Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 22 2023 15:55:57 FOUS30 KWBC 221555 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1055 AM EST Wed Feb 22 2023 Day 1 Valid 12Z Wed Feb 22 2023 - 12Z Thu Feb 23 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEASTERN MISSOURI TO SOUTHWESTERN MICHIGAN... A distinct mid-level wave over Texas this morning is ejecting northeastward and forecast to reach the Mid-Mississippi Valley by tonight. As this occurs, a surface low will continue to organize over Kansas and northern Missouri along a well-defined frontal boundary. Extending to the east of the low through the Ohio Valley and into the Mid-Atlantic, a slowly lifting warm front will provide a focus for sufficient lift as a 55+ kt 850 mb jet surges anomalous moisture into the boundary. This front is also forecast to stall as it lifts into central Illinois, Indiana, and Ohio later today, leading to the potential for rainfall to train over the same region. Meanwhile, a Pacific front will migrate eastward across the Ozarks and could produce brief periods of heavy rain. The primary focus for heavy rainfall (and potential for flash flooding) will reside across central/northern Illinois and northern Indiana during the forecast period (particularly through 03Z). During that time frame, persistent convergence along the warm front and lift/ascent from the approaching central Plains mid-level wave will result in scattered to widespread convection along that axis. That axis should also be favorably oriented to mid-level flow aloft for training at times. Areas of 1-2 inches of rainfall are probable, with locally higher totals possible where training or repeat convection can occur. Ensemble maximums show the ceiling for this event is around the 3 to 4 inch mark, specifically from central Illinois to northern Indiana. The convection will benefit from very anomalous moisture for this time of year (1.3+ inches just south of the front, which is about 4 standard deviations above the climatological mean according to the 06z GEFS) and speed convergence on the nose of 50-70 knots of low-level flow. Furthermore, FFG thresholds are fairly low (only 1-2 inches/3 hours) and are likely to be exceeded in spots where heavier rainfall can develop. Latest indications from models is that heavy rain ongoing over Missouri and developing cells along the warm front over central Illinois will migrate eastward and merge near central Illinois while spreading into northern Indiana as well. The risk on the northern extent of the outlook is mitigated by the extent of colder air and frozen precipitation, which should limit runoff where temperatures are below freezing. Changes to the outlook area for the 16z update include a small southward shift of the Slight Risk in Illinois and Missouri based on latest radar trends and 12z HREF probabilities. Most notably, the 12z HREF 40 km neighborhood probabilities for 6 hr QPF exceeding 2 inches has a stripe of 25-50% throughout the center of the highlighted Slight Risk. Additionally, the western portion of the Marginal Risk was shaved as the cold front progresses eastward. Snell Day 2 Valid 12Z Thu Feb 23 2023 - 12Z Fri Feb 24 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Cook Day 3 Valid 12Z Fri Feb 24 2023 - 12Z Sat Feb 25 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS COASTAL RANGES OF SOUTHERN CALIFORNIA... A large, deep storm system will amplify southward along coastal waters west of the Pacific Coast Friday and early Saturday. As this occurs, models indicate increasing southerly flow and IVT along an axis extending from near 30N/120W northeastward through the Transverse Ranges and into the southern Sierra. The orientation of the axis relative to the movement of the parent low will allow for persistent IVT (exceeding 400 kg/ms) along that axis throughout the forecast period, with QPF totals ranging from 3-7 inches - highest in terrain-favored areas. It is likely that snow will occur in higher elevations, though lower elevations will experience heavier rainfall (and rain rates exceeding 0.5 inch/hr at times), which could cause flash flooding in a few spots especially near burn scars. A Slight Risk has been introduced for portions of southern California that are expected to experience the heaviest rainfall (Santa Barbara to Orange counties). A Marginal Risk remains in place for areas of heavier rainfall that should either 1) total less than expected in the Slight Risk area or 2) experience snowfall at times. Cook Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6MLhmljeomZ94gQfG3Bh2Eq27FFHE-vcnVLt3u77XPRB= u2GJDqilvoiPbtE5HpTYpkwoxibYmg7oQ2jFbVwqzcnUUyY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6MLhmljeomZ94gQfG3Bh2Eq27FFHE-vcnVLt3u77XPRB= u2GJDqilvoiPbtE5HpTYpkwoxibYmg7oQ2jFbVwqNxXIeCw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6MLhmljeomZ94gQfG3Bh2Eq27FFHE-vcnVLt3u77XPRB= u2GJDqilvoiPbtE5HpTYpkwoxibYmg7oQ2jFbVwqcds4J-E$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .