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ARLINGTON HEIGHTS WEATHER

NWS Forecast for O'Hare International Airport Chicago, IL Last Update: 7:42 am CDT Oct 12, 2024

Hazardous Weather Outlook

Saturday: Scattered showers and thunderstorms after 4pm. Mostly sunny, with a high near 66. East northeast wind around 10 mph, with gusts as high as 20 mph. Chance of precipitation is 40%.

Saturday Night: Scattered showers and thunderstorms before 1am. Mostly cloudy, with a low around 55. North northeast wind 5 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 50%.

Sunday: A 30 percent chance of showers, mainly between 1pm and 4pm. Partly sunny, with a high near 64. North wind 5 to 15 mph becoming west northwest in the afternoon. Winds could gust as high as 30 mph.

Sunday Night: A slight chance of showers before 7pm, then a slight chance of showers after 1am. Mostly cloudy, with a low around 44. Breezy, with a north northwest wind 15 to 20 mph, with gusts as high as 35 mph. Chance of precipitation is 20%. Columbus Day: A 30 percent chance of showers after 1pm. Mostly sunny, with a high near 57. North northwest wind 10 to 15 mph, with gusts as high as 25 mph.

Monday Night: A 50 percent chance of showers. Mostly cloudy, with a low around 39.

Tuesday: A 30 percent chance of showers before 1pm. Mostly sunny, with a high near 54.

Tuesday Night: Mostly clear, with a low around 37.

Wednesday: Areas of frost before 8am. Otherwise, sunny, with a high near 59.

Wednesday Night: Clear, with a low around 41.

Thursday: Sunny, with a high near 68.

Thursday Night: Mostly clear, with a low around 48.

Friday: Sunny, with a high near 71.



Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
424 AM CDT Sat Oct 12 2024


Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
424 AM CDT Sat Oct 12 2024 /524 AM EDT Sat Oct 12 2024/

This Hazardous Weather Outlook is for portions of north central
Illinois...northeast Illinois and northwest Indiana.

.DAY ONE...Today and Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk.

DISCUSSION...

There is a chance for isolated thunderstorms late this afternoon
through the evening mainly northeast of a Rockford, IL to
Rensselaer, IN line.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Monday, Tuesday, and Wednesday nights...
  Elevated Frost Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation will not be necessary through tonight.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east at 30 mph.

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
651 AM CDT Sat Oct 12 2024

.KEY MESSAGES...

- Scattered showers are possible late this afternoon into the   evening with a 20-30% chance of thunderstorms.

- A notable cool-down arrives on Sunday with the potential for   nightly frost and localized freeze conditions through   midweek.

- Lake effect showers are expected downwind of Lake Michigan   late Sunday through Tuesday.

&&

.DISCUSSION... Issued at 340 AM CDT Sat Oct 12 2024

Through Sunday:

As a cold front continues to move south through the forecast area, winds behind it have turned to the northeast with gusts between 20 to 25 mph. Winds should slowly diminish with only sporadic gusts leading into daybreak. As the aforementioned surface front stalls around I-80, cold air advection and northerly flow will help limit temperatures north of the boundary to around more seasonable 60s and low 70s. Whereas the southern part of the forecast area still has a chance for warmer conditions in the upper 70s and low 80s. With dry low- levels still in place, no rain is expected through around lunch time. Higher res guidance still shows a weak mid level wave transiting overhead late this morning/early afternoon. Dry conditions are still expected, but did add some "silent PoPs" (10 to 14 percent chance) for the low probability of maybe a sprinkle or two ahead of the next system.

Later today, a short wave is expected to dig down the broader long wave trough aloft centered over Quebec. As the baroclinic zone along the previous stalled front tightens, scattered showers are expected to develop to its north during the afternoon and into the evening. While better lapse rates aloft will likely be featured to the south of the front coinciding with the warm advective wing, model soundings suggest an axis of instability extends along and ahead of the front providing support for elevated thunderstorms. The one lingering bit of uncertainty will be the amount of moisture available. Increased mid level moisture is expected to advect over the area this afternoon and evening, but models have been struggling with the amount. Not only does that impact the "will it/won`t it" rain/thunder question, but also how much rain falls. There remain some ensemble members that have isolated higher amounts, and if there is enough moisture present perhaps some minor training could occur. However, confidence in that scenario playing out is low and most areas are unlikely to receive significant rainfall. PoPs will steadily diminish into Sunday morning. Temperatures in the city of Chicago are expected to be in the upper 50s for a low temperature. With subsiding winds and potentially drier conditions, it is not looking like a bad way to start the day for early morning outdoor activities. Though the chance for increasing winds and shower chances return by midday.

