< Day 2 Outlook
WPC Day 3 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 2033 UTC Fri Feb 22, 2019
Valid: 12 UTC Feb 24, 2019 - 12 UTC Feb 25, 2019
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 PM EST Fri Feb 22 2019
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.
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt