Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 13 2024 20:15:00 FOUS30 KWBC 132014 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 313 PM EST Tue Feb 13 2024 Day 1 Valid 16Z Tue Feb 13 2024 - 12Z Wed Feb 14 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20=20 =20 Otto Day 2 Valid 12Z Wed Feb 14 2024 - 12Z Thu Feb 15 2024 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHWEST OREGON & NORTHWEST CALIFORNIA... Portions of coastal OR and northwest CA... The southern lobe of an elongated mid to upper-level trough/closed low, currently between 140W and 150W, is forecast to near the Oregon/California coasts around 00Z Thursday. While uncertainty remains in the evolution of this feature and its interaction with a developing closed low off of the Washington coast, the 12Z models have come into better agreement with the pattern evolution through 12Z Thursday. Warm advection driven precipitation should be ongoing at the start of the period across southwestern Oregon into northern California but the highest intensity rainfall should arrive with an occluded/cold front with the 12Z HREF indicating the probability of exceeding 0.5 in/hr rainfall at 10 to 30 percent near the Oregon/California border near the coast and 30 to 50 percent between Cape Mendocino and the Santa Lucia Range. However, the progressive nature of the front and very weak instability (< 250 J/kg) should limit the duration/magnitude of these higher rates with localized 2-4 inch totals over the 24 hour period ending 12Z Thursday. The highest rainfall should focus along south to southwesterly facing slopes given a similar orientation of the low level wind. Across the northern foothills of the Sierra Nevada, there will be a narrow region below snow levels of 5,000 to 6,000 feet where locally heavy rain of 2-3 inches and brief rainfall rates over 0.5 in/hr will be possible. However, this inland region appears too low end for a Marginal at this time. Relatively dry weather over the past week across northern California into southwestern Oregon has allowed area rivers/streams to return to near normal levels after heavy rainfall from earlier in the month. Given the relatively short duration of higher rainfall rates at a given point (2-3 hours), the threat for flash flooding is expected to remain very isolated and perhaps best focused in recent burn scars. The Marginal Risk along the Coastal Regions was left in place with only minor adjustments from continuity. Otto Day 3 Valid 12Z Thu Feb 15 2024 - 12Z Fri Feb 16 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Lower Rio Grande Valley of Southern TX... A southern stream upper level trough is forecast to track east, reaching western Mexico by Friday morning. low level moisture return will increase precipitable water values into the 1.5 to 2.0 inch range by 12Z Friday for southern Texas, with the 12Z NAM/GFS/ECMWF in good agreement on the moisture return. While there is no defined frontal boundary returning north in the western Gulf of Mexico, the guidance shows a low level low forming south of the Rio Grande in northeastern Mexico with enhanced moisture transport to its east. Low level winds are expected to remain mostly weak except near the end of the period as the upper trough edges closer. Nonetheless, relatively dry weather over the past couple of weeks, a lack of better instability (12Z consensus of <500 J/kg MUCAPE), should limit rainfall totals to 2-4 inches localized maxima through 12Z Friday. These values do not rise up to the level of concern for flash flooding with agreement from the local WFOs. The area will continue to be monitored for changes with future forecast cycles. Otto Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9tt7CFfNRm9RoQbZLJsS55j56ZYaA5J8r3czksjDPjJm= 6_K2T3o89gA8UdxHo4-XMaLo7ktpsMG0W1Ad12kLwYxiNIg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9tt7CFfNRm9RoQbZLJsS55j56ZYaA5J8r3czksjDPjJm= 6_K2T3o89gA8UdxHo4-XMaLo7ktpsMG0W1Ad12kLKyHavs0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9tt7CFfNRm9RoQbZLJsS55j56ZYaA5J8r3czksjDPjJm= 6_K2T3o89gA8UdxHo4-XMaLo7ktpsMG0W1Ad12kL0dntZQ8$=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) .