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ARLINGTON HEIGHTS WEATHER

NWS Forecast for O'Hare International Airport Chicago, IL Last Update: 6:57 pm CDT Oct 28, 2024

Record Warmth Possible This Week
Near record to record high temperatures are in the forecast on Tuesday October 29th. In addition, record warm low temperatures are also in jeopardy on Tuesday October 29th and Wednesday October 30th.

Monday Night:
Mostly cloudy, with a low around 61. South wind around 15 mph, with gusts as high as 25 mph.

Tuesday: Mostly sunny, with a high near 81. Breezy, with a south southwest wind 15 to 25 mph, with gusts as high as 40 mph.

Tuesday Night: Mostly cloudy, with a low around 66. Breezy, with a south southwest wind 20 to 25 mph, with gusts as high as 40 mph.

Wednesday: Partly sunny, with a high near 80. Breezy, with a south southwest wind 20 to 25 mph, with gusts as high as 40 mph.

Wednesday Night: Showers after 1am. Low around 58. Breezy, with a south wind around 20 mph, with gusts as high as 35 mph. Chance of precipitation is 90%.

Thursday: Showers and possibly a thunderstorm before 10am, then a chance of showers between 10am and 1pm. High near 67. Chance of precipitation is 90%.

Thursday Night: Partly cloudy, with a low around 40.

Friday: Sunny, with a high near 55.

Friday Night: Partly cloudy, with a low around 40.

Saturday: Mostly sunny, with a high near 61.

Saturday Night: A chance of showers. Mostly cloudy, with a low around 48.

Sunday: Showers likely. Mostly cloudy, with a high near 63.

Sunday Night: Showers. Cloudy, with a low around 53.

Monday: Showers likely. Mostly cloudy, with a high near 64.



Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
624 PM CDT Mon Oct 28 2024

.KEY MESSAGES...

- Fire Weather Watch in effect for areas along and south of I-80   Tuesday for the risk of rapid fire spread due to dry fuels,   dry air, and strong southwesterly winds.

- Near-record warmth and windy conditions Tuesday-Wednesday   (southerly gusts up to 45 mph), followed by cooler   temperatures on Halloween.

- Widespread rain/showers are expected Wednesday evening into   early Thursday, likely clearing out in time for trick or   treating.

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.DISCUSSION... Issued at 241 PM CDT Mon Oct 28 2024

Through Tuesday:

It`s a very seasonable Monday out there today with temperatures across the area sitting in the 60s beneath mostly cloudy skies. Conditions are marginally breezy as we`ve been mixing down some 20 to 25 mph gusts. A southwesterly low level jet will build atop the area this evening and into tonight with as many as 50 kt of flow being modeled at 925mb. A stout drawnly inversion should prevent us from taking full advantage of that flow, but even shallow mixing beneath the inversion should allow for at least intermittent gusts to roughly 25 to 30 mph down at the surface later this evening and overnight. Efficient warm advection will also take off with the arrival of the LLJ and keep temperatures rather stagnant in the lower 60s through the night, if not result in a one or two degree warm up prior to daybreak.

Winds will really get going during the day tomorrow after we begin to destabilize in the morning. A handful of high res models have consistently been resolving a "pop" of wind during the morning tomorrow in the brief window of time after mixing takes off and before the LLJ relaxes some for the rest of the day. During this time, a few-hour period of regular 40 to 45 mph wind gusts appear very attainable. Some disparities in mixing heights and magnitude of the low level winds make it a bit unclear where we`ll find winds during the afternoon tomorrow, but most of us are probably looking at regular 35 to 40 mph gusts during the better part of the day with occasional gusts as high as around 45 mph. Being that frequent 45+ mph gusts are not expected at this time, opted out of issuing a wind headline for tomorrow as the forecast reads just below true advisory thresholds. Gusts look to ease some tomorrow night as the boundary layer stabilizes. However, forecast soundings show notably weak static stability during the night which should make it relatively easier to tap into the stronger flow aloft. Therefore, gusts are anticipated to remain above 25 mph through the night, but could end up being closer to 30 to 35 mph, at least at times.

