MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 214 AM EST TUE FEB 02 2016 VALID FEB 02/0000 UTC THRU FEB 05/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 0Z GUIDANCE EVALUATION INCLUDING FINAL MODEL PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SURFACE LOW TRACKING NORTHEAST INTO THE GREAT LAKES BY WED AND COLD FRONT MOVING THROUGH THE EAST COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 0Z OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE MODELS REMAIN IN GOOD AGREEMENT ON THE LARGE SCALE WITH THIS SYSTEM. THE GFS HAS SLOWED DOWN FROM ITS RUN LAST NIGHT...AND IS NOW IN LINE WITH THE TIMING SEEN IN THE OTHER DETERMINISTIC GUIDANCE WITH REGARDS TO THE SURFACE LOW MOVING INTO THE GREAT LAKES. DESPITE THE SYNOPTIC AGREEMENT THERE ARE SOME MINOR DIFFERENCES STILL WITH REGARDS TO THE QPF DISTRIBUTION WITH THE SYSTEM...LIKELY DUE TO SMALL MESOSCALE DIFFERENCES IN HOW THE MODELS HANDLE CONVECTION AND THE EVOLUTION OF PRECIPITATION SHIELDS. THE 0Z GFS CONTINUES TO OUTPACE THE OTHER GUIDANCE WITH THE COLD FRONTAL PROGRESSION INTO THE EAST COAST THROUGH WEDNESDAY. THE 18Z GEFS MEAN MAY BE A TOUCH SLOWER THAN THE DETERMINISTIC GFS...AND THE GFS HAS TRENDED SLIGHTLY SLOWER. ALSO...GIVEN THE USUAL QUICK BIAS OF THE GFS...AND THE FACT THAT ALL THE OTHER DETERMINISTIC GUIDANCE IS SLOWER WITH THE FRONT...THINK THE FAST GFS REPRESENTS A LESS LIKELY SOLUTION. ALSO THE GFS DRY BIAS FROM THE LOWER MS VALLEY EAST INTO THE TN VALLEY AND SOUTHEAST IS QUITE APPARENT. THUS IN GENERAL THE GFS IS CONSIDERED LESS USEFUL WITH THE FRONTAL ASPECT OF THIS SYSTEM...WITH MORE WEIGHT TOWARDS THE ECMWF/UKMET/GEM. 07Z UPDATE: VERY GOOD CLUSTERING SEEN IN THE THE GUIDANCE WITH REGARDS TO THE LOW TRACK AND SPEED. THUS A GENERAL 0Z OPERATIONAL MODEL BLEND IS PREFERRED. WITH REGARDS TO THE COLD FRONTAL PROGRESSION..THE GENERAL MODEL BLEND PREFERENCE CAN BE CONTINUED WITH A FEW CAVEATS. THE NEW 0Z UKMET NOW APPEARS A BIT TOO SLOW WITH THE FRONTAL PROGRESSION IN GENERAL. THE 12Z GFS APPEARS TOO QUICK WITH THE FRONT...ESPECIALLY ACROSS THE SOUTHEAST...WHERE IT SHOULD BE AVOIDED GIVEN THIS FACT AND ITS CONTINUED DRY BIAS. SHORTWAVE SHEARING THROUGH THE MEAN PACIFIC RIDGE TOWARD THE NORTHWEST TUE REINFORCING THE BASE OF THE CENTRAL U.S. TROF BEFORE SHIFTING EAST INTO THE EASTERN THIRD OF THE U.S BY THURS EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE A HIGHLY ELONGATED TROUGH MOVING INTO THE NORTHWEST TODAY WILL REINFORCE THE BASE (AND WESTERN SIDE) OF THE LARGER SCALE TROUGH ACROSS THE SOUTHWEST...WITH THE TROUGH MOVING TOWARDS THE EAST COAST BY THURSDAY. THE TROUGH EVENTUALLY CATCHES UP TO THE DEPARTING COLD FRONT...WHICH SHOULD ALLOW FOR A SURFACE LOW REFLECTION TO DEVELOP ALONG THE FRONT OFF THE EAST COAST. MODELS ARE GENERALLY IN GOOD AGREEMENT WITH THIS SYSTEM. THE 12Z