Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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422 FXUS63 KILX 110944 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 444 AM CDT Tue Jun 11 2024 .KEY MESSAGES... - An upper disturbance may spark a few isolated showers late this afternoon through tonight. Chances remain pretty low (<15%) with most expected to stay dry. - Temperatures become unseasonably warm Wednesday onward with highs peaking in the upper 80s to middle 90s. This paired with a more humid airmass will send heat indices near 100 as early as Thursday. - There is a 30-50% chance for showers and storms Thursday afternoon into night as a cold front drops through the area. A few of these storms could be severe north of I-70. && .DISCUSSION... Issued at 334 AM CDT Tue Jun 11 2024 An expansive area of ~1017 mb surface high pressure currently covers a large portion of the country`s midsection, spanning from the Missouri Valley northward into the Great Lakes Region. Another day of deep mixing yesterday brought down much lower dewpoints, especially over eastern parts of the state where upper 30s to low 40s dewpoints are noted as of 3 am. Temperatures have steadily fallen overnight with most areas in the upper 40s to low 50s. Light winds and mostly clear skies aside from a few cirrus will support efficient radiational cooling through the remainder of the morning, with lows expected to wiggle down a couple more degrees, possibly putting some sites in eastern Illinois within a few degrees of their low temperature records. Surface ridging spills eastward later today as upper ridging from the western CONUS inches closer. Flow aloft will transition to more zonal, with mid-level heights quickly rising. Southerly surface flow will bring in warmer temperatures today with values expected to approach our seasonal norms. A few disturbances will ride the upper ridge and track through the Great Lakes Region tonight and again Wednesday night. Moisture with the wave tonight will be more so focused in the mid to upper levels with better low-level moisture staying well north of here. Lapse rates will steepen as the upper wave approaches, potentially sparking a few isolated showers (<15% chance) or virga showers. Added the mention of isolated sprinkles from late this afternoon into tonight to account for this, but most will stay dry. Somewhat better chances (30-50%) for precipitation are possible Thursday afternoon into evening as a cold front drops south through the area. A warm, moist airmass ahead of the front characterized by dewpoints in the upper 60s to low 70s should lead to moderately strong instability by late Thursday afternoon. A 60-70 kt mid-level jet will stretch from the northern Plains into the Lower Great Lakes Region by evening, increasing shear as the cold front approaches. Conditions look favorable for storms to develop within a largely uncapped environment by late Thursday afternoon or evening. A few of these storms could become severe north of I-70, posing a threat for damaging wind gusts. Climatologically high PWATs exceeding 2 inches and deep warm cloud layers will bring the threat for heavy rainfall as well. Despite this, the threat for flooding still looks pretty marginal due to the lack of appreciable recent rain and the swift progression of the front. Another big forecast concern going forward is the long duration heat beginning midweek onward. Temperatures will quickly climb into the upper 80s to middle 90s by Wednesday with similar values sticking around through much of next week/weekend. Dewpoints will climb back to more uncomfortable levels ahead of storms on Thursday, sending heat indices into the 90s to near 100. Drier air behind the front will bring a brief "break" in oppressive dewpoints Friday and Saturday, but air temperatures will remain unseasonably hot. Dewpoints return back to the upper 60s to low 70s Sunday onward as southerly return flow is reinforced underneath amplified upper ridging. Heat indices will once again approach 100 Sunday through early next week, creating near-dangerous conditions for outdoor activities and vulnerable individuals. A new experimental heat risk product which is essentially a heat stress index geared toward those actively exposed to direct sunlight in the heat approaches moderate to major categories (level 2 to 3 out of 4) Sunday through Tuesday of next week. This is somewhat different from heat index (measured in shade) because the stress on your body can occur much quicker when working or exercising in direct sunlight during the heat. NMA && .AVIATION... (For the 12z TAFs through 12z Wednesday Morning) Issued at 444 AM CDT Tue Jun 11 2024 VFR conditions will continue through the TAF period. Light and variable winds will become south-southwesterly today with speeds generally below 10 kts. High clouds increase through the day ahead of an upper disturbance that will send a weak front through the area this evening. Mid-level stratus will accompany the front, but otherwise no notable impacts are expected. NMA && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$