KLOT issues Area Forecast Discussion (AFD) valid 2019-11-27T07:51:00Z 975 FXUS63 KLOT 270751 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 151 AM CST Wed Nov 27 2019 .MESOSCALE DISCUSSION... 145 AM CST The dry slot of the upper system is giving a nice push to the showers early this morning. The warm front seems to have lifted through a good portion of the area, thus instability, while limited, is present to support gusty showers given the strong wind field aloft. Observations of sustained winds have been in the 25 mph range, with most gusts in the 40-45 mph range, but we have seen more isolated pockets of gusts to 55-60 mph (Peru/De Kalb). We do not feel that the severe winds are widespread, but more localized and thus the current semi-organized area across De Kalb/Kane/McHenry (which is devoid of lightning) will be handled with a Special Weather Statement for mostly sub- severe winds but pockets of higher winds. KMD && .SHORT TERM... 238 PM CST Through Wednesday night... Our potent storm system is taking shape early this afternoon with the core shortwave beginning to eject out across western Kansas. Associated strong upper jet divergence is facilitating pressure falls eastward across the Central Great Plains, and these pressure falls will roughly telegraph the location of the surface low into the evening hours as it tracks northeastward towards central Iowa. Light shower activity continues to develop across the region as low- level warm advection is really beginning to crank upstairs. This activity will remain light through the afternoon hours with perhaps a local minimum in activity south of I-80. As we work into the evening hours, however, the addition of increasing support from an incoming upper-jet should allow the slug of rain currently across Arkansas and southeastern Missouri to spread into our region. Afternoon model guidance continues to support the potential for a sliver of modest elevated instability to develop through the evening hours in the expanding warm sector south and east of the surface low. Forecast soundings show a rather limited potential for truly surface-based inflow, but kinematic profiles depict extremely strong wind fields immediately off the surface. The attendant robust large scale forcing for ascent ahead of this system may support the development of a broken line of low-topped convection, which could attempt to push into the southwestern portions of the CWA after about 11 PM. Given the aforementioned kinematics in place and already fast forward storm motions, it won't take much to translate some 50 to 60 mph wind gusts to surface if this convective line is is deep enough. It continues to look like any linear convection would begin to outpace what little surface-based instability there is after 3-4 AM as it tracks towards the Chicago area and would overall expect a decrease in storm intensity/depth as a result. Finally, as was alluded to in the overnight discussion, in the face of such strong and stretched-out wind fields, we can't completely discount the potential for a brief QLCS tornado spin-up given the presence of line-orthogonal deep layer shear vectors which should help keep convective updrafts propped up against any surging outflow. The main story with this system, however, continues to be on the very strong wind potential into Wednesday. We have upgraded the High Wind Watch to a High Wind Warning for all of northeast Illinois and northwest Indiana with the potential for widespread wind gusts well into the 50 mph range, occasionally to 60 mph. Still some questions about how deeply we can mix in the developing cold advection regime on Wednesday morning/afternoon, but there is enough of a signal in the model guidance to support the wind headline upgrade. The window for highest gusts will be the mid-late morning hours on Wednesday and through the mid-afternoon before things gradually abate into the evening hours. Low precipitation chances will linger for those north of I-80 into the mid-afternoon hours on Wednesday as temperatures fall into the 30s with a strong non-diurnal temperature trend. It continues to look like cloud depths will diminish quickly enough to minimize the potential for any wintry precipitation as surface temperatures fall below freezing Wednesday evening. Carlaw && .LONG TERM... 238 PM CST Thursday through Tuesday... Thanksgiving day continues to look fairly benign after the active weather period on Wednesday. Light winds will prevail although cloud cover will likely be prevalent holding high temperatures down in the mid to upper 30s area-wide. The next lead shortwave disturbance--caught up in the fast southwesterly mid-level flow spread across the nation's midsection--now looks to wash out west of our region Thursday afternoon and evening, thus limiting the potential for additional precipitation during this period. The next strong storm system is currently dropping in towards the Pacific Northwest and California coastline, will finally spread east across the Plains towards the end of the week and weekend. As is typical with these deep upper-level systems, we've noted an incremental slowing trend in today's guidance, and have begun to pare PoPs back a bit, holding them back until later in the day on Friday. This system's current track once again places us more on the warm side, likely greatly limiting the wintry weather aspect although some rain and snow will be possible mainly north of I-80, but no accumulations are anticipated at this time. Could see more in the way of light snow towards the end of the weekend and Sunday night on the backside of this system as the main upper low begins to pivot in overhead. Carlaw && .AVIATION... For the 06Z TAFs... * IFR ceilings through early this morning, with MVFR ceilings continuing for much of the day. * Showers and drizzle through early this morning. * One to two hour window of thunder early this morning. * Southwest to west winds gusting to 45 to 50 kt later today. Active period expected with a high likelihood for impactful weather today. Precip development continues at this hour, though slightly less in coverage and intensity. Do think additional light showers or drizzle will be possible in the very near term across all of the terminals, before the the more intense precip across western IL lifts across the area over the next several hours. Still expect thunder to accompany these showers early this morning, mainly for about a 1-2 hour period, before the more widespread precip development ends. Some light rain showers are still possible for a time through midday today though. Ceilings are currently at their lowest, with ceilings expected to either hold steady or rise slightly through early this morning. VFR ceilings then expected for a brief window later this morning, but with MVFR ceilings then returning for the remainder of the day. Varying winds still expected through the period, with southeast winds becoming southwest this morning, and then west later today. Rather strong gusts approaching 50 kt still expected today, with the highest gusts expected from mid/late morning through mid afternoon. Rodriguez && .MARINE...We have converted the Storm Watch to a Storm Warning for the nearshore waters of Lake Michigan. Southeast to south winds to 30 kt tonight will become southwest and eventually westerly Wednesday morning and through the afternoon hours as they increase in speed. Storm force wind gusts to 50 kt are anticipated on Wednesday. While winds will remain gusty, they will subside markedly Wednesday evening and overnight as high pressure quickly begins to build in from the west. Carlaw && .LOT WATCHES/WARNINGS/ADVISORIES... IL...High Wind Warning...ILZ019-ILZ021-ILZ023-ILZ032-ILZ033- ILZ039...6 AM Wednesday to 6 PM Wednesday. High Wind Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012-ILZ013-ILZ014-ILZ020-ILZ022...9 AM Wednesday to 6 PM Wednesday. IN...High Wind Warning...INZ001-INZ002...9 AM Wednesday to 6 PM Wednesday. Lakeshore Flood Advisory...INZ002...noon Wednesday to 6 AM Thursday. High Wind Warning...INZ010-INZ011-INZ019...6 AM Wednesday to 6 PM Wednesday. LM...Small Craft Advisory...nearshore waters until 6 AM Wednesday. Storm Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...6 AM Wednesday to 10 PM Wednesday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO