Sunrise 5:15 AM   Sunset 8:23 PM Moonrise 2:43 AM   Moonset 4:12 PM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 942 Am Cdt Sun Jun 2 2024
Rest of today - North winds 5 to 10 kt becoming east late. Partly cloudy. Waves 1 to 2 ft. Tonight - East winds 5 to 10 kt becoming southeast overnight. Partly cloudy in the evening, then becoming mostly cloudy. Waves around 1 ft. Monday - Southeast winds 10 to 15 kt becoming south. Slight chance of showers in the morning, then chance of showers and Thunderstorms in the afternoon. Waves 1 to 3 ft. Monday night - South winds 10 to 15 kt diminishing to 5 to 10 kt. Chance of showers and Thunderstorms, mainly in the evening. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 021713 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1213 PM CDT Sun Jun 2 2024

KEY MESSAGES

- Patchy fog possible early this morning, mainly near the IL/WI border and in northwest IL.

- Scattered thunderstorms possible Monday and Monday evening and Tuesday, with a possible period of higher thunderstorm coverage Tuesday evening in parts of the area.

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

DISCUSSION
Issued at 343 AM CDT Sun Jun 2 2024

Through Monday:

Weak surface low pressure was over western lower Michigan early this morning, with a weak surface cold front trailing across the southeastern cwa counties and into southeast Missouri. A few spotty showers were decreasing in coverage but were still present along the front mainly across northwest Indiana as of 3 AM, and a slight (<20%) chance will persist southeast of a Bloomington to Kankakee to Burns Harbor IN line until the front clears the forecast area a few hours after sunrise. Behind the front some patchy fog (briefly somewhat dense earlier) had developed, though a combination of extensive low stratus and 9-12 kts or so of northerly flow above the boundary layer has limited the extent of dense fog across the area.

We can't rule out some patchy denser fog developing in spots west of the Fox River Valley and north of I-88 across far northern IL through sunrise, where a couple of holes were noted in the stratus deck and boundary winds are lighter, though the threat of any widespread dense fog appears low. After sunrise, stratus and any fog should gradually lift and break up through mid-late morning, with partly cloudy skies by this afternoon.
Temperatures should rebound into the mid-upper 70s in most areas, though east-northeast lake breeze winds will limit highs to the mid-upper 60s along the Lake Michigan shore.

Quiet weather will continue this evening, with attention then turning to our west/northwest where several clusters of thunderstorms are expected to develop ahead of a cold trailing from surface low pressure which is progged to lift northeast across northern MN by Monday morning. While the best large-scale forcing for ascent looks to be focused well to our northwest, several models suggest that evening storms over the mid-Missouri Valley may generate an MCV/convectively enhanced vort which will then track into the IA/WI/IL border region toward sunrise, accompanied by weakening convection (poor diurnal timing, outrunning better MUCAPE to the west). Some of these may spread across the I-39 corridor as in a decaying mode around sunrise, with coverage and thunder potential decreasing farther east into the Chicago metro area.

Scattered thunderstorm potential will likely increase by Monday afternoon however, as low-level southerly flow strengthens ahead of the cold front off to our west, and another mid-level short wave (also potentially convectively-enhanced by storms across the TX/OK panhandle region the previous evening)
approaches during move favorable diurnal conditions and increasing low-level instability (warmer and more humid Monday with temps in 80s/dew points in the mid- 60s), especially across western portions of the forecast area. Various CAM runs have depicted regeneration of storms across parts of western IL by mid-late afternoon, though some spread remains and confidence in details/evolution remains low at this time. Background deep shear is not too impressive in the global guidance, but would likely be enhanced if a well-developed MCV were present. SPC has included our western cwa in a marginal (level 1/5 risk) for severe weather in their day 2 outlook for Monday into Monday evening.

Ratzer

Monday Night through Saturday:

- Scattered thunderstorms possible Monday evening and Tuesday, with a possible period of higher thunderstorm coverage Tuesday evening in parts of the area

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

On Monday evening, any lingering scattered thunderstorms past sunset should dissipate with the diurnal loss of heating and instability. See the short term discussion above for details on the lower end (level 1/marginal) severe threat Monday PM.
Primarily quiet conditions are expected overnight, though can't completely rule out a few isolated showers or non-severe thunderstorms (~20% PoPs).

Tuesday's forecast has been oscillating a bit regarding the potential for daytime convection. On the most recent (00z 6/2)
model suite, there was a shift toward a coherent mid-level impulse lifting northeast across the area during peak heating.
Much more favorable mid-level moisture with this feature entails a quicker erosion of capping as temps rise into the mid to upper 80s with dew points in the upper 60s to around 70F.
Even with the mid-level wave traversing the area, height falls and mid- level cooling will be modest at best, as well as only 20-30 kt of southwest flow from 700-500 mb (sub-marginal deep layer shear). Uncapped 1500-2000 J/kg of MLCAPE intercepted by the mid-level impulse should result in scattered pulse-type convection. The lack of wind shear but moderately strong instability and steep low- level lapse rates may support a localized downburst threat. Relatively slow storm motions and seasonably high PWATs between 1.5-1.75" also suggest the potential for ponding on some roads.

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.

Castro

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/
Issued at 1213 PM CDT Sun Jun 2 2024

Aviation weather concerns are:

- Potential for mainly afternoon/evening showers and storms in the region on Monday.

MVFR cigs continue to lift and scatter, with VFR conditions returning to all terminals this afternoon. Variable winds will turn predominantly NEly at the Chicago-area terminals with the passage of a lake breeze. Thereafter, winds will ease and become southeasterly area-wide.

Southeasterly are expected to become breezy with time through Monday morning before veering to a 180-200 direction through the afternoon with intermittent gusts into the mid 20 knots.

A decaying complex of showers and storms is expected to move across eastern Iowa early Monday morning and may deliver some showers (can't rule out a storm), mainly INVOF RFD for which a PROB30 has been introduced. Thereafter, afternoon TS changes will hinge entirely on the track of a convectively-augmented disturbance for which there is low skill in anticipating at this range. Based on the available guidance today, have introduced a PROB30 group for TSRA after 21z on Monday in the ORD/MDW extended TAFs since confidence in storms is not high enough to justify prevailing VCTS of TEMPO TSRA conditions.

Carlaw

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

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