304  
FXUS10 KWNH 310631  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
230 AM EDT TUE OCT 31 2017  
 
VALID OCT 31/0000 UTC THRU NOV 03/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SHORTWAVE OVER THE SOUTHWEST SHEARING EAST TOWARD WEST TX
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A COMPACT MID LEVEL LOW CENTER AND ASSOCIATED TROUGH OVER THE  
SOUTHWEST WILL EJECT EAST AND GRADUALLY SHEAR OUT THROUGH TUESDAY  
TOWARD WEST TX AS IT ENCOUNTERS LARGER SCALE CONFLUENT FLOW ALOFT.  
THIS DRAWS MOISTURE FOR SOME SHOWERS/STORMS ACROSS THE SOUTHERN  
PLAINS INTO THE WESTERN LOWER MS VALLEY WED/THURS. LITTLE CHANGE  
IN THE 00Z NAM/GFS KEEPS STRONG CONTINUITY AND ALLOWS FOR A  
GENERAL MODEL BLEND PREFERENCE AT ABOVE AVERAGE CONFIDENCE.  
 
...SHORTWAVE OVERTOPPING THE GULF OF AK RIDGE AXIS TUES SETTLING  
SOUTHEAST ACROSS THE DAKOTAS/UPPER MIDWEST WED/THURS WITH  
DEEP/BROAD SURFACE WAVE SLIDING DOWN CANADIAN ROCKIES INTO THE  
SOUTHERN PLAINS WED EJECTING ACROSS UPPER MIDWEST/GREAT LAKES WITH  
A SECONDARY WAVE DEVELOPING IN THE SOUTHERN PLAINS ALONG THE  
TRAILING FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE (WED/THURS) TOWARD AVERAGE (FRI)  
 
THE MODELS TAKE AN UPPER LOW AND ASSOCIATED SHORTWAVE TROUGH  
ACROSS AREAS OF SOUTHWEST AK THROUGH TONIGHT AND EARLY TUESDAY AS  
IT TOPS AND GRADUALLY BREAKS DOWN THE STRONG GULF OF AK RIDGE  
AXIS. A PORTION OF THIS ENERGY ALONG WITH A LEAD SHORTWAVE AHEAD  
OF IT WILL GRADUALLY LEAD TO A MID LEVEL TROUGH EVOLUTION ACROSS  
THE NORTHERN PLAINS AND UPPER MIDWEST THROUGH WEDNESDAY BEFORE THE  
ENERGY THEN CROSSES THE GREAT LAKES AND THEN EXITS BY LATER  
THURSDAY ACROSS ONTARIO. A STRONG SURFACE LOW ACCOMPANYING THE  
DIGGING SECONDARY SHORTWAVE ENERGY WILL SLIDE SOUTHEAST DOWN THE  
EAST SIDE OF THE CANADIAN ROCKIES AND CROSS THE NORTHERN PLAINS  
AND UPPER MIDWEST AS A TRAILING COLD FRONT GRADUALLY SETTLES DOWN  
TOWARD THE SOUTHERN PLAINS. WITH CONTINUED WESTERLY FLOW OVER THE  
ROCKIES A SFC LOW FORMS ALONG THE TRAILING FRONT IN LEE OF CO HIGH  
PLAINS SETTLING TOWARD SOUTHERN PLAINS THURS.  
 
