Marine Weather and Tide Forecast for Lake Forest, IL

UPDATE
Issued at 904 PM CDT Thu Apr 17 2025

Most of the showers have moved out over the lake. This will allow for a period of drier conditions. Forecasted temperatures currently/tonight were knocked down a few degrees owing to the warm front still in eastern Iowa and down into west-central Illinois. Temperatures should remain steady if not nose upwards as that front moves east tonight.

A lot of attention has been paid tonight on the severe weather around the Omaha, Nebraska area. The convection out west is expected to move east and become more elevated through the overnight. While most models have it arriving sometime after midnight, they still disagree on what will happen. The forecast kept the best threat for showers and storms around and north of Interstate 88, with the stateline having the best chances. The main adjustment was to slow down the arrival of the storms. With steep mid level lapse rates and a strong low level jet, the main risk from these storms will be strong wind gusts and large hail. Last but not least, some of recent the high res guidance is showing a bit of a southerly shift in the evolution so PoPs were brought slightly farther south.

DK

DISCUSSION
Issued at 307 PM CDT Thu Apr 17 2025

Through Friday Night:

The primary weather concerns continue to focus on the threat of strong to severe convection, particularly late tonight and again Friday evening.

In the near term (late this afternoon through early evening), a batch of showers will shift east-northeastward across the area.
Severe weather is not expected with this activity, though some instances of small hail and possibly a few lightning strikes cannot be ruled out given some rather steep lapse rates aloft.
This activity is expected to move out of the area shortly after sunset this evening. A few isolated to widely scattered showers could persist for a couple hours this evening, but the coverage of showers is expected to decrease through the evening as we await our next period of showers and thunderstorms north of I-80 after midnight tonight.

The thunderstorm threat overnight has increased a bit over the previous forecast, though the best chances continue to be favored across southern WI and far northern IL. This thunderstorm activity overnight is expected to develop across eastern NE and far western IA early this evening. As this activity develops in advance of a cold front well to our west, the thermodynamic and kinematic envionrment will be supportive of eastward moving supercells, with an attendant very large hail threat. We will be watching the evolution of these storms closely through the evening, as it appears that this activity will shift eastward across southern WI and far northern IL after midnight tonight.

There does continue to be some uncertainty as to how far south into IL this storm threat will reach, owing largely to the presence of a stout EML capping inversion, which is expected to strengthen with southward extent into IL. At the present time, areas roughly along and north of I-88 have the best shot at seeing a few of these strong storms overnight. This is the general area that will remain near the northern periphery of this EML capping inversion. Accordingly, there will be a corridor across southern WI and far northern IL in which an eastward focus will exist to steer this evenings severe convection over IA eastward into parts of our area overnight. The primarily threat with these storms will be large hail (1-1.5" diameter), given the presence of very steep mid-level lapse rates. This threat will especially be maximized with any lingering elevated supercell structures.

These overnight storms are expected to come to an end by, or shortly after, daybreak Friday morning. In their wake, the spine of the elongated EML capping inversion will overspread the whole area again for the daylight hours of Friday. This will thus result in robust capping overhead, and relative dearth of showers and storms for much of the daylight hours of Friday. In the absence of showers and storms, deep atmospheric mixing into increasing southerly flow will result in gusty south winds (35-40 mph)
through the day. Temperatures will turn much warmer on these warm southerly winds, with readings likely peaking in the lower 80s in most locations.

Our second window of potential severe thunderstorms looks to come as a cold front shifts into northern IL into Friday evening, likely after 6 pm. Gradually increasing large-scale ascent is expected as this front moves into the area in the evening, and should thus foster sufficient low-level moistening and weakening of the residual capping inversion to support developing storms along the frontal boundary after 6 PM Friday evening. Still think that the highest storm coverage into Friday night should be near and east of I-55, where our forecast PoPs are in the categorical range.

Thermodynamic and kinematic profiles will be supportive of strong to severe thunderstorms developing across the frontal zone, though it appears that most convection that develops will either form atop the EML's base or quickly become undercut by the cold front. The elevated nature of the convection and progged front-parallel storm motions, plus uncertainties regarding lingering inhibition and how quickly storms will be able to intensify do raise questions about the extent to which storms will be able to fully harness the parameter space that will be in place. That said, any robust convection that manages to develop should possess a threat for large hail, while any convection that manages to stay along or ahead of the cold front will also feature a threat for damaging winds. Some potential for flash flooding also appears evident in our southeastern CWA given the aforementioned storm motions and potential for training convection.

KJB

Saturday through Thursday:

On Saturday, the cold front moving across the area late Friday through Friday night will stall out south of the CWA as surface high pressure sets up from the northern Plains to the Great Lakes region. The low-level baroclinic zone will also be nudged south, but remain close enough by to present a chance for at least scattered showers into areas well south of I-80. Can't rule out shower activity at times drifting northward toward the I-80 corridor, but by and large areas near and especially north of I-80 should remain dry (albeit mostly cloudy) Saturday through early Sunday. High temperatures Saturday afternoon are expected to be just shy of normal for the date inland, ranging from the upper 50s to around 60F/low 60s, but only near/around 50F along the lakefront due to onshore flow through the day.

