Sunrise 5:38 AM   Sunset 7:57 PM Moonrise 4:41 AM   Moonset 6:31 PM

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LMZ741 Expires:202405061515;;713294 Fzus53 Klot 060843 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 343 am cdt Mon may 6 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>742-061515- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 343 am cdt Mon may 6 2024
Today - East winds 5 to 10 kt becoming northeast 10 to 15 kt. Mostly cloudy in the morning then clearing. Waves 1 to 2 ft. Tonight - East winds 10 to 15 kt becoming southeast overnight. Mostly clear in the evening, then becoming mostly cloudy. Waves 1 to 3 ft. Tuesday - Southeast winds 10 to 20 kt becoming south in the afternoon. Showers and Thunderstorms in the morning, then chance of showers and Thunderstorms in the afternoon. Waves 2 to 4 ft.Tuesday night - Southwest winds 10 to 15 kt. Mostly clear. Waves 1 to 3 ft subsiding to around 1 ft.

LMZ700
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FXUS63 KLOT 061123 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 623 AM CDT Mon May 6 2024

KEY MESSAGES

- Thunderstorms likely Tuesday morning, with at least scattered redevelopment in the afternoon especially across east and southeast portions of the forecast area. Severe weather threat will exist with afternoon storms.

- Potential of severe thunderstorms across our southern CWA into central Illinois Wednesday afternoon and evening.

DISCUSSION
Issued at 336 AM CDT Mon May 6 2024

Through Tuesday:

Mainly dry and quiet weather conditions are expected through this evening, as surface high pressure drifts slowly east across the Great Lakes region. The only exception to this will be across our far southern counties, where a few scattered shower may affect areas south of about a Pontiac to Rensselaer line in association with a mid-level short wave tracking across the lower Ohio Valley and downstate IL/IN. Weak mid-level lapse rates (5-5.5 C/km) should provide little or no lightning threat.
Otherwise, morning high clouds will move off to the east, making for mostly sunny skies across the north and partly to mostly cloudy conditions south later this morning and afternoon.
East-southeasterly winds 10-15 mph will maintain lake-cooling along the Illinois shore of Lake Michigan, where temperatures will only top out in the lower 60s, while areas farther west and south of the lake should moderate into the mid-70s in most locations.

Benign weather continues into this evening, before attention turns to increasing shower and thunderstorm chances which will ramp up from the west in the pre-dawn hours of early Tuesday morning. An organized extensive north-south area of thunderstorms is expected to be ongoing across the Plains this evening, along a cold front trailing from an area of deep surface low pressure over the northern Plains. This front is expected to push east toward the Mississippi River through Tuesday morning, as a stout mid-level short wave trough lifts northeast into the mid/upper Mississippi Valley. Various CAM guidance and HRRR ensembles depict the Plains linear thunderstorm complex spreading east ahead of the front, reaching the WFO LOT forecast area pre-dawn Tuesday morning and reaching the Chicago metro area just after sunrise. While severe weather is expected well west/southwest of the area overnight, indications (HRRR calibrated severe probs, forecast soundings indicated elevated inflow bases) are that the primary severe threat area will remain well west/southwest of the cwa through Tuesday morning. However, sub- severe hail and wind gusts will be possible with the stronger cores here. Current CAM/HRRR guidance suggests storms will be largely through our IL counties by mid-morning and our northwest IN area prior to noon, though some scattered redevelopment appears possible on the trailing flank of the complex due to a southwesterly 35-40 kt low level jet.

Convective redevelopment and coverage then becomes less clear during the midday and afternoon hours on Tuesday. Both the footprint of the morning cold pool and the eastward movement of the now-occluding cold/warm fronts across the area will likely have an impact on if/where redevelopment occurs through the remainder of the day. Current high-res guidance indicates that the better low-level moisture and instability will be increasingly focused across the far east/southeast parts of the forecast area (and into IWX, IND and ILX's areas) during the afternoon, with shallower boundary layer moisture and mid-level drying (and likely clearing) farther to the west. That said, the area will remain beneath a favorable diffluent exit region of the upper jet, with steepening mid-level lapse rates associated with cooling provided by the mid-level trough axis and strong mid (40-50 kts) and upper level (70+ kts) flow providing substantial, mainly unidirectional deep-layer shear. HRRR/HRRR develop 1000-1500+ J/kg MLCAPEs during the afternoon (highest generally from the south Chicago burbs south and southeast), potentially supporting robust updrafts and a severe weather threat. Forecast hodographs are generally long and straight given the unidirectional wind/shear profiles, with wind/hail the primary severe threats. However, there would also be a non-zero tornado threat where boundary interactions or bowing segments might alter the low-level shear profiles. SPC has adjusted their day 2 outlook to pull the slight risk a little farther into our southeast cwa with a marginal risk for the remainder, and this looks appropriate.

Ratzer

Tuesday Night through Sunday:

While deep-layer drying behind Tuesday's rounds of potential convection is expected to greatly limit or end precip potential by Tuesday evening, a trailing mid-level wave along with steep mid-level lapse rates could result in a couple widely isolated showers or storms across the northern CWA through mid evening.
Otherwise, dry conditions amid mid-level ridging is expected across the area Tuesday night into Wednesday morning.

A mid-level low digging across the central Great Plains on Wednesday in conjunction with a departing right entrance of an upper jet streak and associated enhanced low-level flow will support another period of convection across the Ohio Valley Wednesday afternoon and evening. Robust low-level moisture advection ahead of an elongated and partly occluded surface low from western Iowa into central Illinois will result in a warm front nearing or possibly shifting northward into the southern CWA by late afternoon. Around and south of the warm front, ample instability and impressive shear profiles support discrete supercell structures capable of all severe hazards. We will need to closely monitor trends in our southern CWA over the next couple days given the proximity of the warm front and triple point and diurnally favorable time of the day.

Beyond Wednesday evening, a mid-level trough extending southwest across Quebec and southern Ontario will begin to phase with Wednesday's low. While some differences in guidance remain with regards to the exact degree of phasing and timing of trough and low, scattered showers and perhaps some diurnally driven thunderstorms are favored on Thursday. 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. Like Thursday, scattered diurnally-enhanced showers and a few storms appear likely on Saturday. Diverging solutions with regards to the residence time of the upper-low over the region next weekend may support a continuation of showers on Sunday.

Kluber

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/
Issued at 623 AM CDT Mon May 6 2024

Key Aviation Messages: - Line of TSRA with potentially gusty winds in the 12-15Z window Tuesday.

VFR conditions with winds between ENE and SE around 10 knots are expected through at least late tonight. Shortly after sunrise Tuesday, a line of TSRA with potentially gusty winds will cross northern Illinois. Confidence is high enough to include TEMPO TSRA from 12-15Z at ORD/MDW. While the TS will move quickly across the area and affect a given location for only two hours or less (favoring 13-15Z for ORD/MDW), a slightly longer TEMPO period was included for the potential of faster storms. After the initial TS period, isolated -SHRA may persist through late morning before another period of isolated to scattered strong TSRA just beyond the end of the TAF period (18Z).

Kluber

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

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