MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 246 PM EDT SUN AUG 21 2016 VALID AUG 21/1200 UTC THRU AUG 25/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING FINAL PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TROF & ASSOCIATED SFC CYCLONE MOVING ACROSS THE GREAT LAKES AND EVENTUALLY SHEARING INTO ONTARIO/PARTS OF THE NORTHEAST U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 12Z NAM IS A BIT BROADER/SLOW WITH THE TROF AT 5H CROSSING NEW ENGLAND COMPARED TO OTHERWISE VERY TIGHT AGREEMENT. THIS DOES NOT SEEM TO BE TOO MUCH OF A DETRIMENT IN THE LOWER LEVELS...PERHAPS A TAD SLOW AT TIMES BUT NOT SIGNIFICANT ENOUGH TO BREAK FROM THE GENERAL MODEL BLEND PREFERENCE. CONFIDENCE REMAINS ABOVE AVERAGE IN THIS BLEND. MID-LEVEL TROF ENTERING SW BC/NW WA BY LATE SUN INTO NORTHERN ROCKIES MON WITH ASSOCIATED SURFACE CYCLOGENESIS IN THE DAKOTAS BY MON NIGHT INTO TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND THROUGH 24/00Z 12Z UKMET/ECMWF/NAM BLEND AFTERWARD CONFIDENCE: SLIGHTLY ABOVE AVERAGE UNTIL 24/00Z SLIGHTLY BELOW AVERAGE AFTERWARD MODELS CONTINUE TO SHOW STRONG AGREEMENT UP TO ABOUT 60HRS (24/00Z) WHEN SPREAD RAPIDLY INCREASES IN LINE WITH TYPICAL BIASES FOR THIS TIME SCALE MAINLY BETWEEN THE 12Z GFS AND 00Z ECMWF...AS SUCH THE ENSEMBLE MEANS ARE MORE REASONABLE AND MORE CENTRALLY LOCATED. THE 12Z GFS ACCELERATES ACROSS THE NORTHERN TIER ON WED WITH SOME BINARY INTERACTION WITH STRONGER WAVE (PERHAPS DUE OVER DOING CONVECTIVE FEEDBACK) EJECTING OUT OF THE CENTRAL ROCKIES (SEE SECTION BELOW). THIS BROKE FROM STRONGER CONSISTENCY WITH THE GFS/GEFS AND IS NOW A FAST OUTLIER. THE 00Z ECMWF REMAINS VERY CONSOLIDATED AND DOES NOT SHOW THE GENERAL WEAKENING/SHEARING TREND SEEN IN THE 00Z UKMET/CMC (WHICH ARE FAST AND SLOW RESPECTFULLY TO THE MEAN...PER THEIR USUAL BIASES). THE 00Z ECMWF APPEARS TO BE A CLEAR OUTLIER WITHIN THE 7H THROUGH SFC COMPARISON MASS FIELDS TOO MAKING IT LESS FAVORABLE FOR INCLUSION AT THIS TIME. THE 12Z NAM ALSO REMAINS STRONG (TYPICAL OF BIAS) AT DAY 3...BUT IS FASTER...IN LINE WITH THE UKMET AND 06Z GFS/GEFS TIMING WITH THE MID-LEVEL WAVE. THE GOOD NEWS IS WITH A FASTER 12Z GFS...AT LEAST THE MODELS ARE BECOMING BETTER AGREED UPON WITH RESPECT TO THE UPSTREAM/KICKER WAVE THAT CARVES OUT A MILDLY DEEP VORT CENTER THROUGH E COLUMBIA RIVER/SNAKE RIVER BASIN INCREASING THE POSITIVE TILT TO THE OVERALL TROF. STILL PREFERENCE TOWARD A BLEND BETWEEN THE 00Z ECENS MEAN AND 06Z GEFS PROVIDES BEST COMPROMISE AS WELL AS KEEPING WITH SOME CONTINUITY AFTER 24/00Z. CONFIDENCE IS SLIGHTLY BELOW AVERAGE GIVEN THIS INCREASED SPREAD. 19Z UPDATE: THE 12Z ECMWF AND UKMET BOTH TRENDED FASTER WHILE THE CMC REMAINED ON PAR WITH THE WEAKENING OF THE INNER CORE OF THE LOW CROSSING THE NORTHERN TIER. WHILE THE UKMET IS EQUALLY PACED IS NOT A WEAK/SHALLOW AS THE GFS; THE ECMWF PACED JUST AHEAD OF THE 12Z CMC AND 00Z ECENS MEAN. THE 12Z GEFS SIMILAR TO THE GEFS SUPPORTS A SHALLOWER FASTER SOLUTION BUT IS ALSO FURTHER NORTH TOWARD THE DEEPER HUDSON BAY CYCLONE. ALL SUGGEST A FASTER SHIFT THAN EARLIER PREFERENCE BUT STILL BELIEVE THE GFS IS TOO FAST BUT MORE IMPORTANTLY TOO WEAK. AS SUCH WILL INCORPORATE THE ECMWF/UKMET/NAM BLEND AS A COMPROMISE TOWARD THE 00Z ECENS MEAN AND 06Z GEFS BUT KEEP SLIGHTLY BELOW AVERAGE CONFIDENCE IN THIS BLEND AFTER 