Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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751 FXUS63 KILX 290014 AFDILX Area Forecast Discussion...Updated National Weather Service Lincoln IL 714 PM CDT Sun Apr 28 2024 .KEY MESSAGES... - Another round of showers and thunderstorms will push through central Illinois tonight: however, the severe potential has greatly decreased. - Above normal temperatures will prevail for the remainder of the week with occasional rain chances. && .UPDATE... Issued at 714 PM CDT Sun Apr 28 2024 00z surface analysis placed 1004 mb low pressure in northwest IA, with a well defined warm front stretched east into southern WI, and a cold front extending south through the southern Plains. This placed central IL firmly in the warm sector with SSW winds and upper 50s to lower 60s dewpoints. A 40-50 kt SW 850 mb jet was oriented from MO into the southern Great Lakes, providing good moist advection this evening. This will allow an area of showers and storms currently over SW to central MO to expand northeast, affecting much of the area west of I-57 by midnight to 1 am, then shifting east over the remainder of the area overnight. Looking at convective trends, the severe weather risk appears quite low given weak low level lapse rates, increasing CINH, and meager instability (MLCAPEs 200-400 J/kg). 40-50 kt of deep layer shear will be present well into the overnight owing to the LLJ, which could favor a few sustained updrafts that would be capable of producing small hail. Locally heavy rain will also be a risk, with latest CAM output pointing to 1-2" totals east of I-55, where the LLJ shows better convergence late tonight. 3-hr flash flood guidance is around 2-3" in this region and with most of the rain falling in a 3-6 hour period this shouldn`t pose much of a flash flood risk, but will be something to monitor should localized training develop. 25 && .SHORT TERM...(Tonight through Monday) Issued at 322 PM CDT Sun Apr 28 2024 19z/2pm regional radar mosaic is mostly devoid of convection across the Midwest...with the closest lightning strikes observed across Arkansas. Aside from a stray shower along/west of I-55, the balance of the afternoon will remain mostly dry across central and southeast Illinois. As has been the case for the past couple of nights, convection will once again be largely driven by the nocturnal low-level jet. 18z NAM shows the 850mb jet oriented from eastern Texas into Missouri/Illinois strengthening to 40-50kt after dark. Given the increasing forcing ahead of a cold front extending from western Iowa into Texas, think showers and thunderstorms will blossom within the jet by mid-evening. Most CAMs suggest convection will develop upstream across Missouri, then develop/spread northeastward into locations along/west of I-55 before midnight...with a line of showers/thunder then progressing eastward to I-57 overnight. The atmosphere preceding the convection this evening will be highly sheared, but only weakly unstable. Current mesoanalysis shows 0-6km bulk shear of 45-55kt west of I-55, but MLCAPEs well under 500J/kg. There will be a slight uptick in instability as the LLJ strengthens, but MLCAPE values are only expected to climb into the 500-1000J/kg range. This may be enough energy to produce a few stronger cells with gusty winds/small hail, but the overall severe weather risk appears to be minimal. Showers will push into east-central Illinois late tonight and diminish in intensity/areal coverage by dawn. Other than lingering showers along/east of I-57 early in the morning, Monday looks mostly dry across the KILX CWA. Will still need to watch for the potential for scattered convective development along the slowly departing cold front during the afternoon: however, none of the CAMs are particularly bullish at this time. Deep-layer shear and instability parameters are both meager, so am not anticipating widespread severe weather with any storms that fire along/east of I-57 late in the day. Barnes .LONG TERM...(Tuesday through Next Sunday) Issued at 322 PM CDT Sun Apr 28 2024 Once the front exits into the Ohio River Valley and high pressure builds into the region, a pleasant spring day with light winds is anticipated for Tuesday as high temperatures top out in the middle to upper 70s. A short-wave trough ejecting northeastward out of the Rockies will track N/NW of Illinois Tuesday night into Wednesday. This feature will push a weak cold front into the NW CWA, potentially triggering scattered showers/thunder mainly along/northwest of I-55 Tuesday night. Once the main forcing lifts into Canada, Wednesday will be a dry day across central Illinois despite the lingering nearly stationary frontal boundary. Temperatures will climb above normal into the lower to middle 80s. The next significant chance for rain will arrive Thursday afternoon into Thursday night as a stronger wave approaches from the west. With strong forcing along/ahead of an associated cold front and GFS precipitable water values increasing to 1.50-1.75, have opted to carry likely PoPs west of I-55 Thursday afternoon and everywhere Thursday night. There is a possibility that rain chances will need to be delayed by 6-12 hours, focusing mainly on Thursday night/Friday morning, if the slower ECMWF/GEM verify. Once this system passes to the east, cooler/drier weather will be on tap for next weekend with highs dropping back into the upper 60s and lower 70s. Barnes && .AVIATION... (For the 00z TAFs through 00z Monday Evening) Issued at 613 PM CDT Sun Apr 28 2024 An area of SHRA and embedded TSRA will spread northeast across the terminals later this evening, lasting several hours before tapering off late tonight. This should predominantly produce high MVFR to low VFR conditions, with brief but significant drops possibly down to IFR in TSRA. Have TEMPOed in some lower MVFR periods to account for this. After the rain pushes off, MVFR ceilings are expected Monday morning, with bases rising to VFR levels during the afternoon. South to southwest winds will persist through the period, gusting over 20 kt for much of Monday. 25 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$