In other news, the aforementioned warm advection will continue through the day tomorrow with the LLJ overhead. This will put us in a place where we will be flirting with record warm temperatures. Highs for tomorrow afternoon are forecast to hit the lower 80s area- wide; 78F is the current daily record at Chicago. There is quite the spread among guidance in where dewpoints end up tomorrow afternoon, especially south and east of I-55. Best guess is that dewpoints will bottom out in the lower 50s, possibly tapping upper 40s, in our south and southeast. This would yield midday RHs in the 30 to 35 percent range across areas south of I-80. These numbers could prove lower if we trend toward some of the drier solutions. Given the strong winds and notably dry fuels to make up for the marginally "higher" RHs, decided to issue a Fire Weather Watch for tomorrow for areas along and south of I-80 for the risk of rapid fire spread. Tonight`s overnight shift will then reassess the need to upgrade any or all of the watch to a Red Flag Warning.

Doom

 Tuesday Night through Monday:

The main focus during the day on Wednesday will once again be the winds and dewpoint/relative humidity trends. Winds will likely remain gusty coming out of Tuesday night, and should quickly increase through the mid-late morning hours as mixing into the base of strong, but diurnally-weakening low-level jet ensues. The question continues to be just how deeply things mix which will effectively control how dewpoints and wind gusts trend during the afternoon. At this time, with 850-925 mb winds nearing 40 knots, suspect 40+ mph gusts are a good bet on a widespread basis, with some potential for wind advisory level gusts (45 mph+) during peak heating. Dewpoints should continue to gradually climb with the persistent/continued stout southerly flow, and with highs fairly similar or just a smidge lower than Tuesday, minimum RH values should be a tick higher. This may still lead to an elevated fire danger given the state of fuels in our region, and something we`ll be keeping a close eye on.

The broad, slow-moving longwave trough across the western CONUS will finally kick eastward Wednesday into Thursday which will result in a gradual increase in large scale forcing with mid- level height falls and increasing upper-level divergence over the region Wednesday night. While mid-level lapse rates will not be particularly steep, there are signs in recent guidance that a narrow sliver of near-surface-based instability may attempt to develop ahead of the incoming cold front late Wednesday night into Thursday morning with a narrow line of strongly-forced convection resulting along the incoming boundary. While this setup doesn`t scream severe weather with overall muted instability, unfavorable time of night, etc., the eye-popping kinematic parameter space means we`ll have to keep an eye on things, particularly if any parcels manage to remain surface based given enlarged and strongly looping hodographs.

Intense forcing interacting with the cold front will lead to the development of a widespread showers even behind the cold front (elevated above the surface), including a few embedded thunderstorms. There`s a decent signal for total rainfall amounts nearing a half inch, with localized amounts over an inch within any regions of transient f-gen/embedded thunderstorm clusters.

While some showers may persist a bit through Thursday morning, conditions look to clear out in time for trick or treaters through the afternoon and evening, with breezy conditions and temperatures dropping into the 40s. There`s some indication that winds could overperform a bit on Thursday afternoon in the cold advection push, and have nudged gusts up a bit to account for recent model trends. Thursday night will feature clearing skies, diminishing winds, and seasonably chilly 30s-40s lows as high pressure overspreads the area.

Thursday night and beyond:

On Friday, mid-level subsidence and the passage of a quickly- moving surface high pressure system will deliver sunny skies and light surface winds. With our area on the back edge of the post- frontal pocket of cool air (850mb temperatures of -1 to +1C centered over Lower Michigan Friday afternoon), afternoon high temperatures in our area will be limited to the low to mid 50s. While such temperatures will feel noticeably cooler compared to the near-record warmth earlier in the week, average high temperatures for November 1 are in the low to mid 50s.

The period of seasonable temperatures will be very short as the surface high settles to our east and deep troughing develops in the western United States this weekend. The net result will be the reestablishment of broad south to southwesterly low-level flow into the Great Lakes with associated increases in temperatures and eventually moisture. With ensemble median 850mb temperatures soring toward +10 to +12C (which is above the 90th percentile of 850mb temperatures for this time of year at both DVN and ILX per SPC sounding climatology), high temperatures may make a run toward the mid 60s Saturday and especially Sunday. The degree of cloud cover may ultimately modulate the achievement of high temperatures, so for now, will offer a conservative forecast with highs in the lower 60s both days.