24/00Z. SHORTWAVE EJECTING INTO CENTRAL PLAINS MON EVENING AND CROSSING INTO GREAT LAKES PRECURSORY TO DEEPER NORTHERN STREAM TROF ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET BLEND CONFIDENCE: AVERAGE BROAD TROUGH OVER THE SOUTHWEST ALONG WITH RETURN FLOW AROUND WESTERN PERIPHERY OF SUBTROPICAL RIDGE THAT HAS DOMINATED THE NORTHERN GULF BEGIN TO CONFLATE ACROSS THE CENTRAL PLAINS/GREAT LAKES WITH THE LEAD WAVE(S) EJECT ON MONDAY EVENING. THE 12Z NAM HAS BACKED OFF A STRONGER FASTER LEAD WAVE FAVORING EJECTION OF TWO LESSER YET CONCENTRIC WAVES WHILE CONCURRENTLY FAVORING THE SUBTROPICAL RETURN FLOW STREAM SUPPORTING A FURTHER SE ZONE OF ACTIVITY ACROSS SE IA/N IL COMPARED TO THE MORE CONSISTENT 00Z ECMWF/UKMET WHICH FAVOR THE CENTRAL ROCKIES WAVE PULLING THE AXIS OF ACTIVITY FOCUSED ACROSS CENTRAL IA INTO S WI. THE 12Z GFS TRENDING FASTER WITH THE NORTHERN STREAM TROF...DRAWS THE ENERGY FURTHER NORTH THAN EVEN THE ECWMF FAVORING A TRACK THROUGH W IA/S MN...DIFFICULT TO SAY IF THIS IS A TREND AT THIS POINT...BUT CURRENTLY APPEARS TO BE MORE RELATED TO ITS KNOW FAST BIAS BY DAY 3...THE 06Z GFS/GEFS DID NOT SHOW THIS DRAMATIC OF A SHIFT...AND THEREFORE IS PREFERABLE TO THE 12Z RUN. THE 00Z CMC IS VERY SLOW EJECTING OUT OF THE CENTRAL ROCKIES AND FAST IN THE RETURN FLOW STREAM LEADING TO AN ALMOST WEST TO EAST TROF ORIENTATION THAT SEEMS OUT OF PHASE WITH EVEN THE NAM AND PRIOR RUNS. AS SUCH WILL FAVOR A *06Z GFS* AND 00Z ECMWF/UKMET BLEND AT AVERAGE CONFIDENCE. 19Z UPDATE: 12Z ECMWF KEPT FAIRLY SIMILAR IN SHAPE/TIMING OF THE LEAD WAVE EJECTING INTO THE PAINS THE UKMET IS A BIT SHARP AND STRONG BUT CONTINUES TO MATCH ORIENTATION AND TIMING OF THE ECMWF. THE 00Z CMC CONTINUES TO LAG WITH THE TIME OF THE WAVE. AS SUCH WILL CONTINUE A 12Z ECMWF/UKMET BLEND (INCLUSION OF THE 06Z GFS MAY SUPPORT/STRENGTHEN THE BLEND IF DESIRED). BROAD BASE OF THE TROF/SHORTWAVE CROSSING S CA/SOUTHWEST MON/TUES AND CENTRAL ROCKIES WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM BLEND CONFIDENCE: AVERAGE THE WESTERN PORTION OF THE BROAD BASE OF THE SOUTHWEST UPPER LEVEL TROF SHOWS BETTER AGREEMENT THROUGH ITS EVOLUTION ACROSS THE FOUR CORNERS BY TUES EVENING THAN THE LEAD WAVE (LIKELY DUE TO LESSER INTERACTION WITH THE RETURN FLOW STREAM OUT OF NORTHERN MEXICO. THE 12Z NAM IS GENERALLY A BIT DEEPER AND DUE TO SLOWER UPSTREAM KICKER WAVE COMING THROUGH THE EASTERN COLUMBIA/SNAKE RIVER VALLEYS...IS GENERALLY SLOWER LIFTING OUT OF NEW MEXICO BY THE END OF THE PERIOD...SHOWING SOME OF THE END OF DAY 3 BIASES THAT MAKE IT NOTORIOUSLY UNFAVORABLE AT THIS POINT IN THE FORECAST PERIOD. ON THE OTHER SIDE IS THE 00Z ECMWF SUPPORTED BY THE 00Z CMC WHICH IS LIFTING NORTH FASTER THAN SAY THE UKMET OR EVEN THE 12Z GFS. STILL THE DIFFERENCES TO SENSIBLE WX AND OVERALL TIMING/ORIENTATION SEEM MINOR EVEN THOUGH THE SPREAD IS MODERATE BY THE END OF DAY 3...AS SUCH WILL FAVOR A NON-NAM BLEND AT AVERAGE CONFIDENCE. 19Z UPDATE: LITTLE TO NO CHANGE IN INITIAL THINKING AS THE ECMWF/UKMET/CMC SHOWED SIMILAR SOLUTIONS TO THEIR 00Z RUNS; WITH EXCEPTION OF THE 12Z ECMWF WHICH WAS A BIT SLOWER/FURTHER SOUTH WHICH WAS A POSITIVE TREND TOWARD BETTER ALIGNMENT WITH THE GFS. AS SUCH WILL KEEP A NON-NAM BLEND PREFERENCE AT AVERAGE CONFIDENCE. GALLINA www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...