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LMZ741 Expires:202311291630;;592280 Fzus53 Klot 290935 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 335 am cst Wed nov 29 2023
for waters within five nautical miles of shore on lake michigan
waves are provided as a range of significant wave heights, which is the average of the highest 1/3 of the waves, along with the average height of the highest 10 percent of the waves which will occasionally be encountered.
lmz740>742-291630- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 335 am cst Wed nov 29 2023
.small craft advisory in effect until noon cst today...
Today..Southwest winds 20 to 25 kt becoming west and diminishing to 15 to 20 kt. Mostly Sunny. Waves 1 to 3 ft.
Tonight..Southwest winds 15 to 20 kt. Mostly clear in the evening, then becoming mostly cloudy. Waves 1 to 3 ft.
Thursday..Southwest winds 15 to 25 kt becoming west 10 to 15 kt in the afternoon. Mostly cloudy. Waves 1 to 3 ft.
Thursday night..Northwest winds 10 to 15 kt becoming northeast overnight. Slight chance of rain in the evening, then chance of rain overnight. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 291148 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 548 AM CST Wed Nov 29 2023

SHORT TERM
Issued at 320 AM CST Wed Nov 29 2023

Through Thursday...

Key messages:

- Following a chilly early morning start, temperatures will turn warmer this afternoon, with highs nearing 40 degrees. High temperatures then warm well into the 40s for Thursday.

- With most areas remaining dry during the daylight hours of Thursday, rain chances will begin to gradually increase late in the day across central IL and IN (areas well south of I-80).

While temperatures currently remain on the chilly side, with readings in the low to mid 20s as of this writing, these values are a good 5 to 10 degrees warmer than they were during the evening. Conditions will continue to warm through the 30s during the day today as mostly sunny skies combine with a warming lower- level airmass. High temperatures this afternoon will be in the upper 30s to around 40 degrees.

Higher level cloud cover will gradually begin to increase across the area in advance of the next storm system taking shape across the Texas Panhandle on Thursday. While this will result in partly sunny skies during the day, most areas are likely to remain dry and seasonably mild through the day. High temperatures are expected to be in the mid to upper 40s. Rain chances will be on a gradual increase late in the day across far southern sections of the area well south of I-80 as deeper Gulf moisture begins to surge northward into the area in advance of an approaching frontal trough. Precipitation chances continue to ramp up with the approaching weather system Thursday night into Friday morning.
For more on that period reference the long term discussion below.

KJB

LONG TERM
Issued at 320 AM CST Wed Nov 29 2023

Thursday night through Tuesday...

Key Messages...
- Widespread precip event into much of the forecast area Thursday night into Friday morning, with the potential for minor snow accumulations for areas northwest of a Chicago to Mendota line (all rain south of this line).
- An active weather pattern with multiple periods pf precipitation will persist Friday night through early next week.

A small but strong mid-level wave will track from the southern Great Plains into the western Great Lakes during a gradual weakening phase Thursday through Friday. While deep-layer moisture is lacking across the central CONUS at this time, 00Z RAOBs in Mexico around the southwest Gulf of Mexico indicate Pwats comfortably over 2". This moisture is expected to quickly advect NNE with persistent low-level 30-40kt flow over the next 48 hours, ultimately bringing PWATs nearing 1" into as close as central Illinois by late Thursday night. Meanwhile, a loosely coupled upper-jet structure over the mid- Mississippi River Valley combined with a nearly 100kt 500 hPa jet nosing into the southern half of Illinois will promote an impressive dynamic setup for widespread precip well into our forecast area late Thursday night through Friday morning. Ensemble clustering continues to differ in the handling of some important features, notably the northward placement of a strengthening low-level baroclinic zone across northern Illinois. EPS/CMC ensembles favor a slightly colder solution that would bring increasing snow chances into the northwest third or so of the CWA while the GEFS favors a slightly slower and therefore warmer solution (but still support changes in precip type).

Some caveats with this event include an overall weakening system (surface low strength peaks late Thursday evening over Oklahoma)
and a decent antecedent layer of dry air aloft to the north.
Increasing low-level ENE flow on the northern periphery of the system, owing to a 1020 hPa surface high shifting across Minnesota, should offset precip amounts to some degree. But unlike a more typical Hudson Bay setup with very dry air upstream into Lower Michigan, trajectories of much drier air will focus from Wisconsin toward Iowa. Therefore, the abundant moisture and strong forcing should overwhelm the existing dry layer well into the CWA.

Putting this altogether, expectations are for a widespread precip event across a vast majority of the forecast area Thursday night and Friday morning. Precip type will be rain south of a Chicago to Mendota line, with increasing chances for a transition to all snow from north of Dixon to McHenry County. Where the cutoff in the precip shield settles is a looming big question that will have implications with how much (if any) accumulating snow occurs into the northwest third of the CWA. Given the increasing signal in guidance (especially EPS and CMCens) for accumulating snow and the factors noted above, have increased snow probs with some minor accumulations (<1") in the forecast late Thursday night into Friday morning. While still a lower (~20%) chance exists for several inches of accumulating snow in the aforementioned area, this solution is no longer an outlier within the broader ensemble of guidance. This is especially the case if the low-level baroclinic zones further contracts and supports a band of f-gen in a dynamically cooled thermal profile.

Beyond Friday morning, guidance remains in an active WSW/SW flow pattern with multiple systems traversing the region through the weekend until deeper troughing drifts east across the Great Lakes region by mid-week. A secondary jet streak behind the system Thursday night into Friday will force another (lighter) swath of precip into the area Friday night along the existing low-level baroclinic zone. While thermo profiles generally favor rain for most of the area, some wet snow accumulations are possible on the northern edge of the system into far northern Illinois and southern Wisconsin.

Kluber

AVIATION
For the 12Z TAFs...

SKC conditions are expected today, with some passing cirrus through the remainder of the period. SSW winds gusting over 15 knots at times will veer WSW this morning before lowering under 10 knots with surface decoupling after sunset. A 35-40 knot LLJ will shift over southern Wisconsin and far northern Illinois late tonight, with LLWS introduced at RFD prior to 12Z. The core of the LLJ will remain northwest of the Chicago terminals until daytime mixing leads to surface gusts over 20 knots Thursday morning.
Meanwhile, increasing low-level moisture with the LLJ and within a strong inversion may result in some MVFR clouds developing late tonight through Thursday morning.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM
Small Craft Advisory
IL and IN nearshore waters until noon Wednesday.

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