Sunrise 5:27 AM   Sunset 8:06 PM Moonrise 1:26 PM   Moonset 2:30 AM

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LMZ742 Expires:202405160930;;286089 Fzus53 Klot 160247 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 947 pm cdt Wed may 15 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>742-160930- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 947 pm cdt Wed may 15 2024
Rest of tonight - North winds 5 to 10 kt becoming east around 5 kt late. Mostly clear. Waves 1 to 3 ft. Thursday - Southeast winds 5 to 10 kt increasing to 10 to 15 kt. Scattered showers and Thunderstorms in the afternoon. Waves 1 to 3 ft. Thursday night - South winds 10 to 15 kt diminishing to 5 to 10 kt. Chance of showers and Thunderstorms in the evening, then slight chance of showers and Thunderstorms overnight. Waves 1 to 2 ft. Friday - Southeast winds 5 to 10 kt becoming east in the afternoon. Slight chance of showers and Thunderstorms in the afternoon. Waves around 1 ft building to 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 160555 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1255 AM CDT Thu May 16 2024

KEY MESSAGES

- Scattered thunderstorms are expected area-wide Thursday afternoon and evening. A few of these storms could become strong to severe and contain hail and gusty winds late afternoon and early evening northwest of a Mendota to Chicago line.

- Periods of showers and storms may occur Friday into Saturday, but looking mostly dry for the weekend.

- Active pattern looks to develop next week bringing several opportunities for showers and thunderstorms.

DISCUSSION
Issued at 250 PM CDT Wed May 15 2024

Through Thursday Night:

With the recent upper-low around our region finally drifting southeast this afternoon, dry conditions are expected through tonight amid passing mid to upper-level clouds.

Focus then turns to developing convection over northeast NM and southeast CO this afternoon as it grows upscale across the central Great Plains overnight. A resulting convectively- enhanced wave should traverse somewhere across central Illinois late Thursday morning into mid-afternoon. Potential for the coverage of convection into our area will hinge both on the degree of low-level moistening as well as any changes in the expected timing/location of the wave. The expected late morning arrival of the wave will align with gradually increasing surface-based instability, so any delay in arrival of the wave would further support increasing coverage of convection. As for the low-level moisture profile, surface high pressure still anchored over LA this afternoon has continued to suppress low- level Gulf moisture return. Therefore, most of the increase in low-level moisture into the CWA will be highly driven by ET and from recent rainfall. Given only modest mid-level lapse rates and dew points struggling to rise much above 60F, CAPE profiles support more of a scattered pulse-like set-up during the afternoon hours.

If the convective wave remains well south or does not fully materialize during the morning, the thermodynamic and kinematic field will become increasingly favorable for a few strong to possibly severe storms with small hail and gusty winds across the northwest third of the CWA ahead of a late-arriving cold front. This scenario remains conditional on several of the above factors as well as the ability for any storms to stave off mid- level entrainment.

Chances of convection will wane after sunset and with the passage of the slowing cold front from northwest to southeast Thursday night.

Kluber

Friday through Wednesday:

In the wake of Thursday's showers and thunderstorms a separate disturbance moving across the southern CONUS may be expansive enough on the north side for renewed shower and thunderstorm development into portions of the area on Friday, particularly south of I-80. Depending on how how slowly this feature drifts east, precipitation may linger into Saturday morning. The GFS continues to be most favorable for precipitation lingering into Friday with a broader extent to precipitation north of the low.
Meanwhile higher-res guidance starting to capture this time range has precipitation shifting east a bit more quickly and keeps much of the precipitation south of the area. Accordingly, PoPs have been lowered a bit with this update to account for this trend. Nevertheless, there remains a window for a few thunderstorms to develop in our south in the afternoon on Friday.

Other than a few showers potentially lingering into Saturday, dry weather is forecast for the weekend with surface high pressure settling over the region in the wake of a dry cold frontal passage late Saturday. This will set up what looks to be a great late-spring weekend with temperatures warming into the upper 70s to lower 80s inland from the lake (expect upper 60s to near 70 near the shore).

Confidence is increasing in a return to a more active pattern early to mid next week as the upper jet begins to orient southwest to northeast across the western half of the CONUS.
This would allow for multiple disturbances to potentially lift across the region. Accordingly, long-range ensemble meteograms highlight this as a period favorable for accumulating precipitation paired with a signal for an unstable air mass building across the region. While there is still plenty of time for the details to be ironed out, this will be a time to watch for severe weather and heavy rainfall somewhere in the region.

Petr

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
Issued at 1255 AM CDT Thu May 16 2024

Forecast concerns for the terminals...

- Scattered showers and thunderstorms Thursday afternoon

- Potential for patchy fog late Thursday night into Friday morning

The first 6-hours or so of the TAF period will be relatively quiet with VFR conditions and light easterly winds. Though wind directions will gradually veer towards the southeast by daybreak and then eventually settle into a southwesterly direction by mid-morning Thursday. The southwest winds will aid in moving warmer and more humid air into the area which will allow for instability to increase and give way to scattered showers and thunderstorms Thursday afternoon. While the greatest storm coverage continues to be near RFD closer to an upper disturbance, confidence in storms was high enough to warrant the transition to TEMPO groups at all TAF sites with this issuance. However, the timing was left rather broad given uncertainties with when greatest coverage will reach the Chicago terminals so will likely need to refine that with future updates.

Heading into Thursday evening, the aforementioned instability should wane and allow showers and storms to come to an end.
Though, southerly winds are expected to prevail Thursday night which should maintain dew points in the upper 50s to lower 60s.
Couple this humid airmass with light winds and gradually thinning cloud cover and conditions look favorable for the development of patchy fog late Thursday night into Friday. While guidance is in very good agreement with fog developing at the terminals (including ORD and MDW), the density of the fog remains in question. Regardless, I felt confident enough to include a formal BR mention at ORD and MDW with this issuance, but left it out of the 24-hour sites given that the greatest fog threat appears to be after 06z Friday.

Yack

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

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