NWS Forecast for O'Hare International Airport Chicago, IL Last Update: 3:42 am CST Nov 4, 2024

Hazardous Weather Outlook (below forecast)
Hydrologic Outlook (below forecast)

Overnight Sunday/Monday: Rain. Low around 63. South wind around 15 mph, with gusts as high as 25 mph. Chance of precipitation is 100%. New precipitation amounts between a tenth and quarter of an inch possible.

Monday: Rain before noon, then a slight chance of showers between noon and 4pm, then a chance of showers and thunderstorms after 4pm. High near 70. Breezy, with a south southwest wind 15 to 20 mph, with gusts as high as 30 mph. Chance of precipitation is 100%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday Night: A chance of showers and thunderstorms, then showers and possibly a thunderstorm after 8pm. Some of the storms could produce heavy rainfall. Low around 64. Breezy, with a south wind 15 to 25 mph, with gusts as high as 40 mph. Chance of precipitation is 100%. New rainfall amounts between 1 and 2 inches possible.

Tuesday: Occasional showers and possibly a thunderstorm before 9am, then a chance of showers between 9am and noon, then showers likely and possibly a thunderstorm after noon. High near 68. Breezy, with a south wind 20 to 25 mph, with gusts as high as 40 mph. Chance of precipitation is 80%.

Tuesday Night: A 40 percent chance of showers before midnight. Mostly cloudy, with a low around 45. Southwest wind 5 to 15 mph becoming west northwest after midnight. Winds could gust as high as 30 mph.

Wednesday: Mostly sunny, with a high near 56.

Wednesday Night: Partly cloudy, with a low around 43.

Thursday: Sunny, with a high near 59.

Thursday Night: Mostly clear, with a low around 42.

Friday: Sunny, with a high near 60.

Friday Night: Partly cloudy, with a low around 43.

Saturday: A chance of showers. Partly sunny, with a high near 59.

Saturday Night: Showers likely. Mostly cloudy, with a low around 48.

Sunday: A chance of showers. Partly sunny, with a high near 61.

Hazardous Weather Outlook

National Weather Service Chicago/Romeoville IL

349 AM CST Mon Nov 4 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- 349 AM CST Mon Nov 4 2024 /449 AM EST Mon Nov 4 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...

Elevated Flooding Risk.  

Limited Thunderstorm Risk...with an associated:      

Level 1 of 5 Damaging Wind Risk...up to 60 mph.   

Limited Non Thunderstorm Wind Risk.

DISCUSSION...

There is a slight chance of thunderstorms this afternoon.

Thunderstorm chances will increase tonight. There is a very low, around 5 percent chance, of a localized severe weather threat developing tonight. If severe weather were to occur, localized damaging winds would be the primary threat.

Of greater concern, areas of heavy rainfall are likely tonight. Rainfall could be sufficient in localized areas to result in flash flooding of low lying and poor drainage areas.

Finally, winds could gust to around 40 mph for a time this morning south of I-80. Also, wind gusts over 40 mph are possible tonight, especially in the Chicago area and south and east of the I-57 corridor, including northwest Indiana.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...   

Limited Thunderstorm Risk.   

Elevated Non Thunderstorm Wind Risk.

.SPOTTER INFORMATION STATEMENT...

Due to the very low threat of severe weather, spotter   activation is not expected tonight. However, any reports of  flooding, damaging winds, and measured heavy rainfall totals would be greatly appreciated.

$$

Hydrologic Outlook

National Weather Service Chicago IL

415 AM CST Mon Nov 4 2024

...Heavy Rainfall Could Lead to Localized Flooding Tonight...

An approaching storm system will interact with a record moist and unseasonably warm air mass to bring the threat of locally very heavy rainfall tonight. While there are uncertainties exactly where, there are indications that a swath of 2 to potentially over 4 inches of rain could occur somewhere over northern Illinois tonight.

Despite the ongoing drought and resultant low stream flow and below average soil moisture; if rainfall on the higher end of the forecast range were to occur, it would likely result in flash flooding, particularly of low lying and flood prone areas. If rainfall totals on the lower end of the forecast range were to occur, some minor flooding could still occur.

Very heavy rainfall and flash flooding are possible, but not yet certain. Persons should closely monitor forecasts including the possibility of flood watches, warnings, and advisories. Clear storm drains and gutters of leaf debris to allow storm waters to drain.

$$

- Izzi

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

403 AM CST Mon Nov 4 2024

.KEY MESSAGES...

