Sunrise 5:46 AM   Sunset 7:50 PM Moonrise 1:10 AM   Moonset 9:36 AM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 344 Am Cdt Mon Apr 29 2024
Today - South winds 10 to 15 kt becoming southwest 15 to 25 kt. Areas of fog in the morning. Showers likely and slight chance of Thunderstorms in the morning, then slight chance of showers in the afternoon. Waves 2 to 4 ft subsiding to 1 to 3 ft. Tonight - West winds 10 to 20 kt diminishing to 5 to 10 kt. Mostly cloudy in the evening then clearing. Waves 1 to 2 ft. Tuesday - West winds 5 to 10 kt becoming east 10 to 15 kt in the afternoon. Sunny. Waves 1 ft or less. Tuesday night - Southeast winds 10 to 15 kt becoming south overnight. Chance of showers overnight. Waves 1 to 2 ft.

LMZ700
No data

FXUS63 KLOT 290822 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 322 AM CDT Mon Apr 29 2024

KEY MESSAGES

- Locally heavy rainfall may result in ponding in poor drainage areas through daybreak.

- There is a low chance (20%) for an isolated storm or two this afternoon, mainly east of I-55.

- After a break on Tuesday, a stormy pattern returns midweek along with continued unseasonably warm temperatures.

DISCUSSION
Issued at 322 AM CDT Mon Apr 29 2024

Through Tuesday:

GOES water vapor imagery early this morning depicts a sprawling low pressure system currently centered over southwest Minnesota with showers extending southeast along the warm front into southeast Wisconsin. Out ahead of the trailing cold front an expansive area of showers and isolated embedded thunderstorms continue in the warm sector extending from northern Illinois down through southeast Missouri along the western and northern edge of a 40-50kt low-level jet well ahead of the trailing cold front. Current RAP mesoanalysis highlights that marginal mid- level lapse rates have limited the amount of instability to work with (MUCAPE 500 J/kg or less) though this combined with effective shear of 35-45kt south of I-80 have allowed for a few isolated elevated non-severe storms to develop early this morning. If a more persistent updraft can become established some small hail can't be ruled out prior to daybreak east of I-55 and south of I-80. The broader northeast motion of the showers suggest rain will continue across much of the area through daybreak and then gradually decrease in coverage from west to east through mid-late morning.

Highest rainfall rates earlier this morning were confined to a pencil thin line extending from western Livingston county, through Joliet and toward O'Hare where ponding on roadways and poor drainage areas may linger through daybreak due to how much rain fell over the past 30 hours in the same areas. The localized nature of the highest amounts will limit the potential for broader flooding issues this morning.

A few spotty showers and maybe even an isolated storm or two (20% chance) may develop later in the morning and into the afternoon along the surface cold front as it moves through.
Strong to severe weather is not anticipated. Temperatures today will warm into the upper 60s to around 70 with breezy southwest winds. Heading into tonight surface high pressure settles over the region ushering in a less humid day on Tuesday with clear skies and warm temperatures in the 70s. An afternoon lake breeze may limit warming and cool down temperatures near the lakeshore.

Petr

Tuesday Night through Sunday:

Tuesday afternoon, an upper-level shortwave trough will trek into the northern Plains/Upper Midwest and ignite convection in/near the central Missouri River Valley. This convection is likely to consolidate into a line or broken arc and track towards northern Illinois Tuesday night, but will likely start to fall apart as it approaches our forecast area as it loses some forcing support and outruns the better instability to our west. Nevertheless, most available guidance has this activity surviving long enough to produce measurable rainfall and perhaps a few lightning strikes in our CWA, so will continue to carry chance PoPs and slight chance thunder probabilities that are focused primarily in our western counties for the Tuesday night time frame. Assuming that it makes it here, this activity should disperse no later than mid-morning on Wednesday. Wednesday is otherwise shaping up to be a dry and mild first day of May with highs currently forecasted to be in the mid- upper 70s across most of the area. There are signs that a backdoor cold front could make a push inland off of the lake late in the day, but this may come too late to have an appreciable effect on the day's high temperatures near the lakeshore.

Additional periods of showers and thunderstorms appear likely in the Wednesday night through Friday time frame as a deeper upper-level trough swings into the Upper Midwest. An initial bout of warm air advection-driven convection may be seen Wednesday night into early Thursday. While some spread still remains in ensemble guidance, this precipitation is favored to lift north of the area by Thursday afternoon in tandem with a surface warm front, which would leave our forecast area in the breezy warm sector of a 1000-1004 mb low pressure system passing to our northwest. If this does indeed occur, then much of our forecast area should see temperatures climb into the upper 70s to mid 80s Thursday afternoon. However, if the warm front doesn't lift as far north as presently expected, then locations that remain north of this frontal boundary on Thursday will see cooler temperatures than presently advertised in our gridded forecast database.

In either scenario, the low pressure system's cold front will eventually track through the area Thursday night into Friday, bringing an additional wave of showers and storms with it. We will need to monitor the potential for hydrologic concerns during this time frame given the recent rainfall and that precipitable water values near or in excess of 1.5" (near-record values for this time of year here, per DVN and ILX sounding climatology) are progged to be drawn northward out ahead of the cold front, but it's still too early to have much confidence in that with a few questions still remaining about the track and overall evolution of the low pressure system. In the wake of the cold frontal passage, temperatures are favored to return closer to normal going into the weekend before another warm-up appears to be on the horizon going into next week.

Ogorek

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/
Issued at 113 AM CDT Mon Apr 29 2024

Key Messages:

- Rain through the early to mid-morning with a few embedded storms. Spottier showers may then continue into this afternoon.

- MVFR ceilings possible at times through the early afternoon.

Rain coverage has begun to increase across the area at the start of this TAF period, and widespread rainfall is expected to affect the terminals through the early to mid-morning hours.
Limited instability should keep the threat for lightning fairly isolated, but did recently note a few lightning strikes southwest of the Chicago within the leading flank of shower activity, so have maintained the inherited VCTS for the Chicago metro TAF sites, but pushed the timing up a bit. Based on the observed progress of an elongated outflow boundary stretching from central Illinois down through the Ozarks, it's possible that the threat for lightning may end a little earlier than presently advertised in the TAFs, but will err on the side of caution and maintain a more pessimistic end time for the VCTS mentions for now.

In addition to MVFR visibilities beneath the steadiest showers, MVFR ceilings may be observed at times as well. This could initially occur with the steadier shower activity and then perhaps again later this morning into the early afternoon after the bulk of the rain has moved out of the area, per the latest ceiling guidance. However, as diurnal mixing commences, any MVFR ceilings should gradually lift towards VFR levels with time.
Even after much of the rain has ended, some spottier showers may continue near the terminals through the early afternoon or so, so will continue to carry a VCSH mention in the TAFs to highlight that.

Lastly, southwesterly winds will become breezy once again after the rain departs. Gusts are not expected to be as strong as they have been the past two days, with peak gusts this afternoon likely to be somewhere around 25 kts. Winds will then turn westerly and subside this evening behind the passage of a cold front.

Ogorek

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

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