Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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681 FXUS63 KILX 211737 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1237 PM CDT Sat Sep 21 2024 .KEY MESSAGES... - Very warm weather will continue today as afternoon high temperatures once again top out in the upper 80s and lower 90s. - Beneficial rainfall is on tap for all of central and southeast Illinois from late tonight through Monday night. Storm total rainfall will range from 1 to 2 inches...with some locations along and south of I-70 potentially picking up 3 inches. && .UPDATE... Issued at 1105 AM CDT Sat Sep 21 2024 15z/10am surface analysis shows a stationary frontal boundary extending from Evansville, Indiana northwestward to near Kirksville, Missouri. Easterly flow to the N/NE of the front has brought lower dewpoint air into much of central Illinois this morning...with readings in the upper 50s/lower 60s along and north of I-74. Further south closer to the boundary, lower 70s dewpoints persist south of I-70. Scattered showers and thunderstorms presently across southern Iowa into Missouri will continue to shift slowly eastward today: however, they will be encountering a drier environment as they cross the Mississippi River and will thus decrease in intensity and areal coverage. Have maintained low chance PoPs (20-30%) along/west of the I-55 corridor through the afternoon as the showers gradually try to work eastward. Otherwise it will be another very warm day. Highs will be held in the middle to upper 80s west of the Illinois River due to increased cloud cover and shower chances, but will reach the lower 90s further east where sunshine will be more prevalent. Barnes && .DISCUSSION... Issued at 345 AM CDT Sat Sep 21 2024 Areas of fog had developed past few hours east of I-55 with patchy dense fog from Champaign to Decatur to Taylorville east where more moist air present with low to mid 60s dewpoints and very light to calm winds. Some cirrus clouds arriving from the west has been keeping the dense fog from getting too widespread while less high clouds further east over Indiana to allow more widespread dense fog formation and they have a dense fog advisory until 8 am cdt. Have increased fog wording in eastern IL until 9 am, and will continue to monitor dense fog coverage and dense fog advisory possibility early this morning. A special weather statement will be issued for the patchy dense fog in eastern IL early this morning with visibilities restricted to a quarter mile at times. A frontal boundary over southeast IL and into sw IL, will lift back northeast across central IL during this afternoon. Dewpoints to increase back up into the upper 60s and lower 70s while highs reach the upper 80s and lower 90s, with afternoon heat indices peaking back in the 90s. Limited forcing today, but MLCAPES rising to 2k j/kg over western/sw CWA by mid/late afternoon with wind shear values of 20-30 kts could support a few strong storms western and sw CWA from mid afternoon into early evening for hail and gusty winds. SPC day1 outlook officially keeps marginal risk nw of CWA over much of Iowa, nw MO and central/western WI closer to a cold front. This cold front progged by CAMs to track se into nw IL late tonight and moving into central IL during Sunday afternoon. This system has stronger forcing and will produce more widespread showers and a chance of thunderstorms arriving late tonight into Sunday. SPC day2 outlook has marginal risk of severe storms sw of St Louis over central/southern MO. Cooler highs Sunday in the mid to upper 70s central IL and around 80F in southeast IL. Frontal boundary will be near southeast IL Sunday night and Monday as another system moves along it and likely brings another round of showers and a few thunderstorms with the heavier rains focused in southeast IL during that time frame. SPC day3 has marginal risk of severe storms over far southern IL from Carbondale to Evansville south on Mon/Mon night. Precipitatable water values of 1.5-2 inches are expected Sunday into Monday so heavier rain showers are possible at times. Between 1-2 inches of rainfall expected over CWA Sunday through Monday night with 2-3 inches possible in southeast IL where rain likely linger into Tue morning. Even cooler Monday with highs in the lower 70s over much of central IL with mid to upper 70s in southeast IL. Models diverge with handling upper level pattern during mid/late week so stayed close to model blend with this forecast package. Generally dry conditions forecast for Tue night through Thu with below normal temperatures with highs in the low to mid 70s and lows in the low to mid 50s from Tue night through rest of the week. There is potential for tropical system to move northward over the Gulf of Mexico and into the central Gulf coast or southeast States late next week. Consensus of models keep its moisture south and southeast of central and southeast IL. Highs get closer to normal for late September in the upper 70s on Friday and next Saturday. 07 && .AVIATION... (For the 18z TAFs through 18z Sunday Afternoon) Issued at 1237 PM CDT Sat Sep 21 2024 1730z/1230pm radar imagery shows a broken line of convection extending from KGBG to just west of KIJX. This activity has been steadily pushing eastward, but is encountering a drier/more stable environment as it does so. Based on latest radar trends, have opted to add thunder mention at both KPIA and KSPI between 18z and 20z...but have left the remaining sites dry as the line will eventually dissipate as it crosses I-55. Winds are initially southeasterly, but will veer to the south late this afternoon and evening, then to the southwest overnight. The next wave of precipitation is still on target for late tonight, with HRRR/RAP timing similar to the previous TAF forecast. Have only made a few minor adjustments, bringing predominant light rain into KPIA by 09z then further east to KCMI by 12z. Ceilings will initially be VFR, but will lower to MVFR an hour or two after the rain begins. MVFR ceilings will then persist through the remainder of the 18z TAF period. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$