- Rain is expected this morning, possibly heavy at times,

  tapering off an ending most areas by late morning

- There`s a chance of a few hours of 40+ mph gusts this morning,

  mainly south of I-80

- Showers and thunderstorms will increase in coverage very late

  this afternoon or more likely this evening, with potential for

  locally very heavy rainfall and flooding tonight

- A low chance (~5%) of a localized severe weather threat

  tonight

- Strong southerly winds gusting over 40 mph are possible

  tonight, mainly eastern IL and northwest IN

- Strong winds are likely area wide Tuesday with gust over 40

  mph likely and a chance (~30%) of gusts 50+ mph

&&

.DISCUSSION... Issued at 317 AM CST Mon Nov 4 2024

Through Tuesday:

Active weather expected over the next 36 hours with heavy rainfall, flooding, severe weather, and record warmth all possible to varying degrees at times.

This morning -

Large shield of rain, some of it rather heavy, will affect the area this morning in association with a convectively enhanced shortwave riding the brisk southwesterly mid-upper level jet northeastward. This shortwave should lift north of CWA by mid- late morning with coverage of precipitation expected to decrease in its wake. A band of at least scattered showers is expected to persist across our southeast CWA into the afternoon along a bit of a weak low level baroclinic zone.

One other item to briefly note is that the HRRR and RRFS have been consistently showing a period of strong southeasterly winds moving across mainly our southern/southeastern CWA this morning (12-16z time frame). It would appear that the models are trying to resolve some pseudo wake low like process with forecast soundings in this area showing the classic adiabatic warming/subsident footprint. Have noted some 30kt gusts over eastern MO with 3mb/2h pressure falls in the area the HRRR suggests turn into this intensifying swath of winds. Low confidence at this time, so didn`t include this in the grids, but will watch observational trends and probably handle it with an SPS if it becomes clear it will develop. Some of the runs have shown peak gusts over 40kt and given the strong winds just off the deck with the low level jet, this doesn`t seem out of the realm of possibility.

This afternoon -

Aforementioned weak NNE-SSW oriented baroclinic zone over our southeast CWA late this morning is expected to buckle northwestward across the area this afternoon. Sfc frontogenesis along this boundary is expected in response to cyclogenesis taking place over the southern Plains this afternoon. The axis of showers should lift northwest with the boundary, with some potential for some isolated thunderstorms as well this afternoon; assuming some weak destabilization can take place northwest of the boundary where there should be an appreciable break in the rain and perhaps some thinning of the cloudiness.

Tonight`s heavy rain threat -

Slowly deepening southern plains sfc low is expected to ride u Pthe sharpening low level baroclinic zone, which should serve as a focus for potentially very heavy rainfall and embedded thunderstorms. Ensemble mean PWATs are progged to approach 1.8 inches which would be not just record breaking but approaching the bounds of what is even possible this time of year. GEFS and EPS puts these PWATs at or above 4 standard deviations above normal, which would be about a 0.01% chance of happening. A very strong low level jet (70kt+ at 850mb) is expected to develo Pthis evening, with moisture convergence also progged to be off the charts near the northern terminus of the low level jet, which should coincide closely with where the low level baroclinic zone sets up. It seems quite plausible that this low level boundary could stall resulting in potentially several hours of very heavy rainfall occurring in a focused SW-NE axis. Freezing levels near 11kft means efficient warm rain processes could dominate and given some modest upright and slantwise instability, there will probably be some convection as well.

As has been noted in our discussions for days now, the ongoing drought has left ample capacity for area streams and rivers to handle a lot more rain than they typically could. However, given the record obliterating moisture content of the atmosphere and potential for axis of very heavy rainfall to set up for a period of several hours, it wouldn`t be hard to envision rainfall totals significantly exceeding 3 hour flash flood guidance (around 2.25-2.5") and 6 hour FFG (2.5-3") if this happens. There is some variability and uncertainty where, if, and to what magnitude this could occur, so opting to hold off on a flood watch at this time.

There is a threat for rainfall that significantly exceeds flash flood guidance, so it is important not to downplay the flood threat just because of the current drought. A reasonable worst case scenario would include the potential for more than just minor flooding to occur, particularly if this axis were to set up in a more urbanized area. Even if rainfall doesn`t get that extreme, flooding of low lying and poor drainage areas would be a concern. Plan to issue an ESF this morning to highlight this threat and allow later shifts to access observational trends and potentially consider a targeted flood watch for tonight as trends hopefully become clearer.

Tonight`s convective threat -

In addition to the heavy rainfall/flood threat, we will also need to keep a close on a potential localized high shear/low CAPE severe wx threat to develop in or near our CWA. This threat is HIGHLY conditional on some boundary layer destabilization taking place. Low and mid level lapse rates look to be fairly poor, but advection of mid 60 degree dewpoints northward could be sufficient to result in just enough instability (given the strong forcing) for there to be a localized severe threat. Low level shear and wind fields are going to be absolutely extreme, so if we get some boundary layer destabilization some low topped, strongly forced convection could pose a localized damaging wind or maybe even a brief QLCS-type tornado threat.

