Harrison, WI Weather

Key Messages

- Dense fog overnight into Wednesday morning across east-central Wisconsin and areas west of Green Bay, locally dropping visibilities below 1/2 mile. More fog possible early Thursday and early Friday.

- Dry and mild through Saturday afternoon with inland high temperatures warming into the upper 60s to lower 70s. Warmest days Wednesday and Saturday.

- A 20 to 30 percent chance of light rain showers Saturday night into Sunday across especially northern Wisconsin. Chances for at least some showers are increasing on Monday.

- Cooler early next week, with highs mainly in the 50s.

Discussion

Issued at 1044 PM CDT Tue Oct 20 2026

Fog trends through late this week...More dense fog is possible late tonight into Wednesday morning. Return SW flow is kicking in just off surface, compared to light E-SE flow last night. Still with lingering moisture and conditions saturating late tonight, could see patchy to areas of dense fog. Latest trends not as pessimistic with visibility perhaps due to the less favorable flow off the deck, so do not plan to issue Dense Fog Advisory yet, but will have to watch this overnight. Areas most favored for dense fog would be near the lakeshore and inland to the west/northwest of the Fox Valley. High pressure remains overhead until late this week. A weak boundary moving through tonight will switch winds back to NE direction late tonight into Thursday morning, which could lead to slightly better setup for fog with added light flow off bay and Lake Michigan. Still an onshore wind and cooling late Thursday night and Friday morning as well, so that spells more fog. Pattern breaks down Friday night with strengthening SW winds and warmer nighttime temps.

Dry through Saturday, then at least small chances for showers... Brush of a northern stream wave is too moisture starved to produce any rain late today into this evening. Main impact will be the surface trough/wind shift dropping through. Omega block pattern will then remain in place the rest of this week. Stronger shortwave trough shifts across central Canada Saturday, but most of the lift with this remains over northern Manitoba and Ontario Canada. Increasing PWATs (toward 90th percentile) pooling along front tied to the trough may bring a few showers (20-30% chances) especially to northern WI Saturday night. May see an isolated shower over rest of the area on Sunday morning, but chances no more than 10-25%. Chances of some showers on Monday seem to be trending higher as weekend frontal boundary settles across and there are signs of tighter low-mid level thermal gradient (frontogenesis) in right entrance region of jet over the upper Great Lakes. Based on probabilities of exceeding 0.10 inch, rain looks pretty light at this point, maybe heading toward a high POP/low QPF type setup. Deterministic GFS and ECMWF and associated MOS guidance supporting LREF idea right now as well, and latest NBM is trending higher as well with 20-40% chances, so confidence is increasing for at least some lighter showers around.

Cooler early next week: Post-frontal cold advection will usher in a cooler and more seasonable airmass for Monday and Tuesday as surface high pressure builds south from Manitoba. This could really be the case Monday if more clouds and some rain are present to the north of cold front. Overall daytime highs early next week will be in the upper 40s to mid 50s, coolest over the northwoods. Low temperatures will drop back into the low to mid 30s as the building high promotes ideal radiational cooling at night.

Aviation

for 06Z TAF Issuance Issued at 1238 AM CDT Wed Oct 21 2026

Main aviation impact will be a round of fog developing early this morning. Confidence is highest for impacts over east-central WI (KMTW, KGRB, KATW), remaining lower farther west. LIFR to VLIFR will be possible between 08-14z Wed.

Otherwise mostly clear skies tonight, scattered mid and high clouds will pass across the region later today. Winds will be light at less than 10 kts through the period.

Grb Watches

None.