Marine Weather and Tide Forecast for Lake Bluff, IL

DISCUSSION
Issued at 258 PM CDT Sun Apr 20 2025

Through Monday Night:

A swath of showers is moving across northern IL early this afternoon. These showers are blooming north of a warm front as it progresses northward into our CWA As of around 2 PM, the boundary resides near the Kankakee River and conditions are dry immediately along and behind it. A few embedded thunderstorms and heavier showers have been clinging onto a MUCAPE gradient immediately north of the front. The showers and embedded thunder will continue to be pushed along by the front until they get shunted north of the CWA late this afternoon and the area should be largely dry then until later in the evening.

The warm front is expected to get hung up over our CWA, roughly near the I-88/90 corridors later this afternoon before surging northward again this evening with the approach of the low center and cold front. A pretty sharp temperature gradient is setting up across our area on either side of the front, especially now that our south has dried out and is beginning to see some sun. Temperatures should be rather steady this evening while this front remains stationary. After the front begins its trek northward again, much of the area north of I-80 will likely even warm a couple of degrees tonight.

The storm's cold front will propagate across the CWA late this evening into tonight, bringing with it an additional push of rain and probably some embedded thunderstorms. Continued low level warm advection this evening will generate a pool of elevated instability sufficient for thunderstorm development just ahead of the cold front. While severe weather is not really anticipated, we could see some stronger winds associated with these storms. Several pieces of guidance are resolving a corridor of gusty winds coincident with a narrow opportunity for the low levels to become only weakly stable near the front. An impressive low level jet will track just off the deck and it's very possible that some of these stronger winds could punch through to the surface, especially with the heavy rain and storms to help out. This is especially true closer to central and western IL where they could maintain a little bit of mixed- layer instability into the evening. An SPC marginal risk abuts our southwest CWA for this wind potential.

The storms will be off to our east prior to daybreak tomorrow. A trailing secondary cold front will move across the area during the morning hours. In fact, morning low temperatures tomorrow will likely occur well after daybreak behind this boundary. With appreciable low level moisture hanging on behind the initial front, some drizzle may materialize during the morning before the secondary front passes. Conditions should also be windy tomorrow, especially during the morning, but confidence is shaky in what sort of winds we'll be looking at. The lack of confidence boils down to two primary discrepancies among models: the magnitude of the low level flow and the quality of low level moisture. The Euro and UKMET bring in much drier near- surface air behind the initial cold front than other camps leading to slightly deeper and overall more efficient mixing in the morning. These are two of the more aggressive solutions for winds tomorrow. 925mb winds during the morning are also being modeled at anywhere between 35 and 45 kt. The HRRR for instance is stronger with the low level flow so, despite being Monday Night saturated in the low levels with lesser mixing, it's still wanting to resolve gusts to around 40 mph. So it's tough to say exactly what sort of flow we will have upstairs and how efficiently we can mix that down to the surface. But a period of at least 30 to 35 mph gusts looks likely tomorrow morning, although 40 to 45 mph certainly looks attainable.

Winds could remain strong into the early afternoon but should start stepping down during the afternoon as the low level flow relaxes. After the morning drizzle potential moves away, no rain is expected for the rest of the day. A feed of dry air will chip away at the cloudy skies and some good sunshine should fall on the area later in the day while afternoon temperatures look to be in the 50s.

Doom

Tuesday through Sunday:

The upper level pattern across the CONUS will transition to more of a quasi-zonal flow (west-to-east oriented) pattern for the middle part of the week, before becoming more amplified again later this week into next weekend. This is expected to curtail the threat of any stronger (and persistent precipitation generating)
storm systems from impacting the eastern half of the country Tuesday through at least Thursday. In spite of this, ensemble and deterministic guidance are in agreement in tracking some smaller scale perturbations eastward across our region during this period. Accordingly, while there is likely to be mainly precipitation free hours, there will be some on-and-off shots of showers and thunderstorms through much of the week.

Guidance remains in good agreement with tracking an initial low amplitude disturbance eastward across the Midwest into the western Great Lakes through Tuesday night. Weak height falls associated with this waves should encourage the development of a modest southerly low-level jet and strengthen theta-a advection Tuesday night. This will in turn support our first decent potential (50-60% chance) for showers and storms late Tuesday into Tuesday night. At this time the best chances for this reside along and north of I-80. Another, similar quick moving impulse may shift into the area and result in another period of (~30% chance) of rain late Wednesday into Wednesday night. Otherwise, our next good shot (50-60% chance) of showers and storms comes late in the week (Thursday night into Friday) as a stronger cold front moves across the area.

Temperatures are expected to be on a warming trend to solidly above average temperatures through the middle of the week, particularly for inland sections of northern IL and IN. As is often the case this time of year, lake breezes each afternoon will keep temperatures notably cooler along and near the Lake Michigan shore. Temperatures are then likely to cool back closer to seasonable levels next weekend following a cold front passage late this week.

KJB

AVIATION /00Z TAFS THROUGH 06Z MONDAY/
Issued at 630 PM CDT Sun Apr 20 2025

Aviation forecast concerns for the 00Z TAFs:

- Scattered TSRA possible late this evening.

- MVFR ceilings develop overnight and persist through most of Monday while slowly rising.

- Breezy ESE winds become WSW by morning. Gusts 30-35 kt possible Monday, easing later in the day.

Surface low pressure was analyzed over MO early this evening, with a northward lifting warm front extending southeast across west-central IL into southwest IN. Breezy east-southeast winds with gusts 20-25 kts will persist across the terminals this evening ahead of the approaching warm front, eventually veering southwest after midnight tonight as the low moves across WI and the occluding frontal boundary shifts east of the area. West- southwest winds are expected to strengthen in the wake of the low, with gusts 30-35 kts likely during the morning and early afternoon hours before diminishing quickly early Monday evening.

High-res CAMs are in generally good agreement in bringing a line of convective SHRA/TSRA (currently approaching the MS River from eastern IA/MO) northeast into the area late this evening, with some potential for isolated elevated SHRA/TSRA development ahead of the main are of precipitation in strong warm-advection.
Thus have introduced a VCTS by 03Z/10pm and a tempo for TSRA in the 04Z-06Z window (an hour earlier for KRFD). SHRA coverage should diminish to scattered/widely scattered coverage during the remainder of the overnight hours. Current VFR conditions are expected to deteriorate within the heavier precip late this evening, with MVFR ceilings likely then persisting into much of Monday before eventually scattering to VFR from the west later in the day/evening.

Ratzer

MARINE
Issued at 258 PM CDT Sun Apr 20 2025

A Small Craft Advisory is in effect today. A Gale Warning goes into effect tonight and lasts into tomorrow evening.

Low pressure at or just under 1000 mb will track from Iowa tonight to northern Lower Michigan Monday afternoon and across Lake Huron Monday evening. Breezy east-southeast winds tonight will result in hazardous waves for small craft along the Illinois and Indiana nearshores. A period of gales is also possible late tonight coincident with a push of showers and thunderstorms. Then in the wake of the system on Monday, winds will quickly shift to southwest and then west while rapidly increasing. While some uncertainty remains, felt confidence was high enough to upgrade the watch to a Gale Warning for tomorrow.
Also made the decision to have the warning go into effect at 06Z for the brief gale potential tonight.

Doom/Yack

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory until 1 AM CDT Monday for the IL and IN nearshore waters.

Gale Warning from 1 AM to 7 PM CDT Monday for the IL and IN nearshore waters.