Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 06 2023 08:09:28 FOUS30 KWBC 060809 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 308 AM EST Mon Nov 06 2023 Day 1 Valid 12Z Mon Nov 06 2023 - 12Z Tue Nov 07 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHWESTERN WASHINGTON INTO NORTHERN CALIFORNIA... The Marginal risk was left mainly unchanged across portions of northwest OR into southwest WA. Both IVT and PW magnitudes are lower today compared to some of the previous days, so not really looking at an AR type of event today across this area. Instead rainfall will be more showery in nature, driven by the approaching surface low, mid level trough and embedded shortwaves. The increased synoptic ascent associated with these features and the steepening lapse rates will drive the showery rainfall threat. With the height falls and aforementioned steep lapse rates some instability will be present today...thus expecting we will see scattered heavier convective elements move across the area, locally enhancing rainfall rates. Convective cells will be quick moving, but 00z HREF guidance supports some localized 0.5" an hour rainfall within any heavier cells. Additional rainfall after 12z of 1-3" is expected across this area, with a few of the more orographically favored areas exceeding 3". This is on top of the 5"+ amounts that have fallen over the past few days, which has helped saturate the top levels of soil. Given this increased saturation most of this additional rainfall will become runoff..and thus localized areas of excess runoff within the aforementioned convective cells could result in some isolated areas of flooding. We did opt to add in a Marginal risk across portions of northwest CA and southwest OR as well. Generally the same story here, with steepening lapse rates resulting in embedded convective cells moving across the area today. The core of heaviest rainfall here should be exiting by 12z but can not rule out some heavier cells lingering just beyond 12z. Also, some additional convective cells appear likely to move ashore through the day as well...although the activity after 12z should generally be less organized. Nonetheless sub hourly rainfall of over 0.25" appears possible through the day...which combined with the antecedent rainfall and some sensitive burn scars in the area...suggests some localized flood risk could linger. A Marginal risk was also extended into portions of the western slopes of the northern Sierra as well. This area has not seen as much antecedent rainfall, and thus is generally not as sensitive to localized flooding. However this is the corridor where the highest rainfall rates appear likely today, which may offset the drier soils and still produce a localized threat. Areas of enhanced convergence as a cold front drops south and interacts with the terrain should result in a few periodic linear backbuilding convective segments, which may be capable of dropping localized 0.5"-1" an hour rainfall.=20 Chenard 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!5z4B80Ci5vkrs6ze2b6sih5obfvA4birsDSLyWrx4O6X= 8KBsFPKt48Sv52sfebc8eWF5EjKyCIRFjxstXen5Cc1ejYQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5z4B80Ci5vkrs6ze2b6sih5obfvA4birsDSLyWrx4O6X= 8KBsFPKt48Sv52sfebc8eWF5EjKyCIRFjxstXen5tRIVPj8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5z4B80Ci5vkrs6ze2b6sih5obfvA4birsDSLyWrx4O6X= 8KBsFPKt48Sv52sfebc8eWF5EjKyCIRFjxstXen5EH56VR0$=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) .