Sunrise 5:42 AM   Sunset 7:51 PM Moonrise 3:02 AM   Moonset 1:22 PM

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LMZ743 Calumet Harbor Il To Gary In-gary To Burns Harbor In- Burns Harbor To Michigan City In- 359 Am Cdt Thu May 2 2024
Today - East winds 10 to 15 kt becoming southeast 15 to 20 kt late in the morning then becoming south mid afternoon. Slight chance of showers and Thunderstorms in the morning, then chance of showers and Thunderstorms in the afternoon. Waves 1 to 2 ft.Tonight - South winds 10 to 15 kt diminishing to 5 to 10 kt overnight. Showers and a chance of Thunderstorms. Waves 1 to 2 ft. Friday - West winds 5 to 10 kt becoming north in the afternoon. Showers likely and a chance of Thunderstorms in the morning. Waves 1 to 2 ft. Friday night - Northeast winds 5 to 10 kt becoming north. Mostly cloudy in the evening, then becoming partly cloudy. Waves 1 to 2 ft.

LMZ700
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FXUS63 KLOT 020844 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 344 AM CDT Thu May 2 2024

KEY MESSAGES

- Waves of showers and thunderstorms expected through Friday AM.

- Short window for strong to severe storm development this afternoon into early evening (~3-7pm).

- Periodic chances for showers and thunderstorms again this weekend into next week, with some potential for severe weather on Tuesday.

DISCUSSION
Issued at 344 AM CDT Thu May 2 2024

Through Friday:

All is quiet early this morning with light northeast winds and temperatures in the 50s. Well to our west, an expansive complex of showers and thunderstorms is ongoing across northern Kansas and eastern Nebraska with scattered warm advective showers and embedded thunderstorms extending well ahead of it across much of Iowa. Coverage of showers farther southeast along the surface warm front across northeast Missouri and southern Illinois is much lower than expected just 24 hours ago, likely due to more persistent dry air in the lower levels, though there are a few spotty showers attempting to develop near and south of Springfield, IL that may try to lift into the area toward daybreak.

While there remains a fair amount of variability in the timing and coverage of upstream showers and storms through the morning and early afternoon hours into portions of the local area, the general expectation is that the NE/KS complex of storms will continue to drift east northeast toward the area and gradually decay upon approach with spotty showers and isolated non-severe storms potentially reaching the Rockford area by mid-morning. Can't rule out gusty winds and small hail with any more persistent cores along/west of I-39 late morning. The afternoon strong to severe storm potential will likely be dependent upon the evolution of the morning showers/storms. A faster movement and persistence of precipitation across far northern Illinois could limit the north and westward extent of the warming, keeping the better instability east of the more favorable shear parameters. Meanwhile an earlier weakening of the line would allow for a further north/northwest expansion of the warm unstable air toward the WI/IL state line and west of I-39. In this scenario, the more favorable instability and shear parameters would be supportive of at least isolated strong to severe thunderstorm development with damaging hail and wind being the primary hazards. Will also note that with the location of the surface warm front hugging the lake, there is a narrow axis where slight backing of the winds at the surface could be supportive of a localized brief tornado threat. The timing of the strong to severe potential still looks to be confined to roughly a 3-7 PM CDT window as instability diminishes with sunset.

Additionally, with the anomalously high PWATS for this time of year combined with the antecedent wet soils, there remains the potential for localized flooding where heaviest rain rates develop.

As far as temperatures go, as mentioned above, they will be dependent on the coverage of AM showers and the resultant placement of the warm front. Locations that manage to stay dry through early afternoon (most likely south and east of a Mendota to Elgin, IL line) will be warm and even a bit muggy for this time of year with highs in the low-mid 80s and dew points in the lower 60s. Where showers persist through the morning may only warm into the 70s.
One final note on temperatures: those along the immediate Illinois lakeshore may struggle to warm out of the 60s, especially into Lake County.

Looking ahead to the evening hours, waves of showers and embedded non-severe thunderstorms are expected to continue through the overnight hours as the system and associated cold front very slowly drift east with time. Expect showers to clear out from northwest to southeast with the front during the morning hours on Friday, with perhaps a few showers/storms lingering toward central Illinois into early afternoon. Temperatures on Friday will be cooler than today with highs in the upper 60s to lower 70s.

Petr

Friday Night through Wednesday:

An active weather pattern is expected going into next week with periodic chances for showers and storms. An initial shortwave impulse arriving in tandem with a cold front at the surface may bring some showers and storms into the area on Saturday, likely during the latter half of the afternoon or at night. Another disturbance will likely pass to our south late Sunday into Monday, but may still be in close enough proximity for showers and possibly some storms to spread into our forecast area, particularly into our southern counties. With both disturbances being fairly subtle and somewhat detached from the stronger flow aloft, there is still quite a bit of spread amongst the EPS and GEFS ensemble members in their evolution and how that will translate QPF-wise, but enough of a signal for measurable precipitation exists to continue carrying slight chance and low- end chance PoPs as output by the NBM during the Saturday afternoon through Monday time frame. High temperatures during this three-day stretch look like they'll end up in the 70s inland with cooler temperatures closer to Lake Michigan each day as a result of onshore flow prevailing through much of this time frame.

A much more potent upper-level trough will eject out of the Rockies and morph into a closed-off low over the northern Great Plains Monday into Tuesday, with another follow-up wave likely to then be thrusted towards the Great Lakes as it navigates a belt of strong, predominantly westerly flow along the upper low's southern periphery. This process will likely culminate in at least two episodes of cyclogenesis across the central part of the CONUS that will encourage the poleward advection of warm, moist air of Gulf origin into the Midwest. The increased warmth and moisture, coupled with the strong dynamics at play, will likely result in consecutive days of severe weather from the Great Plains to the Appalachians during the first half of the upcoming week. It's still too early to say with much confidence whether we will get in on the action here in northern Illinois and northwest Indiana as there are several moving parts and pieces that still need to be resolved, but it looks like Tuesday should be the main day for us to monitor for potential severe thunderstorms and/or heavy rainfall. Though, depending on how everything evolves, some potential for severe weather may ultimately present itself on Monday night and/or Wednesday as well.

Ogorek

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
Issued at 126 AM CDT Thu May 2 2024

Key Messages:

- Periods of showers likely today and tonight.

- Potential for thunderstorms this afternoon into this evening.

- Low confidence in wind direction/wind speed this afternoon into this evening.

Periods of showers are likely to be observed over a good chunk of the TAF period as a low pressure system and its associated fronts approach from the southwest. An initial wave of showers is possible after daybreak this morning out ahead of a warm front lifting northward into the area. However, confidence in these showers developing is only medium, and their coverage may be isolated enough to not affect the terminals much anyways.

There will probably be a break in the shower activity late this morning into the early afternoon before an additional wave of showers and scattered thunderstorms approaches from the southwest ahead of a cold front. While confidence is medium to high in thunderstorms occurring in northern Illinois today, particularly along the leading edge of this second wave of precipitation, confidence in the timing of these storms and whether the storms will affect any particular TAF site remains somewhat low due to the somewhat disorganized character of this convective activity. Have elected to largely retain the inherited PROB30 groups for TSRA for now and will continue to reassess. If storms do end up passing over the terminals, they may produce some stronger winds and will likely reduce visibility below VFR levels.

Going into tonight, shower coverage is expected to become more widespread, but thunderstorm coverage should dwindle due to the loss of instability with time. Ceilings will likely lower as the showers continue over the course of the night, with MVFR ceilings possible towards the end of the current TAF period.

Lastly, the wind forecast for this afternoon into this evening is not an easy one. Initially easterly winds should veer more southeasterly later this morning into the early afternoon as the aforementioned warm front approaches. Winds may then become southerly south of the warm front as it passes by, but some uncertainty remains as to how far north the front will get as the influence of onshore flow off of Lake Michigan will probably cause it to get hung up somewhere in the Chicago metro, which would tend to favor winds remaining east of south at the Chicago metro terminals. If thunderstorms end up passing near or over the terminals this afternoon and evening, then that will likely cause winds to become quite messy for a time before a general trend towards a southwesterly wind direction is expected tonight. Finally, winds should turn westerly towards the end of the current TAF period as the cold front passes through.

Ogorek

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

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