Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 29 2024 08:09:58 FOUS30 KWBC 290809 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 309 AM EST Thu Feb 29 2024 Day 1 Valid 12Z Thu Feb 29 2024 - 12Z Fri Mar 01 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF COASTAL OREGON AND NORTHERN CALIFORNIA, AS WELL AS THE LOWER ELEVATIONS AT THE FOOT OF THE SIERRA NEVADA... Current WV satellite imagery shows a large, closed upper-low off the Pacific Northwest with a funnel of moisture aimed into coastal WA and OR with a persistent southwest to northeast orientation. Rainfall totals of 2-4" with locally up to 5" have been seen across the Olympic Range in northwest WA down into the northwest corner of OR where the atmospheric plume has since settled over the past several hrs. We'll continue to see a steady southward progression of the moisture plume with flow generally perpendicular to the coastal plain of southwest OR into northern CA with the highest precip totals shifting to those areas through the forecast cycle. A modest surge is anticipated in the initial stages of the precip this morning with 1-3" likely falling across coastal OR and the adjacent ranges just inland over a 6-8 hr period. This will advance into northern CA by the late-morning and afternoon time frame with the main target now focused in-of the Klamath Range out to Mount Shasta and the Northern Sierra's. Snow levels will take a tumble through the period as the first cold front advances inland and changes the higher elevations quickly over to snow with the lower hills and coastal plain leftover as the primary rain beneficiaries. Totals of 2-4" with locally up to 5" are forecast within all of southwestern OR and northern CA with the highest totals mainly within the Sierra where snow will be the primary weather focus. Marginal Risk remains in place from previous forecast issuance, but the primary concern will not be about rates, but the prolonged moderate to heavy rainfall regime thanks to the stout moisture flux pattern associated with our closed upper-level circulation. Localized flooding concerns will be highest within the complex terrain situated below 3000ft MSL, especially within the windward confines of the coastal ranges just inland of OR and CA. Kleebauer Day 2 Valid 12Z Fri Mar 01 2024 - 12Z Sat Mar 02 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER COASTAL SOUTHWEST OREGON AND NORTHERN CALIFORNIA, AS WELL AS THE LOWER ELEVATIONS AT THE FOOT OF THE SIERRA NEVADA... A secondary surge within the life cycle of the atmospheric river will occur during the period with an IVT pulse between 300-500 Kg/ms aimed over northern and central California. A continued onslaught of precip with heavy rain confined to elevations below 3000ft MSL will generate flood potential through much of Friday. Daily totals between 2-3" will be common, on top of what fell the previous period bringing local totals to 3-6" within the concerned areas over the 48 hr time frame. Will be monitoring the progression of the snow levels closely as some guidance is becoming more bullish with the drop of the snow levels further than what has been forecast thanks to an anomalous height fall pattern with the mean trough responsible. Any deviation in the snow level will cause a shift in where any expected flooding could occur, so the adjustments made from the previous forecast package were in reference to the ensemble snow level forecast, and where multiday precip totals are reaching upwards of 2.5" or greater. Highest risk of flooding is the coastal plain north of Eureka on the windward side of the Klamath Range, as well as at the foot of the Sierra's within the Sacramento and San Joaquin Valleys.=20 Kleebauer 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!52vS3OCxYfTWzl__SgWLbSLwWJiA9dPi9GWc7fdxHuGk= DY8h3nQY4LXsAsn67tepdNOkmC-play2SVf_jAsTbGrQVNY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!52vS3OCxYfTWzl__SgWLbSLwWJiA9dPi9GWc7fdxHuGk= DY8h3nQY4LXsAsn67tepdNOkmC-play2SVf_jAsT-A4qwSE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!52vS3OCxYfTWzl__SgWLbSLwWJiA9dPi9GWc7fdxHuGk= DY8h3nQY4LXsAsn67tepdNOkmC-play2SVf_jAsTpS8aUkE$=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) .