Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
000
FOUS11 KWBC 200807
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
406 AM EDT FRI OCT 20 2017

VALID 12Z FRI OCT 20 2017 - 12Z MON OCT 23 2017


DAYS 1 THROUGH 3...

...PACIFIC NORTHWEST/NORTHERN CA INTO NORTHERN INTER-MOUNTAIN
WEST...

AN AMPLIFIED SHORT WAVE TROUGH WILL TRACK EAST ACROSS THE NORTHERN
ROCKIES AND CENTRAL ROCKIES TODAY AND INTO THE PLAINS TONIGHT. AN
INITIAL BURST OF SNOW OCCURS WITH THE 700 MB WAVE AND ASSOCIATED
CONVERGENCE UNTIL THE WAVE DEPARTS.
ON FRI THE STEADY RATE OF SNOW LEVELS DROPPING ACROSS THE PACIFIC
NORTHWEST/NORTHERN ROCKIES WITH HEIGHT AND THICKNESS FALLS
LEADS TO GREATER COVERAGE OF SNOW.  SNOW OCCURS IN THE WA/OR
CASCADES ON DEEP WEST SOUTHWEST FLOW WITH HIGH LAYER RELATIVE
HUMIDITY. THE GUIDANCE IS PINPOINTING ACCUMULATIONS FROM THE
CASCADES TO THE BLUE MTNS/SAWTOOTH RANGES AND BITTERROOTS/NORTHERN
ROCKIES AND TETONS.

ON SAT THE JET AXIS LIFTS NORTH ACROSS OR AND ID INTO WA AND
MT...SO SNOW TAPERS OVER OR/ID/NORTHWEST WY AND FOCUSES ON THE WA
CASCADES. STRONG 700 MB THETA-E ADVECTION ON THE NOSE OF THE 50 KT
700 MB JET PRODUCES STRONG ASCENT IN THE WA OLYMPICS AND CASCADES.
EXPECT HEAVY SNOW ACROSS THE WA CASCADES (ESPECIALLY NORTHERN)
WITH LIGHTER SNOW DOWNSTREAM IN THE ID PANHANDLE AND FRONT RANGE
IN MT.

STEADY ZONAL FLOW WITH ANOMALOUS MOISTURE TRANSPORT WILL CONTINUE
INTO WA ON SUN. THE RISING HEIGHTS WITH THE DEVELOPING RIDGE
APPROACHING FROM THE EASTERN PACIFIC SUPPORTS SNOW LEVELS RISING
AND KEEPS THE HEAVY SNOWFALL THREAT TO THE HIGHEST PEAKS OF THE
NORTHERN WA CASCADES/NORTHERN ROCKIES. THE ECMWF/GFS/NAM HAD
SIMILAR FORECASTS SO THE MODEL QPF AND TEMPERATURE PROFILES WERE
WERE WEIGHTED EQUALLY IN THE FORECAST.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT DAYS
1-3.

PETERSEN


$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.