Sunrise 5:12 AM   Sunset 8:29 PM Moonrise 12:15 PM   Moonset 12:54 AM

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LMZ741 Expires:202406140915;;977817 Fzus53 Klot 140238 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 938 pm cdt Thu jun 13 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>742-140915- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 938 pm cdt Thu jun 13 2024
Rest of tonight - Southeast winds 5 to 10 kt becoming northwest overnight and north late. Isolated showers and Thunderstorms late in the evening. Waves around 1 ft. Friday - North winds around 10 kt increasing 15 to 20 kt in the afternoon. Sunny. Waves around 1 ft building to 1 to 3 ft.Friday night - North winds 10 to 20 kt becoming northeast overnight. Mostly clear. Waves 2 to 4 ft. Saturday - East winds 10 to 15 kt. Partly cloudy in the morning, then becoming mostly cloudy. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 132345 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 645 PM CDT Thu Jun 13 2024

KEY MESSAGES

- Several rounds of severe thunderstorms are possible are likely this afternoon and evening, especially along and south of I-80.

- Hot and humid conditions early next week.

- Periodic chances for showers and storms next week as well.

UPDATE
Issued at 555 PM CDT Thu Jun 13 2024

The initial round of convection that developed across the south half of the Chicago metro earlier this afternoon has sagged southeast across the Kankakee River Valley. These storms continue to feed into an increasingly narrow corridor of higher MLCAPE as low-level moisture profiles become less favorable with southeast extent. With low-level flow and deep-layer shear vectors also becoming generally parallel to existing low-level confluent axes, expectations are that thunderstorms will maintain pulse-like characteristics. The strongest cores may produce large hail, while an antecedent DCAPE reservoir supports the potential for damaging wind.

Eyes then turn to a cluster of impressive severe storm cores around the IL/IA/MO tri-state region and its downstream evolution toward the southern CWA in the next few hours. By the time any upscale MCS growth occurs in the vicinity of the southern CWA, the southward-moving cold front (analyzed almost just north of and parallel to I-80 as of 5pm) will have shifted south to roughly a Pontiac to Rensselaer line. The downstream environment into our area will remain favorable for maintenance of strong to severe storm clusters with primarily damaging wind swaths in the 8-11pm window.

Also of note is a west to east axis of 800-650 hPa moisture across northern Iowa ahead of the main broad mid-level trough.
Marginal mid-level lapse rates to around 6.5C/km could support some a corridor of isolated to scattered showers and storms south of I-88 and especially into the IL/Kankakee River Valleys from 9pm-midnight. Steep lapse rates below the LPL/cloud base could support gusty sub-severe winds with any more formidable cores.

Kluber

DISCUSSION
Issued at 236 PM CDT Thu Jun 13 2024

Through Friday Night:

Recent satellite imagery depicts an axis of agitated cumulus clouds extending from waukegan to Davenport within a broad zone of low-level confluence across the Lower Great Lakes. Lingering capping has thus far kept a lid on early attempts for sustained convection. However, continued surface heating (temperatures rising toward 90F), low-level moistening/pooling via southwesterly flow and evapotranspiration (dew points rising toward 70F), and mid-level cooling/moistening via evaporation of convective turrets into the base of the cap should eventually win the battle and lead to explosive thunderstorm development within the next few hours. Extrapolating the position of the axis of agitated cumulus clouds, such explosive development is poised to occur between the I-88 and I-80 corridor sometime between 2 and 4 PM. With MLCAPE >2500 J/kg (including some 1000 J/kg in the hail growth layer) and convective-layer shear >45kt (largely focused from 2-6 km), sustained thunderstorms will be poised to become supercells with a threat for destructive hail locally greater than 2" in diameter through the afternoon. With time, clustering of cells may lead to an increasing damaging wind threat including localized gusts as high as 75 mph.
Coverage of thunderstorms this afternoon remains an item of lower than average confidence, with anything from just an isolated cell or two to literally an entire line of supercells plausible.

