Sunrise 5:39 AM   Sunset 7:58 PM Moonrise 5:10 AM   Moonset 7:52 PM

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LMZ742 Expires:202405080315;;805948 Fzus53 Klot 072123 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 423 pm cdt Tue may 7 2024
for waters within five nautical miles of shore on lake michigan
waves are provided as a range of significant wave heights, which is the average of the highest 1/3 of the waves, along with the average height of the highest 10 percent of the waves which will occasionally be encountered.
lmz740>742-080315- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 423 pm cdt Tue may 7 2024
.tornado watch 195 in effect until 8 pm cdt this evening - .
Late this afternoon - Southwest winds 10 to 20 kt. Scattered showers and Thunderstorms early. Waves 2 to 4 ft. Tonight - Southwest winds 10 to 20 kt becoming west 10 to 15 kt. Isolated showers and Thunderstorms in the early evening. Waves 1 to 3 ft. Wednesday - Southwest winds 5 to 10 kt becoming east 10 to 15 kt in the afternoon. Chance of showers in the afternoon. Waves 1 to 2 ft.Wednesday night - Northeast winds 15 to 25 kt. Showers likely and slight chance of Thunderstorms in the evening, then showers likely and a chance of Thunderstorms overnight. Waves 2 to 4 ft building to 3 to 5 ft. Thursday - North winds 15 to 25 kt increasing to 30 kt. Showers likely in the morning, then chance of showers in the afternoon. Waves building to 4 to 7 ft occasionally to 9 ft.

LMZ700
No data

FXUS63 KLOT 072107 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 407 PM CDT Tue May 7 2024

KEY MESSAGES

- Threat for any additional severe thunderstorms ending by 5-6 PM CDT today

- Another round of thunderstorms may develop late Wednesday into Wednesday night, some of which could be strong to severe, mainly south of I-80 into central Illinois and Indiana

- Cooler with periodic showers Thursday and then Friday night into the weekend

MESOSCALE
Issued at 407 PM CDT Tue May 7 2024

Surface trough/confluence zone continues to move eastward across extreme eastern IL. Storms developing along this boundary continue to struggle, likely a result of weak low level convergence and a very dry mid-upper level air mass. Air mass ahead of this boundary remains unstable and uncapped based on RAP mesoanalysis and confirmed by blossoming Cu field on visible satellite imagery. Winds are slightly more backed across northwest Indiana, so convergence may be a bit stronger as the boundary gets into northwest Indiana, so it is still possible we could see a ramp upward in the intensity of some of these storms over the next couple of hours.

IND and IWX WSR-88D VWPs both show strong deep and low level shear which will continue to be supportive supercells, even where surface winds are slightly west of due south. Until the boundary clears our CWA, we will need to continue to closely monitor storms for any signs of sustained intensification and growth. Hail and damaging winds would be the main threats if any storms can grow sufficiently and become sustained. However, hodograph derived from latest IND VWP shows sufficient low level shear for a tornado threat given the low LCLs and strong low level CAPE.

- Izzi

DISCUSSION
Issued at 338 PM CDT Tue May 7 2024

Tonight through Wednesday Evening:

A post cold frontal short-wave may touch off a few showers and thunderstorms across portions of far northern Illinois through the early to mid evening, with slight chance (~15-20%) PoPs for this activity. Generally quiet weather is then expected tonight into Wednesday morning, as the mid-level short wave lifts northeast of the area and short wave mid-level ridging develops overhead. Winds will become light to calm tonight as weak surface high pressure slides across the area. Forecast lows tonight are in the mid to upper 50s, locally lower 50s.

The most recent guidance has trended drier through much of Wednesday afternoon, enabling another warm day (mid 70s to lower 80s F) despite increasing cloud cover. The exception to the warmth once to the early afternoon will be lakeshore areas due to winds turning onshore synoptically and aided by lake influence.

From late Wednesday afternoon through Wednesday night, another round of showers and thunderstorms is expected to develop. Some scattered showers may develop across far northern Illinois and across the state line into Wisconsin in the late afternoon. More notably, the approach of the next short-wave will result in a gradual uptick in showers and thunderstorms to the south of I-80 prior to sunset, and then spreading northward in the evening and overnight.

A surface low pressure wave is expected to develop along the cold/stationary front which will trail across the southern Plains in association with this wave, which will then propagate northeast into the mid-Mississippi Valley by Wednesday evening.
Overall, the guidance has come into better agreement in barely returning the front northward into our far southern CWA (south of US-24) as a warm front by Wednesday evening. This is where some potential may exist for surface based severe weather threats, primarily damaging winds and hail.

Otherwise, as most of our area will be on the cool side of the front, the main concern will be elevated hail producing thunderstorms , some of which may become marginally severe (hail up to 1" diameter) as mid-level lapse rates steepen amidst supportive effective bulk shear. In addition, seasonably high PWATs may present a localized ponding or even flooding threat, primarily near and south of I-80.

Castro/Ratzer

Late Wednesday Night through Tuesday:

A mid-level trough extending southwest across Quebec and southern Ontario will phase with a mid-level low over the Missouri Valley late Wednesday night. As the phasing wave crosses the area on Thursday, a residual low to mid-level TROWAL combined with PWATs around 1" and a deep layer favoring warm rain processes supports the potential for a low-end localized band of heavy rain (1-2" totals by mid day Thursday) across portions of northern Illinois into southern Wisconsin. Outside of this band, scattered diurnally enhanced showers and perhaps a few storms are expected. Much cooler conditions are in store, with highs only in the upper 50s to lower 60s inland and lower to mid 50s near Lake Michigan. Adding to the cool feel, northerly winds will gust up to 25-35 mph, strongest near the lake.

After a quick-moving ridge yields dry and seasonable temps on Friday, another upper-level low is progged to cross the western Great Lakes on Saturday. Anomalously cold mid-level temps shifting across the area through the day will yield scattered showers and storms, with some stronger cores likely producing locally strong wind gusts. Diverging solutions by early next week with regards to handling of the departure of Saturday's upper low and a building ridge to the west greatly diminishes the forecast by early next week. It appears temperatures will trend back to above normal by the end of the period.

Kluber/Castro

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
Issued at 1259 PM CDT Tue May 7 2024

Key Aviation Messages:

- Scattered TSRA, possibly locally severe this afternoon - SE winds shifting SW and gusting over 20 knots around 19Z

Satellite analysis depicts MVFR clouds growing in depth to become more concerning for thunderstorm expansion across NE Illinois in the 18z-19z hour and then expanding into NW Indiana after 19z or so. The storms in around Chicago and points westward do pose a threat for hail along with winds in excess of 35 kt. The main window for storms will continue until about 23-0z, longest in NW Indiana, with the main window for the Chicago terminals through 2230z.

VFR conditions will return behind the storms this evening, with initially breezy SW winds easing overnight. Winds will shift southeasterly and then easterly through the late morning into the afternoon Wednesday. Another batch of precipitation will shift toward NE Illinois later in the day. Confidence in thunder toward the tail end of the 30 hr TAF is still below 30 percent.

KMD

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

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