UKMET IS A BIT DEEPER/STRONGER WITH THE ENERGY INITIALLY AS IT DIVES SOUTHEAST REINFORCING THE TROUGH. IT THUS REMAINS DEEP AS THE SYSTEM MOVES INTO THE EAST COAST...BECOMING A NEGATIVELY TILTED WAVE BY 12Z FRIDAY IN THE MID ATLANTIC. THIS SOLUTION HAS LITTLE SUPPORT FROM THE OTHER DETERMINISTIC GUIDANCE AND IS ON THE EDGE OF THE ENSEMBLE ENVELOPE. SO WHILE NOT IMPOSSIBLE...IT SEEMS TO REPRESENT A MUCH LESS PROBABLE SOLUTION AT THIS TIME. THE 12Z ECMWF DOES SEEM A BIT SLOW WITH THE TROUGH APPROACHING THE EAST COAST LATER THURSDAY COMPARED TO THE GEM/NAM/GFS AND EVEN THE 12Z ECMWF MEAN. HOWEVER DIFFERENCES ARE RELATIVELY MINOR...AND THUS IT CAN BE INCLUDED IN THE OVERALL MODEL PREFERENCE. 07Z UPDATE: NO CHANGE TO THE ABOVE PREFERENCE. THE NEW 0Z UKMET/ECMWF/GEM ALL REMAINED PRETTY CONSISTENT WITH THEIR PREVIOUS RUNS WITH REGARDS TO THIS SYSTEM. NEXT DEEPER TROF AND FRONT NEARING THE PACIFIC NORTHWEST COAST WED EVENING AND SETTLING ACROSS THE INTERMOUNTAIN WEST THURS EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 0Z GFS/ECMWF/GEM COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z UKMET HANDLES THE SHORTWAVE ENERGY DIFFERENTLY AS IT APPROACHES THE PACIFIC NORTHWEST. IT IS GENERALLY FURTHER NORTH WITH THE CORE OF THE ENERGY...AND QUICKER WITH THE FRONT. IT APPEARS TO LIE ON THE EDGE OR EVEN OUTSIDE OF THE ENSEMBLE SPREAD...AND THUS WILL CONTINUE LEANING AGAINST ITS SOLUTION. THE 0Z NAM IS NOW A BIT QUICKER THAN THE OTHER DETERMINISTIC GUIDANCE...AND SEEMS TO ALSO OFFER A LESS LIKELY SOLUTION. GOOD AGREEMENT SEEN WITH THE 0Z GFS AND 12Z ECMWF...AND THUS A BLEND OF THEIR SOLUTIONS SHOULD WORK WELL FOR THIS SYSTEM. EVEN THE 12Z GEM LOOKS PRETTY SIMILAR TO THESE SOLUTIONS...AND THUS COULD ALSO BE INCLUDED IN ANY BLEND FOR THIS SYSTEM. 07Z UPDATE: ENSEMBLE SPAGHETTI PLOTS SHOW A LARGE AMOUNTS OF SPREAD WITH THIS SYSTEM BY LATER THURSDAY INTO FRIDAY AS THE WAVE/TROUGH DIGS TOWARDS THE FOUR CORNERS REGION. THUS NO SURPRISE THAT WE CONTINUE TO SEE MODELS FLUCTUATE BETWEEN DIFFERING SOLUTIONS. THE 0Z UKMET TRENDED CLOSER TO THE OTHER GUIDANCE...BUT STILL APPEARS TO REPRESENT A LESS PROBABLE SOLUTION...INITIALLY BEING QUICKER WITH THE WAVE/FRONT AND FOCUSING THE SHORTWAVE ENERGY FURTHER NORTH. THE 0Z ECMWF REMAINS A BIT SLOWER THAN THE CONSENSUS BRINGING THE FRONT ONSHORE WEDNESDAY...BUT IS STILL WITHIN THE RANGE OF PLAUSIBLE SOLUTIONS. THE 0Z ECMWF THEN DIGS THE WAVE DEEPER INTO THE SOUTHWEST TO NEAR THE MEXICAN BORDER BY 12Z FRIDAY. THE 0Z GEM IS CLOSER TO THE GFS SOLUTION. HOWEVER AS MENTIONED ABOVE...THERE IS LARGE ENSEMBLE SPREAD BY THIS TIME...AND THE ECMWF SOLUTION DOES FALL WITHIN THE BROAD ENSEMBLE RANGE. THUS WILL CONTINUE TO INCLUDE IT IN THE WPC PREFERENCE...WHICH IS A COMPROMISE BETWEEN THE GFS/ECMWF/GEM. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... CHENARD