Sunrise 5:53 AM   Sunset 7:45 PM Moonrise 8:51 PM   Moonset 6:02 AM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 926 Pm Cdt Wed Apr 24 2024
Rest of tonight - Northeast winds 5 to 10 kt becoming east late. Mostly clear. Waves 3 to 5 ft subsiding to 1 to 3 ft. Thursday - Southeast winds 5 to 10 kt becoming east 10 to 15 kt in the afternoon. Mostly Sunny. Waves 1 to 3 ft. Thursday night - East winds 10 to 15 kt becoming southeast 15 to 20 kt overnight. Mostly clear. Waves 1 to 3 ft building to 2 to 4 ft. Friday - Southeast winds 15 to 25 kt. Slight chance of showers in the morning, then showers in the afternoon. Waves 3 to 5 ft building to 4 to 6 ft occasionally to 8 ft.

LMZ700
No data

FXUS63 KLOT 242326 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 626 PM CDT Wed Apr 24 2024

KEY MESSAGES

- Widespread frost and sub-freezing temperatures, outside of Chicago, tonight

- Periods of showers and thunderstorms expected starting Friday and continuing at times through the weekend, with some threat for severe weather, particularly later in the weekend. Locally heavy rainfall possible as well.

DISCUSSION
Issued at 250 PM CDT Wed Apr 24 2024

Through Friday:

High pressure will continue to drift into the Great Lakes tonight which will aid in eroding the lingering lake effect cloud cover in northwest IN and diminishing the breezy northeast winds. Therefore, conditions look favorable for a decent night of radiational cooling, which should allow temperatures to dip into the upper 20s and lower 30s outside of Chicago with readings in the mid-30s in the city. Dew points are also expected to remain in the upper 20s to lower 30s tonight which will keep maximum RH values near saturation and promote widespread frost development, especially outside of downtown Chicago. While confidence in these frost/freeze conditions remains high, there is some mid-level cirrus across the central Plains that is progged to drift overhead tonight. Given that the cirrus should thin as it moves into the drier airmass overhead I suspect it will do little to reduce the aforementioned radiational cooling and resultant frost development. Thus, the Freeze Watch for areas north of I-88 has been upgraded to a Freeze Warning and expanded to include DuPage county. A Frost Advisory was also issued to encompass the rest of our forecast area with the exception of central Cook County.

After a chilly start to our Thursday temperatures are expected to rebound into the lower 60s as winds become southeasterly and warm advection begins. However, a lake breeze is forecast to develop and surge inland Thursday afternoon resulting in notably cooler temperatures for areas along the lakeshore. Otherwise, skies will remain mostly to partly sunny before cloud cover starts to increase Thursday night ahead of our next weather system on Friday.

Yack

Friday Night through Wednesday:

Large scale pattern change is expected as a pair of vigorous shortwave troughs will help carve out a deep western trough.
Amplification of a downstream ridge over the eastern U.S. will allow for much warmer weather, though the expected proximity of the jet stream should result in stormy periods starting Friday and continuing through the upcoming weekend.

First shortwave trough is progged to eject out onto the central High Plains Friday, with strong model consensus in closing off a mid-upper level low as trough acquires negative tilt with time.
First slug of warm air advection driven showers and eventually some thunderstorms should overspread the area Friday afternoon and continue into Friday evening. Strong moisture transport associated with a broad 50-60kt low level jet should drive PWATS to 200-250% of normal by Friday evening. This certainly suggests that some locally heavy rainfall totals are possible, with probs of precip totals >1" in around half of the GEFS and EPS members.

By 12z Saturday, this lead trough is expected to lift north to the Upper Mississippi Valley, which should drive the sfc low and associated warm front well north of the area. Though NBM maintains some precip chances on Saturday, it is increasingly looking like Saturday could be a good candidate for a potentially dry day this weekend. With warm front well to our north and height rises in the wake of the departing trough, potential will be there for temps to get quite warm if stratus doesn't linger into the afternoon. With some sunshine, high could make a run at the lower 80s and with dewpoints at least in the upper 50s, that would feel "muggy" compared to today!

Another round or two of showers and thunderstorms are possible in the Saturday night through Sunday night time frame as the next strong shortwave trough ejects out from the western long wave trough. Hard to pinpoint timing at this distance as a lot will depend on upstream convective coverage and eventually evolution.
Synoptically, general set-up looks generally favorable for a severe threat in the region Sunday afternoon/evening, but where that threat set-ups will likely hinge on how things evolve Saturday and Saturday night.

Cold front is expected to move across the region Sunday night, likely bring an end to the shower/thunderstorm threat. Pacific air mass behind this front means temps will remain mild early next week, with highs possibly still in the upper 60s/low 70s behind the front early next week. A warming trend is expected heading into the middle of next week back to well above average temps.

- Izzi

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/
Issued at 625 PM CDT Wed Apr 24 2024

Key Aviation Messages: - Potential for a brief period of MVFR ceilings late this evening

NE winds around 10 knots at TAF issuance will diminish through the night. A surface ridge crossing the area combined with the potential for a weak land breeze to develop will likely result in VRB winds under 5 knots for several hours late tonight through sunrise Thursday. Winds will settle SE under 10 knots Thursday morning followed by a lake-enhanced shift E at around 10 knots during the afternoon.

While VFR conditions are expected for much of the period, an area of MVFR ceilings over far southern Lake Michigan may begin to spread westward this. These clouds are currently expected to remain just south of ORD/MDW, but trends this evening may warrant inclusion of BKN MVFR clouds for a period late this evening.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES
IL...Freeze Warning from midnight tonight to 8 AM CDT Thursday for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012- ILZ013-ILZ103.

Frost Advisory from midnight tonight to 8 AM CDT Thursday for ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ105- ILZ106-ILZ107-ILZ108.

IN...Frost Advisory from midnight CDT /1 AM EDT/ tonight to 8 AM CDT /9 AM EDT/ Thursday for INZ001-INZ002-INZ010-INZ011- INZ019.

LM...Small Craft Advisory until 10 PM CDT this evening for the IL and IN nearshore waters.

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