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Chicago Weather Forecast (O'Hare Official) 8:18 am CDT Oct 16, 2017 with Forecast Discussion


Today: Sunny, with a high near 61. West southwest wind 5 to 10 mph, with gusts as high as 15 mph.

Tonight: Clear, with a low around 45. Southwest wind around 5 mph.

Tuesday: Sunny, with a high near 67. Southwest wind 10 to 15 mph, with gusts as high as 25 mph.

Tuesday Night: Clear, with a low around 48. South southwest wind around 10 mph.

Wednesday: Sunny, with a high near 68. Breezy, with a south southwest wind 10 to 20 mph, with gusts as high as 30 mph.

Wednesday Night: Mostly clear, with a low around 50.

Thursday: Sunny, with a high near 69.

Thursday Night: Mostly clear, with a low around 51.

Friday: Sunny, with a high near 72.

Friday Night: Partly cloudy, with a low around 56.

Saturday: Mostly sunny, with a high near 72.

Saturday Night: A chance of showers. Mostly cloudy, with a low around 58.

Sunday: A chance of showers. Mostly cloudy, with a high near 69.


Amf Ohare IL
 41.98°N 87.9°W

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AREA FORECAST DISCUSSION
National Weather Service Chicago/Romeoville, IL
GO Current Forecast Discussion

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555 AM CDT Mon Oct 16 2017

.SHORT TERM... 208 AM CDT

Through tonight...

It feels a bit more like autumn this morning with readings in the upper 30s to mid 40s or so. Other than some passing mid clouds this morning, plentiful sunshine will be rule as high pressure becomes established across the Ohio valley. This will be the coolest day of the week, but the southwest winds on the back side of the high will allow temps to recover to around normal, upper 50s to lower 60s. Northwest flow aloft may bring a few passing clouds tonight, otherwise it will be another relatively cool night with readings back in the 40s.

KMD

&&

.LONG TERM... 208 AM CDT

Tuesday through Sunday...

We re-enter another period of dry and unseasonably warm weather throughout most of the long term as high pressure settles over the upper Tennessee Valley. The ridge axis will extend southwest across Texas and thus prevent moisture from spreading into the midwest, while southwest flow locally will allow for a gradual warming trend to occur throughout the week as southwest winds dominate. A weak front will graze the northern tier of counties on Thursday which will shift winds around to northerly briefly. Otherwise the high will strengthen and build across the eastern third of the county, and in conjunction with low pressure across the plains will act to reinforce the mild southerly flow across the region. Afternoon highs are expected to rise into the upper 60s Tuesday and Wednesday, upper 60s to low 70s Thursday, low 70s Friday, and mid 70s by Saturday. Seasonal highs are typically around 60/low 60s for the early-latter portion of October.

An upper trough is expected to move onshore over the west coast late in the week and spread across the Great Plains and Midwest over the weekend. Surface ridge axis will get shunted farther east out ahead of the wave allowing gulf moisture to flow back up across the plains and Midwest with dew points pooling back around 60F along a cold front. The front is expected to sweep across the local area either late Saturday night or Sunday, with the latter time frame favored at this distance. This still looks to be the next decent chance for showers and possibly a few thunderstorms in the area, though the t-storm threat appears on the low side as the system is upper level support is rather broad. A bit more fall-like conditions return behind this front.

KMD/Deubelbeiss

&&

.AVIATION... For the 12Z TAFs...

Surface high pressure will dominate across the Central Mississippi Valley through the period. This will result in quiet weather across the region, with a westerly wind. VFR conditions are expected through the period.

KJB

&&

.MARINE... 301 AM CDT

The main weather concern over Lake Michigan this week is the increasing potential for a period of high end southerly gales over the northern half of the lake on Wednesday.

In the near term, northwesterly winds up to 25 kt continue across southern Lake Michigan early this morning, and as of 240 am CDT, waves at 45170 continue to be up over 7 ft. As a result, it is likely that the small craft advisory will have to be extended through the morning hours over the Indiana near shore waters. The winds are expected to ease and back westerly during the day as surface high pressure moves over the Mid Mississippi Valley. So, waves will subside, but it may not be until late this morning, or early this afternoon, that they drop below 4 ft.

