Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jan 26 2025 00:40:54 FOUS30 KWBC 260040 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 740 PM EST Sat Jan 25 2025 Day 1 Valid 01Z Sun Jan 26 2025 - 12Z Sun Jan 26 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE TRANSVERSE/PENINSULAR RANGES AND LOS ANGELES BASIN OF SOUTHERN CALIFORNIA... ....Southern California... Showers will overspread southern CA tonight into early Sunday and will be capable of producing briefly heavy rain...although any=20 higher rates short be short lived given the transient nature of the showers. Overall not expecting rainfall amounts to be that high=20 through 12z Sunday, with totals mostly peaking in the 0.25"-0.5"=20 range. Thus generally not anticipating significant impacts from=20 this rainfall. However, given the ongoing wildfire/burn scar sensitivities over the region, and especially Los Angeles County, can not rule out=20 some highly localized debris flow/mudslide concerns later tonight=20 into Sunday morning. Although this risk will be greater later=20 Sunday into early Monday when embedded convective elements are more likely to result in areas of higher rainfall rates. Chenard Day 2 Valid 12Z Sun Jan 26 2025 - 12Z Mon Jan 27 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE TRANSVERSE/PENINSULAR RANGES AND LOS ANGELES BASIN OF SOUTHERN CALIFORNIA, AS WELL AS FOR PORTIONS OF THE TEXAS GULF COAST INTO THE LOWER MISSISSIPPI VALLEY... ...20Z Update: Limited changes were necessary for either risk area during the period as general continuity in the magnitude and orientation of convection for both areas was relatively maintained. Some minor details were added/emphasized within the "Texas Gulf Coast..." sub-heading below. Kleebauer ...Previous Discussion.. ....Southern California... Localized areas of moderate to heavy shower activity look to continue into Sunday and Sunday night for upslope portions of the Transverse and Peninsular Ranges (and to a lesser extent the adjacent Los Angeles Basin and coastal areas), though snow levels will be falling and that should help to mitigate runoff issues at higher elevations. An additional 0.75" to 1.50" is generally forecast for much of the same areas as Day 1, and concerns are greatest for isolated convection with 0.25"+/hr rates interacting with recent burn scar areas resulting in the potential for localized flash flooding and potential debris flows/mudslides (driven primarily by sub-hourly rates of 0.25", if able to manifest with very limited instability). While the bulk of the rainfall should be beneficial for the region, interests in the burn scars (and more sensitive flash flooding areas) should stay tuned to the forecast. Churchill ....Texas Gulf Coast into Lower Mississippi Valley... As a shortwave trough departs eastward this afternoon, low-level return flow will return to the western Gulf Coast along with a wave of low pressure, resulting in areas of moderate to heavy rainfall by Sunday morning. While areal average QPF is generally expected to be capped near 1" over a 3-6 hr period, 24-hr totals could add up to be locally as high as 3-4". While instability will be rather limited, MU CAPE up to 700 J/kg could support localized embedded convection capable of intra-hour rates closer to 2"/hr which adds to the threat, especially within any urbanized zones. There was a better consensus on the threat within the latest CAMs suite with the ECMWF still a bit further southwest with one of the primary QPF maxima compared to the other global deterministic. This is skewed compared to ML output which is pointed further northeast over far east TX into LA with less of an emphasis closer to Houston proper. The current output is still within reason for the MRGL risk but will monitor for any trends in the short term guidance that could sway for a targeted higher risk (SLGT) over the urban corridor. Churchill/Kleebauer Day 3 Valid 12Z Mon Jan 27 2025 - 12Z Tue Jan 28 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill/Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-urrkyMccIQFKhkJ5voETJf_9itWdfyh_Ksg0uJvdkCw= CMju3xOJzsJWx_d7Fp4KocCARPUBJB3j0iXl1j3VkL_PiT4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-urrkyMccIQFKhkJ5voETJf_9itWdfyh_Ksg0uJvdkCw= CMju3xOJzsJWx_d7Fp4KocCARPUBJB3j0iXl1j3VlfJ-Q2c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-urrkyMccIQFKhkJ5voETJf_9itWdfyh_Ksg0uJvdkCw= CMju3xOJzsJWx_d7Fp4KocCARPUBJB3j0iXl1j3VeDIzewU$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .