Sunrise 5:20 AM   Sunset 8:07 PM Moonrise 5:30 PM   Moonset 3:43 AM

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LMZ779 Expires:202405201515;;527510 Fzus63 Kmkx 200750 Glflm
open lake forecast for lake michigan national weather service milwaukee/sullivan wi 250 am cdt Mon may 20 2024
for waters beyond 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 wave, along with the average height of the highest 10% of the waves which will occasionally be encountered.
Synopsis -
southeast winds this morning will become more southerly by this afternoon as a weak area of low pressure around 29.7 inches tracks over wi and lake michigan. Expect to see more west to southwesterly component of the winds briefly overnight tonight. Winds will turn more south to southeasterly again Tuesday. Breezy southerly winds are expected as a deepening low pressure around 29.4 inches approaches the upper great lakes region and tracks northeast into Wednesday. There looks to be periods of Thunderstorms over the lake, especially southern portions Monday through Wednesday morning.
lmz080-669-671-673-675-777-779-870-872-874-876-878-201515- lake michigan from michigan city in to st. Joseph mi 5 nm offshore to mid lake- lake michigan from sheboygan to port washington wi 5 nm offshore to mid lake- lake michigan from port washington to north point light wi 5 nm offshore to mid lake- lake michigan from north point light to wind point wi 5 nm offshore to mid lake- lake michigan from wind point wi to winthrop harbor il 5 nm offshore to mid lake- lake michigan from winthrop harbor to wilmette harbor il 5 nm offshore to mid lake- lake michigan from wilmette harbor il to michigan city in 5 nm offshore to mid lake- lake michigan from whitehall to pentwater mi 5 nm offshore to mid lake- lake michigan from grand haven to whitehall mi 5 nm offshore to mid lake- lake michigan from holland to grand haven mi 5 nm offshore to mid lake- lake michigan from south haven to holland mi 5 nm offshore to mid lake- lake michigan from st. Joseph to south haven mi 5 nm offshore to mid lake- 250 am cdt Mon may 20 2024
sheboygan wi to pentwater mi south - .
Today - Southeast winds 10 to 15 kt becoming south 10 to 20 kt. Slight chance of showers and Thunderstorms this morning, then chance of showers and Thunderstorms this afternoon. Waves 1 to 3 ft. Tonight - Southwest winds 10 to 20 kt diminishing to 5 to 10 kt. Chance of showers and Thunderstorms in the evening, then slight chance of showers and Thunderstorms overnight. Waves 1 to 3 ft. Tuesday - Southeast winds 5 to 10 kt increasing to 10 to 20 kt. Chance of showers in the morning. Waves 1 to 3 ft. Tuesday night - South winds to 30 kt. Showers likely with a chance of Thunderstorms in the evening, then chance of showers and Thunderstorms overnight. Waves 3 to 5 ft building to 6 to 9 ft occasionally to 12 ft. Wednesday - Southwest winds to 30 kt diminishing to 15 to 25 kt. Waves 5 to 8 ft occasionally to 10 ft subsiding to 4 to 7 ft occasionally to 9 ft. Wednesday night - West winds 10 to 20 kt. Waves 3 to 5 ft. Thursday - West winds 10 to 20 kt becoming southwest. Waves 2 to 4 ft. Friday - East winds 10 to 20 kt. Waves 1 to 3 ft.

LMZ700
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FXUS63 KLOT 200825 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 325 AM CDT Mon May 20 2024

KEY MESSAGES

- Scattered t-storms likely today, a few severe storms with large hail and damaging winds possible this afternoon.

- Another round of thunderstorms is expected Tuesday evening into the nighttime hours. Severe thunderstorms with damaging winds and brief QLCS type tornadoes are possible with this round.

