Sunrise 5:38 AM   Sunset 7:57 PM Moonrise 4:18 AM   Moonset 5:14 PM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- 323 Am Cdt Sun May 5 2024
Today - North winds 15 to 20 kt diminishing to 10 to 15 kt late. Partly cloudy in the morning then clearing. Waves 1 to 3 ft. Tonight - Northeast winds 5 to 10 kt. Partly cloudy. Waves 1 to 2 ft. Monday - East winds 10 to 15 kt. Mostly Sunny. Waves 1 to 2 ft. Monday night - East winds 10 to 15 kt becoming southeast overnight. Chance of showers and slight chance of Thunderstorms overnight. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 051110 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 610 AM CDT Sun May 5 2024

KEY MESSAGES

- Active pattern with periodic shower/thunderstorm chances expected Tuesday onward. Severe weather and locally heavy rainfall threat likely for parts of the area Tuesday and Wednesday.

DISCUSSION
Issued at 353 AM CDT Sun May 5 2024

Through Monday:

Last evening's storm system and trailing cold front have shifted well east of the area early this morning, ushering in a period of tranquil weather today and Monday ahead of another period of active weather mid-week. Residual post-frontal stratus across roughly half of the CWA should gradually drift southeast through early afternoon while being replaced by scattered cirrus. Max temps will range from the upper 60s well inland to the mid 50s along the shore amid modest NE flow through the day.

Persistent NE flow within a very dry air mass tonight will allow dew points to fall through most of the evening. Shallow decoupling under generally clear skies within the dry airmass will support a relatively cool night with min temps in the low to mid 40s. It wouldn't be surprising to even see some rogue upper 30s readings in the typically coldest spots of interior northern Illinois.

Ongoing robust convection across central Texas early this morning has generated a fairly substantial mid-level wave that is expected to drift ENE across Ohio River Valley by Monday afternoon. The wave will remained trapped under a pseudo-Rex block traversing broader mid-level westerlies across the central CONUS, with forecast guidance generally supporting a gradual degeneration of the wave with time. Slowly veering low-level flow ahead of a large trough across the Rockies may begin advecting better moisture into the far southern CWA late Monday afternoon, ultimately interacting with the northern periphery of the decaying wave to generate some sparse showers toward central Illinois. Otherwise, seasonably warm conditions away from Lake Michigan are expected Monday.

Kluber

Monday Night through Saturday:

Surface low pressure is progged to be lifting northeast across the Dakotas Monday evening, in association with a deepening level trough/closed low across the region. Within the south/southeast periphery of the trough, a strong negative-tilt short wave is expected to propagate northeast into the mid-upper Mississippi Valley and western Great Lakes region overnight and into Tuesday, in association with a strong 80-90 kt mid-level jet. Increasing forcing for ascent with this wave, combined with isentropic ascent atop a northward-advancing warm front and diffluent upper flow ahead of the jet streak, is expected to allow showers and thunderstorms to spread into the IL portion of the forecast through Tuesday morning. The initially largely- elevated nature of these storms, and only modest mid-level lapse rates suggest little/no significant severe threat with these storms as the continue to lift northeast across the area Tuesday morning/midday.

A weak surface wave/triple point is indicated passing north of the forecast area in WI by midday, along what will then be an occluding warm/cold front pushing east into the cwa. This looks to shunt the better low-level moisture and conditional instability axis across our far east/southeast cwa by afternoon, during the more favored diurnal timing for renewed surface- based convective development. The extent of cloud cover and residual cold pool stabilization from the morning activity makes Tuesday afternoon and evening thunderstorm redevelopment/evolution somewhat uncertain, however. Provided enough afternoon clearing and heating can occur, a severe weather threat will likely exist. Forecast soundings suggest 1500-2000 J/kg of MLCAPE and nearly 70 kts of mainly unidirectional 0-6 km bulk shear (nearly 50 kt 0-1 km shear) by mid-late afternoon across our far east/southeast cwa, where the low-level moist axis looks to be ahead of the occluded front.
Thunderstorms would likely be less numerous across our western cwa, away from the stronger low-level instability. SPC Day 3 outlook (marginal for most of the area, slight far southeast)
appears reasonable at this point.

The upper trough/low over the northern Plains is progged to wobble east-southeast Wednesday into Thursday, with the main vort moving across the forecast area later Wednesday/Wednesday night. This is expected to result in a surface low pressure wave tracking across the region, with a renewed shower and thunderstorm and conditional severe weather threat ramping up again Wednesday afternoon/night, especially across our southern cwa.

The upper trough is then expected to amplify across the eastern CONUS through the end of the week. Cooler mid-level temperatures and a series of smaller scale short waves rotating through the trough should maintain a periodic shower/thunderstorm threat, focused on the afternoon/evening peak diurnal heating hours. After daytime temperatures in the 70s to near 80 Tuesday and Wednesday, cooler 60s are expected for the second half of the week beneath the upper trough.

Ratzer

AVIATION /12Z TAFS THROUGH 18Z MONDAY/
Issued at 606 AM CDT Sun May 5 2024

Aviation Key Messages:

- MVFR ceilings linger around KGYY early this morning,then VFR.

- NNW winds shift to NE by mid-morning.

Weak surface high pressure will build across the area today, then shift east by Monday morning. Patchy MVFR ceilings will linger over Lake Michigan and northwest IN through mid-morning, otherwise VFR conditions are expected. Breezy north winds 10-15 kt will settle to around 10 kt from the northeast this morning, and eventually east-southeast on Monday.

Ratzer

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

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