The surface high is expected to become extended from the Lower Ohio Valley to the Mid-Atlantic tonight into Tuesday, and will remain dominate here through much of the week. Meanwhile, at least two storm systems of note will shift eastward across Canada through mid to late week. Ultimately, this looks to set up an optimal surface pressure gradient over the lake to support a prolonged period of stout west-southwest winds.

The first storm system, is forecast to reach a modest strength as it shifts towards James Bay Tuesday morning. This system will result in an uptake in the west-southwesterly winds over the lake later today into tonight. However, expect the strongest southwest winds to reside over the northern half of the lake tonight, where 30 to possibly a few 35 kt gales will be likely.

The second storm system is expected to be the main story of the week, however, as it is forecast to be a much more potent area of low pressure. As such, this will set up a very strong gradient over the lake on Wednesday and Wednesday night. During this period high end south-southwesterly gales of 40 to 45 kt will be probable, especially over the northern half of the lake. If forecast guidance continues to advertise this strong storm system, a gale watch will likely be needed in the near future.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...IN nearshore waters until 10 AM Monday.

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Chicago Weather Forecast (O'Hare Official) 2:18 am CDT Oct 14, 2017 with Forecast Discussion


Overnight: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 4am. Cloudy, with a low around 61. East northeast wind 5 to 10 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.

Saturday: Showers and possibly a thunderstorm before 11am, then a chance of showers and thunderstorms between 11am and 2pm, then showers and possibly a thunderstorm after 2pm. High near 72. East wind 5 to 10 mph becoming south in the afternoon. Chance of precipitation is 90%. New rainfall amounts between a half and three quarters of an inch possible.

Saturday Night: Showers and possibly a thunderstorm. Low around 56. Breezy, with a south wind 10 to 20 mph, with gusts as high as 25 mph. Chance of precipitation is 90%. New rainfall amounts between a half and three quarters of an inch possible.

Sunday: Showers and possibly a thunderstorm before 8am, then a chance of showers between 8am and 2pm. High near 57. Northwest wind around 15 mph, with gusts as high as 30 mph. Chance of precipitation is 90%.

Sunday Night: Mostly clear, with a low around 41. Northwest wind 5 to 10 mph, with gusts as high as 15 mph.

Monday: Sunny, with a high near 60.

Monday Night: Mostly clear, with a low around 45.

Tuesday: Sunny, with a high near 66.

Tuesday Night: Mostly clear, with a low around 51.

Wednesday: Sunny, with a high near 68.

Wednesday Night: Partly cloudy, with a low around 52.

Thursday: Sunny, with a high near 68.

Thursday Night: Mostly clear, with a low around 52.

Friday: Sunny, with a high near 72.


Amf Ohare IL
 41.98°N 87.9°W

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AREA FORECAST DISCUSSION
National Weather Service Chicago/Romeoville, IL
GO Current Forecast Discussion

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250 AM CDT Sat Oct 14 2017

 .SHORT TERM... 250 AM CDT

Through tonight...

The main forecast concerns for today and tonight are, the increasing threat of very heavy rainfall from multiple rounds of showers and thunderstorms, and also the threat of a line of strong to severe thunderstorms this evening.

Showers and thunderstorms have been developing across portions of north central Illinois over the past couple hours in response to an increase in isentropic upglide, and moisture advection atop a surface boundary located near the I-80 corridor. This activity is likely to continue to overspread much of northern Illinois over the next few hours as warm and moist advection continues to occur atop the surface boundary. The eastward movement to these storms is likely to set up training of cells over the same areas into this morning, and unseasonably high precipitable water values (in excess of 1.5") setting up over the area, expect these storms to be efficient heavy rainfall producers. Any break in the activity this morning looks to be short lived, as several additional waves of showers and thunderstorms are expected to shift across northern Illinois later this morning into the afternoon.

The surface boundary over the area this morning will try to begin shifting northward as a warm front later today in response to a deepening and fast moving area of low pressure shifting over eastern IA and into WI. The northward movement of this front may initially be halted due to the extensive shower and storm activity this morning, but as the low shift towards WI this evening, expect this warm front to be forced northward.

