Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 PM EST Fri Feb 22 2019
 
Day 3
Valid 12Z Sun Feb 24 2019 - 12Z Mon Feb 25 2019 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE NORTHERN COAST OF CALIFORNIA AND THE EXTREME SOUTHWEST 
PORTIONS OF THE PACIFIC NORTHWEST...

An elongated mid-level trough will dive slowly southward along the 
Pacific Northwest Coast while Pacific Jet energy aloft transports 
robust moisture into northern CA and southern OR. Focused moist 
advection on rich W/SW 850-700mb flow will drive PWAT values into 
the area of 1.5 standard deviations above the climatological mean, 
favorable for periods of heavy rainfall. Synoptic ascent due to 
height falls and diffluence within the Pacific Jet streak will 
produce a relatively narrow but prolonged band of heavy 
precipitation south of the sinking upper trough.

This long duration of moisture transport and orographic 
enhancement into the terrain due to nearly orthogonal 700mb winds 
has the potential to produce widespread heavy rain, and there is a 
multi-model signal for 3-6 inches of rainfall during this time. 
Rain rates are not expected to be extraordinarily heavy as noted 
by SREF probabilities remaining low for 1" in 6 hours, but will 
likely become enhanced along the upwind side of the terrain. 
Additionally, snow levels rising to around 5000 feet will allow 
for rain falling on top of snow-covered ground, potentially 
exacerbating flooding concerns locally.

Weiss
 
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt