Sunrise 5:51 AM   Sunset 7:42 PM Moonrise 9:56 PM   Moonset 6:28 AM

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LMZ744 Expires:202404260315;;363394 Fzus53 Klot 251940 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 240 pm cdt Thu apr 25 2024
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.
lmz743>745-260315- calumet harbor il to gary in-gary to burns harbor in- burns harbor to michigan city in- 240 pm cdt Thu apr 25 2024
Tonight - Northeast winds 10 to 20 kt becoming southeast late. Mostly clear. Waves 1 to 3 ft. Friday - Southeast winds 15 to 25 kt. Showers likely in the afternoon. Waves 1 to 3 ft. Friday night - Southeast winds 15 to 25 kt becoming south overnight. Showers likely and a chance of Thunderstorms. Waves 2 to 4 ft. Saturday - South winds 20 to 25 kt. Chance of showers and Thunderstorms, mainly in the morning. Waves 2 to 4 ft. A small craft advisory will likely be needed.

LMZ700
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FXUS63 KLOT 251916 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 216 PM CDT Thu Apr 25 2024

KEY MESSAGES

- Scattered showers and thunderstorms will move over the area Friday afternoon and evening. A few may linger through the overnight hours into Saturday.

- Saturday and Sunday look warm and breezy with unseasonably warm highs in the lower 80s and overnight lows in the low to mid 60s.

- Waves of showers and thunderstorms appear poised to parade near and west of the Mississippi River Saturday and Sunday.
Much of our area may end up on the outer edge of all activity until Sunday night.

- Lowering humidity levels will be realized Monday and Tuesday before the next system approaches toward the middle of next week.

DISCUSSION
Issued at 216 PM CDT Thu Apr 25 2024

Through Friday Night:

Seasonable temperatures are expected tonight, with cloudiness increasing in advance of approaching lead shortwave ejecting out of the developing long wave trough over the western U.S. The first wave of warm air advection-driven precipitation should begin encroaching on the area Friday morning. Strengthening low level easterly flow should also serve to advect in some drier air, which should chip away at the leading edge of the precipitation Friday. As the rain begins to run into drier air, its forward progress should slow as it moves across the CWA Rain should begin during the morning toward the I-39 corridor, with rain chances likely spreading east into the Chicago metro area early- mid afternoon, then into northwest IN by mid afternoon.

While an isolated thunderstorm cannot be ruled out west toward the I-39 corridor Friday afternoon, the better chances of some scattered thunderstorms will hold off until Friday night as better (elevated) instability surges into the CWA Scattered showers and thunderstorms are expected areawide Friday night in advance of the northward surging warm front. The warm front is expected to lift north and east of the area by late evening with decreasing chances/coverage of showers and thunderstorms overnight.

The low temperatures Friday night will occur during the evening hours. Strengthening southerly winds will usher in an unseasonably warm and humid (by April standards) air mass. By sunrise Saturday morning, temperatures should rise to the 60s with dewpoints not far behind, readings far more typical of June than April!

- Izzi

Saturday through Thursday:

Friday night into Saturday, a secondary upper-level trough will dig into the southern United States, causing upper-level heights to rise across the Great Lakes in the wake of a departing, and decaying, lead wave. As a result, increasing subsidence should cause any leftover showers and thunderstorms to decay after daybreak Saturday morning. Even with a cloudy start, temperatures on Saturday are poised to jump into the upper 70s to lower 80s as an axis of 850mb temperatures of +12 to +14C builds into the region.
However, if clouds thin quickly, temperatures may even jump into the mid 80s. Meanwhile, aggregate troughing across the central United States will keep the local low-level pressure gradient tight, allowing for southwesterly winds to become gusty from mid-morning onward. The strength of the winds will depend on how quickly clouds erode, with more aggressive mixing supporting gusts as high as 45 mph.

Even with a warm and moist airmass in place on Saturday, a lack of robust forcing mechanisms and the presence of a capping inversion support a dry forecast. However, if a thunderstorm were to develop, marginal shear profiles (along the southeastern flank of the jet stream positioned well to our west) may support pulses to severe intensity. For now, opted to cap PoPs at 20% areawide Saturday afternoon.

Saturday night, the secondary upper-level trough will shift northeastward into the Plains and induce the development of a broad low-level jet across the Mississippi River Valley. With the terminus of the low-level jet focused near the Mississippi River, it appears that a large chunk of our area should remain dry through daybreak Sunday. However, parts of northwestern Illinois (along and west of a line from Mendota to McHenry) may get grazed by waves of showers and thunderstorms throughout the night and especially toward daybreak.
Saturday night will be unusually mild with lows in the low to mid 60s. In fact, the record warm low temperatures may be threatened for the April 27 calendar date at Rockford (61F, 1990) and Chicago (67F, 1915). In addition, the moist boundary layer may prevent full decoupling and allow for southwesterly winds to continue gusting near or above 30 mph.

Sunday remains a day with low forecast confidence owing to an apparent dependence on the evolution of convection the night before, and a continued modest slowing trend of the arrival of the secondary upper-level trough. At this point, it appears prospects are increasing for remnant convection Saturday night to decay as it moves across northern Illinois after daybreak on Sunday, setting the stage for another warm and breezy day. With the later arrival of the secondary upper-level trough, the next round of showers and thunderstorms during the afternoon and evening to be focused near/west of the Mississippi River. For now, felt a middle of the road approach was fair with highs near 80 degrees, breezy southwesterly winds gusting near 40 mph, and low-end chances for thunderstorms (40 to 60% chances, highest west of I-39)
throughout the day. Whatever develops to our west in the evening may then move through overnight in a decaying form into Monday with the supporting instability axis and cold front, though again, confidence is low.

Taken altogether, our area may end up just on the outside of the episodes of severe weather through the weekend (not that we're complaining).

Assuming the cold front does sneak through without much noise Sunday night through early Monday, early next week looks decidedly quiet. The cold front itself doesn't look particularly strong, so temperatures Monday and Tuesday should still be above average and in the low to mid 70s. Humidity levels will also be noticeably lower. Ensemble model guidance advertises the arrival of a trough in the general region in the Wednesday to Friday timeframe, which will present the next opportunity for showers and thunderstorms.

Borchardt

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/
Issued at 1224 PM CDT Thu Apr 25 2024

VFR conditions and easterly winds expected through the forecast period. Lake influence will likely cause winds to back northeasterly this afternoon at ORD, MDW, and GYY, before settling back east to east-southeast tonight. East-southeasterly winds will increase Friday morning and likely become gusty.
Some high based, mostly light, showers are expected toward the end of the RFD 24 TAF and during the final few hours of the 30 hour ORD and MDW TAFs.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...None.

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