The wind field through the atmospheric column is expected to increase dramatically through the day in response to strong dynamics of this deepening low. As a result, very impressive low and deep layer shear profiles are expected to set up across much of the warm sector by this evening. With another line of showers and thunderstorms expected along and ahead of an eastward advancing cold front this evening, there is concern that severe storms could be a real concern over northern Illinois given the strong wind field. Overall, this still appears to be a high shear- lower CAPE environment, so we will have to rely on the strong dynamics of the storm system to help produce the severe storms this evening. These are always trick types of setups for severe storms, and as a result, the latest forecast and observational information will need to be monitored closely today. At this time, it appears that that damaging winds would be the primary potential severe concern with a possible squall line shifting eastward across northern Illinois. There will also be a nonzero threat of tornados as well given the high low-level shear and proximately to the area of low pressure entering southern WI this evening.

Given the likelihood of several rounds of very heavy rainfall training over the same areas today into tonight, flooding will be a big concern. For this reason, we have opted to issue a flash flood watch for areas mainly north of I-80 through tonight.

KJB

&&

.LONG TERM... 248 PM CDT

Saturday night through Friday...

A powerful cold front will sweep across the region Saturday night into Sunday morning. Surface low is projected to track from eastern Iowa Saturday evening to southern Wisconsin Saturday night with a trailing cold front sweeping across most of the CWA overnight. Out ahead of the low track, a strong low level jet will transport unusually high PWat air of 1.7-1.9 inches over the local area driving heavy rainfall. An axis of one to two inches of rainfall appears likely with locally higher amounts plausible. Where exactly this sets up remains a bit uncertain at this point, but somewhere along or just north of the IL/WI state line is favored depending on where the strongest convergence ahead of the 60kt+ LLJ aligns. Within the warm sector, lapse rates are fairly weak and unfavorable diurnal timing will contribute to overall weak instability. Still guidance shows 200-300 J/Kg MLCAPE possible ahead of the cold front superimposed by very strong deep layer shear. Despite the lack of any appreciable instability, given the strong kinematic environment, any convective elements would bring some risk of strong and potentially damaging winds and bears close watching as the event nears.

Prefrontal 850mb temps of 15-17C Saturday will fall to around -1C by midday Sunday behind the front. The strong cold advection will result in steep low level lapse rates. Meanwhile, as precipitation along the front exits the CWA to the east Sunday morning, high pressure will build across the Great Plains resulting in a strong gradient and isallobaric response. GFS indicates a corridor of 6- 7mb/3hr pressure rises will move across northern Illinois mid to late in the morning. This combination of factors will result in strong and gusty winds across the region. Expect winds gusting in excess of 30 mph Sunday morning, very gradually tapering in magnitude through the day as the gradient relaxes and the strongest pressure rises move to our east. In addition Sunday, expect the area to remain locked under stratus cloud cover with moisture trapped atop the shallow cold airmass by a strong inversion. Expect early morning high temperatures Sunday with falling or steady non-diurnal temperatures trends through the day.

Ridge axis will move across the local area Monday then settle to our east Tuesday through the end of the upcoming week. Seasonably cool temperatures on Monday will return to above normal conditions Tuesday through the end of the week as southerly flow dominate on the western periphery of the ridge. No significant chances for precipitation are noted as upper ridge gradually strengthens over the eastern CONUS.

Deubelbeiss

&&

.AVIATION... For the 06Z TAFs...

The concerns for the Chicago area airports through Saturday are:

- Winds with mainly an easterly component likely through mid   Saturday morning, with some variance in speeds

- Showers likely by overnight with isolated thunder in the area

- Periods of showers likely again Saturday mid-late morning into   Saturday night, with increasing chances for thunder after dark

- Winds becoming near due south Saturday afternoon

The next wave of showers and embedded thunder has developed along the warm front early this morning across Illinois and extending back into Iowa. Expect these to spread east across the Chicago terminals in the coming hours. Initially thunder will be low and ceilings are not expected to fall with this first wave, but the secondary surge with the activity in Iowa looks to expand the coverage of showers, embedded thunder, and possible lower cigs. This activity will decrease in coverage towards or slightly after daybreak, but not likely completely dissipate with the warm front lingering and lifting northward. At this point (mid morning) winds will shift at ORD/MDW back to more SE and eventually S.

Confidence in a minimum in coverage of showers Saturday morning is medium high, but it may not be long lived as the wave currently in the Texas panhandle lifts northeast and interacts with the northward moving warm front. There is increasing confidence in IFR ceilings being an issue. These are likely along and north of the warm front, which is expected to be just south of ORD and possibly MDW too. The warm front will ease northward during Saturday and as it passes the Chicago airports winds will turn to southerly. Speeds will increase, especially after dark Saturday and some gusts will be occasionally seen.

Periods of showers are favored during Saturday afternoon, especially along/northwest of a PIA to ORD line. It is challenging to say what thunder coverage would be in these showers, but instability progs have been trending upward some, so an expansion of the thunder mention may be warranted in future TAFs. Ahead of the cold front later Saturday evening into the early overnight, a band of convection is likely, some of which will have strong winds, possibly damaging winds.

KMD

&&

.MARINE... 248 PM CDT

Low pressure is expected to track across Lake Michigan this weekend bringing a period of strong gales as a trailing cold front sweeps across the region. A leading warm front will begin to lift across Lake Michigan this evening and tonight with strengthening northeasterly flow expected across the northern 2/3 or so of the lake while southerly winds overspread the south end of the lake. By Saturday evening, expect south to southeast winds to be in place across most of the lake, increasing to around 30 kt. A few southerly gales are possible by Saturday evening ahead of the low, but gales will become widespread and potentially strong Saturday night into Sunday as winds veer around to the west and northwest behind a trailing cold front. Expect wind gusts to peak around 40 to 45 with the potential for a few occasional 50 kt gusts with any showers that help mix down stronger winds aloft. A Gale Watch has been hoisted for the open waters, though there may yet need to be refinements to timing before the event begins. Winds should ease back below gale force mid to late Sunday afternoon or early Sunday evening.

Deubelbeiss

&&

.LOT WATCHES/WARNINGS/ADVISORIES... IL...Flash Flood Watch...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-      ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020 until 4 AM Sunday.

IN...None. LM...Gale Watch...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM      Sunday to 4 PM Sunday.

     Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-      LMZ745...10 PM Saturday to 7 AM Sunday.

     Gale Warning...LMZ777-LMZ779...10 PM Saturday to 7 PM Sunday.

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Chicago Weather Forecast (O'Hare Official) 2:18 pm CDT Oct 11, 2017 with Forecast Discussion


This Afternoon: Cloudy, with a high near 60. Northeast wind around 10 mph, with gusts as high as 15 mph.

Tonight: Cloudy, with a low around 53. East wind 5 to 10 mph.

Thursday: Cloudy, with a high near 61. East wind around 5 mph becoming south southeast in the afternoon.

Thursday Night: Cloudy, then gradually becoming partly cloudy, with a low around 53. South southeast wind around 5 mph.

Friday: Mostly sunny, with a high near 73. South wind 5 to 10 mph.

Friday Night: Showers likely and possibly a thunderstorm, mainly after 2am. Mostly cloudy, with a low around 61. Chance of precipitation is 70%.

Saturday: Showers likely and possibly a thunderstorm, then showers and thunderstorms after 2pm. High near 74. Chance of precipitation is 80%.

Saturday Night: Showers and thunderstorms, mainly before 2am, then showers and possibly a thunderstorm after 2am. Cloudy, with a low around 60.

Sunday: Showers and possibly a thunderstorm before 8am, then showers likely. Mostly cloudy, with a high near 66.

Sunday Night: A slight chance of showers before 8pm. Partly cloudy, with a low around 45.

Monday: Sunny, with a high near 61.

Monday Night: Mostly clear, with a low around 47.

Tuesday: Sunny, with a high near 66.


Amf Ohare IL
 41.98°N 87.9°W

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National Weather Service Chicago/Romeoville, IL
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242 PM CDT Wed Oct 11 2017

.SHORT TERM... 1259 PM CDT

Through Thursday...

