Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 22 2023 08:18:30 FOUS30 KWBC 220818 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 318 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 initially over Texas at 12Z will eject northeastward, reaching the Mid-Mississippi Valley by 00Z Feb 23.=20 As this occurs, a surface low will continue to organize over Kansas and northern Missouri. A strong warm front will remain lift northward across Indiana and Illinois, but stall at some point during the forecast period. Meanwhile, a Pacific front will migrate eastward across the Ozarks, but should also stall during the latter half of the forecast period. The primary focus for heavy rainfall (and potential for flash flooding) will reside across northern Illinois and northern Indiana during the forecast period (particularly from 21Z through 06Z). 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. The convection will benefit from very anomalous moisture for this time of year (1.3+ inches just south of the front) 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.=20 Latest indications from models is that heavy rain (ongoing over Missouri early in the day) will migrate eastward through Illinois in the 18-03Z timeframe while spreading into northern Indiana after 21Z. The risk on the northern extent of the mitigated by the extent of colder air and frozen precipitation, which should limit runoff where temperatures are below freezing. A secondary area of concern for flash flooding exists in Missouri and northeastern Oklahoma along the Pacific front earlier in the day (from 12Z-00Z). Most storms should be fairly progressive along the front, which should limit rainfall totals in most areas. QPF peaks in central Missouri through the afternoon, however, and these rainfall totals could be exacerbated where convective training can occur. Isolated instances of flash flooding are possible in this scenario, and a Marginal Risk remains in place. Lighter rainfall totals are also expected in northern Ohio, and the Marginal Risk area here is a bit more conditional compared to areas upstream. Cook 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!4wh_7cElYGPdkC9bFWdBLCEjy-vb46PR0HWopzR3vAJz= U1jks8H2_ndnCsdbuDgvFn4jTx_mBjOiMlugpJJSkgbv1zc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4wh_7cElYGPdkC9bFWdBLCEjy-vb46PR0HWopzR3vAJz= U1jks8H2_ndnCsdbuDgvFn4jTx_mBjOiMlugpJJS_ii3Whg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4wh_7cElYGPdkC9bFWdBLCEjy-vb46PR0HWopzR3vAJz= U1jks8H2_ndnCsdbuDgvFn4jTx_mBjOiMlugpJJSopz7c2c$=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) .