UPDATE
Issued 937 PM CDT Thu Sep 12 2024

Patchy ground fog near Sheboygan is expected to remain patchy and not become widespread, although areas near Lake Michigan in Ozaukee and Sheboygan Counties may continue to see patchy fog through tonight. Otherwise, a few patchy areas of fog are also possible in the Wisconsin River Valley, although temperatures are falling slower than the previous nights due to upper level cloud cover moving in from the outer cirrus bands of Francine, and may keep the dewpoint depression large enough to prevent fog formation in the valley.

MH

SHORT TERM
Issued 335 PM CDT Thu Sep 12 2024

Tonight through Friday night:

Synopsis/Mesoanalysis: Surface observations place a pair of high pressure centers near the Hudson Bay and off the northeastern coast of the CONUS this afternoon. Under the influence of the aforementioned surface features---in addition to longwave ridging in place aloft---light surface winds and mostly sunny skies prevail across southern Wisconsin. These conditions have allowed for efficient surface heating across the region, with most stations away from the immediate Lake Michigan shoreline reporting temperatures in the mid-upper 80s as of 2 PM. Janesville has eclipsed the 90 degree mark, with a few more isolated 90+ degree temps possible over south- central Wisconsin through late afternoon. Upper ridging currently moving overhead will migrate to our east through the short term period, allowing an upper trough affiliated with the former Hurricane Francine to migrate into the mid-Mississippi Valley. The trough will remain well south of the region through the short term period, though increasing moisture along/ahead of it will result in increasing clouds and humidity by daybreak Saturday.

Tonight: Mid to upper clouds will gradually thicken as upper level moisture increases ahead of the trough tied to the former Hurricane Francine. Areas of fog are possible near daybreak in the Wisconsin River Valley. Be sure to slow down, use low beam headlights, and allow for extra following distance if encountering fog on Wisconsin Valley roads late tonight.

Friday Night: A deeper fetch of low-level Gulf moisture will start to push into the region, resulting in increasing dew points and muggier conditions. Showers and storms are expected within the plume of returning moisture, though activity is expected to remain to the west of the region through daybreak Saturday & the conclusion of the short term period.

Quigley

LONG TERM
Issued 335 PM CDT Thu Sep 12 2024

Saturday through Thursday:

Synopsis: The long term period will begin with upper ridging positioned over the Lake Huron vicinity, and an upper trough connected to the former Hurricane Francine lingering over the mid- Mississippi Valley. The core of the trough will remain well to the south of the area, though a series of smaller impulses connected to the feature will cross the region during the Saturday to Monday time period. Lift associated with these impulses will support isolated to widely scattered shower and storm chances Saturday through Monday.
The upper disturbance tied to the former Francine will migrate into the mid-Atlantic during the middle half of next week, shutting off shower and storm chances in the process. An upper low will eject into the Northern Plains & Canadian Prairie Provinces during the Wednesday-Thursday time frame, supporting chances for showers and thunderstorms primarily to the west of the area. It's possible that some of the aforementioned shower/storm activity could clip western portions of the area by Thursday. While some fluctuation to the surface pattern will occur, predominantly south-southeast winds will maintain an above-normal temperature pattern through the long term.

Saturday Through Monday: Periods of isolated to widely scattered showers and storms (~15-30% chances daily) are expected. Expect that the best overall precip potential will be along & west of I-39 in our area, where guidance is suggesting upper impulses are most likely to track. A sampling of forecast soundings show ~750-1500 J/kg of surface-based CAPE during peak convective periods, though weak effective shear and approximately moist adiabatic lapse rates should keep severe potential low. 1.50-1.75" precipitable water values---readings that fall anywhere between 0.5 and 1.0 standard deviations above the early-mid September climo---will support brief heavy downpours in any thunderstorms.

Tuesday & Wednesday: Above normal temperatures continue, though humidity will be a touch lower with drier air working into southern Wisconsin.

Wednesday Night & Thursday: Above normal temperatures continue.
Linked to WAA along/ahead of the ejecting trough in the Northern Plains, isolated shower and thunderstorm chances return to western areas. Despite the return of precip chances, QPF progs from available guidance suggest that the bulk of the heaviest shower/storm activity will remain to our west/closer to the better upper dynamics during this time frame. Will continue to monitor trends over the coming forecast cycles.

Quigley

AVIATION
Issued 937 PM CDT Thu Sep 12 2024

Patchy fog is possible along northern Lakeshore terminals tonight, although this fog is expected to remain low-lying with minor impacts. Trends will be monitored through the remainder of the night, especially in SBM. High level cloud cover is slowly moving in from the southwest, keeping temperatures in southwestern Wisconsin higher and reducing fog potential. Light easterly to calm winds are expected through tonight, becoming easterly at 5 to 10 kt Friday morning. VFR ceilings expected throughout the TAF period.

MH

MARINE
Issued 335 PM CDT Thu Sep 12 2024

Patchy fog is possible over the northern third of the open waters of Lake Michigan tonight. Widespread dense fog is not anticipated, though trends will be monitored during the evening and overnight hours. 1030 mb high pressure will remain centered over the Hudson Bay & Quebec through Friday, supporting east-northeast winds over the open waters. The high will gradually shift into the northeastern United States this weekend, allowing winds to turn out of the east- southeast across the lake. Winds will turn predominantly southerly across the open waters through the beginning of next week as 994 mb low pressure develops over the northern Great Plains. Shower and thunderstorm chances are low across the lake through the middle of next week.

Quigley

MKX WATCHES/WARNINGS/ADVISORIES
WI...None.
LM...None.