The system responsible for last night`s rain is lifting away from the region.  Any lingering showers should come to an end through the afternoon today, but an expansive area of low stratus will remain in place through tonight and likely, through tomorrow as well.  Latest forecast sounding suggest that some drier air will overspread the nearly saturated lower levels late tonight and tomorrow, bring a chance for some patchy drizzle and for for the late night into early morning hours.  The blanket of stratus will also limit the diurnal temperature trends with temps topping out today in the low 60s. Lows tonight are expected to be in the low to middle 50s, but highs tomorrow should only be a couple degrees higher than today, reaching only the low 60s.

&&

.LONG TERM... 241 PM CDT

Thursday night through Wednesday...

Main concern in the extended is multiple rounds of rain Friday night into Sunday. After an above average end to this week, next week starts with more seasonal temperatures and a slow warm u Pthrough mid week.

Dry weather is expected Friday as the upper level ridge hangs over the region. Warm air advection will also result in high temps in the low to mid 70s. Cloud cover will play a big part in how efficiently we warm Friday with more cloud cover leading to cooler temps. Precip forms to our north and west along an upper level vorticity streamer Friday evening. Showers and a couple of embedded thunderstorms spread across the region Friday night.

A surface low surges from northwest Missouri to Quebec Saturday afternoon to Sunday afternoon. The low`s warm front lifts through the region Saturday bringing another surge of warm air. High temps will range from the low 70s along the IL/WI state line to around 80 south of I-80.

Morning showers dissipate, but I`m expecting scattered afternoon showers to form within the  warm sector. GFS suggests CAPE and shear values that could support strong to maybe severe storms. Similar to many systems lately, CAPE will be the limiting factor for severe storms. PWATs will be well above average at around 2 inches, and this much liquid could lead to heavy rain. The line of showers and storms pushes east of the forecast area Sunday morning or early afternoon along with the low`s cold front.

Northwest winds and a push of cooler air follow the front with highs Sunday in the 60s. Sunday night looks particularly blustery as a secondary upper level trough and cold pool spread across the region. Wind gusts around 25 MPH are possible. Lows in the low to mid 40s are expected. The upper level trough should only produce precip over the lake early next week.

The dry period continues through mid next week under high pressure. Temps also climb into the upper 60s by mid week as well.

JEE

&&

.AVIATION... For the 18Z TAFs...

Main forecast concerns for the period are cigs, any lingering shra and the potential for fog late tonight into early tomorrow morning.

A widespread deck of ifr-mvfr cigs will remain over the region as nely flow on the swrn periphery of a slowly lifting upper low persists through tonight and tomorrow. There has been some diurnal improvement to cigs this afternoon, with many locations lifting to lower end mvfr, but expect that this improvement will be brief and cigs should lower again to widespread ifr toward sunset. Latest cig guidance suggests that cigs in some locations could lower to lifr, but expect that ORD/MDW will likely remain at 500 ft or above, with DPA/RFD/GYY possibly seeing cigs lower to less than 500 ft. Latest radar imagery indicates some sct shra lingering over nern IL/nwrn IN in nely-enely flow. Any lingering shra should end early this afternoon as the main upper low continues to lift to the northeast. A ridge of high pressure building across the region overnight tonight should allow winds to drop off the generally lgt/vrbl. With the diminishing winds will come a chance for fog development in the very moist air mass in place. Drier air spreading in aloft over the nearly saturated lower levels could bring some patchy drizzle overnight as well. As the high moves to the east tomorrow and a trough of low pressure moves out across the nrn/cntrl Plains, winds will trend to more sely tomorrow and cigs should improve to mvfr through the day, though a bkn-ovc cig should persist through the day.

&&

.MARINE... 241 PM CDT

Kept current Small Craft Advisory as is as winds and waves will slowly subside through tonight.

Low pressure over Ohio weakens as it continues east, and high pressure spreads over the Great Lakes this evening. East winds diminish this evening and veer to southwest by Thursday night. A stationary front over the southern end of the lake Friday night will lead to north winds to the north of the front and southerly winds to the south of the front.

The next surface low forms over northwest Missouri Saturday afternoon. The low`s warm front surges two thirds up the lake before the low passes over the lake Saturday evening/night. Wind gusts up to 30 kt are expected. Winds become north to northwest behind the cold front and gales are expected Sunday.