- Another chance for showers Friday into Saturday

DISCUSSION
Issued at 325 AM CDT Mon May 20 2024

Today and tonight:

A pair of MCVs will likely be the significant players in our weather today. MCV #1 located over northeast IA as of 07z will continue to move northeastward and generally away from the area this morning. A north-south line of convection extending south of this vort across eastern IA should begin a weakening phase in the next couple of hours as it progresses east-northeast into a more stable air mass. Nonetheless, some showers and perhaps a t-storm could affect our western and northwestern CWA early this morning in association with this feature before dissipating and/or moving north into WI by mid morning. Severe wx with this activity is unlikely.

MCV #2 should be the more problematic feature today. Currently over northwest Missouri, hi-res model guidance matches well with simple extrapolation, both have this features moving into southwest WI early this afternoon. A formidable mid level jet accompanies this feature with the latest VWP from KEAX showing 50-55kt winds from 700-500mb. While this MCV will probably weaken some this morning given the waning convective activity, the RAP (which seems to have initialized this feature pretty well when compared with observational data) maintains a 40-50kt 700mb jetlet and 35-45kt at 500mb into the early/mid afternoon on the southeastern flanks of this MCV across far northern IL into southern WI.

This stronger flow with the vort max results in some respectable low-mid level hodographs for a time late this morning through early-mid afternoon. While 0-6km bulk shear is only progged to be around 30kt, almost all of the shear will be focused in the 0-3km layer where hodographs are somewhat elongated and a bit curved. Ongoing convection with MCV #2 is expected to weaken/dissipate this morning and likely allow for at least some mixed sunshine to heat the moistening boundary layer as warm front lifts north across the CWA this morning.
Assuming convective debris isn't more extensive than expected, then MLCAPE of around 2000 J/kg could be realized by early afternoon with minimal inhibition left. Assuming convection develops over northern IL this afternoon, and that looks pretty likely, the next question will be how soon. If robust convection can develop by early afternoon, favorable shear profiles will be in place to support an storm scale organization and including maybe some messy supercell structures. Given the shear maximized in the low levels with largely streamwise vorticity in the 0-1km layer, there could even be a couple hour window with some low end tornado threat. This would particularly be near the northward retreating warm front and assuming robust convection develops early enough to reap the benefits of the stronger mid- level flow associated with the MCV.

Heading into the mid and especially late afternoon, shear profiles will quickly weaken and hodographs collapse in on themselves. This means our severe threat should become relegated to mainly a pulse type severe threat with accompanying brief marginal hail and localized microburst where any updrafts find some untapped CAPE to feed on. Thunderstorms should dissipate and then end this evening as the MCV lifts north out of the area and the boundary stabilizes. Maintained some slight chance pops late this evening and overnight as a nod to the RAP which has another MCV and associated convective complex rolling across the area. Not seeing any evidence of this feature upstream now and this scenario seems unlikely, with most likely scenario being mostly dry conditions tonight.

Tuesday into Tuesday night:

Guidance varies with where the warm front will be to start the day, likely due to models' attempts to resolve convective influences. If the warm front starts out in our area in the morning, a strong and deepening cyclone to our west should drive it quickly north into Wisconsin. Another MCS and associated MCV should organize over the central Plains tonight with this system likely moving toward the MS River late tonight into early Tuesday morning. Can't rule out some weakening form of this MCS bringing some showers and storms to our NW CWA in the morning, with the warm front and synoptic scale ascent shifting north into WI, would tend to think the synoptics will overwhelm this system and lead to it decaying Tuesday morning.

Barring any unexpected surprises from any meandering MCVs, Tuesday afternoon looks to be windy, largely rain free, and unseasonably warm to hot. Expecting high temps to reach at least into the upper 80s with lower 90s a distinct possibility given decent amount of sunshine during the afternoon.

Potentially explosive severe thunderstorms are expected Tuesday afternoon across western or central IA south into northern Missouri. This activity is expected to eventually congeal into a QLCS that will march east and northeastward toward the MS River by early to mid evening Tuesday. Gusty southerly winds should keep the boundary layer somewhat mixed and temps warm Tues evening, likely slowing the nocturnal stabilization of the boundary layer. Even with that, still expect convection to be encountering much weaker and weakening instability and growing boundary layer convective inhibition as it moves into our CWA mid-late evening Tuesday. Assuming the convection doesn't outrun the strong synoptic ascent, a still somewhat formidable, but weakening QLCS could march across much of the CWA Tuesday night.