This time of year, above average temperatures often comes with periods of rainfall. Indeed, even amongst vast spread in exactly how the upper-level pattern will evolve early next week, ensemble meteograms of QPF paint a clear picture that periods of rainfall will return to the general region, particularly from Sunday onward.

Carlaw/Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/... Issued at 624 PM CDT Mon Oct 28 2024

Forecast concerns include...

Strong/gusty south/southwest winds. Low level wind shear tonight.

Southeast winds will slowly turn southerly this evening and then to the south/southwest overnight. Speeds/gusts will slowly increase this evening with gusts into the mid 20kt range expected overnight. Low level winds will also steadily increase this evening with low level wind shear expected through daybreak Tuesday morning. Once the low levels begin to mix and into these strong winds aloft, surface gusts are expected to quickly increase into the mid 30kt range by mid morning. These gusts are then expected to continue through Tuesday afternoon and into Tuesday evening though there may be some fluctuations to the gusts with occasional higher gusts possible.

There is a sct/bkn low vfr deck between 3-4kft currently. This is expected to slowly shift east through the evening, though there may be brief high mvfr cigs associated with this cloud layer. cms

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.MARINE... Issued at 300 PM CDT Mon Oct 28 2024

A prolonged period of south-southwesterly gales to 40 kt are likely starting tomorrow morning and lasting through at least Wednesday evening as an elongated area of low pressure gradually shifts from the Plains into the Upper Midwest. The strongest gales, which may exceed 40 kt at times, are expected closest to the Illinois and Indiana shorelines of Lake Michigan. A Small Craft Advisory remains in effect through tonight, before a Gale Warning goes into effect tomorrow morning.

Borchardt/Doom

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.FIRE WEATHER... Issued at 300 PM CDT Mon Oct 28 2024

The combination of strong winds, dry fuels, and low relative humidities will result in an elevated risk for rapid fire spread tomorrow. Southwesterly winds are expected to regularly gust to 35 to 40 mph during the day tomorrow, with occasional gusts to around 45 mph. Additionally, near-record warmth is expected tomorrow with highs forecast in the lower 80s area-wide. While there is some uncertainty in where dewpoints end up tomorrow afternoon, lower 50s to around 50 degrees are a best guess. This would result in afternoon RHs between 30 and 35% across areas near and south of the I-80 corridor. Given the magnitude of wind gusts and state of fuels in the region, a Fire Weather Watch has been issued for tomorrow afternoon for areas near and south of I-80. This watch may later be upgraded to a Red Flag Warning as confidence in fire weather conditions grows.

Doom

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.CLIMATE... Issued at 300 PM CDT Mon Oct 28 2024

Record Warmth Possible This Week

Near record to record high temperatures are in the forecast on Tuesday October 29th. In addition, record warm low temperatures are also in jeopardy on Tuesday October 29th and Wednesday October 30th.

Here are the current daily records at Chicago and Rockford:

Chicago: 10/29: Record High: 78F in 1999; Record Warm Low: 65F in 1946 10/30: Record High: 85F in 1950; Record Warm Low: 62F in 1974

Rockford: 10/29: Record High: 81F in 1922; Record Warm Low: 61F in 2004 10/30: Record High: 83F in 1950; Record Warm Low: 56F in 1924

NWS Chicago

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.LOT WATCHES/WARNINGS/ADVISORIES... IL...Fire Weather Watch from Tuesday afternoon through Tuesday      evening for ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-ILZ032-      ILZ033-ILZ039.

IN...Fire Weather Watch from Tuesday afternoon through Tuesday      evening for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 9 AM CDT Tuesday for the IL      nearshore waters.

     Gale Warning from 9 AM Tuesday to 9 PM CDT Wednesday for the      IL and IN nearshore waters.

     Small Craft Advisory from 10 PM this evening to 9 AM CDT      Tuesday for the IN nearshore waters.

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