EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1252 PM EST TUE FEB 14 2017 VALID 12Z FRI FEB 17 2017 - 12Z TUE FEB 21 2017 ...HEAVY PRECIPITATION EXPECTED FOR PORTIONS OF THE WEST AS WELL AS THE SOUTHERN PLAINS AND GULF COAST... ...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... A SPLIT FLOW WILL BE THE PREDOMINANT LARGE SCALE PATTERN THROUGH THE MEDIUM RANGE. POSITIVE HEIGHT ANOMALIES WILL BE IN PLACE ON DAY 3 /12Z FRI FROM THE CENTRAL/NORTHERN PLAINS TO NORTH TO BAFFIN BAY. THIS ANOMALOUS RIDGE WILL DEFLECT LARGE SCALE WESTERLY FLOW NORTH TOWARD THE POLE AND SOUTHWARD ACROSS MEXICO AND THE SOUTHERN PLAINS AND INTO THE SOUTHEASTERN U.S. BY DAYS 6 AND 7 (MON AND TUE) MODELS SHOW GOOD AGREEMENT THAT THE POSITIVE HEIGHT ANOMALIES WILL BEGIN TO SHIFT EAST. BY DAY 7 /12Z TUE THE MID/UPPER RIDGE AXIS SHOULD BE CENTERED MORE ACROSS THE GREAT LAKES AND INTO THE MID-ATLANTIC AND SOUTHEAST. DESPITE THE EASTWARD PROPAGATION OF THE RIDGE, THE SPLIT FLOW PATTERN WILL CONTINUE. AT 12Z FRI MODEL AGREEMENT IS GOOD THAT A MID/UPPER LOW WILL INITIALLY BE IN PLACE ACROSS WEST CENTRAL TX. WHILE THE 00Z ECMWF INITIALLY LAGS THE 06Z GFS WITH RESPECT TO TIMING, AGREEMENT IMPROVES BETWEEN THESE TWO SOLUTION AS THE WAVE REACHES THE SOUTHEASTERN U.S. BY SUN. FARTHER WEST, MODEL AGREEMENT IS ALSO RELATIVELY GOOD WITH RESPECT TO BRINGING AND AMPLIFYING TROUGH TO THE WEST COAST BY SAT MORNING. THE DETERMINISTIC 06Z GFS/00Z ECMWF CLOSE OFF AN ANOMALOUS LOW AT THE MID/UPPER LEVELS BY SUN MORNING ACROSS NORTHWESTERN MEXICO. MODEL AGREEMENT IS REMARKABLY GOOD FOR DAY 7 AS THE LOW/TROUGH MOVES INTO THE CENTRAL/SOUTHERN PLAINS BY TUE MORNING, WITH THE 06Z GFS/00Z ECMWF/00Z EC MEAN REMAINING NEARLY IN PHASE. BY 12Z TUE CONSENSUS IS GOOD THAT AN ADDITIONAL SIGNIFICANT TROUGH WILL BE LOCATED OFF THE WEST COAST. WHILE MODELS SHOW SOME SPREAD AND DIFFERENCES WITH RESPECT TO THE SPECIFIC DETAILS AND TIMING OF THIS FEATURE, AGREEMENT IS STILL RELATIVELY GOOD AND AN ENSEMBLE APPROACH IS FAVORED BY THIS TIME. DIFFERENCES AMONG THE MODELS ARE A BIT LARGER WITH RESPECT TO THE NORTHERN STREAM COMPONENT OF THE SPLIT FLOW. THESE MAINLY AMOUNT TO TIMING AND INTENSITY DIFFERENCES FOR A NUMBER OF SHORTWAVES THAT BECOME DAMPED AS THEY PROPAGATE INTO THE LONG WAVE RIDGE. WPC MODEL PREFERENCES FOR THIS FORECAST PACKAGE WERE LARGELY FOCUSED ON THE DETERMINISTIC 06Z GFS/00Z ECMWF AS WELL AS THE 06Z GEFS MEAN/00Z ECMWF ENS MEAN. THE FORECAST WAS WEIGHTED MORE HEAVILY ON THE THE DETERMINISTIC SOLUTIONS INITIALLY, WITH WEIGHT SHIFTING MORE TOWARD THE ENSEMBLE MEANS (ESPECIALLY THE 00Z ECMWF ENS MEAN) LATER INTO THE FORECAST PERIOD. ...WEATHER HIGHLIGHTS/THREATS... THE WESTERN U.S. WILL SEE THE LIKELIHOOD FOR TWO ROUNDS OF PRECIPITATION THROUGH THE MEDIUM RANGE PERIOD. THE BIGGEST THREAT SHOULD EXIST FOR MUCH OF CALIFORNIA, WHERE SEVERAL INCHES OF OF LIQUID PRECIPITATION ARE EXPECTED. THE ANOMALOUS TROUGH/UPPER LOW IMPACTING THE WEST COAST ON FRIDAY SHOULD RESULT IN THE MOST SIGNIFICANT ROUND OF HEAVY PRECIPITATION FOR CALIFORNIA. SNOW LEVELS ARE FORECAST TO BE RELATIVELY HIGH, BUT HEAVY SNOW WILL STILL BE POSSIBLE AT THE HIGHER ELEVATIONS OF THE SIERRAS. AS THE SYSTEM MOVES INLAND, THERE WILL ALSO BE THE POTENTIAL FOR HEAVY RAIN AT THE HIGHER ELEVATIONS OF THE SOUTHWESTERN U.S. FINALLY, AS THIS SYSTEM REACHES THE SOUTHERN/CENTRAL PLAINS BY LATE SUN/MON, SIGNIFICANT NORTHWARD FLOW OF LOW-LEVEL MOISTURE/INSTABILITY COULD RESULT IN THE POTENTIAL FOR HEAVY RAINFALL, ESPECIALLY ACROSS PORTIONS OF THE GULF COAST AND LOWER MS VALLEY. ADDITIONAL PRECIPITATION WILL BE POSSIBLE ALONG THE WEST COAST BY DAYS 6-7 AS THE NEXT MID/UPPER TROUGH APPROACHES. IN TERMS OF TEMPERATURES...THE PERSISTENT RIDGE WILL RESULT IN ABUNDANT WARMTH WHICH WILL EXPAND FROM WEST TO EAST THROUGHOUT THE PERIOD NEAR AND EAST OF THE ROCKIES. FORECAST HIGHS SHOULD RANGE FROM 15-30 DEGREES ABOVE CLIMATOLOGY ACROSS THE CENTER AND EASTERN PORTIONS OF THE COUNTRY. THE ONLY COOL SPOT WILL BE ALONG THE WEST COAST GIVEN THE PERSISTENCE OF CLOUDS AND PRECIPITATION. RYAN