Meanwhile, a second area of explosive thunderstorm development is expected in southern Iowa this afternoon near an area of focused low-level convergence along a cold front (e.g. the Level 3/5 threat area in the SPC outlook). Upscale growth into one or more clusters appears plausible as they move east-southeastward into western and central Illinois this evening. If coverage of thunderstorms this afternoon is relatively sparse, incoming convection from Iowa may provide a "round 2" of sorts along and south of I-80 where the receiver of MLCAPE >2500 J/kg remains.
Similar to this afternoon, any storm this evening will carry a threat for destructive hail >2" and, if clusters can become established, winds >75 mph. Moreover, if a west-to-east axis of thunderstorms were to materialize within a mesoscale zone, PWATS >2" would certainly support efficient downpours with a threat for localized flash flooding. The WPC threat level 2/5 area for flash flooding highlights the area well. In all, "round 2" may occur from 7 PM to as late as 3 AM.

Tomorrow will be decidedly quiet with seasonable temperatures (highs in the low to mid 80s) and a northwesterly breeze. A lake breeze should surge inland during the afternoon leading to cooling temperatures along the lakeshore.

Borchardt

Saturday and beyond:

An upper-level ridge is expected to begin to drift into the southern CONUS on Saturday which will continue to support dry conditions. While winds will begin to turn southerly on Saturday, the strongest warm advection is expected to be west of our area which will likely keep temperatures near more seasonable readings in the low to mid- 80s. Though, a lake breeze is forecast to develop and keep highs in the 70s near Lake Michigan, particularly the IL lakeshore.

Heading into Sunday, the aforementioned ridge is forecast to shift into the Mid-Atlantic region as a large upper-level trough establishes over the northwest CONUS. As this occurs southwest flow is expected to develop and advect in warmer and much more humid air. While guidance remains in decent agreement on the upper-level pattern, there continues to be uncertainty on how far east the ridge will drift on Sunday into the early part of next week. Therefore, the exact magnitude of heat remains a bit of a question mark. Regardless, there continues to be a strong signal (around 70-80% chance) for highs Sunday through at least Tuesday to be within the low to mid-90 range with the potential for readings to overperform, especially on Monday. Couple these temperatures with the forecasted increase in humidity (dew points in the mid to upper 60s to near 70) and there is a growing threat for heat indices to top out in the upper 90s to near 100 degrees early next week.

Depending on where exactly the aforementioned ridge sets up will also dictate whether or not the troughing over the western CONUS will be able to eject shortwaves into northern IL and generate periods scattered showers and thunderstorms. Given the previously mentioned uncertainty in the ridge position, the confidence on whether or not we will see any storms remains on the lower side. That said, any days that do see showers and storms may also see highs verify cooler than forecast which would in turn lower the threat for heat related concerns. To encompass this potential in the forecast I have maintained a 20% chance for showers and thunderstorms for most of the area Sunday through the middle of next week, but specifics on timing and coverage will likely need to be adjusted with future forecasts. Though, latest guidance is eyeballing the late Saturday night into Sunday timeframe as a favored period for showers and storms.

As for when this period of heat and humidity will break, guidance continues to hint at a cold front moving towards the region towards the later portion of next week. However, timing on when exactly the front, and associated relief, will move through continues to vary amongst the guidance. Couple this with the fact that guidance typically struggles with blocking patterns and confidence to say when a break in the heat will occur remains low at this time. Therefore, we recommend keeping updated on the forecast as we head into next week for any changes.

Yack

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/
Issued at 645 PM CDT Thu Jun 13 2024

Forecast concerns for the terminals...

- Scattered showers and thunderstorms this evening, mainly south of I-80

- Lake breeze to move through the Chicago terminals Friday afternoon

A cluster of thunderstorms continues to propagate southeastward across portions of northwest IN with another strong to severe storm cluster advancing across western IL. These storm clusters are expected to remain south of I-80 (roughly a VPZ to VYS line)
before gradually tapering after midnight, but could still pose a threat for gusty winds and large hail in this area. As for the terminals, mostly dry conditions are expected for this evening but there is an area of showers (and occasional lightning) in northern IA that may brush the Chicago terminals between 03z and 06z. While confidence on these showers/storms actually reaching the terminals is low, I have decided to introduce a TEMPO at ORD, MDW, DPA, and GYY for this potential regardless.

Any showers/storms this evening will come to an end at the terminals by 06z leaving dry and VFR conditions for the rest of the forecast period. Winds will generally maintain a northwesterly direction through the night, but may become variable (between 350 and 010) at the Chicago terminals Friday morning. Though speeds should remain light with values generally under 5 kts. A lake breeze is expected to develop and surge through the Chicago terminals Friday afternoon (between 18z and 20z) which will fully turn the winds northeasterly and increase the speeds to around 10 kts before winds ease Friday evening.

Yack

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

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