Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 24 2022 20:31:27 FOUS30 KWBC 242031 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 330 PM EST Sat Dec 24 2022 Day 1 Valid 16Z Sat Dec 24 2022 - 12Z Sun Dec 25 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE COASTAL MOUNTAINS AND CASCADES OF SOUTHERN WASHINGTON AND OREGON... ....16Z Update... No changes made to the inherited Marginal Risk area in the Pacific Northwest. The front is approaching the coast as of the time of this writing. Thus, rainfall rates are expected to increase over the next few hours into the coastal mountains. This will be the prime time for the greatest chances of excessive rain causing flash flooding, especially in the Olympic Mountains. As the front moves inland this afternoon, the rain will both weaken and align more perpendicular to the coast. Both of these factors will greatly diminish the overall rainfall threat for the rest of today through tonight. Thus, the Marginal Risk may be able to be canceled early. For additional details, please reference MPD 1169 recently issued at https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/metwatch/metwatch= _mpd_multi.php?md=3D11__;!!DZ3fjg!_quE6YQovXaU8JDDUcS8ack2AfIKs7U8dPNjsvPzV= xIyvtgrhky0xwLYngbjDDhIFF-ezbA90SSmgLweuHLDqqNk5pI$=20 69&yr=3D2022. Wegman ....Previous Discussion... A weak shortwave trough will arrive over British Columbia today. The surface wave associated with this system will advect a shallow plume of moisture into the Pacific Northwest along a weak and progressive cold front. PWAT's between 0.5-1.25 inches and anomalies of 2-3 standard deviations will support periods of heavy rain throughout the day before wrapping up early this evening. Isolated instances of flash flooding are possible, especially over the higher elevations of the Olympics and Washington/Oregon Cascades. Kebede Day 2 Valid 12Z Sun Dec 25 2022 - 12Z Mon Dec 26 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE COASTAL MOUNTAINS OF WASHINGTON AND OREGON... ....2030Z Update.... Very few changes needed for this afternoon's update. Rain will be fairly light for the morning hours as an upper level front and disturbance move into the coast, largely north of the area into British Columbia, so only the southern end of the front impacts Washington State in the morning. The primary event of concern begins in the evening, and continues through the overnight, as a much stronger upper level front with an attendant surface front plow into the Washington and Oregon coasts. There is some disagreement in the high resolution guidance as to how this event will evolve, with some suggesting steady rain into the Olympic Peninsula for the first half of the overnight until a stronger front expands the rain shield south into Oregon for the second half of the night, while others having it largely dry until the stronger front moves in. Regardless, the primary threat for flash flooding remains along the Olympic Peninsula, especially along south and southwest facing mountains. Wegman ....Previous Discussion... Another weak shortwave trough will break off from an upper low and arrive over British Columbia early Monday morning. Therefore, any rain impacts associated with this system will take place later in the day 2 period (early Monday morning). Moderate to heavy rainfall may focus along the higher elevations of the Washington/Oregon coastal ranges. PWATs hovering around 1 inch will be 2-3 standard deviations above average for the region. The progressive nature of this system will mitigate any impacts from potential heavy rainfall as well. Kebede 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!_quE6YQovXaU8JDDUcS8ack2AfIKs7U8dPNjsvPzVxIy= vtgrhky0xwLYngbjDDhIFF-ezbA90SSmgLweuHLDEZSVIi0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_quE6YQovXaU8JDDUcS8ack2AfIKs7U8dPNjsvPzVxIy= vtgrhky0xwLYngbjDDhIFF-ezbA90SSmgLweuHLDmjgxkmc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_quE6YQovXaU8JDDUcS8ack2AfIKs7U8dPNjsvPzVxIy= vtgrhky0xwLYngbjDDhIFF-ezbA90SSmgLweuHLDDqfEjCg$=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) .