Sunrise 5:35 AM   Sunset 8:00 PM Moonrise 5:39 AM   Moonset 9:13 PM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 309 Pm Cdt Wed May 8 2024
Tonight - Northeast winds 5 to 10 kt increasing to 10 to 20 kt in the evening. Slight chance of showers in the evening, then showers and slight chance of Thunderstorms after midnight. Waves 1 to 3 ft building to 2 to 4 ft. Thursday - Northeast winds 15 to 20 kt becoming north 20 to 25 kt. Showers and slight chance of Thunderstorms in the morning, then showers likely in the afternoon. Waves 3 to 5 ft. A small craft advisory will likely be needed. Thursday night - North winds 15 to 25 kt diminishing to 10 to 15 kt. Slight chance of showers in the evening. Waves 4 to 6 ft occasionally to 8 ft subsiding to 2 to 4 ft. A small craft advisory will likely be needed. Friday - North winds around 10 kt becoming east in the afternoon. Mostly Sunny in the morning, then becoming partly cloudy. Waves 2 to 4 ft subsiding to 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 082333 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 633 PM CDT Wed May 8 2024

KEY MESSAGES

- Showers and a few thunderstorms are expected this evening and tonight. Some thunderstorms may feature small hail and gusty winds, primarily outside of the Chicago metro area.

- Cooler weather arrives Thursday, with periodic showers Thursday and again Friday night into the weekend.

DISCUSSION
Issued at 246 PM CDT Wed May 8 2024

Through Thursday night:

Today has been awfully pleasant for us so far with sunny skies and temperatures having reached the middle 70s to near 80 degrees area- wide. This is not the story across the rest of the Midwest, however.
Early this afternoon, we find two centers of surface low pressure in the region: one subtle little system in northwest IA and a broad, more prominent low marching across the Ozark Plateau. The former is producing nothing more than light showers out west while the latter is responsible for a swath of severe storms extending from western MO into south-central Kentucky. These two systems will phase into one over the next several hours before moving into central IL this evening. This will bring showers and likely a handful of storms to the area this evening through the better part of tomorrow.

We should begin to see isolated to widely scattered showers move into the SW CWA early-mid evening and progress across the rest of the area. With only a little bit of elevated instability squeezing into the CWA, thunderstorms look rather unlikely with this first little push any farther north than say the US Rt 24 corridor. More widespread activity will work in not long after midnight along the northern flank of the low as it passes through central IL. It looks like the overnight period will be our best chance at seeing embedded thunderstorms when several hundred joules of elevated CAPE look to build over parts of the area. The greatest thunder potential will exist in our western and southern CWA where we'll find the most appreciable instability with notably steeper low-mid level lapse rates. The environment becomes less and less favorable approaching the lake. While CAPE values certainly won't stand out tonight, most of it will be confined within the hail growth zone and we will have a respectable amount of mid level shear to work with, roughly 25-30 kt at 3-6 km. This means it's not out of the question to see some small hail develop within any relatively stronger elevated cores. Some dry air in the low levels and a ~30 kt LLJ could also promote some gusty winds with any thunderstorm or heavier shower tonight.

The instability will wane to the east early tomorrow pretty much driving the thunder potential out of here through the morning.
Scattered showers are expected to continue through much of the afternoon before high pressure builds in and clears conditions up during the evening. A tight pressure gradient on the backside of the system will bring breezy winds to the area during the day. Between the cloudy, rainy conditions and cold advection, tomorrow will be noticeably cooler with highs forecast near 60 south of I-80 and stuck in the 50s farther north.

Doom

Friday through Wednesday:

Shortwave ridging will produce stout mid-level warming through the day Friday, though low-level moisture will remain sufficient for a decent coverage of shallow cumulus during the afternoon.
On the heels of the ridge, a compact upper-level low will dig southeast over the western Great Lakes Friday night into Saturday. Earlier guidance had advertised a diurnally favorable passage of the low directly over our area midday Saturday, but has since supported a faster solution with the low passing to the northeast around daybreak. Additionally, more favorable thermodynamic profiles with anomalously cold mid-level temperatures will remain to the northeast. Have therefore continued to cap PoPs in the chance range with the expectation that shower coverage will be no greater than scattered.

Northwest flow aloft will persist Sunday into early next week.
Another shortwave trough is progged to cross the area sometime late Sunday afternoon through Sunday night. Low-level moisture availability looks marginal at best for any widespread precipitation as a sprawling surface ridge remains anchored in the Deep South, but an earlier arrival of the trough could support isolated to scattered storms in our forecast area during the late afternoon and evening.

Beyond Sunday night, substantial differences in guidance regarding the evolution of a building ridge across the eastern seaboard and a central CONUS trough support leaving the NBM's slight chance and chance PoPs untouched from Monday through Wednesday.

Kluber/Ogorek

AVIATION /00Z TAFS THROUGH 06Z THURSDAY/
Issued at 633 PM CDT Wed May 8 2024

Key Aviation Impacts for the current TAF period:

- Rain moves in after midnight to Chicago terminals (just before midnight for KRFD) with MVFR cigs and vis

- Thunder cannot be ruled out but the probability is less than 30 percent so it remains out of the current TAFs

- Breezy northeast winds Thursday morning as the system exits to the east as lingering showers hang around

VFR conditions continue as a BKN deck at 10000 feet AGL moves in. Storms that are firing (currently) over western Iowa are scheduled to gradually move eastward through the night and into tomorrow morning. Light rain could arrive as early as 03Z, but the strongest showers are not expected until after midnight at Chicago terminals (just before midnight at KRFD). The stronger showers are expected to bring cigs down to near IFR levels with reduced visibility for MVFR conditions through Thursday morning. With instability overnight expected to be pretty meager, it provides the risk for lightning around 10 to 30 percent. While it cannot be completely ruled out, thunderstorms were left out of the TAF at present and will be closely monitored through the night. Strongest storms are expected to move south and east of the area after 12Z. Based on the modeled track, if there was an area where stronger storms might hold on a little longer, it would be around KMDW and KGYY. But confidence remained in leaving the TEMPOs ending at 12Z

As the center of the system moves east of the area, rain will gradually transition to more showery activity through Thursday.
Winds will remain out of the northeast, but the potential for gusts around or just over 20 knots is possible through the morning and early afternoon, diminishing thereafter. Despite remaining at MVFR conditions through the day, cigs should gradually improve to around or over 2000 feet Thursday afternoon, but confidence is low on the exact timing for cigs improvement and when wind gusts diminish.

DK

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

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