Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 09 2023 08:17:43 FOUS30 KWBC 090817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 317 AM EST Mon Jan 09 2023 Day 1 Valid 12Z Mon Jan 09 2023 - 12Z Tue Jan 10 2023 ....A MODERATE RISK OF EXCESSIVE RAINFALL CONTINUES ACROSS A LARGE PORTION OF CALIFORNIA, INCLUDING THE BAY AREA AND MUCH OF THE CENTRAL VALLEY... ....NUMEROUS FLASH FLOODING EVENTS LIKELY, SOME POSSIBLY SIGNIFICANT, ESPECIALLY OVER BURN SCARS... A more significant, elongated Atmospheric River (or AR) event is already beginning to impact much of CA ahead of a more amplified upper trough, effectively tapping into the subtropical regions of the north Pacific. Guidance continues to show PWs climbing between 1.25-1.5" (highest along the coast, and easily surpassing the max moving average per OAK and VBG sounding climatology), with southwesterly 850 mb flow peaking between 60-70 kts. Low to mid-layer moisture transport will be quite robust, as the 850-700 mb moisture flux peaks at 5 standard deviation range above normal, per the GEFS. Meanwhile, some elevated instability (at least 200-400 J/kg per the ECMWF, GFS, and HREF mean), along with the degree of deep-layer forcing and moisture, would support peak hourly rainfall rates of 0.75-1.00+ inch (especially within the Moderate Risk area). Overall, guidance consensus remains quite good with respect to the QPF, with 24 hour totals between 2-4+ inches over most areas (along with pockets of 5-8+ inches along the coast-coastal ranges and across the western slopes of the Sierra Nevada). This will be a fairly significant event as far as ARs go, with the latest deterministic QPF indicating a 5 to 10 year average recurrence interval (or ARI) within portions of the Moderate Risk area. In addition, the latest HREF 40km neighborhood probabilities of 3 hourly QPF exceeding current 3 hour FFGs climb to >50% within the Moderate Risk area after 15Z Monday. Considering how wet the soils will be ahead of this event (over the 90th percentile within the top 100 cm across the majority of the outlook areas per the latest NASA SPoRT), impacts from flash flooding or more rapid inundation will become increasingly likely -- especially across the several burn scars since 2020. Churchill/Hurley Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7HXkTLcVZ1ERPwqaFhQ5sPZCE7uNoDjGhap-Bbd16K8G= VyQELuOWgwuRNYqciqvyF3z2K10cmamLnNn-jmrlK_eslxM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7HXkTLcVZ1ERPwqaFhQ5sPZCE7uNoDjGhap-Bbd16K8G= VyQELuOWgwuRNYqciqvyF3z2K10cmamLnNn-jmrlCpe-dD4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7HXkTLcVZ1ERPwqaFhQ5sPZCE7uNoDjGhap-Bbd16K8G= VyQELuOWgwuRNYqciqvyF3z2K10cmamLnNn-jmrl0FmXBdg$=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) .