Marine Weather and Tide Forecast for Shorewood Forest, IN

DISCUSSION
Issued at 309 PM CDT Fri Apr 18 2025

Through Tonight:

Extensive cloud cover persists across the area this afternoon within the warm sector of a surface low centered near Dubuque, IA.
In spite of the cloud cover, breezy south winds continue to aid in the advection of warmer temperatures. In fact, as of this writing temperatures have warmed into the mid to upper 70s, save areas along the Lake County IL Lake Michigan shore. Cooler temperatures (in the 60s) have persisted here due to the continued onshore flow following this mornings outflow boundary.
Expect these breezy and warm conditions to persist into this evening as a cold front gradually shifts eastward into the area.

The primary weather concern continues to center around the threat for strong to severe thunderstorms, particularly this evening (roughly 6 PM through 11PM) as the cold front shifts eastward across the area. A persistent and exceptionally strong EML and associated capping inversion continues to be sampled in recent AMDAR soundings out of MDW and RFD. This is expected to curtail near surface based storm development, at least for the next few hours mid to late this afternoon. In spite of this, elevated storms, based above the EML inversion, will continue to fester across far northern sections of IL for the next few hours as a weak impulse tracks northeast into southern WI. Any severe threat with these initial storms should be confined to some instances of marginally severe hail near and north of the WI state line.

As we head into early this evening (after 6 PM), the surface cold front, which as of this writing resides west of the area across eastern IA, will slide eastward across northern IL. It is near this boundary in which additional (potentially near surface based) storms look to develop. As mentioned in previous discussions, questions remain with the exact timing and overall coverage of storms near the frontal boundary this evening. Much of this continued uncertainty revolves around how effectively the EML capping inversion will erode into this evening, especially considering that most of the forced ascent and cooling looks to come as a result of frontal scale forcing.

Nevertheless, any storms that do develop near the front this evening will do so in an environment quite favorable for severe storms. The combination of strong deep layer shear and very steep mid-level lapse rates would be supportive of some supercells capable of producing instances of very large hail (1.5"+). Large hail looks to be the primary severe threat this evening with these storms, though cannot rule out the potential for some damaging wind gusts and possible a brief tornado, particularly with any storms that are able to become near surface based. The highest threat area for these severe storms will largely be along and south of a line from near LaSalle-Peru to Chicago, with overall lower potential the farther northwest of this line you are. Expect the threat of storms to end north of I-80 later this evening. However, storm activity is likely to linger overnight well south of I-80, though the severe potential is expected to gradually ease here after midnight.

KJB

Saturday through Friday:

Some showers from decaying overnight convection moving across our southern CWA should linger through the 7-10am CDT timeframe on Saturday across our far southern CWA, primarily south of US-24 (60-70% PoPs). The rest of the day and through Saturday night/early Sunday, additional impulses interacting with the low-level baroclinic zone focused to our south may bring occasional (primarily light intensity) showers at times to portions of central Illinois and south of the Kankakee River in Indiana (20-50% PoPs/highest south of US-24). Otherwise, it will be notably cooler on Saturday with cloudy skies and perhaps some sunny breaks in the afternoon. Highs will only reach the mid 50s to around 60F inland and likely be limited to the upper 40s along the immediate lakeshore. This will be followed by lows in the lower to mid 40s on Saturday night.

On Sunday, the negatively tilted upper trough ejecting from the southern Plains and associated surface cyclogenesis will result in a surface low tracking to the mid MS Valley late Sunday night to central Lake Michigan early Monday afternoon. This is expected to result in a breezy (easterly gusts to 30 mph), cool, and showery at times Easter Sunday, unfortunately. It doesn't look to be an all-day washout, however, with a few rounds of forcing interacting with the warm/moist advection over-topping the warm frontal zone.

The forecast surface low path and timing represents a further slowing trend vs. a few model cycles ago. This is important with respect to the northward progression of a warm front lifting north and the potential for a conditional surface based severe threat late day Sunday into the evening. Given the system's slowing trend, it appears the warm front will be hung up just south of our southern CWA, with perhaps a chance for isolated thunderstorms south of the Kankakee River Sunday afternoon.

Sunday night is when the most widespread showers and isolated to scattered embedded thunderstorms are anticipated, along with gusty southeast winds. Rainfall totals may end up near or just upwards of an inch near and west of I-39 in northwest to north central Illinois, with amounts tapering gradually off to the east. Can't rule out some ponding on roads with any heavier convective rain rates Sunday night, though the overall flooding threat appears low.
The surface low will track just to our northwest late Sunday night and then to our north on Monday, with a few lingering showers possible until late morning/midday in the cold advection regime behind the cold front. The afternoon will feature breezy west- southwest winds gusting to 35 mph, and some upside potential remains with this.

Castro

For Tuesday onward, the upper-level pattern is forecast to become more zonal (west-east oriented) and persistently milder.
Both deterministic and ensemble guidance continues to indicate that subtle shortwaves may pivot through the pattern and result in additional periods of showers and perhaps thunderstorms (first window would be late Tuesday-Tuesday evening). Given the uncertainty in timing and coverage of such activity, see no reason to alter the periodic 20-50% POPs offered by the NBM through the end of next week, but suspect that many dry hours will occur as well. On a more positive note, continued mid-level warm advection (850mb temps forecast in the 10-12C range) is expected to keep temperatures in the above normal category for mid-April with highs in the upper 60s to 70s and overnight lows in the 40s to around 50F. The exception however, will be for those near the lake where the potential for daily lake breezes may keep readings notably cooler.

Yack/Castro

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/
Issued at 1256 PM CDT Fri Apr 18 2025

The main weather concerns for the 18Z TAF period include:

* Scattered showers and thunderstorms this evening with hail and associated gusty winds possible.

* MVFR cigs likely this evening through Saturday morning.

A system of showers and thunderstorms will move into the area from the west later today. Scattered showers could get going as early as the late afternoon with a few embedded thunderstorms possible, although chances are greatest after around 02Z. A few storms this evening could be strong to severe and feature damaging hail and locally strong winds. Storms should move away later in the evening with scattered showers lingering into the early overnight.

MVFR cigs are expected to park over the TAF sites later this evening, although periods of MVFR may be possible earlier in the evening with the rain. MVFR should then hang overhead through Saturday morning before lifting to VFR for the afternoon. There is a signal for a possible few hour period of IFR cigs overnight tonight. Confidence was too low for a mention in the TAF for now, except at RFD where a TEMPO for IFR was introduced for 03-07Z.

SW winds will gust into the 25 to 30 kt range this afternoon with a couple of gusts over 30 kt possible. They'll gradually ease during the evening and overnight while veering to NW.
Confidence in wind trends on Saturday is on the lower side. A signal exists for a few hour period of NNE winds Saturday morning (mainly 09-12Z timeframe) before flopping back to NNW for the better part of the morning, although persistent NNW is slightly favored. Additionally, we're expecting a quick shift to easterly at the Chicago sites, but timing is uncertain. Best guess at this point is mid-late afternoon, but we could see this shift as early as around noon.

Doom

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory until 9 PM CDT this evening for Winthrop Harbor to Wilmette Harbor IL.

Gale Warning until 9 PM CDT this evening for Wilmette Harbor IL to Michigan City IN.