THE 12Z UKMET CONTINUES TO BE QUITE VIGOROUS WITH THE LEAD HEIGHT  
FALLS AND FAVORS THE NORTHERN STREAM WAVE ACROSS THE DAKOTAS INTO  
THE GREAT LAKES...THOUGH CLEARLY MUCH TOO FAST. THE 12Z CMC  
WHILE AT FIRST VERY CENTRAL TO THE ENSEMBLE SUITE THROUGH WED AS  
FLOW IS MORE LAMINAR BEGINS TO SHOW THE SLOW/OVER CYCLOGENIC BIAS  
ACROSS THE WESTERN LAKES...OVER DEVELOPING/SLOWING THE PROGRESS OF  
THE WAVE IN A POINT IN THE LARGER SCALE GLOBAL TROF REGIME THAT IS  
A BIT TOO AGGRESSIVE. THE 00Z NAM HAS SETTLED A BIT TOWARD THE  
FLATTER/SLIGHTLY FASTER SOLUTION PRESENTED BY THE ENSEMBLE MEANS.  
THE 00Z GFS IS QUITE CENTRAL TO THE ENSEMBLE SCATTER AND ONLY  
REALLY SHOWS THE FAST BIAS LATE THURS/FRIDAY WITH THE WAVE ACROSS  
QUEBEC; WHILE FRONT AND SECONDARY SURFACE LOW NEAR THE RED RIVER  
MATCH NICELY TO THE NAM/ENSEMBLE SUITE. THE 12Z ECMWF IS MUCH  
MORE FAVORABLE WITH THE TIMING OF THE SURFACE LOW AND SHORTWAVE  
ALOFT ACROSS WITH THE ENSEMBLES BUT IS A BIT TOO SLOW WITH THE  
FRONT ACROSS THE NORTHEAST BY FRI. STILL A COMPROMISE BETWEEN THE  
00Z GFS/NAM AND 12Z ECMWF SEEMS TO KEEP THE BEST WITH CONTINUITY  
WHILE ADJUSTING POSITIVELY FOR THE RUN TO RUN TREND. CONFIDENCE  
IS FAIRLY GOOD THROUGH WED/EARLY THURSDAY BUT GIVEN THE INCREASED  
SPREAD IN FAIRLY FLAT/BROADER HIGHER SCALE FLOW LEAVES CONFIDENCE  
TO AVERAGE BY FRI.  
 
07Z UPDATE: THE 00Z CMC SHIFTED A BIT FASTER AND WEAKER MORE ON  
PAR WITH THE 00Z GFS AND THE 00Z ECMWF (WHICH SHOWED A BIT MORE  
AMPLIFICATION BUT STILL REMAINS OVERALL WEAKEST IN THE SUITE. THE  
00Z UKMET HAS ALSO SLOWED BUT CONTINUES TO REMAIN OUT A BIT TOO  
FAST FROM THE GROWING CONSENSUS. AS SUCH WILL SELECT A NON-UKMET  
BLEND AS PREFERENCE BUT GIVEN THE MODEST SPREAD STILL IN  
TIMING/PLACEMENT OF THE SURFACE WAVE IN SOUTHEAST CANADA BY  
FRIDAY...CONFIDENCE SHIFTS FROM SLIGHTLY ABOVE AVERAGE WED/THURS  
TO AVERAGE ON FRI.  
 
...AMPLIFYING UPPER LOW NEAR VANCOUVER ISLAND BY THURSDAY AND  
ASSOCIATED SURFACE LOW JUST OFF THE PACIFIC NORTHWEST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A FAIRLY STRONG ALASKAN ARCTIC WAVE DROPS THROUGH THE YUKON ON WED  
AND IN COMBINATION WITH LINGERING DOWNSTREAM THIN TROUGHING BEGINS  
TO AMPLIFY INTO A STRONG/COMPACT CLOSED LOW NEARLY STALLING NEAR  
VANCOUVER ISLAND THURS. UNCHARACTERISTICALLY THE 12Z ECMWF WITH  
FAIRLY TIGHT AGREEMENT IN THE ECENS MEMBERS IS SLIGHTLY  
FASTER/EARLIER WITH THE EVOLUTION OF THE CLOSED LOW AND AS THE  
WAVE SLOWLY LOOSENS THE INNER CORE TOWARD EARLY FRIDAY STARTS TO  
ELONGATE SW TO NE INTO WA. THE 00Z NAM/GFS AND UKMET ARE A BIT  
WEAKER WITH THE WAVE AND SLIGHTLY SLOWER LEADING TO A SLIGHTLY  
BROADER CLOSED LOW...BUT SHOW ENOUGH SIMILARITY TO HAVE CONFIDENCE  
IN BLENDING WITH THE ECMWF. THE 12Z CMC IS THE ONLY 'OUTLIER' IN  
THAT IT HAS A LITTLE SLOWER IN TIMING OF THE WAVE BUT ALSO IN  
BREAKING DOWN THE DOWNSTREAM TROF...NEARLY RETAINING A STRONGER  
WAVE OVER THE NORTHEAST PACIFIC. THIS LEADS TO A WESTWARD TUG OF  
THE INNER CORE AND SLOW DOWN OVERALL AND THE SURFACE REFLECTION IS  
FURTHEST WEST BY THE END OF THE FORECAST PERIOD. HOWEVER...WHILE  
IT IS SLIGHTLY DIFFERENT THE 12Z CMC EVOLUTION IS WELL WITHIN THE  
ENSEMBLE SUITE AND IS ABOUT AS DIFFERENT WEST/SLOW AS THE ECMWF IS  
FAST/SOUTHEAST OF THE NAM/GFS/UKMET. THIS IS VERY MINOR ENOUGH TO  
SUPPORT A GENERAL MODEL BLEND EVEN AT A SLIGHTLY ABOVE AVERAGE  
CONFIDENCE.  
 
