Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
317 AM EST Sun Jan 26 2020
 
Day 2
Valid 12Z Mon Jan 27 2020 - 12Z Tue Jan 28 2020 

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR COASTAL 
AREAS OF THE PACIFIC NORTHWEST...

...Southwest Washington to northwest California...

Strong energy and moisture will be directed into the Pacific 
Northwest resulting a vast area of precipitation. A broad area 
with enhanced vertical motion will develop over the coast and 
inland over the Cascades as the trough nears the coast and 
eventually moves inland. During this time low-level, W/SW flow of 
35 to 50 knots will be transporting PW values of 0.50 to 1 inch 
nearly orthogonal to the terrain; which will help sustain several 
hours of moderate to the heavy rainfall. Model guidance continues 
to focus 1 to 3 inches all along the Washington to northern 
California coast with local maxes of 4 to 6 inches. Rainfall rates 
0.50 inch per hour or greater could quickly lead to an increased 
risk for flash flooding, or debris flows in sensitive areas such 
as steep terrain or burn scars. As previously noted, portions of 
this region have had >150% percent of normal precipitation 
resulting in saturated soils with additional rainfall quickly 
becoming runoff. The Marginal Risk for excessive rainfall that was 
in effect for southwest Washington to northwest California remains 
valid for this issuance.

Campbell

 
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt