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LMZ741 Expires:202312082245;;116033 Fzus53 Klot 081517 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 917 am cst Fri dec 8 2023
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>742-082245- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 917 am cst Fri dec 8 2023
.small craft advisory in effect until 3 pm cst this afternoon...
Rest of today..South winds 20 to 30 kt diminishing to 15 to 20 kt. Partly cloudy. Waves 2 to 4 ft subsiding to 1 to 3 ft.
Tonight..South winds 10 to 20 kt. Chance of rain in the evening, then rain overnight. Waves 1 to 2 ft building to 2 to 4 ft.
Saturday..Southwest winds 15 to 25 kt becoming west. Chance of rain in the morning. Waves 2 to 4 ft.
Saturday night..West winds 10 to 15 kt becoming northwest. Mostly cloudy. Waves 1 to 3 ft.

LMZ700
No data

FXUS63 KLOT 081811 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1211 PM CST Fri Dec 8 2023

SHORT TERM
Issued at 255 AM CST Fri Dec 8 2023

Through Saturday...

Key Messages:

* Unseasonably mild today with high temperatures in the mid-upper 50s

* Gusty showers expected overnight into Saturday AM, may be preceded by period of drizzle this evening.

Early this morning a negatively tilted shortwave is located over the northern Plains along the US-Canadian border with the broader trough axis and southern vort max moving across the Rockies. Mid- level ridging across the eastern CONUS places us in a warm advective regime with persistent southwesterly flow. This has held overnight low temperatures in the 40s across the area (5-10 degrees above the 30-yr normal for highs!) With a 45-50 kt LLJ overhead, at least sporadically gusty winds have been able to reach the surface with peak gusts in the 20-30 mph range. This will continue through the morning hours. Temperatures should easily warm into the 50s today. Just how warm we get will likely be tied to the timing of increased coverage of low stratus (currently trying to develop across west central Illinois). If cloud cover is slower to fill in then a few spots may manage to reach 60.

The aforementioned southern wave/vort max will translate east across the Central Plains toward the area today and will be responsible for our next round of precipitation. While earlier in the week there were precipitation type concerns as well as the potential for severe weather. Latest guidance continues to be warm enough for precipitation to remain all rain. Additionally, instability continues to look rather meager (<100 J/Kg) though a few lightning strikes can't be ruled out (10% chance). A weak surface low will develop along the frontal boundary and lift across the area. Placement of the highest precipitation amounts (QPF) exists generally north of I-55 (0.20-0.40) closest to the center of the associated surface low with lighter amounts south along the trailing front.

There remain timing differences on the order of a few hours with how quickly showers then lift across the area, with HRRR/RAP arriving the earliest along/west of I-39 (by 12-3am) versus a slower ECMWF/NSSL-WRF (by 3-6am). The official forecast is a bit of a blend of the two. Regardless of the exact timing, what is more certain is that winds will become increasingly gusty again out of the southwest (south of the low), potentially in the 30-40 mph range overnight into early Saturday morning, currently favored in areas along/southeast of I-55. Precipitation ends from west to east during the morning hours after daybreak along with an easing of the highest gusts.

In the wake of front winds turn westerly, with temperatures stalling out in the 40s NW to lower 50s SE during the day as cold advection generally equals out the rate of diurnal warming.

Petr

LONG TERM
Issued at 255 AM CST Fri Dec 8 2023

Saturday night through Thursday...

Key Messages:

- Low impact lake effect snow showers in NW Indiana on Sunday - Dry conditions region-wide most of the upcoming week - Seasonally cool start to the week, above normal temperatures mid to late week

A trailing northern stream upper trough will send a secondary cold front across the lower Great Lakes Saturday night. The bulk of the precipitation will split the region, mainly remaining both north and south of the local area. However, with a slightly colder air mass and a favorable low level flow direction out of the northwest, some lake effect precipitation may be in the offing. A perusal of forecast soundings indicate that moisture depths and equilibrium levels are not all that impressive. Boundary layer temperatures are also marginal for accumulations as well, and the bulk of the forcing is below the main snow production region. At this time areas east of Porter County would be favored. NBM probabilities of accumulation are limited to 20% in eastern Porter County, and with surface temperatures above freezing, impacts would be limited.

More seasonal conditions will return for early next week behind this front, and this will be reinforced one final cold frontal passage on Tuesday. This front will pass through dry thanks to sprawling high pressure that will set up from the central Plains, across the Ohio Valley and to the eastern seaboard. This feature will remain anchored in place for most of the upcoming week.
Southwest flow aloft will set up ahead of developing low pressure across the southwest. The result for the Midwest will be dry and mild conditions through the latter portion of the week.

KMD

CLIMATE

Issued at 255 AM CST Fri Dec 8 2023

Unseasonably mild temperatures are expected through early Saturday. While record high temperatures appear safe, a record warmest low is likely at Rockford today. The record high temperatures for the calendar day, December 8th are:

Rockford...
Friday, December 8th.....60 in 1980

Chicago...
Friday, December 8th.....64 in 1946

The record warmest low temperatures for the calendar day, December 8th are:

Rockford...37 in 1987

Chicago....53 in 1946

AVIATION
For the 18Z TAFs...

Key Aviation Concerns: - Increasing coverage of MVFR ceilings by early evening lowering into IFR levels late tonight.
- RA/DZ transitioning to SHRA tonight.
- Increasing south winds overnight, with a period of 30 knots gusts (possibly higher) 09-13Z Saturday.

A strengthening low pressure system over Oklahoma this afternoon will track to just northwest of the Chicago metro late tonight.
Increasing low-level moisture and weak warm-air advection this afternoon will begin to promote the development of MVFR ceilings before ceilings gradually lower into low-end MVFR levels with- RA/DZ late this evening into the early overnight hours. A band of -SHRA with IFR ceilings is then expected to cross the area late tonight ahead of a cold front. -SHRA will diminish through the morning Saturday while MVFR ceilings likely persist through the day.

SSW/SW winds gusting over 25 knots early this afternoon will diminish into early evening, settling S/SSW around 10 knots by 00Z. The northwest fringe of a developing 50 knot LLJ will bring increasing S winds late this evening and especially overnight.
Gusts to 25 knots will back just east of south (170 degrees) late this evening before shifting back west of south (190 degrees) and increasing with gusts to around 30 knots in the 09-13Z window.
While some low-level stability at a diurnally unfavorable period for mixing will likely limit the upper potential for gusts, some sporadic gusts to 35 knots will be possible. Winds will then veer WSW/W behind the front (around 12-13Z for ORD/MDW) with gusts to around 25 knots through the day Saturday.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM
Small Craft Advisory
IL and IN nearshore waters until 3 PM Friday.

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