Sunrise 5:45 AM   Sunset 7:51 PM Moonrise 2:32 AM   Moonset 12:06 PM

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LMZ742 Expires:202405020315;;448766 Fzus53 Klot 011947 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 247 pm cdt Wed may 1 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.
lmz740>742-020315- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 247 pm cdt Wed may 1 2024
Late this afternoon - West winds 10 to 20 kt becoming northwest. Partly cloudy. Waves 1 to 2 ft. Tonight - Northwest winds 5 to 10 kt becoming northeast late. Slight chance of showers after midnight. Waves around 1 ft. Thursday - East winds 10 to 15 kt. Chance of showers and slight chance of Thunderstorms. Waves 1 to 2 ft building to 2 to 4 ft. Thursday night - Southeast winds 10 to 15 kt becoming south 5 to 10 kt overnight. Chance of showers and Thunderstorms in the evening, then showers likely and a chance of Thunderstorms overnight. Waves 2 to 4 ft subsiding to 1 to 3 ft. Friday - West winds 5 to 10 kt becoming north 10 to 15 kt in the afternoon. Showers likely and a chance of Thunderstorms in the morning, then chance of showers and slight chance of Thunderstorms in the afternoon. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 020006 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 706 PM CDT Wed May 1 2024

KEY MESSAGES

- Widely scattered showers with a few embedded non-severe storms are expected late Wednesday night into Thursday morning

- Showers and storms are expected late Thursday into Friday. A few storms late Thursday afternoon into Thursday night could be strong to severe

- Wet antecedent conditions and strong storms may also occur Thursday into Friday, most likely near and west of the I-39 corridor

- Periodic chances for showers and thunderstorms next week, with the best chance possibly Tuesday afternoon/evening when there may be a severe potential.

DISCUSSION
Issued at 235 PM CDT Wed May 1 2024

Through Friday:

Despite the clearer skies over Illinois, stratus clouds over central Iowa are slowly moving east. While there are some weak returns showing up on radar, drier air in place will keep conditions dry. As additional moisture moves north with isentropic upglide providing enough lift that may result in some showers or even an elevated thunderstorm overnight, though the highest probability (around 30 percent) will be in northwest Illinois. Winds are expected to turn east-northeasterly overnight in response to the next area of low pressure shifting towards the Mid-Missouri Valley. The continued influx of a drier low-level airmass on these easterly winds is leading to models b backing off on rain potential tonight.

With a surface low out in the Central Plains today, it will move north and east through the end of the week, drawing a warm front northward Thursday. As the warm front moves, temperatures and dew points to its south will steadily increase through the afternoon, with highs in the upper 70s and low 80s forecast.
However, exact temperature values across far northern IL will be strongly dependent on how far north the warm front actual reaches. However, as winds will be out of the east to northeast on Thursday north of the warm front, cooler conditions (in the 60s) can be expected along the immediate Illinois lakeshore.

Model soundings show a strong capping inversion for much of the day with all instability aloft. While scattered showers and even isolated elevated thunderstorms are possible through much of the day, there is increasing chances for storms to develop in the late afternoon if the cap does erode. While deep layer shear does not look particularly strong tomorrow, there would be enough instability with steeper lapse rates loft to allow for some strong to even severe convection to develop. While it appears to be a conditional threat, it prompted the expansion for the convective threat to a level 1 out of 5 for tomorrow.

By Thursday night, the cold front associated with a surface low will arrive and finally move east through northern Illinois through the overnight. This would allow for another chance for showers and some storms to pass over the area. Additionally, with the anomalously high moisture content for this time of the year (above 1.3") and the antecedent wet soils, there is a potential for localized flooding to occur in the area where heaviest rain rates develop. The front is expected to move east of the area Friday morning as winds switch back to the west to northwest. Lingering showers may provide pockets of light rain through the early afternoon, though probability for precipitation diminishes through the day. Cooler air behind the front will keep high temperatures in the upper 60s to 70s on Friday.

DK

Friday Night through Wednesday:

The extended period looks active with various systems expected to transverse the region, the first on Saturday/Saturday evening and a second Sunday night into Monday. Still uncertainty for timing and neither of these systems look all that strong and instability/ shear also remain limited. Nevertheless, low chance pops for both time periods are warranted.

The pattern begins to shift on Monday, with warmer and more humid air expected to spread north and across the region. Precip chances certainly warranted during this time period but trends are unclear for timing/coverage Monday and Monday night. Its possible that convection is focused further west of the area on Monday afternoon/evening and if it moves into the local area, it would be in a decaying phase later Monday night. However, by Tuesday, there has been some consensus that thunderstorms will develop across/near the area in both previous runs and the ensembles. With highs possibly tagging 80 and dewpoints in the 60s, there should be plenty of instability. While not yet shown in SPC outlooks, this time period will need to be monitored for a severe potential. Precipitable water values also look to increase into the 1.5 inch range, which if these materialize would lead to the potential for heavy rain. cms

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/
Issued at 706 PM CDT Wed May 1 2024

Forecast concerns for the terminals...

- Isolated to widely scattered showers Thursday morning

- Better coverage of showers and thunderstorms Thursday afternoon into Thursday evening

- Winds turning easterly tonight and then south-southeasterly in the wake of a warm front Thursday afternoon

Mid-level VFR clouds will continue to increase this evening as the developing surface low in the western Plains begins its trek towards the Mississippi River Valley. While forecast soundings continue to show copious amounts of dry air in the low-levels, some saturation is expected to occur as the surface low gets closer. Couple this modest saturation with weak instability aloft and conditions continue to look favorable for isolated to widely scattered showers to develop late tonight into Thursday morning. However, guidance has continued to become less excited about the already meager shower coverage Thursday morning so confidence remains on the lower side.

Better shower coverage is expected for Thursday afternoon as a warm front lifts into the area. Forecast soundings continue to show instability increasing Thursday afternoon which will also support thunderstorms, a few of which could be strong to possibly severe with a threat for gusty winds and maybe some hail. Though, there is growing uncertainty as to how far north the warm front will get on Thursday which will likely dictate how far north the better instability and storm coverage gets.
Regardless, confidence remains sufficient to warrant the maintaining of PROB30s at ORD and MDW and the addition of PROB30s to the other terminals for this potential. While thunderstorm coverage is expected to wane Thursday evening as we lose the instability, showers are expected to persist through Thursday night as a cold front pushes through the area.

Finally, winds will become east-northeasterly late this evening and overnight and should remain as such through Thursday afternoon for terminals north of the warm front. However, uncertainty is growing as to how the cooler lake may alter the warm front as it tries to lift through the area. Therefore, wind directions at the Chicago terminals could become squirrelly if the front gets hung up nearby but should maintain an easterly component regardless. As for speeds, light winds are expected overnight before winds increase Thursday afternoon into the 10 to 12 kt range. Though, some gusts around 20 kts are possible especially for those within the warm sector (south of the warm front).

Yack

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

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