Sunday, for those celebrating the Easter holiday, it unfortunately will be a rather inclement (breezy, showery at times, cool) day.
The main trough responsible for the approaching surface low on Friday will finally eject northeastward while becoming negatively tilted over the Upper Mississippi River Valley late Sunday. The various ensemble model suites have remained in better agreement with the evolution of the surface low, with the favored mean track across eastern Iowa or far northwest Illinois Sunday night. This track will keep most of the area on the cool side of a warm front slowly lifting northward in advance of the surface low, resulting in highs in the 50s (mid-upper 40s IL shore) and easterly winds gusting to 30 mph.

Mass response ahead of the aforementioned trough/low will quickly advect the moisture-rich airmass south of the front northward across the area on Sunday. This will result in an axis of showers lifting northward through early afternoon and then perhaps additional waves of showers in the mid to late afternoon. While there's too much uncertain in exact precip timing, there is a signal for the guidance in some dry periods, so it doesn't currently look like an all day washout. As the effective warm front slowly lifts back north toward and into the far southern CWA during the afternoon, enough MUCAPE may build to support a chance for isolated to scattered thunderstorms.

As impressive deep layer forcing nears from the southwest late in the day, arcs of convection racing northeast should expand into the CWA Sunday evening. Regarding the effective warm frontal position, there may be a window of overlap of modest uncapped MLCAPE in the late afternoon and early evening in parts of the southern CWA (generally near/south of US-24). We'll need to keep a close eye on trends for a conditional severe storm threat in these areas within a highly sheared environment from the late afternoon through the early to mid evening. Right moving Bunkers motions could result in any supercells quickly crossing the front, which may limit the tornado threat in the CWA, even if a severe storm risk does materialize. Can't rule out a threat for strong storms expanding northward with the front in the evening, though the diurnally unfavorable timing and already minimal instability may limit the threat farther north to localized wind gusts stronger than the already breezy background wind field.

Regardless of how the potential conditional severe threat pans out or not, the dynamic system will still bring widespread showers and scattered embedded storms over the area through part of the overnight, with thunderstorm coverage diminishing as instability further wanes into the pre-dawn hours of Monday.

After Sunday's system departs across the Great Lakes region early Monday, a mostly zonal regime will prevail across much of North America for several days. This will bring a period of seasonable (Monday) to seasonably warm (Tuesday-Thursday) weather to the region, with locally cooler conditions from daily lake breezes around the Lake Michigan shore. Monday's main weather of note will likely be gusty westerly winds, with gusts up to 35 mph in the official forecast and advisory (45+ mph gusts) criteria upside per the ECMWF/EPS ensemble. Can't rule out a few light showers in the morning, though suspect most areas will be dry.

The one notable perturbation in the zonal pattern next work week will be a low-amplitude wave tracking along the U.S./Canadian border Tuesday into Wednesday. An associated weak cold front may slow or stall across the area Tuesday night into Wednesday, with marginal moisture profiles resulting in perhaps isolated to scattered showers near the front.

Castro/Kluber

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
Issued at 1258 AM CDT Fri Apr 18 2025

Forecast concerns for the terminals...

- Scattered showers and thunderstorms possible late tonight mainly along and north of a RPJ to ORD line.

- Gusty southwest winds Friday with gusts in the 30-35 kt range.

- Another round of showers and thunderstorms Friday evening followed by MVFR ceilings Friday night.

A subtle shortwave disturbance is traversing across IA this evening which has lead to the development of scattered showers and thunderstorms. While this disturbance is expected to pivot into northern IL and southern WI overnight, confidence on the coverage of showers and thunderstorms surviving through northern IL remains low. That said, forecast soundings do show a large amount of elevated instability remaining over northern IL tonight into early Friday morning which in the present of the disturbance and strong low-level jet may allow for a few showers and/or storms to reach the terminals particularly those along and north of a RPJ to ORD line. Therefore, have decided to maintain the PROB30s at the Chicago area terminals for now but did upgrade RFD to a TEMPO since confidence is a bit higher. Any storms that do survive will have the potential of producing reduced visibilities along with locally gusty winds in excess of 30 kts.

The shortwave and associated precipitation will move east of the terminals Friday morning resulting in mostly dry conditions for Friday. However, a developing surface low will begin to move towards the area which will cause winds to increase and become gusty by later morning/early afternoon. Confidence is high that gusts of 30-35 kts will occur through much of the day on Friday, but there is a chance that locally higher gusts may occur especially if deeper mixing is achieved. Otherwise, expect SCT to BKN VFR clouds through Friday afternoon.

The aforementioned surface low will move into southern WI Friday evening which will force a cold front through northern IL and northwest IN. As this occurs, another period of showers and thunderstorms is expected at the terminals a few of which could be on the strong side with locally gusty winds and hail.
However, a few showers may develop as early as 22z near RFD as the front begins to enter the area. Given the quick movement of the front, showers and storms should be short lived and move through by 05z Friday night. Behind the front winds will become northwesterly and gradually lose their gustiness but occasional 18 to 20 kt gusts may linger through Friday night. Additionally, ceilings will also lower to MVFR and remain as such through the remainder of the forecast period.

Yack

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT this evening for the IL and IN nearshore waters.