Quantitative Precipitation Forecast
Issued by NWS

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000 FOUS11 KWBC 251944 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 344 PM EDT SAT OCT 25 2014 VALID 00Z SUN OCT 26 2014 - 00Z WED OCT 29 2014 DAYS 1 THROUGH 3... ...PACIFIC NORTHWEST/NORTHERN AND CENTRAL ROCKIES... A DEEP LAYER LONGWAVE TROUGH IS FORECAST TO CROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES ON DAY 1...AND THEN ACROSS THE NORTHERN PLAINS AND EXITING THE CENTRAL ROCKIES TO THE CENTRAL PLAINS ON DAY 2. THE FORECAST WAS DERIVED FROM A BLEND OF THE 00Z ECMWF/12Z NAM/12Z GFS QPF AND TEMPERATURE PROFILES. ON DAY 1...THE STRONGEST MOISTURE FLUXES AND ANOMALIES CROSS WA STATE AND THEN NORTHERN ID AND NORTHWEST MT. PRE-FRONTAL 700 MB CONVERGENCE/300 MB DIVERGENCE OCCURS AHEAD OF THE WAVE...RESULTING IN ASCENT ACROSS THE NORTHWEST AND NORTHERN ROCKIES. SEVERAL INCHES ARE POSSIBLE ACROSS THE NORTHERN CASCADES OF WA......SOUTHERN CASCADES OF OREGON...THE SEVEN DEVILS AND SAWTOOTH RANGES OF ID...AND THEN INTO THE RANGES OF NORTHWEST WY/ADJACENT SOUTHWEST MT ON SUNDAY. SNOW CONTINUES EARLY DAY 2 IN WY AS THE UPPER TROUGH CONTINUES TO MOVE EAST...WITH A SECONDARY AREA IN THE RANGES OF CENTRAL TO NORTHERN ID IN DIFLUENT FLOW ALOFT AS THE 300 MB JET MAXIMA CROSSES WA AND OR AND THEN ID ON MON. LOWERING SNOW LEVELS AND PERSISTENT UPSLOPE FLOW WILL PRODUCE AREAS OF LIGHT SNOW ACROSS THE HIGHER TERRAIN OF NORTHWEST WY. ON DAY 3...THE UPPER RIDGE PROGRESSES INLAND ACROSS THE NORTHWEST AND NORTHERN ROCKIES...FOLLOWED BY ZONAL WEST TO EAST ALOFT. THE 300 MB JET MAX FCST BY THE GFS/ECMWF TO 110 KT PRODUCES DIVERGENCE IN THE LEFT JET EXIT REGION ACROSS THE OLYMPICS AND CASCADES. STRONG 700 MB THETA-E ADVECTION AND CONVERGENCE ON THE NOSE OF A 50 KT JET MAXIMA NEAR THE WA/OR COAST HELPS TO PRODUCE WIDESPREAD ASCENT. HEIGHT FALLS LATER IN THE PERIOD START TO RESULT IN DECREASING SNOW LEVELS ONCE THE WARM ADVECTION CEASES. THE PRIMARY UNCERTAINTY IN THE SNOW FORECAST IS THE INITIAL BURST OF WARM ADVECTION RAISES SNOW ELEVATIONS TO NEAR THE PEAKS OF THE CASCADES...SO CHANCES ARE A TRANSITION TO RAIN OCCURS AT LOWER ELEVATIONS. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. PETERSEN $$

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