Weekend Flood Concerns
By Rod Hill on 2020-12-18
Heavy weekend rains may lead to flooding issues in typical smaller water way basins and near burn scars
left from September’s wildfires. Forecast models show 2.25 - 3.00” of total rainfall tonight through the day
Monday over the Willamette Valley and southwest Washington. Coast rain totals may reach 3.00 - 4.50”
and mountain rain totals could reach 6.00” through Monday.
The wildcard is the unknown potential for rapid runoff over the wildfire burn scars areas along the west slope
of the Cascades and in Lincoln County. Assuming weather models are correct with rain projections, the rain
totals spread out over 3-4 days would likely not produce widespread issues, but again the runoff potential over burn
scars is an unknown.
Current timing of rain shows a separate front bringing around 1/4” of rain this evening and then hours of steady rain
arriving late Saturday afternoon and pouring through the day Monday.
A classic flood risk would deliver 6” of mountain rain over a 24-36 hour time frame. This weekend’s rain event will
be spread out over 3 days as mentioned, which will help minimize the flood risk. The graphic below shows total rainfall potential Friday night through Monday evening:
Snow levels will be high, rising to 7,500’ Saturday night and holding near to above 6,000 feet through Monday morning.
Rod Hill
December Winter Outlook Update