What Happened? Three storms in quick succession First two were standard PNW winter storms Third fueled by remnants of Typhoons Hagibis and Mitag. Heavy rain, rapid warm-up and snowmelt, hurricane-force winds.
What Happened? Flooding closed 20 miles of I-5 for several days Four data buoys damaged/set adrift Extensive power outages Eleven fatalities (five from avalanches) Total damage $1B+
First two storms 1 Dec: Heavy snow in mountains. 2 Dec: More snow, rain at lower elevations. Several inches of rain; 2-6” snow Coast Range; 12-20” Cascades
3-day precip, E foothills of Coast Range in Oregon
Third Storm Tropics-based storm brought heavy rain, rapid warming, strong winds Temp rose 30 ¡ F in 2h at low levels Coast Range snowpack melted Hurricane-force winds for 30h with many trees down, 40-50' seas, beach erosion
Third Storm One river rose 5 feet in 90 min, another 22 feet in 12 hours Five river forecast points exceeded highest stage of record A stretch of Interstate 5 submerged under 10 feet of water
Challenge 1 – Long Lead Times NWS Ocean Prediction Center issued excellent 96h forecast of the event Portland WFO issued a Hurricane Force Wind Warning with 33h lead Heavy rain predicted well in advance
Challenge 2 – Getting the Word Out Both Portland and Seattle WFOs use tone-alert on the weather radio for “major” flood warnings This was requested by customers and is effective However, it's a manual process in the wx radio software Both offices hosted Web conferences the day before the storm
Challenge 3 – Land/water Interface NWS issues separate warnings for land and water areas along coasts/Great Lakes shores “Busy” boundaries can result in less-than- optimum warned areas and extra work for forecasters
Challenge 4 – Multiple Warning Systems While the three warning-support programs at WFOs all work well, the fact that there are three can make life difficult for forecasters The NWS Service Assessment for this event (issued Sep 08) calls for “a single software application” for the outlook/watch/warning task.