Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jan 18 2024 15:57:34 FOUS30 KWBC 181557 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1057 AM EST Thu Jan 18 2024 Day 1 Valid 16Z Thu Jan 18 2024 - 12Z Fri Jan 19 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF WESTERN WASHINGTON... ....16z Update... The inherited Marginal Risk area was cut back on the southern tip over northwestern Oregon, since the heaviest rainfall should be done over northwestern Oregon by 16/17z. Precipitation is still on track to spread north along a warm front. IVT and moisture transport are forecast to increase over western Washington this afternoon and evening, where hi res guidance also signals for the heaviest 24hr QPF totals ending at 12z Friday. Southerly flow into the Pac NW could create runoff concerns along the southern slopes of the coastal ranges and Olympics. Kebede ....Previous Discussion... A Marginal Risk was maintained across portions of the Olympic Peninsula southward into northwestern Oregon, where moderate to heavy rainfall, along with snow melt in some areas may lead to excessive runoff. Guidance shows precipitation spreading north with a well-defined warm front lifting across the region today.=20 GFS and ECMWF IVT indicate significant moisture transport into the region beginning later this morning. Model consensus shows 1-2 inches, with locally heavier amounts across the region. The heaviest amounts are expected along the southern slopes of the Olympics, where upslope flow is likely to bolster amounts. This along with rising snow levels and low-level snow melt may raise the threat for isolated excessive runoff. Pereira Day 2 Valid 12Z Fri Jan 19 2024 - 12Z Sat Jan 20 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN CALIFORNIA... Guidance continues to show a well-defined mid-level shortwave and its associated frontal system moving into Northern California by early Saturday. As noted in the previous discussion, the need for a Marginal Risk remains borderline with guidance showing the associated IVT plume steadily weakening as it moves onshore. In addition, the 00Z model cycle is overall slower to develop heavier amounts and areal averages have generally come down in this latest run, especially for the more inland areas. However, there remains some spread with some models including the ECMWF/CMC and their ensemble means still showing some potential for locally heavy amounts, especially along the coast north of SF Bay. This is where the models continue to indicate some of the stronger forcing and deeper moisture will coincide, especially late in the period.=20 Therefore, given the wet antecedent conditions and at least some potential for localized heavier amounts, opted to maintain a Marginal Risk from SF Bay northward into the Northern Coast Ranges. Pereira Day 3 Valid 12Z Sat Jan 20 2024 - 12Z Sun Jan 21 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON... Precipitation will continue to spread across the region as a mid-to-upper level shortwave slowly drifts onshore. While guidance shows the leading IVT plume continuing to weaken as it moves further inland, westerly to southwesterly flow south of the parent low is forecast to tap some deeper moisture, directing it inland across the region as it weakens and nears the coast on Saturday. The 00Z deterministic and ensemble guidance was overall in generally good agreement indicating that 1-2 inches, with locally heavier amounts likely within the highlighted region.=20 This along with the wet antecedent conditions may raise isolated runoff concerns. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9EyNS_EqU0RXlmgakAPaCMGL8ihuLikbF-sw7uavc9v6= WeHINlfnCdahV8LOzwpT23XuI49FfX4_OqD-o-zDQmX3vdQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9EyNS_EqU0RXlmgakAPaCMGL8ihuLikbF-sw7uavc9v6= WeHINlfnCdahV8LOzwpT23XuI49FfX4_OqD-o-zD3FwwmJo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9EyNS_EqU0RXlmgakAPaCMGL8ihuLikbF-sw7uavc9v6= WeHINlfnCdahV8LOzwpT23XuI49FfX4_OqD-o-zDXKF2qns$=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) .