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
Area Forecast Discussion below ad ...
AREA FORECAST DISCUSSION
National Weather Service Chicago/Romeoville, IL
GO Current Forecast Discussion
ARCHIVED
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.
MORE BELOW
+ + + + + +
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Arlingtoncardinal.com/uvindex
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Hazardous Weather Outlook National Weather Service Chicago/Romeoville IL 354 PM CDT Fri Oct 13 2017
ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 142100- Winnebago-Boone-McHenry-Lake Illinois-Ogle-Lee-De Kalb-Kane- DuPage-Cook-La Salle-Kendall-Grundy-Will-Kankakee-Livingston- Iroquois-Ford-Lake Indiana-Porter-Newton-Jasper-Benton- 354 PM CDT Fri Oct 13 2017 /454 PM EDT Fri Oct 13 2017/
THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS... NORTHEAST ILLINOIS AND NORTHWEST INDIANA.
.DAY ONE...Tonight.
WEATHER HAZARDS EXPECTED: Limited Thunderstorm Risk. Limited Flooding Risk.
DISCUSSION:
Scattered thunderstorms are expected this evening and overnight, staying mainly along and north of the I-80 corridor. Severe thunderstorms are unlikely, but some of the storms could produce locally heavy rainfall.
.DAYS TWO THROUGH SEVEN...Saturday through Thursday.
Saturday... Elevated Flooding Risk. Limited Severe Thunderstorm Risk. Sunday... Limited Non Thunderstorm Wind Risk.
DISCUSSION:
Additional thunderstorms are expected Saturday and Saturday night. Saturday evening and overnight in particular may see strong to possibly severe storms and very heavy rainfall. The potential for heavy rainfall and flooding will be greatest farther north near the Illinois and Wisconsin state line.
.SPOTTER INFORMATION STATEMENT...
Spotter activation will not be necessary through tonight.
GENERAL STORM MOTION OF THE DAY:
Moving east at 50 MPH.
&&
$$
Flash Flood Watch Flood Watch National Weather Service Chicago/Romeoville IL 255 AM CDT Sat Oct 14 2017
ILZ003>006-008-010>014-019-020-141600- /O.NEW.KLOT.FF.A.0005.171014T0755Z-171015T0900Z/ /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/ Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-DeKalb-Kane-DuPage-Cook- La Salle-Kendall- Including the cities of Rockford, Belvidere, Woodstock, Waukegan, Oregon, Dixon, DeKalb, Aurora, Elgin, Wheaton, Chicago, Ottawa, and Oswego 255 AM CDT Sat Oct 14 2017
...FLASH FLOOD WATCH IN EFFECT THROUGH LATE TONIGHT...
The National Weather Service in Chicago has issued a
* Flash Flood Watch for portions of north central Illinois and northeast Illinois, including the following areas, in north central Illinois, Boone, DeKalb, La Salle, Lee, Ogle, and Winnebago. In northeast Illinois, Cook, DuPage, Kane, Kendall, Lake IL, and McHenry.
* Through late tonight.
* Several waves of showers and thunderstorms will move across the area today into tonight. These storms will produce heavy rain, and are likely to move over the same areas. This heavy rain is likely to result increased runoff, which will result in rises on area streams and rivers, and may also result in areas of flash flooding.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A Flash Flood Watch means that conditions may develop that lead to flash flooding. Flash flooding is a very dangerous situation.
You should monitor later forecasts and be prepared to take action should Flash Flood Warnings be issued.
Hydrologic Outlook
ILC007-031-037-043-089-097-103-111-141-201-141245-
Hydrologic Outlook National Weather Service Chicago IL 741 PM CDT Fri Oct 13 2017
...PERIODS OF HEAVY RAINFALL POSSIBLE LATER TONIGHT THROUGH SATURDAY NIGHT...
A surface front will stall across northern Illinois tonight, and act as the focus for a period of showers and thunderstorms into Saturday morning. A strong storm system is then expected to drive a cold front eastward across the area Saturday night, with another round of very heavy rainfall possible. Given the unseasonably high amounts of atmospheric moisture, these showers and storms will be capable of producing locally heavy rainfall, with amounts in excess of two inches possible in some locations by Sunday morning. Also, due to the fact that these storms will move over the same areas that recently received heavy rain, increased runoff may result in significant rises on area streams and rivers.
Flash Flood Watch
National Weather Service
Chicago/Romeoville IL
255 AM CDT Sat Oct 14 2017
ILZ003>006-008-010>014-019-020-141600- /O.NEW.KLOT.FF.A.0005.171014T0755Z-171015T0900Z/ /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/ Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-DeKalb-Kane-DuPage-Cook- La Salle-Kendall- Including the cities of Rockford, Belvidere, Woodstock, Waukegan, Oregon, Dixon, DeKalb, Aurora, Elgin, Wheaton, Chicago, Ottawa, and Oswego 255 AM CDT Sat Oct 14 2017
...FLASH FLOOD WATCH IN EFFECT THROUGH LATE TONIGHT...
The National Weather Service in Chicago has issued a
* Flash Flood Watch for portions of north central Illinois and northeast Illinois, including the following areas, in north central Illinois, Boone, DeKalb, La Salle, Lee, Ogle, and Winnebago. In northeast Illinois, Cook, DuPage, Kane, Kendall, Lake IL, and McHenry.
* Through late tonight.
* Several waves of showers and thunderstorms will move across the area today into tonight. These storms will produce heavy rain, and are likely to move over the same areas. This heavy rain is likely to result increased runoff, which will result in rises on area streams and rivers, and may also result in areas of flash flooding.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A Flash Flood Watch means that conditions may develop that lead to flash flooding. Flash flooding is a very dangerous situation.
You should monitor later forecasts and be prepared to take action should Flash Flood Warnings be issued.