A more robust shortwave with a 120+ knot jet core will slowly move towards the region on Sunday. A cooler air mass will continue to move south over the forecast area with high temperatures on Sunday in the 60s (warmer to the south, cooler to the north). As the pressure gradient strengthens through the day, northwest wind gusts will increase out of the northwest in the afternoon to 25 to 30 mph. With lingering moisture present, there is a (20 to 30 percent) chance for some pop-up showers in the afternoon. While much of the forecast area will probably remain dry, the better chances will be closer to Lake Michigan. Those shower chances become more focused over northwest Indiana Sunday as night, as mentioned in the discussion below.

DK

 Sunday Night through Friday:

A vigorous upper-level wave and closed upper low will continue to dig across the broader Great Lakes Region late Sunday. This will usher in a multi-day stretch of below normal temperatures. Strong northwesterly winds are forecast to continue well after sunset in the wake of an associated surface trough axis/reinforcing cold front. While the official wind gust forecast is closer to 25-30 mph, gusts in excess of 30-35 mph can`t be ruled out if the low-level pressure gradient ends u Pbeing stronger. In fact, wind chills are forecast to dip into the 30s Sunday night into early Monday morning.

We continue to head toward needing Frost/Freeze related headlines sometime during the Monday night-Wednesday night period. At this time, Tuesday night has the best potential (~30-50% chance) to see sub-freezing temperatures outside of the urban core of the Chicago metro and away from the lakeshore/lake effect clouds. It`s still too far out for a potential Freeze Watch with some lingering questions on overnight wind speeds and potential cloud cover influences. Nevertheless, those with sensitive plants should plan to cover or bring them indoors during this period.

In addition to the cooler temperatures, a favorable pattern for a long duration lake effect shower event will exist periodically Sunday night through Tuesday. Modeled equilibrium levels exceed 15-25 kft at times as continued shots of cold low-mid level air steep lapse rates over a warm lake. Deep saturation (and a narrow unstable layer) extends well into the -10 to -20C layer, suggesting there is some potential for enough charge separation for lightning as well (particularly Monday night into early Tuesday morning). The initial band of lake effect showers will extend mainly into portions of Northwest Indiana and southwest Michigan. However, as another mid-level wave rounds the closed upper low late Monday into Tuesday morning, this band may drift back to the west into northeast Illinois. In fact, the wave itself could support scattered showers further inland across the area.

Ensemble guidance continues to suggest a return to near to even above normal temperatures late week as upper ridging builds back across the region in the wake of the departing eastern CONUS upper level trough/closed low.

Petr

&&

.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/... Issued at 650 AM CDT Sat Oct 12 2024

* Potential for SHRA late this afternoon through the evening   (30% chance for TS) * MVFR ceilings develop overnight

East to northeast winds are expected today generally in the 10-15 kt range with occasional gusts up to around 20 kt.

There remains a signal for a narrow axis of SHRA developing over portions of the area late this afternoon through the evening hours. However, there continues to be lower confidence on the timing and placement of this axis. SHRA could develop as early as mid-late afternoon and is accounted for with PROB30 groups for SHRA in the 22-0Z period. After 00Z, an axis of elevated instability supports maintaining a PROB30 group for TSRA between 0-4Z. This has been kept out of RFD/GYY for now due to recent hi-res guidance trends placing the band slightly further north and east.

In the wake of any potential SHRA/TS, a period of MVFR (to potentially near IFR) stratus appears likely overnight. Expect winds to return to a northwesterly direction early Sunday morning with the stratus scattering out after daybreak.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT this evening for the IL
     nearshore waters.

     Small Craft Advisory until 10 AM CDT this morning for the IN
     nearshore waters.

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