MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1136 PM EST FRI DEC 11 2015 VALID DEC 12/0000 UTC THRU DEC 15/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING THE NAM/GFS ...PACIFIC LOW WEAKENING ACROSS THE INTERIOR NORTHWEST EARLY SATURDAY MORNING... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A PACIFIC SURFACE LOW WILL MOVE INLAND IN THE NORTHWEST BEFORE WEAKENING SATURDAY MORNING. MODELS SHOW GOOD AGREEMENT WITH RESPECT TO THIS FEATURE BEFORE IT DISSIPATES...AND NO ONE MODEL APPEARS TO HAVE A SUPERIOR SOLUTION. ...UPPER-LEVEL TROUGH CROSSING THE FOUR CORNERS REGION ON SATURDAY... ...CLOSED UPPER-LEVEL LOW AND SURFACE CYCLONE ACROSS THE CENTRAL U.S. SAT NIGHT/SUNDAY... PRELIMINARY PREFERENCE: GFS/12Z ECMWF BLEND CONFIDENCE: AVERAGE THE NAM AND GFS LINE UP WELL WITH THE MODEL CONSENSUS WITH RESPECT TO THIS FEATURE AS IT CROSSES THE FOUR CORNERS REGION ON SATURDAY AND EMERGES INTO THE SOUTHERN/CENTRAL PLAINS ON SUNDAY. AFTER 00Z SUNDAY...THE NAM APPEARS TO LIFT THE UPPER LOW NORTHEASTWARD A LITTLE TOO QUICKLY COMPARED TO THE CONSENSUS. THE SURFACE LOW SHOWN BY THE NAM ACROSS THE UPPER MIDWEST EARLY MONDAY IS ALSO ON THE NORTHEAST SIDE OF THE SPREAD. THE GFS FITS REASONABLY WELL WITHIN CONSENSUS WITH RESPECT TO BOTH THE SURFACE AND UPPER-LEVEL LOWS. WITH RESPECT TO THE SURFACE COLD FRONT CROSSING THE MISSISSIPPI/OHIO/TENNESSEE VALLEYS...THE NAM MAY BE SLIGHTLY TOO FAST WITH THE EASTWARD PROGRESSION SUNDAY EVENING...BUT APPEARS CLOSER TO THE CONSENSUS AFTER THAT TIME. THE GFS ALSO APPEARS A SHADE QUICK WITH THE COLD FRONT OVER THE SAME AREA...WHEN COMPARED TO THE 12Z ECMWF AND 18Z GEFS MEAN. OVERALL...A BLEND OF THE GFS AND 12Z ECMWF SHOULD BE A REASONABLE SOLUTION. ...PACIFIC STORM SYSTEM AFFECTING THE NORTHWEST SATURDAY AFTERNOON THROUGH SUNDAY... PRELIMINARY PREFERENCE: GFS/12Z ECMWF/12Z UKMET BLEND CONFIDENCE: AVERAGE MODEL AGREEMENT REMAINS GOOD WITH RESPECT TO THE SURFACE LOW ARRIVING AT THE BRITISH COLUMBIA COAST SATURDAY AFTERNOON/EVENING. THE NAM CONTINUES TO SHOW A STRONG WAVE DEVELOPING ALONG THE FRONT OFF THE PACIFIC NORTHWEST COAST EARLY SUNDAY MORNING...WHICH ALSO RESULTS IN A LATER ARRIVAL OF THE FRONTAL BOUNDARY TO THE COAST. THE GFS SOLUTION IS REASONABLY CLOSE TO THAT SHOWN BY THE 12Z ECMWF/ECMWF ENSEMBLE MEAN/UKMET. AS THE SYSTEM MOVES INLAND ON SUNDAY...THE NAM REMAINS ON THE SLOW SIDE WHILE THE GFS/12Z ECMWF/12Z UKMET CONTINUE TO SHOW SIMILAR TIMING AND STRENGTH OF THE SYSTEM. A BLEND OF THE GFS ALONG WITH THE 12Z ECMWF/UKMET IS RECOMMENDED AT THIS TIME. ...UPPER-LEVEL TROUGH CROSSING THE GREAT BASIN SUNDAY NIGHT AND EVOLVING INTO A CLOSED UPPER LOW OVER THE ROCKIES ON MONDAY... ...SURFACE LOW DEVELOPING EAST OF THE ROCKIES ON MONDAY... PRELIMINARY PREFERENCE: 12Z ECMWF/12Z UKMET CONFIDENCE: BELOW AVERAGE ENERGY ALONG THE SOUTHERN EDGE OF THE WESTERN U.S. TROUGH WILL CROSS THE GREAT BASIN SUNDAY NIGHT BEFORE CLOSING OFF INTO AN UPPER-LEVEL LOW ON MONDAY ACROSS THE CENTRAL ROCKIES. A SURFACE LOW IS FORECAST TO DEVELOP EAST OF THE ROCKIES LATE MONDAY BEFORE MOVING INTO THE CENTRAL PLAINS ON TUESDAY. THERE IS A RANGE OF SOLUTIONS WITH RESPECT TO HOW QUICKLY THE SURFACE LOW MOVES EAST INTO THE PLAINS. THE NAM AND GFS (AND THE 12Z CMC) DEPICT A DEEPER UPPER-LEVEL LOW BY 12Z TUESDAY ACROSS COLORADO...WHICH RESULTS IN A SLOWER EASTWARD PROGRESSION...WHILE THE 12Z ECMWF/UKMET ARE WEAKER WITH THE UPPER-LEVEL LOW AND MOVE THE SURFACE LOW EASTWARD INTO THE CENTRAL PLAINS MORE QUICKLY. SOME LIGHT MAY BE SHED ON THIS SCENARIO BY THE ENSEMBLE MEANS. THE 12Z ECMWF ENS MEAN/18Z GEFS MEAN BOTH SEEM TO SHOW A SOLUTION CLOSER TO THAT SHOWN BY THE 12Z ECMWF/UKMET. THE 12Z ECMWF ENSEMBLE MEAN ACTUALLY KICKS THE SURFACE LOW EAST ACROSS THE PLAINS EVEN MORE QUICKLY THAN ITS DETERMINISTIC SOLUTION. IN LIGHT OF THIS...WILL FAVOR THE 12Z ECMWF/UKMET SOLUTION AT THIS TIME...AND WILL WAIT AND SEE IF THE 00Z RUNS OF THESE MODELS SHED ANY ADDITIONAL LIGHT ON THE SITUATION. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN