Sunrise 6:02 AM   Sunset 7:42 PM Moonrise 4:40 PM   Moonset 4:49 AM

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LMZ740 Winthrop Harbor To Wilmette Harbor Il- Wilmette Harbor To Northerly Island Il- Northerly Island To Calumet Harbor Il- Calumet Harbor Il To Gary In- 322 Am Cdt Sat Apr 20 2024
Today - West winds 15 to 25 kt becoming northwest 10 to 20 kt this afternoon. Mostly Sunny this morning, then becoming mostly cloudy. Waves 3 to 5 ft subsiding to 2 to 4 ft. Tonight - West winds 10 to 15 kt. Mostly cloudy in the evening then clearing. Waves 1 to 3 ft. Sunday - West winds 10 to 15 kt. Sunny. Waves 1 to 2 ft. Sunday night - West winds 10 to 15 kt. Clear. Waves 1 to 2 ft.

LMZ700
No data

FXUS63 KLOT 200701 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 201 AM CDT Sat Apr 20 2024

KEY MESSAGES

- Areas of frost late tonight/early Sunday morning away from Chicago.

- Next rain/shower chances Monday night through Tuesday.

- Another period of inclement weather with periods of showers and storms possible towards the end of next week into the weekend.

DISCUSSION
Issued at 201 AM CDT Sat Apr 20 2024

Through Sunday:

Temperatures are slowly dropping into the mid 30s across northwest IL early this morning and with dewpoints in the 20s, its possible some locations will see lows near freezing across these areas, along/west of the Fox Valley and north of I-80.
Winds are expected to remain in the 10 mph range which should limit any frost formation early this morning.

While this morning will start sunny, clouds will be on the increase through mid/late morning with mostly cloudy skies expected this afternoon into this evening. This cloud cover may keep temps down a few degrees than previously expected and now have highs generally in the upper 40s north to lower 50s south.
If the cloud cover arrives faster, limiting the amount of sun and warming, these temps may still be a few degrees too warm.
Northwest winds will also be gusting into the mid 20 mph range.

There have been some flurries and sprinkles with this cloud cover across the upper midwest early this morning and its possible there could be a few sprinkles here later this afternoon into the early evening but confidence is too low for any mention at this time.

This cloud cover is expected to move out of the area tonight, which will allow for clearing skies and light winds, setting up good radiational cooling with low temps likely in the lower 30s across the northwest cwa and mid 30s elsewhere. Frost may become widespread across the northwest cwa by Sunday morning, while temps remain near or perhaps a degree or two below freezing. Its possible that if the clouds do clear, a frost advisory may be needed vs. a freeze warning. And because of this potential, have decided not to go with a freeze watch for tonight/early Sunday morning. Temps look to rebound back to near 60 for highs Sunday under mostly sunny skies. cms

Sunday Night through Friday:

High pressure will shift across the ArkLaTex on Sunday night which will start the process of turning winds out of the southwest. It looks like winds will remain sufficiently decoupled to allow temperatures to fall into the mid 30s with another round of frost development for areas outside of Chicago.

The pressure gradient will tighten up on Monday with increasing high-level cloud cover through the afternoon in advance of the next approaching disturbance. With the increased surface gradient, southwesterly winds look to gust towards 30 mph during the afternoon. Given the state of fine fuels (both the Indiana Dunes and Midewin RAWS sites indicated 9 percent fine fuel moisture on Friday), with afternoon RH values expected to fall towards 30 to 35 percent, Monday looks like it may be another day with an elevated fire danger.

Precipitation chances will increase Monday evening as low-level warm advection ramps up in advance of a notably divergent and compact upper jet streak. It doesn't look like there will be much in the way of instability with this initial batch of forcing, with this initial batch of precip in the form of scattered showers. The core of the main vort max and attendant mid-level height falls (80 to 100 m/12 hours) will then spread overhead through Tuesday afternoon ahead of an incoming cold front. The GFS continues to depict deeply-mixed soundings during a brief window during the early afternoon with sufficiently deep/cold equilibrium levels to support showers and even a few thunderstorms. While notably more subdued, the latest ECMWF also generates just enough surface-based instability to justify a mention of isolated thunder into the evening.

Precipitation chances will diminish Tuesday evening as the main trough axis shifts to the east. Breezy northerly winds will push another cooler airmass into the region, with highs on Wednesday likely not getting out of the mid to upper 40s near the lake.
Winds may also slacken sufficiently Wednesday night for another round of frost development outside of Chicago. Temperatures will then warm back into the 60s through the end of the week, although lakeside locales across NE Illinois will likely remain in the upper 40s and 50s with persistent southeasterly winds. Intermittent shower and thunderstorm chances will return towards Friday and through the weekend.

Carlaw

AVIATION /06Z TAFS THROUGH 12Z SUNDAY/
Issued at 1139 PM CDT Fri Apr 19 2024

There are no major aviation weather concerns. Intermittently gusty NW winds will continue tonight, with breezes lingering through the day on Saturday. BKN to at times OVC VFR cloud cover (bases around 4-5 kft) will develop through the morning and afternoon before diminishing during the evening, along with any lingering gusts.

Carlaw

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

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