Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Nov 04 2023 20:04:21 FOUS30 KWBC 042004 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 403 PM EDT Sat Nov 04 2023 Day 1 Valid 16Z Sat Nov 04 2023 - 12Z Sun Nov 05 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR THE BURN SCARS OF FAR SOUTHWEST OREGON AND NORTHWEST CALIFORNIA... ....16Z Update... The previous MRGL across the Olympic Peninsula was removed with the event coming to an end shortly as the drier air advects in before the cold front. The MRGL risk over FL was also removed as the frontal boundary will stay far enough offshore with the instability gradient far enough off the coast and steering pattern expected to keep primary convection offshore. A few cells may wander onshore within both Miami-Dade and Broward counties, but prospects for heavy rainfall necessary for flash flooding have dropped off precipitously. ....Pacific Northwest... Cold front associated with our low pressure and atmospheric river event is currently positioned just of the coast of WA and northwest OR with low-level WV satellite indicating a tongue of drier air beginning to protrude the immediate coast. This will subsequently diminish the heavy rain potential across WA state where the heaviest rain has fallen overnight through this morning. Further south, seeing the indications of the AR shifting focus into southwest OR with heavier echoes now positioned to come ashore within the next hour. Guidance is very consistent on a period of heavy rainfall between 16-22z across the immediate coast and areas within the Klamath Mtns. 12z HREF blended mean QPF has wavered very little from run-to-run over the past 24 hrs with a general 1.5-2.5" expected over the southwest corner of OR into the very northwest edge of CA over the rest of the morning and afternoon. Smith River complex burn scar just inland of the coastal plain will remain the primary focus for flash flooding as low-topped convection is possible within the area during the peak of the event. With the lower threshold necessary for flash flood risks within the burn scar, there was plenty of merit to continue on with the MRGL risk from prior forecasts. Kleebauer Day 2 Valid 12Z Sun Nov 05 2023 - 12Z Mon Nov 06 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR SOUTHWEST OREGON AND NORTHWEST CALIFORNIA... A general break between AR events is anticipated during the first portion of the period, but a second AR of lower magnitude is forecast to press into the PAC Northwest with locally moderate to heavy rainfall focused over the coastal areas of Northwest California and Oregon. Forecast intergrated vapor transport (IVT) is a full magnitude lower with indices around 350-450 kg/ms leading to a lower scale of AR event, but compounded on top of the previous events over the past 5 days. The primary focus in the initial surge of precip will be over the southwestern OR and northwest CA coast(s) with some protrusion inland across the Klamath Mtns where a few burn scars are located and have the highest sensivity to heavier bouts of precipitation. 12z HREF blended mean guidance, as well as NBM/Ensemble bias-corrected model guidance indicates a general maximum located over the above corridor leading to a limited ability for any appreciable drying from the previous event occurring today. 12z HREF probabilities for rates of 1"/hr or better are not as robust as the current event unfolding, but a solid area of 15-20% across the Oregon coast and adjacent mountains are being depicted which matches well with the HREF EAS probability of where at least 2" of rainfall over the period could occur (30-40%). Further to the north, the rainfall rates will be much lighter and despite the multiple rounds of precipitation the past few days, flash flooding concerns will be much lower, although some nuisance flooding is possible within any urbanized areas. More rain is also expected over the Olympic Peninsula, but exceeding anything greater than 0.3"/hr will be tough to come by given the best ascent aligned further south as the nose of the jet streak off the Pacific is focused over the southern half of OR and northern California. Have removed the MRGL risk from previous forecast issuance across the northern half of the Oregon coast up through northwestern Washington, but maintained the MRGL outlook over southwest OR and northwest CA where the heaviest rain is forecast and within the confines of the remnant burn scars within the terrain.=20 Kleebauer Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_UvUh2UthFPtSdf0D_7jepQ6wCZLz0YQ8gIWedWMIVGP= G2YZMe0vNcTP8Pe9tdanTZ0-1rtoNHSjnbOGA66_RdKoidY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_UvUh2UthFPtSdf0D_7jepQ6wCZLz0YQ8gIWedWMIVGP= G2YZMe0vNcTP8Pe9tdanTZ0-1rtoNHSjnbOGA66_A8fOaVo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_UvUh2UthFPtSdf0D_7jepQ6wCZLz0YQ8gIWedWMIVGP= G2YZMe0vNcTP8Pe9tdanTZ0-1rtoNHSjnbOGA66_C6ASX3Q$=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) .