Marine Weather and Tide Forecast for Evanston, IL

DISCUSSION
Issued at 315 PM CDT Sat Apr 19 2025

Through Tonight:

Low clouds, and even a period of drizzle, have persisted across parts of eastern IL into northwestern IN through the morning following the passage of a lake enhanced cold front early this morning. However, a west-northwesterly wind shift, and the associated influx of some slightly drier low-level air early this afternoon, has allowed for a gradual improving trend across interior parts of northern IL (generally west-northwest of the I-55 corridor as of this writing. I suspect this improving trend will continue eastward across much of the Chicago metro area during the mid-late afternoon hours. With this improving trend, expect temperatures to warm a few degrees (into the mid 50s across eastern IL and northwestern IL and into the low 60s across interior sections of northern IL) mid to late this afternoon before sunset.

For tonight, we are not expecting much in the way of rain, aside from the low (15%) chance for a few showers far south overnight.
However, attention will be focused on the robust mid/upper level trough/low that will spawn low pressure across the southern Plains tonight. This weather system is expected to impact our sensible weather during the day on Sunday. For more on this, reference the discussion below.

KJB

Sunday through Sunday Night:

The vigorous closed mid-upper level low over the desert southwest will track eastward into the southern High Plains tonight, before lifting negatively tilted northward into the Midwest by Sunday evening. As this system ejects east- northeastward, the frontal boundary that will have stalled out downstate will begin lifting northward Sunday into Sunday night in response to a deepening surface low tracking from Oklahoma north into Iowa by late Sunday evening.

As warm air advection ramps up in advance of the approaching system, a band of showers will likely lift northward across our CWA Sunday morning into the early afternoon. Coverage of rainfall will likely be greatest over our IL counties, perhaps focused inland of the lake. While there should be some scattered showers around at times in the mid to late afternoon hours as well, it currently looks like many dry hours are possible (especially with southward extent) as the lead impulse lifts north of the area taking the strongest WAA driven showers with it.

Sunday will be fairly chilly by late April standards for most of the area, especially when factoring in easterly winds gusting to 25-30 mph, overcast skies, and rain at times. Forecast highs are mainly in the lower 50s north of I-80 (only mid to upper 40s along the Illinois shore) and in the mid 50s to lower 60s south (warmest south of US-24 towards evening). Temperatures will steadily rise as the warm front lifts north of the area Sunday night, to 60F or so all the way up to or just north of I-80.

Another round of showers and probably some thunderstorms will occur Sunday night in advance of the approaching cold front.
Within the warm sector Sunday night, some weak destabilization of the boundary layer is possible, which could slow the weakening of an extensive upstream potentially severe QLCS as it moves across our CWA overnight. The most likely scenario is that it will be in a decaying state and sub-severe by the time it reaches our CWA, however given the very strong wind fields just off the deck (>50kt down to about 1500ft AGL), it wouldn't take very much instability for some wind threat to sneak into our CWA (best chance of this far southwest CWA This continues to look like it has a low probability of occurrence at this point, but certainly something worth monitoring.

Castro/Izzi

Monday through Saturday:

The upper trough and its associated surface low that will bring us some rain and thunderstorms on Sunday/Sunday night will be lifting across WI and northern MI on Monday. Isolated to scattered showers will continue until mid morning while lifting north and then largely come to an end by the late morning.
More notably, the tight pressure gradient (6-hr pressure rises on the order of 9-10 mb) and cold advection in the wake of the low pressure will generate gusty west-southwest to west winds through early Monday evening.

In fact, gusts on Monday will likely peak in the 35-45 mph range, with higher gusts up to 50 mph or so possible depending on the degree of mixing. The ECMWF and its ensemble (EPS) have been the most bullish with Monday's winds in the last several model cycles. Given the run to run consistency thus far and better support from the NAM and GFS Bufkit soundings, adjusted gusts up to around the NBM 90th percentile. The ECMWF/EPS scenario would entail a decent chance that we'd need a wind advisory, with 90th percentile gusts from the EPS in the ~50-55 mph range. The cold advection and only slowly diminishing cloud cover will also cap temperatures in the mid-50s to around 60F Monday afternoon before readings cool into the mid 30s to lower 40s Monday night.