Wind profiles will be plenty favorable for a continued threat of damaging winds and perhaps a QLCS tornado threat. These threats appear to be greatest over our western CWA, with the threat lessening with eastward extent. The earlier the storms arrive, the more mesoscale organization that they can attain, the more significant the severe threat will be in our CWA
Certainly, the severe threat should be highest west of our CWA across Iowa and there are scenarios where we dodge a bullet with little or no severe weather in our area. But given the strength of the synoptic system and associated kinematic fields, Tue evening warrants close watching, especially across our western CWA

Wednesday and Wednesday:

GFS is finally starting to cave and give up on the idea of extensive post frontal convection Wednesday afternoon and evening across our CWA The 00z NAM came in dry, in line with the very consistent ECMWF and GEM models which have been steadfast in their dry forecast for our area for days now. NBM pops are still being weighted down by the 12z runs and the GFS and its ensemble members. Have coordinated a significant reduction in pops with neighboring offices and removal of NBM QPF with WPC for Wed into Wed night.

- Izzi

Thursday through Sunday:

Brief upper level ridging should allow for better height rises on Thursday for much drier conditions setting up. Winds should be out of the west and light with the occasional afternoon burst to 15 mph. Afternoon temperatures should warm into the 70s, with slightly cooler conditions in Northern Indiana along the immediate shoreline.

The next upper level trough ejects out of the Rockies Thursday night and starts tracking toward southeastern Manitoba. Despite the system's track being farther to the northwest than earlier in the week. As the reflected surface low passes through the Dakotas and Minnesota, a warm front will slowly enter Illinois on Friday. Southerly winds will slowly advect precipitable water amounts over an inch back into the area. The best instability will be in the warm sector behind the front in a Rockford to Fowler, IN line, but even then forcing does not look impressive.
So PoPs for scattered showers were kept at the chance threshold.

Overnight and into Saturday, the low exits into Canada as a secondary surface low strengthens over the Southern Plains.
Friday's surface front will be come a NW/SE oriented cold front and move over the region on Saturday. With it comes better forcing and instability to allow widely scattered thunderstorms to develop through the day. This far out, timing can be adjusted closer to the event. At this juncture, model soundings have weaker mid level lapse rates and deep layer shear to keep the word severe out of the forecast. There may be isolated showers that stick around through Monday, but there should be breaks in the rain. However, confidence remains to low this far out for specifics at this time.

DK

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/
Issued at 1230 AM CDT Mon May 20 2024

Key Aviation Impacts for the current TAF period:

- Scattered and possibly strong thunderstorms expected today, arriving in the late morning for RFD and around or just after noon for the Chicago terminals

Dry conditions and light winds out of the east, becoming southeasterly ahead of the next storm system arrives. There may be the occasional spotty shower that develops in the morning out ahead of the main system; however, consensus suggests that the early showers will leave RFD and head toward southeastern Wisconsin, so it was kept out of the TAFs for now. As for the main system, winds will increase out of the southeast ahead of the storms with gusts around 25 knots. Widely scattered storms are still likely with the only major change to the forecast being increasing the arrival time to around 15Z at KRFD and as early as 18Z at KORD. Lightning, strong westerly wind gusts, and potentially some hail are the main impacts expected with these storms. Additionally, MVFR cigs and lower vis can be expected during the heaviest rainfall as they pass over terminals.

Latest guidance suggests that the main system should move east of Chicago after 22Z. There could be some lingering light showers behind the line, but with lower confidence in projecting exact location of that, it was kept out of the TAF. Winds are expected to be out of the southeast and below 10 knots behind the rain, but they may be variable in the immediate wake of the storms. Cloud cover is expected to remain over the region, but cigs should be at VFR levels.

DK

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

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