316 FXUS63 KILX 181959 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 259 PM CDT Tue Jun 18 2019 .SHORT TERM...(This evening through Wednesday) ISSUED AT 255 PM CDT Tue Jun 18 2019 A weak shortwave ridge over the region today is resulting in mostly fair conditions across central Illinois. There have been a few pop-up showers in the vicinity of a stationary surface front draped from just south of St Louis ENE across Lawrenceville. There are a couple patches of more agitated cu elsewhere in the forecast area, most notably S/SE of Springfield, but most of the remainder of the CWA will be dry thought tonight with clouds diminishing in coverage as the boundary layer begins to stabilize this evening. Temperatures tonight will fall back into the mid 60s. Couldn't rule out some fog redeveloping overnight, especially along and south of I-72 where dewpoints are in the mid to upper 60s. By Wednesday, attention turns back to the west as a shortwave trough tracks east across the Great Plains with attendant surface wave deepening just to our west during the day and then tracking across portions of central Illinois during the evening. This wave will interact with a very moist environment in place across portions of the Midwest where PWats are progged to be around 1.75-1.90 inches. Surface warm front should lift back north of the I-70 corridor in response to the deepening low, and dewpoints pooling into the lower 70s should overspread southern portions of the forecast area contributing to at least modest instability over the region. Meanwhile, strengthening westerlies aloft will result in increasing deep layer shear over the area supporting a threat for severe thunderstorms. Thunderstorms may initially be scattered in coverage during the afternoon in response to modest mid level height falls overspreading the area with weak convective inhibition in place. Showers and thunderstorms will further increase in coverage by late afternoon through the evening as the main low moves across the region. Models in reasonable agreement showing an axis of 2-3 inches over the forecast area (NAM has locally 4-5 inches); however, there are still differences in the placement of the heaviest precip. Given lingering uncertainty and in collaboration with upstream offices, opted to wait another model/forecast cycle before hoisting any flash flood watch; however, there is a good likelihood one will be needed somewhere in central Illinois for Wednesday afternoon and Wednesday night once convective details become more certain. While flash flood guidance has recovered slightly for areas north of I-72, it remains quite low south, especially in the I-70 corridor which has had multiple bouts of heavy rain the past few days. Precip chances will wind down from the west Wednesday night as the low tracks off to our east and mid level ridge builds overhead from the west. && .LONG TERM...(Wednesday through Monday) ISSUED AT 311 AM CDT Tue Jun 18 2019 Looking at models in terms of agreement for the mid-week system, there remains some discrepancy in track and intensity of rainfall. Track path is through Illinois, however at this time the difference in path is either central Illinois or northern Illinois. This difference is causing some uncertainty in storm total rainfall, which creates a "landslide" effect for other elements. With the current FFA ongoing through 12z Tuesday morning, it was decided to hold off on any new issuance of products, to limit confusion. Even though the path could shift slightly northward, a new FFA will more than likely be issued later today due to the already saturated soils across the region. This wave will slide across the area starting Wednesday midday, lasting through the overnight into Thursday morning, leaving Illinois midday Thursday. As 500mb heights remain flattened, no strong front will aid in movement, which is why heavy rainfall is expected over the 24 hour period. Storm total rain for this event is currently forecast between 0.75-1.50 inches, but could increase based upon final track location. With the boundary in place over the region and a disturbance riding along it, SPC has issued a Slight Risk for severe weather across the east half of the CWA. After this wave, a quiet 24 hours will lead into Friday. A weak ridge will develop across the Midwest, as a deepening Low pressure system digs into the northern Rockies Friday. As this Low lifts back northeast into central Canada, it will lift moisture northward on the backside of the ridge. This will bring another chance for shower activity Friday afternoon, but the heaviest precipitation will arrive during the upcoming weekend. Since switching to the new NBM procedures, storm total accumulations seem to be forecast slightly higher. Looking at the rest of this week into the weekend, totals around the region are forecast to range from 3-6 inches, however the values will likely change with track determination and better atmospheric processes. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1228 PM CDT Tue Jun 18 2019 Light winds and VFR conditions will prevail through the rest of today. There is a very small chance for a pop-up shower or thunderstorms, especially for SPI/DEC/CMI this afternoon and evening, but much better chances for staying dry. Low pressure will move across the region Wednesday. Mid and high clouds will increase ahead, and precip chances will begin to ramp up by early afternoon. Expect showers and thunderstorms to become more widespread through the latter half of the afternoon into the evening, and some of these storms could be strong. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Deubelbeiss LONG TERM...Baker AVIATION...Deubelbeiss