Heading into Tuesday, guidance remains in good agreement that a more zonal (west-east oriented) upper level pattern will establish across the CONUS through the end of next week. While these patterns often offer periods of dry conditions, there has been a persistent signal for shortwaves to traverse the pattern and bring periodic chances for showers and perhaps thunderstorms.

The first window where showers and some storms may occur is forecast late Tuesday and Tuesday night and into Wednesday as a shortwave over the northern Plains forces a cold front through northern IL and northwest IN. Guidance variability precludes higher confidence in this period. Thus expect fairly substantial refinements to be made in the PoP forecast. Sufficient instability may be in place to generate thunderstorms, but the chances for any severe weather look low.

The next potential period of unsettled, at times showery weather is forecast toward the end of next week (later Thursday into Saturday morning timeframe) as a more notable shortwave lifts into the area. However, as is common at this lead time, there is plenty of variability in the timing and evolution of the late week system making this part of the forecast lower confidence. That said, generally maintained the 30-60% POPs from the NBM for now. It does look like expansive high pressure building in north of the Great Lakes should result in dry and fairly pleasant/comfortable conditions the rest of Saturday and through Sunday.

Regardless of the periodic rain chances, temperatures through much of next week look to be above normal for late April.
Therefore, expect high temperatures inland of Lake Michigan well into the 60s and 70s with overnight lows in the 40s and 50s.
Wednesday and Thursday could even make a run at 80F in parts of the area! The typical daily lake breezes will keep readings notably cooler (50s) along the lakeshore most days.

Castro/Yack

AVIATION /18Z TAFS THROUGH 00Z MONDAY/
Issued at 1247 PM CDT Sat Apr 19 2025

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

* MVFR cigs into this afternoon

* Low confidence in wind trends this afternoon

* A system of showers arriving late Sunday morning

IFR cigs around the lake are steadily improving to MVFR. The expectation is to be MVFR across the Chicagoland sites by shortly after 18Z. RFD has gone VFR for the rest of the day and the Chicago sites will follow suit by mid-afternoon. VFR can then be expected through tonight.

Winds have been somewhat variable at the Chicago sites today and that may continue, leading to lower confidence in wind trends through the afternoon. The expectation is for the Chicago sites to go generally W or NW for a few hour period around mid- afternoon before winds turning in off the lake will bring things back to easterly late this afternoon. Winds will then remain easterly through the night and the day on Sunday. Gusts will push 20 kt for the latter part of Sunday morning, building to 20 to 25 kt for the afternoon.

Additionally, a system of rain showers will overspread the area from the south on Sunday. Rain is expected to get going over the terminals late in the morning, although onset time is rather uncertain and could possibly hold off until the afternoon. The rain should largely be on the lighter side and not contribute to any noteworthy vis reductions, although some high- end MVFR cigs are favored later in the daytime.

Doom

MARINE
Issued at 326 PM CDT Sat Apr 19 2025

Have issued a Gale Watch for the Illinois and northwest Indiana nearshore waters from Monday morning through early Monday evening.

Low pressure at or just under 1000 mb will track from Iowa Sunday night to northern Lower Michigan Monday afternoon and across Lake Huron Monday evening. Breezy east-southeast winds Sunday night may result in hazardous waves for small craft along the Illinois nearshore. Then in the wake of the system on Monday, winds will quickly shift to southwest and then west while rapidly increasing due to a tight pressure gradient. While the top end magnitude of the speeds/gusts varies amongst the guidance for Monday, in general felt the signal was strong enough to issue a gale watch given expected Monday morning onset. For now, the forecast will indicate gale speeds/gusts to around 35 kt but the more bullish guidance suggests gales up to 40 kt or even a bit higher are possible. Increasing stability offshore will likely limit the gales to the first 2-3 miles of the nearshore. Westerly winds will steadily ease Monday evening.

Castro

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Gale Watch from Monday morning through Monday evening for the IL and IN nearshore waters.