07Z: THE 00Z ECMWF IS NEARLY IDENTICAL TO THE 12Z RUN REMAINING  
DEEPER AND SLIGHTLY FASTER THAN THE REST OF THE DETERMINISTIC  
SUITE. HOWEVER...THE CMC HAS TRENDED FASTER TO BE ON TRACK WITH  
THE UKMET/NAM LEAVING THE GFS THE SLOWER SOLUTION. OVERALL THE  
CLUSTERING IS TIGHTER AND EVOLUTION IS MUCH MORE IN AGREEMENT TO  
SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
...SOUTHERN STREAM SHORTWAVE CROSSING SOUTHERN PLAINS THURSDAY  
INTERACTING WITH SURFACE LOW/FRONT NEAR THE RED RIVER VALLEY  
THURS/FRI...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: 00Z GFS/ECMWF BLEND  
CONFIDENCE: BELOW AVERAGE  
 
BY 48HRS (00Z THURS) THE NORTHERN STREAM BROAD GLOBAL SCALE TROF  
NEARLY EXTENDS ACROSS THE ENTIRE NORTH AMERICAN CONTINENT WITH  
WEAK SEPARATION FROM A SUBTROPICAL LAMINAR FLOW EXTENDING FROM THE  
OFFSHORE SW CA TO THE LOWER MS VALLEY AND MS/AL...MAINLY THE  
REMNANTS OF TRAILING TAIL OF TROF/SHORTWAVE ENERGY OR BETWEEN THE  
RELATIVELY FLAT POLAR AND SUBTROPICAL JETS. THE MOST COMPACT  
WAVE ENERGY LINGERS THROUGH SW CA INTO THE SOUTHWEST US...THOUGH  
THE PLACEMENT AND STRENGTH BY 60HRS ARE WELL DISPLACED. THE ECMWF  
IS FURTHER EAST AND MORE COMPACT THE 12Z CMC IS FURTHEST WEST AND  
COMPACT WHILE THE NAM/GFS AND UKMET ARE WEST OF THE ECMWF BUT MUCH  
FLATTER. AS THE LAMINAR FLOW ENHANCE WITH VORTEX ROLL-UP  
THURSDAY AND FRIDAY...THE GFS/NAM CMC ARE TAKING LEAD SHORTWAVE  
ENERGY ACROSS THE RED RIVER TRAILED BY THE UKMET AND THE MORE  
COMPACT ECMWF... BY 12Z FRIDAY THE ECMWF IS CENTRAL TO THE OK/TX  
RED RIVER (AND STICKS OUT IN THE 12Z ENSEMBLE SPAGHETTI ANALYSIS)  
WHILE THE GFS'S TRAILING ENERGY WAS FAST TO ACCELERATE EAST TO  
CATCH UP. THIS EVOLUTION PROVIDES VERY LITTLE CONFIDENCE IN ANY  
GIVEN DETERMINISTIC RUN. AS SUCH WILL FAVOR THE FLATTEST  
SOLUTIONS/AND ENSEMBLE MEANS TO A BELOW AVERAGE CONFIDENCE BLEND.  
 
07Z UPDATE: THE 00Z ECMWF SLOWED ITS EASTWARD TRACK OF THE WAVE  
INTO THE RED RIVER BY FRI AND WHILE REMAINING SLIGHTLY FASTER AND  
MORE AMPLIFIED THAN THE GFS OR EVEN THE NAM...IT IS CLOSER IN  
SPACE THAN THE SOUTHERN DISPLACEMENT OF THE UKMET (WESTERN TX  
PANHANDLE BY 12Z FRI). STILL WOULD PREFER THE MEANS IN SUCH WEAK  
FLOW BUT LOOKING LIKE A BLEND OF THE 00Z GFS/ECMWF MAY BE COMING  
TOWARD A COMMON COMPROMISE TO SUGGEST THIS BLEND WILL BEST  
REPRESENT THE ENSEMBLE SOLUTIONS. GIVEN THE WEAKNESS OF THE  
FEATURE LARGE SPREAD CONFIDENCE IS REMAINS BELOW AVERAGE FOR THIS  
BLEND.  
 
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