Secondarily, within the warm sector of this cyclone, coverage of rain could be more sparse over our eastern CWA tonight. Given the strong and strengthening pressure gradient, 3-5mb/3hr pressure falls in advance of the low, and record high temps/dewpoints, there is concern that the boundary layer could remain somewhat mixed tonight, allowing some gusts of 35-40kt to occasionally reach the surface. Confidence is too low for a wind advisory at this time, but this is going to be another thing for later shifts to keep an eye on.

Tuesday -

Widespread showers and thunderstorms are expected to move out of the area as the sfc low and associated shortwave trough lift north of the area. A cold front trailing south from this low will gradually move eastward across the area. Our CWA should spend a fair amount of time in the warm sector ahead of this front. Wind fields are expected to remain very strong and with even just some modest warming of the boundary layer we could begin to mix up into 40-50kt winds not too far above the surface. Have bumped up wind gusts to mid-upper 30kt range for Tuesday, but this is conservative compared to what bufkit soundings from 00z guidance would support. Since tonight`s 00z guidance suite was notably stronger with the system, I didn`t want to go all in on the strong wind potential, however if this morning`s 12z guidance remains similar, a wind advisory would likely be needed for 45-50+ mph gusts Tuesday mid morning through mid afternoon.

If there is some thinning or breaks in the cloud cover in the warm sector Tuesday, then there could be some weak destabilization of the boundary layer. Forcing isn`t expected to be terribly strong along the cold front as the parent mid-upper level shortwave trough are moving away, however there could be some shallow low topped convection develop along the front. Given the presence of strong wind shear, if instability were to be greater than expected, couldn`t rule out there being some low-topped/mini-supercells, but this chance seems quite low, so no plans to message it at this point.

- Izzi

Tuesday Night through Sunday:

The cold front will be either moving through the eastern cwa or will be east of the cwa by early Tuesday evening with showers ending during the evening. Winds will be shifting westerly with the front and then steadily diminishing into early Wednesday morning as directions turn more northwest by daybreak. Dry weather is expected Wednesday and Thursday as high pressure moves across the area. There is some uncertainty for Friday for how soon precip chances will return. The overall trends would support a dry Friday and possibly a dry Friday night but some of the GFS runs are faster thus low chance blended pops have returned for parts of the area Friday and Friday night. However, the best precip chances still look to be tied to the next cold front that will move across the area Saturday night. Likely pops during this time period seem reasonable at this time. No thunder mention for now but isolated thunder may be needed with later forecasts depending on how much instability can move north ahead of the front. Some lingering showers are possible Sunday depending on the track of the system, closer to our area, better chance for showers.

Temperatures will be around or just above normal for early November with highs in the upper 50s/lower 60s with Wednesday looking like the coolest day for high temps. cms

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/... Issued at 1014 PM CST Sun Nov 3 2024

Aviation Forecast Concerns for the 06Z TAFs:

- Periods of SHRA, and MVFR/IFR ceilings likely overnight into   early Monday morning, and again Monday evening/overnight. Low   (15%) but non-zero TS potential early Monday morning. Greater   (30-40%) chance of TSRA expected Monday night.

- Brief period of LLWS at start of TAF with 45 kt low-level   jet.

- South-southwest winds become gusty during the day Monday, with   gusts 25-30 kt possible.

Surface low pressure continues will continue to develop across the High Plains overnight, then move slowly northeast toward the mid-upper Mississippi Valley through Monday night. This will maintain southerly winds across the forecast area, which will pull deep Gulf moisture northward into the region. This will set the stage for continued SHRA chances through the TAF period, with the greatest coverage expected with a couple of individual disturbances early Monday morning, and again Monday evening/overnight. MVFR/isolated IFR visibility and IFR ceilings are likely during these two periods. In addition, there is a non-zero but low (~15%) chance of isolated TSRA early this morning, with a greater (30-40%) chance Monday night. Have maintained a PROB30 mention for TSRA with the Monday night rainfall period.

Winds will be southerly (mostly 180-200 deg, though briefly 170-160-ish at times) through the forecast period. A 45-50 kt low level jet will maintain a LLWS risk for the first few hours of the forecast. By mid-morning Monday, surface winds will increase, with gusts into the 25-30 kt range possible for a time during the day before diminishing late. SHRA/TSRA Monday night could produce locally gusty winds as well.

Ratzer

&& 

.LOT WATCHES/WARNINGS/ADVISORIES...

IL...None.

IN...None.

LM...Small Craft Advisory until 9 PM CST this evening for the IL

     and IN nearshore waters.

     Gale Warning from 9 PM this evening to 6 PM CST Tuesday for

     the IL and IN nearshore waters.

&&

$$