MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 156 PM EST FRI JAN 20 2017 VALID JAN 20/1200 UTC THRU JAN 24/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVE TROUGH OVER THE OHIO VALLEY TODAY...WEAKENING NEWD THROUGH EARLY SAT MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW SIMILARLY WITH THIS SYSTEM. COMPACT CLOSED MID-LEVEL LOW ADVANCING THROUGH THE CNTRL PLAINS TODAY AND REACHING THE UPPER MS VALLEY SAT NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE TRENDS IN THE 12Z NAM/GFS SHOW A QUICKER DEPARTURE OF THE CLOSED LOW AS IT REACHES THE UPPER MISSISSIPPI VALLEY. GIVEN THESE ADJUSTMENTS ARE IN THE F036-FO48 HR TIME FRAME...OR RELATIVELY SHORT TERM...AND ROOM IN THE ENSEMBLE GUIDANCE TO ADJUST QUICKER...THIS TREND MAY BE SEEN IN THE REMAINING ECMWF/UKMET/CMC GUIDANCE WHEN THEIR 12Z RUNS ARRIVE. A BLEND OF THE FASTER 12Z GFS AND SLOWER 00Z ECMWF IS PREFERRED FOR NOW TO TREND IN THE DIRECTION OF THE QUICKER GUIDANCE. 19Z UPDATE...THE 12Z ECMWF/UKMET/CMC FOLLOWED THE LEAD OF THE NAM/GFS TO SPEED UP THROUGH 00Z/23. GIVEN THE STRONG SUPPORT FOR THIS ADJUSTMENT BY ALL OF THE 12Z MODELS...AND GENERAL GOOD AGREEMENT...A GENERAL MODEL BLEND IS PREFERRED. HEIGHT FALLS ACROSS THE WEST TODAY...CLOSED LOW ACROSS THE LOWER MS VALLEY SUN WITH ASSOCIATED STRONG SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS...12Z ECMWF...12Z UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE DESPITE TRENDING SLOWER FROM PREVIOUS RUNS...THE 12Z NAM CONTINUES TO BE QUICKER THAN MOST GEFS/EC/CMC ENSEMBLE MEMBERS WITH AN EXPECTED CLOSED LOW DEVELOPING OVER THE SRN PLAINS SUN. IT IS CONSIDERED UNLIKELY TO VERIFY. THE REMAINING MODELS ARE IN FAIR AGREEMENT BUT THERE ARE DIFFERENCES WORTH NOTING. THE 00Z ECMWF IS MUCH STRONGER WITH THE RESULTING 850/700 MB LOWS BY 12Z/23 OVER THE MID-ATLANTIC REGION. THE 12Z GFS APPEARS TO LIFT THE CLOSED LOW FASTER/FARTHER NORTH BY 00Z/24 AND IS ALSO NOTABLY WARMER AT 850 MB ACROSS OH/PA GIVEN A MORE NORTH-SOUTH ELONGATION TO THE 850 MB LOW NOT SEEN IN THE OTHER MODELS. THE 00Z UKMET IS A BIT SLOWER WITH THE TIMING OF THE PROGRESSION OF THE LOW. WHILE NO MODEL APPEARS IDEAL THROUGHOUT THE F036-FO84 HR TIME FRAME...A BLEND OF THE 12Z GFS...00Z ECMWF AND 00Z UKMET APPEARS MOST REASONABLE WITH RESPECT TO THE ENSEMBLE DISTRIBUTION AND TRENDS. 19Z UPDATE...THE 12Z ECMWF WEAKENED FROM ITS PREVIOUS CYCLE...NOW SHOWING TWO LOW CENTERS...MORE SIMILAR TO THE 12Z GFS WITH WARMER LOW LEVELS ACROSS PA/NY BY MON. THE 12Z UKMET LOOKS SIMILAR TO ITS PREVIOUS RUN AND SO A GFS/ECMWF/UKMET BLEND REMAINS THE PREFERRED COMPROMISE. COLD FRONT REACHING THE WEST COAST SAT NIGHT AND LONGWAVE TROUGH OVER THE WEST COAST BY MON MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: AVERAGE THE LATEST GUIDANCE CONTINUES TO SHOW A STRONG LOW DEVELOPING OFF OF THE WEST COAST ON SUN WITH DIFFERENCES IN TIMING AND PLACEMENT NOTED. THERE IS RELATIVELY TIGHT ENSEMBLE CLUSTERING WITH THE EVOLUTION OF THIS SYSTEM AND ALL OF THE DETERMINISTIC GUIDANCE IS WITHIN REASON HERE. THE MID-LEVEL LOW HAS NO SIGNIFICANT DIFFERENCES AMONG THE NAM/GFS/ECMWF/UKMET/CMC GUIDANCE WITH A GENERAL BLEND RECOMMENDED AT THIS TIME TO IRON OUT INDIVIDUAL DIFFERENCES. 19Z UPDATE...THERE HAVE BEEN MINOR ADJUSTMENTS IN THE 12Z ECMWF/UKMET/CMC TO SHOW THE 12Z GFS FARTHER OFFSHORE WITH THE LOW BY MON OFF OF THE WEST COAST...BUT ALL OF THE MODELS REMAIN SIMILARLY CLUSTERED AND WITHIN THE ENSEMBLE SPREAD. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO