Sunrise 5:41 AM   Sunset 7:54 PM Moonrise 3:32 AM   Moonset 2:39 PM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 314 Am Cdt Fri May 3 2024
Early this morning - Southwest winds 5 to 10 kt. Patchy fog. Showers likely and slight chance of Thunderstorms. Waves around 1 ft. Today - Northwest winds 10 to 15 kt becoming northeast by noon. Patchy fog in the morning. Chance of showers through mid morning. Waves 1 to 2 ft. Tonight - Northeast winds 5 to 10 kt. Mostly clear. Waves around 1 ft. Saturday - East winds 5 to 10 kt increasing to 10 to 15 kt. Slight chance of showers and Thunderstorms in the afternoon. Waves 1 to 2 ft. Saturday night - North winds 5 to 10 kt becoming northwest 10 to 15 kt. Showers likely and a chance of Thunderstorms in the evening, then slight chance of showers and Thunderstorms overnight. Waves 1 to 2 ft.

LMZ700
No data

FXUS63 KLOT 030534 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1234 AM CDT Fri May 3 2024

KEY MESSAGES

- Scattered showers and thunderstorms will increase in coverage this afternoon, and continue through the overnight hours.

- A few storms may be severe this afternoon with hail up to 1 inch in diameter, 60 mph winds, and soaking downpours. The severe threat should wane after sunset.

- Periodic chances for showers and thunderstorms will continue from this weekend onward, with some potential for severe weather on Tuesday.

DISCUSSION
Issued at 253 PM CDT Thu May 2 2024

Through Friday night:

Showers and thunderstorms are off to an early start along the I-55 corridor, seemingly due to the interaction with an eastward-moving mid-level gravity wave and the northward-moving warm front.
Additional showers and storms are expected to develop throughout the afternoon and especially after sunset as the right entrance region of an upper-level jet streak moves over the Great Lakes.
As we already saw with the first batch of showers and thunderstorms, a few may pulse to severe levels with 1" hail and 60 mph "splat" downbursts through about midnight thanks to MLCAPE 1000-1250 J/kg and meager deep layer shear. With that said, widespread severe weather is not expected today, and the threat should wane with the loss of heating after sunset (though a few non-severe thunderstorms may continue through the overnight hours).

Showers will likely continue through daybreak Friday as a cold front sweeps across the area. Chances for rain will then end from west to east Friday morning behind the front as drier air works into the region. Clearing skies and highs in the lower 70s are expected tomorrow afternoon, though stout northerly winds off Lake Michigan will keep lakeshore locations some 10 to 15 degrees colder, particularly in northwestern Indiana.

As a surface high pressure system slides overhead tomorrow night, slacking winds and clear skies will allow for efficient radiational cooling. Overnight lows should dip into the upper 40s with locally cooler readings in typical cold spots. If drier guidance verifies (allowing for even more efficient radiational cooling), some lower 40 degree readings cannot be ruled out.

Borchardt

Saturday through Thursday:

Primary forecast concerns are the potential for severe thunderstorms Tuesday and possibly isolated strong/severe thunderstorms Saturday afternoon/evening.

The models are now showing a compact system moving across the local area Saturday afternoon/evening with a chance for thunderstorms. The ensembles are in reasonable agreement for this potential and there is some instability. There will be the potential for a few strong/severe storms during peak heating in the afternoon/early evening. Blended pops are generally in the low chance range but these may need to be increased if these trends continue.

Sunday looks mainly dry and there is quite a bit of uncertainty for precip chances Sunday night into Monday morning with the Canadian/ECMWF fairly dry with only the GFS showing precipitation. After the wave on Saturday afternoon/evening and as the pattern shifts into early next week, this time period may end up being dry but made no changes to the blended pops which are likely too high, in the chance range, for Sunday night into Monday.

By Monday afternoon into Monday night, convection is expected to develop well west of the area and possibly reach northwest IL by daybreak Tuesday and if it does, most likely in a decaying phase. With temps likely to reach 80 and dewpoints in the 60s on Tuesday, this will provide plenty of instability for additional thunderstorms to form Tuesday afternoon and evening and some of these thunderstorms may become severe. Precipitable water values look to reach into the 1.5 to 1.75 inch range, which will allow for heavy rain.

The pattern stays unsettled into the end of next week with periodic chances for showers and thunderstorms, though there will also be several dry periods. cms

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
Issued at 1220 AM CDT Fri May 3 2024

Aviation Key Messages:

- SHRA persist through pre-dawn hours. Embedded TSRA threat diminishing but non-zero, especially toward KGYY.

- Period of MVFR ceilings develops pre-dawn and lingers until a cold front passes after sunrise.

- Winds shift NNW with cold front after sunrise, then turn NNE- NE by mid-morning. NE winds persist through remainder of period.

Somewhat diffuse area of low pressure was lifting north- northeast across eastern WI as of midnight, with a cold front trailing through far western IL into western MO. This low was associated with a mid-level disturbance over central IL, and will continue to lift northeast with the cold front moving across the terminals by sunrise. SHRA and embedded TSRA will persist ahead of the front, with TSRA growing more isolated with time, with greatest coverage of TS likely toward KGYY. MVFR ceilings along the cold frontal zone will spread across the terminals pre-dawn, eventually scattering out to VFR by mid- morning.

Winds, while somewhat disorganized by earlier stronger convection, will be generally light W-SW ahead of the cold front, then shift NNW behind the front by sunrise. Winds will then continue to veer northeast by mid morning behind the front, and will generally remain northeast through the day.

Winds turn light easterly Friday evening, and there is some model guidance indication that MVFR stratus may form east of the area across Lake Michigan and IN, which could drift west into the terminals later in the night. Confidence is low this far out, but have included a FEW020 mention in TAFs.

Ratzer

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

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