Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 16 2023 00:03:21 FOUS30 KWBC 160003 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 702 PM EST Sun Jan 15 2023 Day 1 Valid 01Z Mon Jan 16 2023 - 12Z Mon Jan 16 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERNMOST CALIFORNIA... ....Washington and Oregon coasts... A low pressure area off the Oregon coast will continue to move north and northeastward...allowing for a fetch of moisture to be transported onshore into Washington. Precipitable water values on the order of 0.5-0.75" will be drawn inland toward the coast and the coastal ranges by low level winds of 20 to 35 kts. MU CAPE of 100+ J/kg also exists per SPC mesoanalyses. While the 18z HREF probabilities of 0.5"+ an hour are negligible, the combination of available moisture and instability could allow hourly rain totals to approach such values. Precipitation over the past week has been 200-400% of average, so some soil sensitivity is possible.=20 Made alterations to continuity to account for radar reflectivity trends. ....California... Moisture transport is ramping up prior to the arrival of the surface low and associated upper level trough later in the evening. Patches of MU CAPE of 100+ J/kg exist in and near northern and central CA per SPC mesoanalyses. IVT values increase to around 500 kg/m/s in southern California near the Peninsular Range as 850 hPa winds approaching 50 kts become normal to the range axis toward the very end of the period/early Monday morning. Thinking is that rainfall amounts of 1-2" would occur in the mountains with a few spots with hourly totals in excess of 0.5", which is seen in the 18z HREF probabilities primarily after 09z.=20 To account for the MTR/Monterey CA flood watches which appears to be due to their soil sensitivity as much as the steady rainfall expected in their area, drug the Marginal Risk north to encompass the Bay area. Otherwise, some rounding off of the risk areas, based on a neighborhood probability approach, were made. ....Arizona... A Marginal Risk area was maintained for portions southeastern AZ with this update due to the short term potential for convection.=20 Radar imagery shows some occasional cell training in this area, but the 18z HREF indicates that any heavy rain related issues should wane over the next few hours. Hourly rainfall rates, which may briefly exceed 0.5 inches/hour, are possible before activity fades this evening. Roth Day 2 Valid 12Z Mon Jan 16 2023 - 12Z Tue Jan 17 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA AND CENTRAL ARIZONA... .....Central and Southern California... Shortwave energy crossing central and southern CA early in the period coupled with a progressive, but fairly robust surge of low to mid-level Pacific moisture is expected to bring areas of heavy showers to the Central Valley and the adjacent foothills of the Sierra Nevada on Monday. The same axis of moisture and energy will also be impacting the Transverse and Peninsular Ranges of southern CA at least early in the period. Additional rainfall amounts of 1 to 2 inches, with isolated heavier amounts, will be possible across the higher terrain where favorable orographics/upslope flow will yield stronger forcing. Lesser amounts of under 1 inch are expected in the Central Valley. However, given the wet antecedent conditions across the region, some spotty runoff problems and flooding can't be ruled out given the additional rains. This will especially be the case across areas of far southern CA where heavy rains will actually be continuing over from late in the day 1 period (Sunday night/early Monday) and carrying over into day 2. The Marginal Risk will be maintained across all of these areas. ....Central Arizona... Moist upslope flow south and west of the Mogollon Rim will be a primary component driving the rainfall ahead of the approaching upstream shortwave that initially impacts central and southern CA this period. PWs rise to between 0.5 to 0.75 inches across much of central AZ near and adjacent to higher terrain, with IVT values that reach on the order of 300 to 500 kg/m/s around the southeast flank of the approaching shortwave trough. This coupled with favorable upper-level divergence/DPVA parameters and the moist upslope flow should help focus some 1 to 2 inch rainfall totals, with a couple of spotty heavier amounts possible across the southwest facing slopes of the higher terrain. Some spotty 0.5"/hour rainfall rates will be possible and the 12Z HREF guidance does advertise some low-end probabilities of this occurring. This coupled with the additional storm totals has the potential to result in minor, localized flooding in poor drainage areas, and near hydrologically sensitive locations including the area dry washes. Bann/Orrison Day 3 Valid 12Z Tue Jan 17 2023 - 12Z Wed Jan 18 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_es2_OyL1foahRdPUNZUj6VJor6erHNnFK1hohOmuniU= 3JVZBNcTfcGa8RAUWpwcjVzqkB2Zwrh6Ti40_27n5jP47aU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_es2_OyL1foahRdPUNZUj6VJor6erHNnFK1hohOmuniU= 3JVZBNcTfcGa8RAUWpwcjVzqkB2Zwrh6Ti40_27npKQQ2i8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_es2_OyL1foahRdPUNZUj6VJor6erHNnFK1hohOmuniU= 3JVZBNcTfcGa8RAUWpwcjVzqkB2Zwrh6Ti40_27nyE5RsQo$=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) .