Sunrise 5:43 AM   Sunset 7:53 PM Moonrise 2:35 AM   Moonset 12:03 PM

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LMZ646 Wind Point Wi To Winthrop Harbor Il- 505 Pm Cdt Wed May 1 2024
Tonight - Northwest wind 5 to 10 knots veering northeast early in the morning. Chance of showers early in the morning. Waves around 1 foot. Thursday - East wind 5 to 10 knots rising to 10 to 15 knots late in the morning, then becoming east 10 to 15 knots in the afternoon. Chance of showers and slight chance of Thunderstorms. Waves 1 to 2 feet building to 2 to 4 feet late in the afternoon. Thursday night - Southeast wind 5 to 10 knots backing east late in the evening, then veering south after midnight becoming south 5 to 10 knots early in the morning. Rain showers likely and a chance of Thunderstorms. Waves 2 to 4 feet subsiding to 1 to 3 feet in the late evening and overnight. Friday - Southwest wind 5 to 10 knots becoming northwest 10 to 15 knots late in the morning, then veering north early in the afternoon veering northeast late in the afternoon. Chance of Thunderstorms in the morning. Chance of showers through the day. Slight chance of Thunderstorms in the afternoon. Waves 1 to 2 feet.

LMZ600
No data

FXUS63 KLOT 012103 CCA AFDLOT

Area Forecast Discussion...CORRECTED National Weather Service Chicago/Romeoville, IL 403 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 acking 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 /18Z TAFS THROUGH 00Z FRIDAY/
Issued at 1251 PM CDT Wed May 1 2024

Key Messages:

- Period of scattered showers (and maybe a storm) early to mid- Thursday morning. Confidence is moderate.

- Possibility for more isolated to widely scattered thunderstorms mid to late Thursday afternoon. Confidence low at this time.

- Easterly winds expected later this evening through the day Thursday.

All will remain quiet this afternoon, though winds will remain gusty from the west through sunset. Winds will turn northeasterly later this evening, then easterly by early Thursday morning as a surface warm front shifts northward across central parts of IL. A few scattered showers (and maybe an embedded thunderstorm or two) may develop around daybreak Thursday morning as this warm front approaches. Opted to convert the PROB30 mention of TS Thursday morning to a tempo for SHRA early to mid-morning. While a brief storm or two cannot be totally ruled out during this time, it appears a slightly better chance of thunder will come in the afternoon.

The surface warm front is likely to remain south of the terminals through most (if not all) of the daylight hours of Thursday, though it should be approaching the I-80 corridor during the afternoon. For this reason, east to southeast winds are expected to prevail across the terminals. Given the close proximity of the warm front Thursday afternoon, there is now some concern that some afternoon thunderstorms could develop near the terminals as the airmass near the front destabilizes through the day. While confidence is not high with the extend of thunderstorms near the terminals in the afternoon, we have opted to add a PROB30 mention for them from mid to late afternoon at the 30 hour TAF sites.

KJB

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

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