High pressure spreads over the Great Lakes Sunday night and then passes south of the lakes Monday night. West to southwest winds 10-20 kt are expected early to mid next week.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...IL nearshore waters until 5 AM Thursday.

     Small Craft Advisory...IN nearshore waters until 11 PM      Wednesday.

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Chicago Weather Forecast (O'Hare Official) 3:19 pm CDT Oct 6, 2017 with Forecast Discussion


This Afternoon: Showers and possibly a thunderstorm. Patchy fog. High near 69. Southeast wind around 5 mph. Chance of precipitation is 80%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers and thunderstorms before 2am, then showers likely and possibly a thunderstorm between 2am and 4am, then a chance of showers and thunderstorms after 4am. Patchy fog. Low around 66. South wind 5 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Saturday: A chance of showers, then showers and possibly a thunderstorm after 1pm. High near 78. Breezy, with a south southwest wind 15 to 20 mph, with gusts as high as 35 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Saturday Night: A 50 percent chance of showers before 1am. Mostly cloudy, then gradually becoming mostly clear, with a low around 55. West southwest wind 5 to 15 mph, with gusts as high as 25 mph.

Sunday: Sunny, with a high near 77. South wind 5 to 10 mph.

Sunday Night: Mostly clear, with a low around 56.

Columbus Day: Sunny, with a high near 75.

Monday Night: Partly cloudy, with a low around 55.

Tuesday: A slight chance of showers before 1pm. Partly sunny, with a high near 67.

Tuesday Night: A chance of showers after 1am. Partly cloudy, with a low around 51.

Wednesday: A slight chance of showers. Mostly sunny, with a high near 66.

Wednesday Night: A slight chance of showers. Partly cloudy, with a low around 53.

Thursday: A slight chance of showers. Mostly sunny, with a high near 67.

Thursday Night: Partly cloudy, with a low around 52.

Friday: Mostly sunny, with a high near 70.


Amf Ohare IL
 41.98°N 87.9°W

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National Weather Service Chicago/Romeoville, IL
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305 PM CDT Fri Oct 6 2017

.SHORT TERM... 304 PM CDT

Through Tonight...

Main forecast concerns/challenges are with precip trends this afternoon into the evening, gusty winds Saturday, and thunderstorm possibility Saturday afternoon.

Latest radar imagery showing upstream area of showers pushing into the west/southwest CWA at this time, ahead of approaching wave. Despite slightly higher coverage of showers expected to move through northern Illinois this afternoon, am seeing showers extending further to the east into northwest Indiana and expect this trend to continue with most locations observing scattered showers. While the afternoon will remain on the wet side, do see somewhat of a back edge to this development and expect by early evening that a trend back towards drier conditions will occur. Still not overly concerned with thunder this afternoon but with some instability overhead and increasing ascent in place, can`t rule out some embedded thunder. Once again, there may be a few hour dry window through mid evening. However, isentropic ascent ramps up across eastern IA and northwest IL by mid/late evening. This should allow for precip to blossom in this location, and then shift east into northern IL during this time. Focused highest pops in northern IL, as don`t have as high confidence for additional shower development over east central IL and northwest IN during this time. If precip does occur in these areas, expect more widely scattered to isolated development. Similar thoughts with thunder continue, but have maintained slight chance thunder given the previously mentioned thoughts on instability and forcing. This precip will then shift north of the area after the midnight time frame, and although expect drier conditions to be in place for the remainder of the night, do have lower confidence of this. The warm front will be well north of the area with the LLJ also focused to the north, however, some weak ascent will likely remain and could support scattered light showers. Highest chances of this occurring look to be across north central IL.

Warm front will lift through the area this afternoon through early evening with mild conditions expected tonight. Maintained similar lows around the mid 60s tonight, with this warm air mass in place and while a steady southerly wind increases through the night.

Rodriguez

&&

.LONG TERM... 304 PM CDT

Saturday through Friday...

