Sunrise 6:01 AM   Sunset 7:37 PM Moonrise 3:36 PM   Moonset 4:27 AM

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LMZ741 Expires:202404200315;;041590 Fzus53 Klot 200000 Nshlot
nearshore marine forecast national weather service chicago/romeoville il 700 pm cdt Fri apr 19 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>742-200315- winthrop harbor to wilmette harbor il- wilmette harbor to northerly island il- northerly island to calumet harbor il- 700 pm cdt Fri apr 19 2024
.small craft advisory in effect until 10 pm cdt this evening - .
Tonight - West winds 20 to 25 kt diminishing to 15 to 25 kt late in the evening. Partly cloudy. Waves 2 to 4 ft.Saturday - Northwest winds 15 to 25 kt diminishing to 10 to 20 kt. Mostly Sunny in the morning, then becoming partly cloudy. Waves 1 to 3 ft. Saturday night - Northwest winds 10 to 15 kt becoming west. Mostly cloudy in the evening then clearing. Waves 1 to 2 ft. Sunday - West winds 10 to 15 kt. Sunny. Waves 1 to 2 ft.

LMZ700
No data

FXUS63 KLOT 192338 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 638 PM CDT Fri Apr 19 2024

KEY MESSAGES

- Gusty west winds 35-40 mph persist this afternoon.

- Potential for patchy frost/temperatures briefly near freezing toward sunrise across northwest Illinois. Freezing temperatures more likely Sunday morning for the same area.

- Next chance for rain Monday night through Tuesday

- Another period of inclement weather possible towards the end of next week

DISCUSSION
Issued at 318 PM CDT Fri Apr 19 2024

Through Saturday Night:

Deep upper level low pressure was evident in water vapor imagery across Ontario this afternoon, with a fast westerly 125+ kt upper level jet streak along the southern periphery of the low across the upper Midwest. At the surface, low pressure was stacked beneath the upper low to our north, while a ridge of high pressure extended from Montana to the lower Missouri and Ohio river valleys. Within the gradient north of the ridge axis, strong west to west-northwest flow was in place across the forecast area, with otherwise dry but cool conditions across the region. The surface ridge is forecast to eventually drift eastward Saturday and Saturday night, allowing winds to gradually ease with time.

In the near term, surface dew points in the 25-30F range were producing relative humidities in the 30-35 percent range in spots this afternoon, and may go a little lower still through mid-afternoon. Combined with winds gusting as high as 35-40 mph at times, this will continue to produce a somewhat elevated fire danger through sunset. The cool, dry airmass will also support temperatures lowering into the 30s across the area tonight, with some potential for dipping near the freezing mark across our northwest cwa for a brief time toward sunrise.
However, winds are expected to remain up a bit overnight within the stronger pressure gradient, and those 7-12 mph will likely prevent widespread freezing temperatures and frost formation for our cooler northwest areas. At this time, in collaboration with WFOs DVN and MKX have elected to hold off on any frost/freeze headlines for tonight but later shifts will monitor for stronger decoupling of boundary layer winds which could portend a greater freeze risk. Winds will remain breezy, with 20-25 mph gusts on Saturday, but will diminish more Saturday night with the surface ridge edging east. Frost/freeze conditions thus look to be more of an issue late Saturday night/Sunday morning.

Otherwise, a period of mid-level cloud cover is expected this evening across our southern cwa, with mainly clear conditions farther to the north. Forecast soundings suggest more of a diurnal scattered to broken stratocu deck on Saturday, before skies clear Saturday night. HRRR/RAP actually depict some light convective precip during the day Saturday, though forecast soundings suggest fairly shallow cloud layer and a stout inversion around 5 kft which argues against carrying any pops/precip mention in the forecast. Persistent low-level cold advection will result in cooler temps through Saturday, with low-mid 30s for lows tonight and highs from the upper 40s to lower 50s Saturday. As indicated above, more widespread lower-30s are possible across parts of northern IL away from the metro late Saturday night.

Ratzer

Sunday through Friday:

High pressure will remain the dominant weather feature for Sunday and most of the day on Monday allowing dry conditions to prevail. Winds are also expected to become southerly Sunday night into Monday which will allow temperatures to gradually warm towards more typical readings in the 60s. While these southerly winds will also advect in higher dew points during the day on Monday, forecast soundings do show that the atmosphere may be able to mix into the base of a stout dry layer aloft. If this is indeed the case then dew points may be slower to increase and/or possibly decrease Monday afternoon leading to lower RH values than forecast. Couple the potential for lower RH readings with the expectation for winds to be gusting around 25 mph at times and there could be the potential for heightened fire weather concerns during this period.

Our next opportunity for rain is expected to arrive Monday night through Tuesday as a shortwave trough pivots through the Great Lakes. Guidance has started to indicate that there could actually be two periods of showers, one initially with the warm advection ahead of the trough Monday night and the second with a cold front Tuesday afternoon. While the impacts are nearly identical with each round, there is the potential for some thunderstorms Tuesday afternoon if sufficient instability can materialize. However, low-level moisture does look to be somewhat limited Tuesday afternoon which may limit the coverage of thunder. Therefore, have decided to introduce an isolated (around 20% chance) mention for now.

As the cold front exits into Indiana Tuesday night, showers and any storms will come to an end as mid-level ridging begins to build into the central CONUS. While this will allow for a period of dry weather for the middle of the week, it will also generate a period of slightly cooler temperatures (highs in the 50s) as colder air filters in behind the aforementioned front.
Unfortunately, the dry weather looks to be short lived as guidance continues to show a series of troughs developing across the western CONUS and ejecting towards the Great Lakes towards the end of next week into next weekend. Obviously there is still some uncertainties in exact timing and specifics, but it does look as if we are in for another period of inclement weather.

Yack

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/
Issued at 635 PM CDT Fri Apr 19 2024

VFR conditions are forecast through the TAF period. Winds remain gusty out of the west northwest to around 30kt this evening. Gusts are expected to gradually ease some with sunset, though gusts in the 20-25kt range likely persist through the overnight hours. A BKN VFR strato-cumulus deck around 5000ft develops mid-late morning on Saturday with sporadic gustiness lingering into the afternoon.

Petr

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory until 7 PM CDT this evening for the IL and IN nearshore waters.

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