Scientific Forecaster Discussion

000 fxus63 kilx 180447 afdilx Area forecast discussion National Weather Service Lincoln Illinois 1147 PM CDT Mon Jun 17 2019 Update... issued at 913 PM CDT Mon Jun 17 2019 Some light rain lingers across east central Illinois this evening, but low clouds prevail over most of the County Warning Area. Main question will be with additional shower/storm development. Seriously considered dropping the Flash Flood Watch near and south of I-70, but decided to leave it in place as the hrrr brings some heavier showers into the area toward 3-4 am. Current activity is generally along the Ohio River and shouldn't impact US, but the new development appears to be focused just north of the frontal boundary, which should be in the general vicinity of I-64 overnight. Temperatures are generally on track, but some updates for the precipitation trends have recently been sent. && Short term...(this evening through tuesday) issued at 332 PM CDT Mon Jun 17 2019 This afternoon, upper low is slowly lifting across the Ozarks towards the local area. At the surface, a stationary front is draped from just south of St Louis east-northeast along and just south of the I-70 corridor. Dew points are pooling in the upper 60s to around 70f near the front, while temperatures have warmed to around 80f in the warm sector. North of the front, low stratus has prevailed through the day and held temperatures in the 60s to lower 70s. Thunderstorms are ongoing along the I-70 corridor this afternoon in response to the shortwave trough that ejected northeast from the main upper low. These storms have been slow moving in the presence of weak low and mid level flow, and what movement there has been is often training over areas already impacted. Anticipate a corridor or 1 to 2 inches of rain through late this evening, with locally higher amounts across areas that have already been well saturated by recent heavy rain events. While the intensity of the rain hasn't been too bad so far today, the other aforementioned factors continue to support a Flash Flood Watch through at least late this evening if not overnight. This wave should exit east of the County Warning Area by around sunset this evening, which coupled with the loss of daytime heating, should allow precip to wane in coverage. Cannot rule out at least some isolated to widely scattered convection to continue overnight as the main upper low begins to accelerate eastward, and the focus will remain in the far southeast counties of the forecast area. Overnight, temperatures remain relatively mild under the presence of cloud cover and high dew points. Clouds should lower again overnight and cannot rule out some patchy fog redeveloping after midnight. On Tuesday, don't expect much in the way of synoptic scale forcing over the region and most of the forecast area will remain dry. Flow aloft becomes zonal in the wake of the damping upper low. The surface boundary likely persists over the region, however, and will serve as the main focus for diurnal convection again across the far southeastern County Warning Area. Guidance suggests modest instability with MLCAPE to around 1000 j/kg will develop within the warm sector Tuesday afternoon. Deep layer shear will be weak in the continued weak mid level flow, so the likelihood of any severe storms is fairly low. Long term...(tuesday night through monday) issued at 332 PM CDT Mon Jun 17 2019 There has been a good signal for several days now that a shortwave trough will track across the mid Mississippi Valley on Wednesday. This wave will intersect moisture rich and unstable air in place over Illinois on Wednesday resulting in additional chances for showers and thunderstorms across the forecast area. Some of these storms could produce heavy rain and will again have to closely monitor flooding potential during this time frame. Yet another wave is progged to dig across the Pacific northwest Thursday and carving out a deep across the Great Basin over the weekend. As this occurs, anticipate downstream amplification of the longwave ridge over the mid section of the country as very warm (20c+) 850mb temps spread into the Midwest by this weekend. Thursday and most of Friday should be dry as a result of the building upper ridge over the region, and a warming trend will kick off in earnest Friday. Saturday in particular could be hot over the area, but there remains some uncertainty in how hot given thunderstorm chances returning along with associated cloud cover. Near 90f or possibly into the 90s not out of the question depending on how things come together. Thermal ridge should persist over the area on Sunday before the upper ridge begins to break down and shift east early next week. && Aviation...(for the 06z tafs through 06z Tuesday night) issued at 1147 PM CDT Mon Jun 17 2019 Ceiling trends will be a challenge the next several hours. Latest surface obs showing generally high clouds northwest of kpia, but low MVFR conditions around 1500-2000 feet prevailing. Hrrr model suggests some periods of IFR ceilings, with such low clouds already seen northeast of kstl. Overall wind field wouldn't favor a major advection to the northeast of this, so will only mention some tempo periods of 800 foot ceilings for now. All sites expected to improve to VFR by midday. && Ilx watches/warnings/advisories... Flash Flood Watch until 7 am CDT Tuesday for ilz062-063-066>068- 071>073. && $$

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