A highly dynamic/strong system consisting of a deep surface trough/low, potent vorticity maxima, and strong mid/upper level flow will push through the region on Saturday. This will provide a time frame to keep an eye on, as gusty winds are likely and with the possibility of thunderstorms across the CWA Saturday afternoon. Guidance still varying with regards to the evolution of the surface trough/low and extent of the speeds aloft. Nonetheless, the pattern would suggest windy/gusty conditions on Saturday. Have continued similar thoughts with gusts as high as 30 to 40 MPH. This is sub advisory, but will need to still monitor later trends as higher gusts are still a possibility. At this time, speeds really ramp up by late morning and then continue through mid afternoon, before diminishing into the late afternoon and evening.

Still monitoring convective trends on Saturday, once again with this anticipated strong system moving through the region. Cloud cover and showers may already be in place Saturday morning, and likely be a limiting factor to the extent of the intensity of any storms on Saturday. With this in mind, at this time, moisture plume and higher instability look to be just to the east of the CWA along with the threat of more organized storms. If this were not to be the case, and instability were able to increase across the area, then could be monitoring for at least an isolated strong to severe storm Saturday afternoon. If this scenario did occur, locations across east central IL and northwest Indiana could see these possible storms. Once again, will continue to monitor trends and adjust forecast/messaging as necessary. Outside of these storms, showers will push east through the area throughout the day on Saturday with the highest chances occurring in the afternoon. Given the strong winds aloft, it would not be out of the question for a stronger shower or isolated storm to mix down some stronger winds. So, the threat of convective gusts is also a possibility on Saturday. Any showers/storms should quickly shift to the east by early Saturday evening, with dry conditions expected for the remainder of the night and into Sunday. Sunday looks dry and sunny, with temperatures rising to the mid/upper 70s by midday.

Rodriguez

&&

.AVIATION... For the 18Z TAFs...

Concerns with the Chicago area TAFs are:

- Low clouds/visibility early afternoon improving mid afternoon

- Showers mid-late afternoon and likely again late this evening

- Winds gusting to over 30 kt from the due south Saturday morning

- Showers, possibly storms, moving through during Saturday   afternoon

Murky conditions continue over the Chicago airports, though improvement in prevailing ceilings and visibility is creeping northward with a warm front. This will spread over the Chicago sites though confidence on the exact timing is low, as pockets of drizzle are continuing to reduce visibility and ceiling per webcams/observations.

Showers are increasing in coverage on upstream regional radar and that will continue through the afternoon. While some thunder is possible, especially toward northwest/north central Illinois, the coverage is expected to be limited enough over Chicago to not include in the TAFs at this time.

A wind shift to south will occur with the frontal passage late this afternoon. Light speeds will see an increase after the shift to southerly and then a gradual increase through tonight. Off the deck, southwest winds around 40-45 kt at 1500 ft are expected late this evening into overnight though true LLWS is not anticipated given the surface wind increase.

Saturday morning winds will be around due south with high confidence. Gusts in excess of 30 kt have medium-high confidence, though confidence is low on how frequent they will be. The winds will shift to southwest and then west-southwest with a cold front during the mid-late afternoon. This front will be accompanied by showers, some of which could be gusty, and even possibly thunder.

MTF

&&

.MARINE... 221 PM CDT

A warm front will gradually advance northward across the southern part of the lake this evening and the northern part of the lake overnight. Winds will shift south with an increase in speed after the passage of this boundary, which will help dissipate any pockets of dense marine fog.

As low pressure lifts from the Central Plains to the Great Lakes a ramp up in southerly wind speeds will occur by late tonight into Saturday morning. Gales of 35-40 kt are expected across the open water during the day Saturday and sporadic gale force gusts are probable along the Illinois and Indiana nearshores. The system cold front will push across the lake early in the evening, turning winds more westerly. Speeds will likely show variability ahead of and behind the front, with possibly some gusty showers at frontal passage time.

West winds will turn back to the south during Sunday and then fli Pto northerly during Sunday night as a backdoor cold front swings down the lake. The northerly winds with gusts toward 25 kt could last through Tuesday.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Gale Warning...LMZ777-LMZ779...3 AM Saturday to 7 PM Saturday.

     Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-      LMZ745...3 AM Saturday to 1 AM Sunday.

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