Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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970 FXUS63 KILX 220801 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 301 AM CDT Wed May 22 2024 .KEY MESSAGES... - There is a 70% chance for thunderstorms Friday, with a level 1 of 5 (marginal) risk some of these storms become severe. The strongest storms could produce damaging wind gusts and large hail. - Scattered thunderstorms are likely (60-70% chance) on Sunday. Severe weather potential is unclear at this time, but the risk appears highest near and south of I-72. && .DISCUSSION... Issued at 300 AM CDT Wed May 22 2024 At 3am, surface observations suggest a cold front is somewhere near I-55; behind it, winds are veering gradually to a westerly direction, while dewpoints are dropping to provide us with a milder and more May-like airmass this midweek. The front is forecast to stall somewhere between I-70 and I-64 this afternoon, serving as a focus for additional thunderstorms that will have a small (5%) chance of turning severe. Looking at the 00z suite of CAMs though, it`s looking like guidance has once more shifted south and severe weather will focus near and southeast of the IL/KY/IND state lines. Tonight, a weak mid level disturbance lifting northeast out of the Ozarks will provide support for showers and perhaps a couple rumbles of thunder near the I-70 corridor, with less than a 10% chance of anything getting to I-72 (or further north). Aside from a couple morning showers near/south of I-70, tomorrow should be dry under the influence of surface high pressure, but we can`t guarantee nothing will fire during the evening in the same area as forecast soundings suggest increasing elevated instability and shear ahead of our next weather maker slowly approaching from the Plains. Temps should reach 80 degF or better most locations - about 5-6 deg warmer than today - given efficient radiational warming with the drier airmass and (near) full sunshine near and north of I-72. Thunderstorm chances return for Friday afternoon/evening as another mid level shortwave ejects out of the Plains and into the Midwest. This feature is subtle and well south of the main upper wave which will be lifting across the Northern Plains and into MN late Friday, but it will bear watching. The NAM and GFS suggest shear will be on the increase late while instability will be waning, and LREF suggests the joint probability for more than 30 kt of shear and 1000 J/kg SBCAPE is only around 35-45% - highest southwest of a Galesburg to Terre Haute line. However, outflow boundaries from upstream convection could offer mesoscale forcing/locally enhanced shear to favor storm development during the afternoon when instability is much higher (NAM suggests upwards of 3000 J/kg SBCAPE in Peoria at 1pm). Friday`s temps are thus tricky to pin down, as the location of the (1) warm front, (2) outflow boundaries, and (3) storms are uncertain at any given time. Right now, we`ve got low to mid 80s for forecast highs, but those are definitely subject to change. Behind that system, we should get another break in precipitation chances on Saturday before the next low comes our way out of the Central Plains. Just looking at the deterministic ECMWF, the set up looks messy with scattered thunderstorms beginning late Saturday night and continuing all day Sunday. Given we`ll once again be near the instability gradient with a stationary boundary oriented northwest-southeast near/over our area, thinking is any of these storms could turn severe with large hail and locally damaging winds, with a conditional risk for more prolific damaging winds if a line can become organized and propagate forward along the boundary; the greatest potential for such a scenario would be once again near and southeast of I-70. We`ll continue to monitor. The pattern does look to finally turn cooler and more stable early next work week, with near or below normal temps and perhaps a break in thunderstorm chances. CPC advertises a roughly 45/33/22 percent chance for below/near/above normal temps during the day 6-10 (Monday, 5/27 to Friday, 5/31) period. Bumgardner && .AVIATION... (For the 06z TAFs through 06z Wednesday Night) Issued at 1138 PM CDT Tue May 21 2024 The cold front will pass during the first 4 hours of this TAF period, as it extends through Peoria county to Schuyler county at 0445Z. Gusty south winds to 35kts will become SW behind the front with a few gusts in the 20s lingering the rest of the night. The terminals should remain rain/storm-free the rest of the night, with mid-level cloud cover remaining just south of DEC-CMI line. Based on the latest high res models, confidence is low that patchy MVFR ceilings will develop behind the front so have continued with just a scattered cloud group for the late night hours. Shimon && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$