Prognostic Meteorological Discussion
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000 FXUS02 KWBC 261557 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1057 AM EST WED NOV 26 2014 VALID 12Z SAT NOV 29 2014 - 12Z WED DEC 03 2014 ...HEAVY PRECIPITATION FOR CALIFORNIA...ESPECIALLY MON/TUE... IN THE MEDIUM RANGE FLOW SPLITS OFF THE WEST COAST OF NORTH AMERICA. A DEEP SOUTHERN STREAM TROUGH FORMS WEST OF CALIFORNIA...AND IS EXPECTED TO COME INLAND...ALTHOUGH THE MODELS VARY IN TIMING. THE NORTHERN STREAM IS ANCHORED BY THE BROAD CIRCUMPOLAR LOW...HANGING OUT WHERE IT WOULD BE EXPECTED IN NORTHERN CANADA. BOTH STREAMS ARE CARVING OUT LARGE SCALE FEATURES...SO THE FORECAST BOILS DOWN TO TWO MAIN EVENTS...THE NORTHERN STREAM RE-ESTABLISHING ARCTIC AIR ACROSS THE NORTHERN TIER OF THE U.S...AND THE SOUTHERN STREAM DELIVERING A SOAKING RAIN AND HEAVY HIGH ELEVATION SNOWS TO MUCH OF CALIFORNIA. SOME OF THIS EVENT WILL SPILL OVER THE SIERRAS...ESPECIALLY IN THE NORTHERN ROCKIES THROUGH THIS WEEKEND...AND THEN INTO THE GREAT BASIN AND SOUTHERN DESERTS NEXT WEEK. THE WPC FORECAST HAS REMAINED CLOSE TO THE ENSEMBLE MEANS...ESPECIALLY THE ECMWF ENSEMBLE MEAN WHICH IS OFTEN PREFERRED FOR ITS DEEPER AND SLOWER SOLUTIONS. IT IS WORTH NOTING...HOWEVER...THAT RUN TO RUN VARIABILITY IN THE OPERATIONAL MODELS DOES LOWER CONFIDENCE A BIT...ESPECIALLY AFTER DAY 4. THE MAIN EFFECTS OF THIS UNCERTAINTY WOULD BE TIMING OF THE WEST COAST PRECIPITATION...AND TEMPERATURE FORECASTS EAST OF THE ROCKIES. THE 00Z RUNS OF THE ECMWF HAVE BEEN PARTICULARLY DEEP AND SLOW OFF THE WEST COAST. THE MOST RECENT RUN SEPARATED THE STREAMS SO MUCH THAT THE NORTHERN STREAM IS ALLOWED TO BECOME VERY DOMINANT OVER THE CENTRAL AND EASTERN U.S. THIS COLDER FORECAST IS IN STARK CONTRAST TO RECENT 12Z RUNS OF THE SAME MODEL WHICH WERE MUCH MORE MILD. THE GFS HAS BEEN MORE CONSISTENT...BUT IS TOO LITTLE AMPLIFIED AND TOO PROGRESSIVE BY DAYS 5-7. FOR THIS CYCLE WE WERE ABLE TO INCORPORATE SOME OF THE 06Z GEFS MEAN...WHICH IS DEEPER...BUT IT TOO FAILS TO CAPTURE THE LIKELY DEPTH OF THE CALIFORNIA TROUGH. A BETTER OPTION WAS THE 06Z PARALLEL GFS WHICH FIT VERY WELL WITH THE 00Z ECMWF ENSEMBLE MEAN AND WITH WPC CONTINUITY. THE 06Z OPERATIONAL GFS WAS A BETTER FIT EAST OF THE ROCKIES EARLY IN THE PERIOD WHEN ARCTIC AIR IS BECOMING RE-ESTABLISHED. AT A QUICK GLANCE...OUR PLAN WILL BE TO MAINTAIN WPC CONTINUITY TO QPF...WHICH IS ALREADY TOWARD THE HIGHER END OF THE AVAILABLE GUIDANCE. CERTAINLY THE PATTERN IS FAVORABLE FOR CALIFORNIA...AND THE PRECIPITATION WILL BE WELCOMED...AND SHOULD HIT THE SIERRAS WITH HEAVY SNOW. BUT CERTAIN MEASURES SUCH AS MOISTURE FLUX AND PRECIPITABLE WATER ANOMALIES DO NOT SHOW THIS TO BE AN EXCEPTIONALLY ANOMALOUS STORM. SEVERAL ADDITIONAL SUCH STORMS WOULD BE NEEDED TO PROVIDE DROUGHT RELIEF. BURKE $$

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