DISCUSSION
Issued at 333 AM CDT Wed Sep 18 2024

Short Term
Today
Tonight...and Thursday

Summer-like conditions continue into Thursday. Only weather concerns will be fog trends early this morning and again tonight/early Thursday, how warm we get and the arrival of shower/storm chances on Thursday.

Fog Trends:

Light southeast winds, clear skies, a low-level inversion and a little extra moisture from Lake Michigan has led to some fog development across mainly eastern WI. Satellite and webcams showing mainly patchy ground fog so far, but may need a SPS if the fog continues to expand. Similar set up for tonight into early Thursday, so will continue/increase fog coverage across much of eastern WI, with some dense fog possible, especially inland of the bay/lake. A little more wind just off of the surface across central and north central WI looks to keep fog chances lower, but some patchy ground fog will be possible.

Temperatures / Humidity:

Will lean toward the warmer/better guidance today (NBM/CMCnhBC)
keeping highs in the low to mid 80s for most locations, with mainly 70s near Lake Michigan. Highs on Thursday look to be close or just slightly cooler than today. Record highs look to be safe as most are in the upper 80s to low 90s. Dewpoints look to stay in the upper 40s and 50s for most of the area, with some near 60 closer to Lake Michigan, keeping the heat index near the actual temp. That said, the area will remain in the "yellow" category for the HeatRisk...which indicates a "Minor" level of heat-induced impacts. This level of heat affects primary those individuals extremely sensitive to heat, especially when outdoors without effective cooling and/or adequate hydration.

With the clear skies, lows dipped into the upper 40s and 50s across much of the area early this morning. Looking pretty similar for tonight, but with a few more upper clouds and some fog, should keep most lows in the 50s to around 60.

Shower/Storm Chances:

Dry conditions will prevail today and tonight as weak high pressure pushes across the Great Lakes. On Thursday, a vertically stacked low pressure system will slowly move from western ND into southern Canada, with a cold front and shortwave advancing toward the region during the day. Looking like the majority of the activity will stay to our west during the daylight hours, but a stray shower or storm will possible across central or north central WI Thursday afternoon.

Long Term...Thursday Night Through Tuesday

The big story during this period will be the chance for much needed rain across the area Thursday night into Friday. Rainfall amounts at Green Bay, Wausau and Rhinelander are running between 0.20 and 0.40 inches for the month through the 18th (expected to be dry again today).

500mb ridging across the western Great Lakes will flatten by the weekend, resulting in temperatures returning closer to normal Sunday into the middle of next week. On Thursday night, the upper level disturbance and weak surface cold front will move into and across the area. Showers and thunderstorms will develop along the cold front Thursday afternoon across Minnesota and western Wisconsin and then move east into the area during the evening and overnight. Based on bufkit soundings, the activity should weaken some as the evening progresses as the storms move into our area.
Some dry air aloft will also inhibit the potential for stronger storms. On Friday, the boundary pushes into far eastern Wisconsin.
The combination of daytime heating and increasing CAPE values could support for a strong storm or two if the boundary is still lurking across eastern Wisconsin. For Friday night, models have caught onto a dry forecast which the models began this trend yesterday. A weak impulse could bring a shower or two to the area on Saturday. Beyond Saturday, the details of the forecast become muddled thus confidence is low in the chances of rain on Sunday through Tuesday. The warmest weather will continue into Friday, then temperatures will return closer to normal and most likely will remain at or slightly above normal for the first half of next week.

AVIATION
for 06Z TAF Issuance Issued at 941 PM CDT Tue Sep 17 2024

Clear skies, light surface winds and good visibility are expected tonight through Thursday, with the exception of some ground fog that is possible in an area around ten miles inland from the shores of Lake Michigan and the bay between 08z and 13z each morning.

GRB WATCHES/WARNINGS/ADVISORIES
None.