Sunrise 5:14 AM   Sunset 8:24 PM Moonrise 2:44 AM   Moonset 4:13 PM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 254 Pm Cdt Sun Jun 2 2024
Tonight - East winds 5 to 10 kt becoming southeast by mid evening. Partly cloudy. Waves 1 ft or less. Monday - Southeast winds 10 to 15 kt becoming south 15 to 20 kt. Slight chance of showers and Thunderstorms in the morning, then chance of showers and Thunderstorms in the afternoon. Waves 1 to 3 ft. Monday night - South winds 10 to 20 kt. Showers likely and a chance of Thunderstorms in the evening, then slight chance of showers and Thunderstorms overnight. Waves 1 to 3 ft. Tuesday - South winds 10 to 15 kt increasing to 15 to 20 kt. Slight chance of showers and Thunderstorms in the morning, then showers likely and a chance of Thunderstorms in the afternoon. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 022346 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 646 PM CDT Sun Jun 2 2024

KEY MESSAGES

- Scattered thunderstorms possible Monday and Monday evening.
Any thunderstorms Monday afternoon and evening could produce locally damaging winds and flash flooding.

- Potential for additional showers and storms Tuesday.

- Last chance of thunderstorms for the week looks to be on Wednesday, mainly in the morning southeast of I-55.

DISCUSSION
Issued at 250 PM CDT Sun Jun 2 2024

Through Monday Night:

After a cloudy start to the morning, stratus has cleared for all but the extreme southern CWA and given way to scattered diurnal cumulus this afternoon. Weak ridging over the area along with a surface high exiting to the east will yield dry conditions through at least this evening and likely through sunrise Monday morning.

Focus then turns to the early stages of developing convection ahead of a mid-level wave across southeast Wyoming into southeast Utah. Loosely organized upscale growth of convection is expected to develop within increasing low-level flow and moisture transport across Nebraska this evening, with a potential remnant MCV lifting northeast across Iowa late tonight into Monday morning. The antecedent airmass across the northwest half of the CWA ahead of this MCV will be marginally favorable for elevated convection to persist into areas west of the Fox Valley and generally north of the Illinois River through late morning. This scenario will be conditional upon sufficient saturation in the LPL (900-850 hPa) fully realizing a higher MUCAPE reservoir amid modest mid-level lapse rates. If storms do materialize, small hail cannot be ruled out.

Veering low-level flow tonight through Monday will draw a relatively moist airmass northward through the Mississippi Valley, with surface dew points likely nearing 70F in portions of the western CWA by late Monday afternoon. A generally uncapped and moderately unstable airmass owing to the higher dew points will support convective initiation with any notable forcing mechanism Monday afternoon before the remnant wave across the central Plains shears out across the western Great Lakes late Monday evening into the overnight hours. Meanwhile potential residual MCS activity across the southern Great Plains will near from the southwest Monday night. Per recent CAM guidance, potential initial foci of convection during the mid- afternoon to early evening range from lingering vort arcs on the tail of the morning MCV to stalled outflow boundaries. So while development is far from certain, steep mid-level lapse rates in a weakly sheared environment suggest that any initial cells would produce pulse-like characteristics, with resultant outflows cascading into a very messy radar representation. Any prominent cells or congealing cold pools will be capable of producing strong to locally severe wind gusts. Furthermore, modest SW low-level flow within weak mid-level flow combined with PWATs up to around 1.8" indicate weak/NE backward propagation vectors supportive of localized flash flooding. If a more expansive growth of convection occurs by early evening, primary concerns will turn to flooding through the remainder of the evening before convection dissipates or shifts east through the overnight hours.

Kluber

Tuesday through Sunday:

Tuesday's evolution remains unclear at this range, with numerous disturbances and potentially convectively-augmented vorticity maxima traversing the region (or very nearby). It seems like most of the morning may end up mainly dry in the wake over Monday's convection. That said, there's at least some signal across the guidance suite that a coherent mid-level impulse will lift north or northeastward across the region towards midday or during the afternoon. This feature looks like it may be associated with the impulse currently sweeping across northern New Mexico, and will likely get several vorticity boosts through mid-level latent heat release processes as several rounds of strong to severe convection develop across the ArkLaTex through Monday evening. It's no surprise that there's a huge spread with this feature's location come Tuesday morning, although it looks like it'll end up somewhere in our vicinity.

The background/synoptic kinematic field is not overly supportive of organized convection Tuesday afternoon, with mainly multicell/pulse-type convection favored with meager deep layer shear. However, a well-developed/intense MCV would certainly locally-augment the low and mid-level wind field and could yield a threat for more organized strong to severe storms, and something that's hinted at by some extended hires guidance.
For now, saw little reason to make alterations to the NBM- delivered likely PoPs during the afternoon given an only weakly- capped airmass during the day and decent agreement that at least scattered convection will develop. Whether a severe risk accompanies this activity will be tied to the evolution of upstream thunderstorm activity today and tomorrow.

Turning ahead to Tuesday evening and overnight, the lead impulse will be exiting to the northeast, with a much stronger short-wave impinging upon the northern Plains and upper Midwest.
Extensive convection out ahead of the system's cold front west of the MS River will translate southeastward into a less supportive environment (diurnal decrease in instability and marginal wind shear). Thus following the probable dissipation of afternoon pulse convection, it's a bit unclear how robust upstream storms will be as they approach from our west in the late evening and overnight. While we do have PoPs peaking in the 60-80% range given the overall global model and ensemble member signal for convection during this time, there conceptually appears to be a path toward lower convective coverage surviving eastward overnight.

The cold front will sweep across the area Wednesday morning.
Unless overnight convection dissipates much quicker and sets up for destabilization ahead of the front by the mid to late morning across much of the area, it appears that areas southeast of I-55 have the best chance for any renewed development ahead of the front, or intensification of existing showers and embedded thunderstorms pushing eastward. The rest of Wednesday will likely be drier, breezy, and increasingly sunny, with seasonable temperatures in the upper 70s to lower 80s.

Deep upper level low pressure from the aforementioned strong mid-week short-wave will then become quasi-stationary from the northern Great Lakes across northeastern North America Thursday through the weekend. This will bring a period of near to slightly below normal temperatures (highs in the 70s away from any lake cooling, primarily dry weather, comfortably low humidity (daytime dew points in the 40s and 50s), and breezy daytime conditions.

Carlaw/Castro

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
Issued at 646 PM CDT Sun Jun 2 2024

Forecast concerns include...

Chance of thunderstorms Monday afternoon/early evening.
Gusty south/southwest winds Monday.

Light easterly winds will become southeasterly this evening and south/southeast Monday morning. Speeds will increase into the 10-15kt range during the mid morning hours with some higher gusts likely. Wind directions are expected to turn to the south/ southwest Monday afternoon with gusts into the mid 20kt range.
Wind directions are somewhat uncertain Monday evening, but speeds are expected to diminish under 10kts.

There will likely be some decaying thunderstorms or showers across far northwest IL after daybreak Monday morning. There remains quite a bit of uncertainty regarding coverage. Current prob mention for showers at RFD seems reasonable for now. While scattered thunderstorms are possible Monday afternoon into early Monday evening, there remains uncertainty for coverage, location and duration. While tempo mention will likely be needed with later forecasts, maintained prob mention for a longer time period when thunder will be possible at the Chicago terminals.
Its possible that the decaying showers noted above will redevelop into thunderstorms by early afternoon, likely west of ORD/MDW and that activity moves across the terminals by late afternoon.
cms

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

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