Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jan 23 2025 20:51:38 FOUS30 KWBC 232051 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 351 PM EST Thu Jan 23 2025 Day 1 Valid 16Z Thu Jan 23 2025 - 12Z Fri Jan 24 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 2 Valid 12Z Fri Jan 24 2025 - 12Z Sat Jan 25 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 3 Valid 12Z Sat Jan 25 2025 - 12Z Sun Jan 26 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS=20 OF THE TRANSVERSE RANGES AND LOS ANGELES BASIN OF SOUTHERN=20 CALIFORNIA... ....Southern California... A developing closed low over central California by late Saturday will foster an area of surface low pressure across the Central Valley which will then refocus offshore of the coastal ranges Saturday night and Sunday morning. This will help set the stage for weak and relatively moist onshore flow to aim into the Transverse Ranges. This onshore flow coupled with DPVA and steepening mid-level lapse rates will allow for the development and expansion of moderate to locally heavy shower activity, and especially by Sunday morning when some pockets of locally stronger convection may be possible. This will include areas from Santa Barbara County on down through Los Angeles County, and also the western portions of San Bernadino and Riverside Counties. A somewhat stronger and wetter solution is being advertised by the latest model guidance compared to previous cycles, and generally as much as a 0.5" to 0.75" of rain is forecast by Sunday morning with the heaviest totals most likely over the San Gabriel Mountains where there will be somewhat stronger orographic ascent/upslope flow facilitating slightly higher rainfall rates (potentially reaching 0.25"+/hour). Given the ongoing wildfire/burn scar sensitivities over the region, these rains Saturday night and Sunday morning may be heavy enough to result in some localized debris flow and related flash flooding activity. Therefore, the Marginal Risk has been maintained over portions of the Transverse Ranges and the Los Angeles Basin. The Marginal Risk area has also been expanded just slightly eastward into portions of western San Bernadino and Riverside Counties along with a small portion of Orange County. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4xd4BPnlV3G9zXLz15tfZ48f86IZ0c1knaztwXxAPybi= 8wc1JL03BCSVwkSYnLPP3jM1GYQqbBOzHio0Y_QfI6zY2Uc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4xd4BPnlV3G9zXLz15tfZ48f86IZ0c1knaztwXxAPybi= 8wc1JL03BCSVwkSYnLPP3jM1GYQqbBOzHio0Y_QfDcl2urs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4xd4BPnlV3G9zXLz15tfZ48f86IZ0c1knaztwXxAPybi= 8wc1JL03BCSVwkSYnLPP3jM1GYQqbBOzHio0Y_Qf9seDQpo$=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) .