshore waters during the early afternoon hours.
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The episode as NWS GRB wrote it up.
Strong thunderstorms produced gusty winds as they tracked over the Lake Michigan nearshore waters during the early afternoon hours.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Green Bay, WI wrote its last area forecast discussion before the first event at Aug 24, 5:01 AM CST, 6 hours 34 minutes earlier.
Area Forecast Discussion National Weather Service Green Bay WI 601 AM CDT Tue Aug 24 2021 Updated aviation portion for 12Z TAF issuance .SHORT TERM...Today...Tonight...and Wednesday Issued at 352 AM CDT Tue Aug 24 2021 The main concern in the short-term portion of the forecast will be the potential for strong to severe storms today and the overall evolution of the thunderstorms this morning into early this afternoon. Radar imagery this morning shows a persistent MCS rolling across west-central MN with some convection developing ahead of the feature near Minneapolis. This secondary area of convection is along the surface frontal boundary. Overall convective evolution may be impacted by interactions with this leading convection, but the latest HRRR guidance seems to have a very good depiction of intensity and placement of the convection. That has been the case through much of the night. Today: A nearly stationary front, draped across central MN eastward through northern WI, will lift slowly north this afternoon as a warm front. Aloft, a shortwave is expected to shift eastward along or just south of the front. The ongoing line of strong to severe thunderstorms over western MN this morning, will continue to shift eastward into central WI by late morning or early afternoon. Provided that the storms remain strong to severe, the most likely impact would be damaging winds and brief heavy downpours. As far as location, most of the hi-res guidance has been inconsistent (model to model/run to run) on placement; however, the HRRR has been more consistent and in line with the latest observed precipitation/convection. The HRRR solution as tends to make sense as the strongest portion of the storms would likely remain south of the aforementioned front and would likely remain along the CAPE gradient. The greatest CAPE gradient is progged to be from roughly Marathon County eastward to roughly Brown and Kewaunee County, where mid-level lapse rates are expected to be near 7 to 7.5 C/km. Again, those areas would run the greatest risk of seeing damaging winds and heavy downpours. Deep-layer shear vectors (similar to 0-3km) are expected to be around 30kts to 40 kts and orthogonal to the the north/south line of storms. This would support surging/bowing sections in the line, again, leading to a damaging wind threat. Otherwise, temperatures are expected to warm into the mid to possibly upper 80s, with more humid conditions. Tonight: Low pressure will slowly approach from the west as the aforementioned warm front becomes nearly stationary along the UP/WI border as a cold front slowly approaches from the west. This will keep scattered showers and thunderstorms in the forecast through much of the night. The greatest threat for seeing showers and storms will remain near the fronts as the forcing will be greater in those areas, but storms can't be ruled out in the unstable airmass, provided that there is enough of a trigger from lingering boundaries. The NAM/GFS are hinting at a shortwave passing through the area tonight, but this has not been a consistent signal over the past few runs. MUCAPE values are expected to be around 1000 J/kg, but shear is only expected to be around 20 to maybe 25kts. This will help to limit any severe potential tonight. Overnight lows are expected to be in the 60s to around 70, warmest central/east-central. Wednesday: The surface low is expected to lift northeast and east as it drags the cold front through the area from west to east throughout the day. Instability is expected to increase ahead of the front, greatest across east-central and far northeast Wisconsin, with values reaching around 1500-2500 J/kg. Deep-layer shear is only progged to be around 20kts, so not expecting widespread severe weather. The storms could pulse up from time to time over east- central and far northeast Wisconsin with the main threat from any storms being small hail, gusty winds and heavy downpours. Otherwise, high temperatures are expected to be in the 80s for much of the forecast area. .LONG TERM...Wednesday Night Through Monday Issued at 352 AM CDT Tue Aug 24 2021 Similar to the past several nights, the extended forecast remains active with several rounds of rain and thunderstorms through early next week. An upper level trough across the Pacific Northwest and a broad ridge across the southeast CONUS will lead to southwest flow across WI. Within this flow will be several embedded shortwaves and sfc boundaries. A cooler/drier airmass will reside north of this upper jet, and to the south a warm and moist airmass with high pwats will be in place. Combine this with effects from daytime heating and the nocturnal LLJ, and bouts of heavy rain and thunderstorms will be possible nearly every day/night. Timing out these episodes is nearly impossible as each event will influence the next, so there will be dry times as well, despite the abundance of PoPs in the forecast. The next main period of interest and potential impact is Thursday into Friday. With a sfc boundary still lingering and a shortwave coming through models are indicating a complex could develop west of the forecast area, and then track through central and/or northeast WI bringing heavy rainfall and storms with strong winds. Timing is still all over the place, but the GFS/ECMWF/CMC all show high QPF amounts of 2+ inches during this stretch. Pwats will be near climatological maximum as well. As a result, WPC has highlighted nearly the entire CWA in the Day3 Marginal Risk of excessive rainfall (level 1 out of 4) with central WI in a Slight Risk of excessive rainfall (level 2 out of 4). Will continue to evaluate trends as the time gets closer. Temps will be above normal each day, sometimes by a degree or two, other times closer to 10 degrees above normal, just depending on where the boundary situates each day. Temps and humidity look to fall back closer to normal Thursday and Friday, and then bounce up again for the weekend. && .AVIATION...for 12Z TAF Issuance Issued at 601 AM CDT Tue Aug 24 2021 Patchy dense fog can be expected at each of the TAF sites through sunrise or just after sunrise. Outside of the dense fog early in the TAF period, a complex of thunderstorms will approach the TAF sites first across central Wisconsin and then into east-central Wisconsin by late morning or early afternoon. Additional development is possible late in the afternoon, but confidence is fairly low at this point. Gusty winds, heavy rain and frequent lightning will be the main threats. Outside of the fog this morning, ceilings and visibilities are expected to be VFR, except as low as IFR in intense rainfall. Some patchy fog may form again tonight, depending on cloud cover and any lingering showers and storms. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM.....Cooley LONG TERM......KLJ AVIATION.......Cooley
Hazardous Weather Outlook National Weather Service Green Bay WI 450 AM CDT Tue Aug 24 2021 WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-251000- Vilas-Oneida-Forest-Florence-Northern Marinette County-Lincoln- Langlade-Menominee-Northern Oconto County-Door-Marathon-Shawano- Wood-Portage-Waupaca-Outagamie-Brown-Kewaunee-Waushara-Winnebago- Calumet-Manitowoc-Southern Marinette County- Southern Oconto County- 450 AM CDT Tue Aug 24 2021 This Hazardous Weather Outlook is for north-central and northeast Wisconsin. .DAY ONE...Today and Tonight Patchy dense fog may cause rapid reductions of visibilities on roadways through the morning commute, which may pose a hazard to motorists. Thunderstorms are expected today and tonight. Some of the storms could be severe, especially late this morning through mid afternoon. The primary risk will be damaging wind gusts. Torrential rainfall and hail are also possible. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thunderstorms are possible at times during the remainder of the upcoming work week. It is too early to determine whether subsequent rounds of storms will pose a severe weather threat; however, very heavy rainfall will be possible at times. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed late this morning into this afternoon. LMZ521-522-541>543-251000- The Bay of Green Bay south of a line from Cedar River MI to Rock Island Passage-Lake Michigan from Washington Island to Sheboygan- 450 AM CDT Tue Aug 24 2021 This Hazardous Weather Outlook is for portions of northwest Lake Michigan and the waters of Green Bay. .DAY ONE...Today and Tonight Thunderstorms are expected today and tonight. Any thunderstorms will pose a hazard to mariners. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thunderstorms are possible at times during the remainder of the upcoming work week. Any thunderstorms will pose a hazard to mariners. Cooley/KLJ
Special Weather Statement
National Weather Service Green Bay WI
1128 AM CDT Tue Aug 24 2021
WIZ036>040-045-048>050-241730-
Calumet WI-Waupaca WI-Kewaunee WI-Outagamie WI-Winnebago WI-
Waushara WI-Manitowoc WI-Portage WI-Brown WI-
1128 AM CDT Tue Aug 24 2021
...Strong thunderstorms will impact portions of Brown, southeastern
Portage, Kewaunee, Calumet, Winnebago, Waushara, southern Waupaca,
Outagamie and Manitowoc Counties through 1230 PM CDT...
At 1125 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from 7 miles northeast of Black Creek to 6 miles
east of Kaukauna to near Central Lake Winnebago. Movement was east
at 30 mph. Additional clusters of thunderstorms were occurring
across much of Waushara County, and will shift east into the Fox
Valley within the next hour.
HAZARD...Winds in excess of 40 mph, half inch hail and torrential
rainfall.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible. Periods of torrential rainfall could result in
some urban flooding in the Fox Valley.
Locations impacted include...
Green Bay, Appleton, Oshkosh, Manitowoc, Waupaca, Kewaunee, Wautoma,
Bay Shore Park, Menasha and Kaukauna.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with these storms and may lead
to localized urban flooding in the Fox Valley. Do not drive your
vehicle through flooded roadways.
&&
LAT...LON 4390 8889 4398 8889 4398 8960 4425 8963
4429 8911 4457 8851 4459 8825 4465 8824
4468 8799 4476 8787 4463 8793 4478 8772
4468 8774 4468 8764 4443 8744 4390 8769
4389 8816 4394 8840 4389 8840
TIME...MOT...LOC 1625Z 257DEG 26KT 4453 8833 4432 8814 4398 8846
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
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</html>The Green Bay radar (KGRB), 60 km away, was scanning. The volume nearest the first event began at 17:36 UTC.
1 marine thunderstorm wind. Local standard time, as filed.
Thunderstorms produced wind gusts to 41 knots at the Manitowoc airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Lake Michigan in 2021Every state in 2021This day in weather history
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-30. Each event’s entry at NCEI: 973261.