Sunrise 5:35 AM   Sunset 7:59 PM Moonrise 5:39 AM   Moonset 9:11 PM

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LMZ741 Expires:202405082115;;848443 Fzus53 Klot 081455 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 955 am cdt Wed may 8 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>742-082115- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 955 am cdt Wed may 8 2024
Rest of today - South winds 5 to 10 kt becoming northeast 10 to 15 kt late. Mostly Sunny. Waves 1 ft or less building to 1 to 2 ft. Tonight - Northeast winds 10 to 15 kt increasing to 15 to 20 kt. Chance of showers and slight chance of Thunderstorms in the evening, then showers and a chance of Thunderstorms overnight. Waves 1 to 3 ft building to 3 to 5 ft.Thursday - Northeast winds 20 to 25 kt becoming north. Showers likely and slight chance of Thunderstorms in the morning, then showers likely in the afternoon. Waves 3 to 5 ft building to 4 to 6 ft occasionally to 8 ft. A small craft advisory will likely be needed. Thursday night - North winds 15 to 25 kt diminishing to 10 to 15 kt. Mostly cloudy in the evening, then becoming partly cloudy. Waves 4 to 6 ft occasionally to 8 ft subsiding to 2 to 4 ft.

LMZ700
No data

FXUS63 KLOT 081136 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 636 AM CDT Wed May 8 2024

KEY MESSAGES

- Another round of showers and thunderstorms develops late today and tonight. A few strong to severe storms are possible mainly this evening, though greater severe chances will be south of the area. Locally heavy rainfall in excess of a half inch is possible tonight into Thursday morning as well.

- Cooler weather arrives Thursday, with periodic showers Thursday and again Friday night into the weekend.

DISCUSSION
Issued at 356 AM CDT Wed May 8 2024

Through Thursday:

A lull in our active weather pattern is expected for most of today, as subsidence develops within mid-level short wave ridging in the wake of a departing disturbance. Weak surface high pressure was reflected at the surface, and will drift east across the area this morning. Light westerly winds will back to the southeast and eventually to the east this afternoon as the ridge moves off to the east, and surface low pressure develops into Missouri to our southwest. Mostly sunny skies are thus expected into early afternoon, with temperatures warming into the mid-70s to lower 80s (warmest south), though developing onshore lake breeze winds will cool the immediate Lake Michigan shore to the mid-upper 60s.

Clouds will increase from the southwest later this afternoon however, especially across southern parts of the forecast area, in response to renewed warm advection/isentropic ascent ahead of a short wave trough (old northern Plains upper low circulation)
wrapping east-northeast across the mid-lower Missouri Valley.
Shower and thunderstorm chances will also increase across the southern and western counties this evening, and eventually across the remainder of the area overnight, as the surface and mid-level waves advance into the region. The effective low-level frontal zone from yesterday's cold frontal passage and convective outflow is expected to remain south of the cwa with the main threat of severe weather remaining to our south, though some near-surface based storms and locally gusty surface winds can't be ruled out along the ILX/LOT WFO border. Otherwise, elevated storms farther north should pose mainly a marginal hail threat, and SPC's Day 1 marginal risk appears reasonably with higher risk categories across central IL/IN. Locally heavy rainfall amounts are likely a greater risk across the WFO LOT cwa later tonight into early Thursday, as the sheared positive- tilt upper trough propagates across the region. EPS and GEFS ensembles probabilities (40-70%) of rainfall amounts greater than a half inch are indicated from northeast IA east-southeast across the southern half of the our forecast area, with WPC including our area in a marginal Excessive Rainfall Outlook during the Days 1-2 period.

A turn to much cooler weather is also anticipated for Thursday, as east winds increase and turn northerly during the day with the passage of the surface low pressure wave to our south. After summer- like temperatures today, highs on Thursday will only reach the upper 50s to lower 60s, with locations near Lake Michigan struggling to make it out of the lower 50s. Showers and blustery north-northeast winds will make for a chilly feel to the day.

Ratzer

Thursday Night through Tuesday:

A southeastward tracking trough responsible for more active weather on Thursday will gradually cross the forecast area Thursday night. Isolated to widely scattered showers may persist well through the evening.

The trough will shift southeast of the CWA by around daybreak Friday. Shortwave ridging will produce stout mid-level warming through the day Friday, though low-level moisture will remain sufficient for a decent coverage of shallow cumulus during the afternoon. On the heels of the ridge, a compact upper-level low will dig southeast over the western Great Lakes Friday night into Saturday. Earlier guidance had advertised a diurnally favorable passage of the low directly over our area midday Saturday, but has since supported a faster solution with the low passing to the northeast around daybreak. Additionally, more favorable thermo profiles with anomalously cold mid-level temps will remain to the northeast. Have therefore limited forecast coverage to scattered showers Friday night into Saturday, with a slight chance of thunder during the afternoon.

NW flow aloft will persist Sunday into early next week. A more formidable shortwave trough is progged to cross the area sometime late Sunday afternoon through Sunday night. Low-level moisture availability looks marginal at best for any widespread precip as a sprawling surface ridge remains anchored in the Deep South. But any earlier arrival of the trough (e.g. late afternoon/early eve), could support isolated to scattered storms.

Beyond Sunday night, substantial differences in guidance regarding the evolution of a building ridge across the eastern seaboard and a central CONUS trough support maintaining consensus forecast guidance with a chance of showers and some storms centered around Tuesday.

Kluber

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/
Issued at 635 AM CDT Wed May 8 2024

Key Aviation Messages: - Wind shift from SW/VRB to E early this afternoon - Scattered SHRA tonight into Thursday morning (20% chance of elevated TS), with MVFR ceilings developing toward sunrise Thursday

VFR conditions with FEW/SCT mid-level clouds are expected through at least this evening. SW winds 5 knots or less will likely become VRB late this morning as a weak surface ridge crosses northern Illinois. However, directions may begin to favor east of south as early as 16Z. Winds are then expected to shift E around 10 knots with a lake- enhanced boundary ahead of a surface low nearing central Missouri. E to NE winds of 10-15 knots are then favored through tonight before increasing Thursday morning.

A band of SHRA and perhaps a widely isolated elevated TS is expected to drift northward over the terminals late this evening and overnight. SHRA should then expand in coverage Thursday morning and may transition to RA. TS potential under a 20% chance remains low enough to keep TS mention out of the TAF during this forecast period, but if future TAF updates require introduction of TS, the favored window would be late tonight into mid-morning Thursday.

Otherwise, MVFR ceilings should advect into the area late tonight, with some IFR ceilings possible Thursday morning.

Kluber

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

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