Sunrise 5:48 AM   Sunset 7:48 PM Moonrise 12:11 AM   Moonset 8:35 AM

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LMZ741 Wilmette Harbor To Northerly Island Il- 350 Pm Cdt Sun Apr 28 2024
Late this afternoon - Southeast winds 15 to 25 kt. Patchy fog. Mostly cloudy. Waves 2 to 4 ft.Tonight - South winds 15 to 25 kt. Chance of showers and slight chance of Thunderstorms in the evening, then showers and a chance of Thunderstorms after midnight. Waves 1 to 3 ft. Monday - South winds 15 to 20 kt becoming southwest late. Showers likely and slight chance of Thunderstorms in the morning, then chance of showers in the afternoon. Waves 1 to 3 ft. Monday night - West winds 10 to 20 kt diminishing to 5 to 10 kt. Partly cloudy in the evening then clearing. Waves 1 to 2 ft. Tuesday - West winds 5 to 10 kt becoming southeast 10 to 15 kt in the afternoon. Mostly Sunny. Waves 1 to 2 ft.

LMZ700
No data

FXUS63 KLOT 282003 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 303 PM CDT Sun Apr 28 2024

KEY MESSAGES

- Showers and storms to redevelop this afternoon/evening, a few of which could become strong to severe near and west of I-39.

- Locally heavy rainfall is also possible with stronger storms which may yield instances of ponding

- Additional shower and storm chances Monday afternoon, mainly east of I-55.

- After a break on Tuesday, a stormy pattern returns midweek along with continued unseasonably warm temperatures.

DISCUSSION
Issued at 303 PM CDT Sun Apr 28 2024

Through Monday night:

Northeast IL continues to reside in the warm sector of a double barreled surface low which is centered over IA. The warm front has made little progress and still resides near the IL-WI line which has allowed for a lake enhanced surface boundary to surge inland across Lake, IL and Cook Counties. As a result, onshore winds behind this boundary have maintained much cooler temperatures (readings in the 50s to lower 60s) and has been advecting in fog off of Lake Michigan. Recent radar trends continue to show the lake boundary gradually pushing northward as south-southwest winds in the warm sector have increased and this is expected to continue through the rest of the afternoon.
Therefore, the advection fog in Lake, IL County and over the open waters of the lake should begin to erode over the next few hours as winds turn and deeper mixing is achieved.

In addition to the lake boundary, the position of the warm front has also trapped mid-level moisture overhead and allowed broken to overcast stratus to prevail. Thus, instability has struggled to increase this afternoon despite the continued warm- moist advection as recent aircraft soundings out of MDW show a weak cap has actually developed instead. While the reduced instability may serve as a hindrance to shower and storm coverage this afternoon, additional showers and thunderstorms are expected to develop this evening and persist through the night as the upper low pivots into the upper Midwest placing northeast IL and northwest IN in the right entrance region of an associated upper jet streak. Since any deeper instability will be waning after sunset the severe weather threat with any storms overnight continues to look low. However, mesoanalysis continues to show 30-40 kts of effective shear in place which could aid in generating an isolated strong to possibly severe storm if sufficient destabilization can occur prior to sunset.
The main threat with any severe storm would be gusty winds and hail and should be largely confined to the I-39 corridor and points west.

Additionally, there is also a growing concern (20-30% chance)
for instances of locally heavy rainfall tonight as PWATs in the 1.3 to 1.5 inch range continue to remain in place. Obviously the main driver for this threat will be the intensity of any storms tonight which as previously mentioned is uncertain. However, any more robust cores should be able to produce locally heavy rainfall and may lead to instance of ponding in lower-lying and flood prone areas. Given the lower confidence in amounts and exact location of any heavier rainfall have decided to hold off on any flood products.

The showers and storms overnight will exit the area on Monday as a cold front begins to move into the area. While another dry period is expected for the middle part of Monday, a final round of showers and storms is forecast to develop Monday afternoon along and east of I- 55. Given the short duration of showers and storms in our area and the marginal instability, no severe weather is expected. The wet weather will finally come to a close Monday evening with dry conditions Monday night into Tuesday. Otherwise, seasonably warm temperatures will prevail through Monday with highs once again in the 70s.

Yack

Tuesday through Sunday:

Ensemble model guidance favors the development and persistence of broad upper-level cyclonic flow centered along the central US/Canadian borders throughout the week, placing the Great Lakes along the western periphery of a synoptic-scale ridge. As a result, above-average temperatures are poised to return to the region with highs climbing back into the 70s by Tuesday, and even the lower 80s Wednesday and Thursday. As is typical this time of year, cooler temperatures can be expected along the Lake Michigan shoreline Tuesday and especially Wednesday due to lake-induced onshore flow (and moreso the passage of a backdoor cold front Wednesday afternoon). However, increasingly breezy southwest winds on Thursday should allow for the warmth to spread as far as the lakeshore.

Embedded shortwaves within the slowly-approaching upper-level cyclonic flow will also present opportunities for showers and thunderstorms next week. The first opportunity will be Tuesday night into Wednesday. At this point, it appears that our area may remain just on the outside of the influence of the first shortwave propagating along the eastern periphery of the steering cyclonic flow aloft. As a result, the highest chances (30 to 40%) for showers and storms Tuesday night into Wednesday are focused west of I-39 (and increase further west of the Mississippi River). The second opportunity for showers and storms will be in Thursday night into Friday timeframe. With the parent upper-level low closer by then, confidence in showers and storms impacting our area is higher with the second shortwave (chances for showers and storms are currently around 60-70% Thursday night into Friday). The forecast for high temperatures on Friday will depend entirely on when the second shortwave and associated showers and storms move through the area.

Behind the second shortwave and as the core of the upper-level low makes its closest approach, ensemble model guidance advertises a signal for brief cool-down toward seasonal temperatures this weekend. Thereafter, there is a signal for the return of above average temperatures and a generally stormy pattern toward the second week of May.

Borchardt

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/
Issued at 1239 PM CDT Sun Apr 28 2024

Key Aviation Impacts for the current TAF period:

- Scattered showers northwest of Chicago with the potential for some thunderstorms around KRFD this afternoon

- Widespread showers and thunderstorms expected this evening and through Monday morning

After a brief window of drier, VFR conditions, the next round of showers moves into the area this afternoon ahead of a front tonight. The risk for thunder was low enough around Chicago terminals to leave it out of the TAF currently; however, a TEMPO for -TSRA was placed into the KRFD TAF given the higher instability aloft expected to the west. Winds are slowly becoming out of the southwest as the warm front drifts northward. As cloud cover erodes, stronger gusts around 25 knots are expected to return to area terminals, though the occasion gust up to 30 knots is not out of the question.

After 00Z, a cold front will start its movement eastward over Illinois through the overnight hours. This will bring a renewed threat of showers and thunderstorms at terminals that will provide another opportunity for MVFR/IFR conditions from lower cigs and vis. Current expectation is for the cold front, and associated heaviest rain, to be over the lake after 12Z Monday morning. However, post frontal showers are expected to linger through the morning hours. While there is lower confidence on the exact timing for when rain cuts off, drier conditions are expected Monday afternoon as southwest winds gust around 20 knots and gradually become slightly more west to southwest by the late afternoon.

DK

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Dense Fog Advisory until 4 PM CDT this afternoon for Winthrop Harbor to Northerly Is. IL.

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