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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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264 FXUS63 KILX 121044 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 544 AM CDT Fri Jul 12 2024 .KEY MESSAGES... - Most of the area will be dry today, but occasional thunderstorm chances exist through Tuesday, some of which could be severe. Much of this activity will be focused across the northern half of the state. - Hot and humid conditions build Saturday through Tuesday, with highs in the upper 80s to mid 90s, and peak heat indices in the upper 90s to 100s. - A cold front moves through mid-week, providing another chance of thunderstorms followed by relief from the heat, with below normal temperatures favored during the latter half of the week. && .DISCUSSION... Issued at 231 AM CDT Fri Jul 12 2024 Upper-level troughing remains in place across the upper Midwest early Fri AM, with a secondary vort max present near the MO/KS border. Elsewhere, strong upper level ridging persists over the western US with 500mb heights approaching 5980m. In the immediate short-term, fog development is the main concern. Shower activity (and the associated cloud debris) have waned quickly after midnight, leaving light winds, mostly clear skies, and moist soils courtesy of the rainfall from Beryl as well as several rounds of convective activity in the 48 hours since Beryl departed. As of 1 AM Fri, locations from Paris to Effingham and southeast had occasionally reported visibility reductions as low as 2 miles, with lower visibility (including some as low as a quarter mile) further east in Indiana. 00z HREF guidance had a 50% chance of vis below 1 mile across much of the CWA, and some HRRR runs have shown patchy dense fog development. Confidence in the development and placement of any dense fog is too low to warrant a special weather statement or dense fog advisory at this time, but will continue to monitor obs/satellite this morning. Over the next several days, occasional thunderstorm chances (some of which could be severe) exist. However, with rather nebulous forcing mechanisms in play and disagreement between the CAMs, forecast confidence is low. First, that aforementioned secondary vort max should progress towards the MO Bootheel today. That could aid scattered precip development, though the favored region for this is south of our CWA, and that is reflected in the CAMs. Kept some low chnc PoPs (15-20%) south of I-70, but the rest of the CWA is favored to stay void of precip today. Late Fri night into Sat AM, models depict scattered precip developing via WAA as well as convergence at the leading edge of a weak LLJ. There is significant variability in the placement of this precip, with some models focusing it across central IL while others keep precip well removed from the ILX CWA. During the day Saturday, continued southerly flow will result in warm/moist advection, which when combined with moderate mid-level lapse rates will result in strong instability. The Grand Ensemble depicts a 60%+ chance of 2500 J/kg of surface-based instability west of I-55. However, deep layer shear is marginal at best, and there is a capping inversion that would need to be overcome and limited forcing to do so. Models are quite limited in their convective coverage Sat evening. Deeper into the period, disturbances riding around the upper ridge could result in repeated MCS activity each night Sat through Mon, but guidance continues to suggest the most likely area for this MCS activity is north of I-80. If this activity were to track into the ILX CWA, the continued presence of strong instability would support some severe storm potential, although deep layer shear continues to appear weak this far south as the upper flow weakens. Barring precip or cloud cover from MCS activity, hot and humid conditions are expected, especially on Sun-Mon. Between continued southerly flow advecting gulf moisture northward as well as moisture from recent rains and developing crops, afternoon dewpoints are on track to reach the mid 70s. With the moist conditions resulting in solar energy being consumed for evaporation, the NBM forecast high temps may be running a tad hot, but at any rate the combination of heat and humidity are expected to push heat indices to uncomfortable levels. If the current forecast holds, a heat advisory will need to be considered for Sun-Mon, when peak heat indices are forecast to be push near or over 105 degrees. Confidence in precip chances increases as a cold front moves through the CWA, with most indications that this occurs during the Tues night-Wed time frame. Due to timing differences in the models, the NBM has 20-40% chance PoPs spread over a broad time range (Tues- Thurs). As confidence increases regarding the timing of this front, expect PoPs to be refined and focused over a much smaller time period. During the latter half of the week, following the cold FROPA, upper ridging over the western US amplifies, with the grand ensemble depicting a 90% chance for 500mb heights to exceed 5940m over the Four Corners region. That subsequently results in troughing over the Great Lakes/Upper Midwest, and below normal temperatures are favored (40-60% chance) across IL from Wed into next weekend. Erwin && .AVIATION... (For the 12z TAFs through 12z Saturday Morning) Issued at 543 AM CDT Fri Jul 12 2024 Patchy visby reductions will continue for the first hour or so of the period. While there is some potential for visbys reductions down to a quarter mile, most of the TAF terminals have remained MVFR or better so far this morning. Light southeasterly winds develop by mid- morning and will persist through the period. There is a low chance of showers near the end of the period, but did not consider a VCSH mention at this time. Erwin && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$