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LMZ745 Expires:202405050330;;620365 Fzus53 Klot 041856 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 156 pm cdt Sat may 4 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.
lmz741>745-050330- wilmette harbor to northerly island il- northerly island to calumet harbor il- calumet harbor il to gary in-gary to burns harbor in- burns harbor to michigan city in- 156 pm cdt Sat may 4 2024
Late this afternoon - East winds 10 to 15 kt. Patchy fog. Waves around 1 ft. Tonight - Southeast winds 10 to 15 kt becoming north after midnight. Patchy fog and gusty showers and Thunderstorms before midnight. Waves 1 to 3 ft. Sunday - North winds 15 to 20 kt diminishing to 10 to 15 kt. Mostly cloudy in the morning, then becoming partly cloudy. Waves 2 to 4 ft. Sunday night - North winds 5 to 10 kt. Partly cloudy. Waves 1 to 3 ft. Monday - East winds 5 to 10 kt increasing to 10 to 15 kt. Partly cloudy. Waves 1 to 3 ft.

LMZ700
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FXUS63 KIWX 041912 AFDIWX

Area Forecast Discussion National Weather Service Northern Indiana 312 PM EDT Sat May 4 2024

KEY MESSAGES

- Light rain and a few embedded thunderstorms are possible at times through Monday but no severe weather is expected.

- Additional showers and storms are likely Tuesday and Wednesday. Some of those storms may be severe.

- After cooler weather Sunday and Monday, highs climb back to around 80 for Tuesday and Wednesday.

DISCUSSION
Issued at 312 PM EDT Sat May 4 2024

Midlevel shortwave currently seen on water vapor imagery over northern MN will continue to lift NE and send a decaying cold front through the region tonight. A line of convection will continue to develop over IL late this afternoon, capitalizing on 1500 J/kg of MLCAPE ahead of the front. However, all ingredients point to a quick demise as it enters our CWA late this evening.
Not only do we lose daytime heating but convection will outrun better forcing and shear as it enters our area, quickly becoming outflow-dominant and weakening. Low level moisture convergence and midlevel lapse rates appear insufficient to maintain robust nocturnal convection in our area, but do anticipate some showers with a few isolated storms to linger into the night with the best chances in our far west 01-04Z. The chance of showers will continue in our eastern zones into Sunday as increasingly broad/diffuse cold front makes slow eastward progress. A few models suggest our extreme E/SE zones may have time for some marginal destabilization by early afternoon yielding the chance for a few storms. However, most hi-res guidance suggests any convection will be well outside of our CWA Maintained a low chance PoP for late tonight into midday Sun but any rain during this period will be very light and very isolated. High temps tomorrow will be much cooler in our NW CWA, especially near the lake where 50s are likely. SE zones still have a shot at mid 70s again before the front passes though.

Another weak shortwave ejects out of the Southern Plains and into the Ohio Valley by Monday. However, the Great Lakes remain firmly under the influence of AVA/subsidence with sharp midlevel ridge approaching from the Upper Midwest. Exactly how far north precip manages to extend remains a bit uncertain but prefer to lean on the dry side with easterly surface winds and marginal 850mb theta-e advection just barely touching our border. High-res guidance available that far out also supports a drier forecast.

Situation changes drastically for Tue and Wed though. Deep upper low just now coming onshore the West Coast will eventually pinwheel its way across the northern CONUS as a second Pacific trough follows quickly behind it. Global models still show some discrepancies in how exactly this pattern will evolve with smaller details crucial to determining the severe weather threat. Initial warm front/theta-e surge occurs Tue AM. A few strong, elevated storms may be possible during this time but the better severe chances appear to be Tue evening when initial trough/upper low (potentially) approaches the Great Lakes with moderate instability in place and (again, potentially) a highly supportive kinematic environment. A second round is then possible Wed evening as the second piece of energy rotates through the region with a similar environment. There is still alot of uncertainty with important details but definitely need to keep an eye on these periods.

The rest of the forecast period is relatively quiet. Light rain and breezy conditions may persist into the late week depending on how the upper low evolves but the instability should clear out by Thu.
Cooler temps are also expected Thu-Sat.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 133 PM EDT Sat May 4 2024

Two boundaries collocated with mid level vorticity and areas of low level convergence allow for times of cloud cover and rain between the start and end of this TAF period. A boundary pushed north and west this morning allowing cloud cover at FWA. CIGs rising from MVFR to VFR start this TAF period there as a result. Light rain and drizzle was observed under that cloud this morning, but with the raising ceilings expect to see less of that for the afternoon. Expect VFR conditions to continue into later portion of the overnight. On the other hand, an area of vorticity and surface convergence associated with a line of convective showers moving eastward from IL encroaches on SBN this evening. With much of the insolation staying west of IN-15 today, low level lapse rates steepen and instability increases ahead of the line.
Even still models, dissipate it as it moves inland from Lake MI. Wouldn't be surprised to see a brief increase of winds from the outflow boundary as well as some showers or perhaps a thunderstorm at SBN before it dissipates. Guidance indicates the cold pool associated with this may leave some MVFR CIGs behind at SBN for late tonight/early Sunday morning and perhaps FWA for Sunday morning. IFR CIGs may also be possible at SBN, but confidence on that is low at this time.

IWX WATCHES/WARNINGS/ADVISORIES
IN...None.
OH...None.
MI...None.
MARINE...None.

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