118  
FXUS10 KWNH 151627  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1226 PM EDT SUN OCT 15 2017  
 
VALID OCT 15/1200 UTC THRU OCT 19/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES WITH CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SYSTEM MOVING INTO THE GREAT LAKES TODAY AND THROUGH NORTHEAST BY  
MON  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
GOES-E WV DEPICTS SHORTWAVE/COMMA HEAD REGION SHIFTING EAST  
ACROSS GREAT LAKES AND IS GOING TO CONTINUE SLIDING EAST-NORTHEAST  
THROUGH MONDAY WITH NEARLY ALL GLOBAL DETERMINISTIC GUIDANCE  
CONVERGING TO A COMMON SOLUTION. THE 12Z NAM AND GFS SHOW LITTLE  
SIGNIFICANT VARIATION FROM A LARGER SCALE/SYNOPTIC STAND POINT TO  
BREAK FROM A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
KICKER SHORTWAVE AMPLIFYING INTO THE GREAT LAKES SUNDAY NIGHT AND  
THROUGH NEW ENGLAND/EAST COAST TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 18/00Z  
NON-NAM AFTERWARD  
CONFIDENCE: ABOVE AVERAGE  
 
GOES-E WV SHOWS BROAD ILL-DEFINED WAVE CROSSING INTO ND/N MN ATTM.  
GUIDANCE CONTINUES TO SUPPORT THE WAVE SHARPENING IN  
AMPLIFICATION AS IT FILLS OUT THE BASE OF THE LARGER MEAN GLOBAL  
SCALE TROF OVER THE GREAT LAKES/UPPER OH VALLEY MONDAY AND  
EVENTUALLY PRESSING THROUGH THE NORTHEAST BY EARLY TUESDAY  
MORNING. THE GLOBAL GUIDANCE LIKE THE UPSTREAM WAVE IS QUITE  
AGREEABLE FOR THE MAIN CORE OF THE WAVE...AND AS SUCH A GENERAL  
MODEL BLEND CAN BE SUPPORTED AT ABOVE AVERAGE CONFIDENCE.  
 
SMALL DISCREPANCIES SEEM TO OCCUR WITH THE TAIL END OF THE TROF  
LINGERING OVER THE SOUTHEAST...AS IT LINGERS OVER THE SOUTHEAST  
TUES/WED AND IS REINFORCED BY UPSTREAM WEAK ENERGY. THE 12Z  
NAM/GFS ARE MOST INTENSE WITH THE LINGERING ENERGY IN PARTICULAR  
THE NAM...WHICH DELAYS THE EASTWARD PROGRESSION ACROSS GA BY WED.  
AS SUCH A NON-NAM BLEND IS PREFERRED AFTER 18/00Z.  
 
SHORTWAVE AND CLIPPING FRONTAL ZONE ACROSS MAINE TUES NIGHT/WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A FAST MOVING SHORTWAVE EMERGING FROM CENTRAL CANADA ARCTIC STREAM  
MON/TUES CONTINUES TO DESCEND ACROSS JAMES BAY/QUEBEC BY  
WED...GIVEN THE ORIENTATION OF THE JET...STRONG DIVERGENCE AT THE  
NOSE ALLOWS FOR SURFACE CYCLOGENESIS THAT CREEPS CLOSE TO NORTHERN  
MAINE WITH THE FRONTAL ZONE LATE TUES/EARLY WED. THE 12Z NAM/GFS  
SHOW GOOD CONTINUITY WITH RESPECT TO THE 00Z/06Z RUNS AND THE 00Z  
ECMWF/CMC AND THE VAST MAJORITY OF THE ENSEMBLE SUITE. THE 00Z  
UKMET CONTINUES TO BE FASTER AND PRESSES THE HEIGHT FALLS FURTHER  
SOUTHEAST AFFECTING THE CONUS GREATER THAN OTHER GUIDANCE. GIVEN  
THE OTHER GUIDANCE AGREEMENT WILL SUPPORT A NON-UKMET BLEND AT  
ABOVE AVERAGE CONFIDENCE.  
 
GULF OF AK TROF REACHING BC LATE MON/TUES WITH TRAILING COLD FRONT  
ACROSS NORTHWEST TUES AND TRACKS ACROSS NORTHERN TIER BY WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS (00Z ECENS MEAN/06Z GEFS MEAN IF AVAIL.)  
CONFIDENCE: AVERAGE  
 
STRONG ZONAL FLOW EXISTS SOUTH OF THE ALEUTIAN ISLANDS...WITH A  
SHORTWAVE STARTING TO CROSS THE NORTHERN GULF OF AK TODAY THAT  
WILL REACH THE N BC COAST/S AK PANHANDLE BY LATE TUESDAY WHILE  
STRONGER FLOW SOUTH OF THE SYSTEM ADVANCES A BROADER AMPLIFYING  
WAVE AT THE NOSE OF STRENGTHENING JET STREAK. THESE TWO FEATURES  
AND THEIR SPACING TOGETHER SUPPORT A SURFACE WAVE THAT REACHES  
HAIDA GWAII 18Z MONDAY AND TRANSLATES ACROSS THE NORTHERN CANADIAN  
ROCKIES ENTERING N ALBERTA BY 12Z TUES ALONG WITH A TRAILING  
FRONTAL ZONE THAT SLOWLY DESCENDS DOWN THE COAST AFFECTING  
SOUTHERN VANCOUVER ISLAND/OLYMPIC PENINSULA TUES. THE  
UKMET/GFS/NAM ALL FAVOR A STRONGER LEAD WAVE/HEIGHT FALL FOCUSING  
ON THE STRONGER SURFACE REFLECTION FURTHER NORTH IN CANADA. THIS  
IS OPPOSED BY THE 00Z ECMWF THAT SHOWS A SHARPER/STRONGER SOUTHERN  
SECONDARY SHORTWAVE FAVORING A STRONGER SURFACE REFLECTION AT THE  
TRIPLE POINT OVER THE SOUTHERN CANADIAN ROCKIES. THE 00Z ECENS  
MEMBERS WHILE SUPPORTING THE OPERATIONAL ECMWF...DOES HEDGE MORE  
MEMBERS CLOSER TO THE GEFS/12Z GFS SOLUTION ESPECIALLY AFTER  
LANDFALL ON TUES. AS IS TYPICAL THE 00Z UKMET BY DAY 3 IS WELL  
FORWARD OF THE GFS AND GIVEN THE WEAKER MEAN FLOW FURTHER  
NORTH...THIS SEEMS A BIT TOO AGGRESSIVE EVEN THOUGH IT IS  
SUPPORTED BY THE 12Z NAM. ALL CONSIDERED WOULD SUPPORT A 12Z GFS  
PREFERENCE BEST REPRESENTING THE 00Z ECENS MEAN/06Z GEFS (THOUGH  
BLENDING WITH THE 00Z ECENS MEAN/06Z GEFS WOULD BE PREFERABLE TO  
ENCOMPASS MORE OF THE SPREAD IF AVAILABLE). CONFIDENCE IS  
AVERAGE.  
 
LARGER/STRONGER GULF OF AK CYCLONE WARM FRONT PASSAGE IN  
NORTHWEST/BC WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/UKMET BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
IN THE WAKE OF THE PRIOR MEDIUM SYNOPTIC SCALE TROF...A MUCH  
LARGER/BROADER CLOSED WAVE TRANSLATES ACROSS THE SOUTHERN GULF OF  
AK WITH LEAD WAA REGIME WITH AMPLE SUBTROPIC MOISTURE POINTING  
DIRECTLY AT SOUTHERN BC AND EVENTUALLY WA COAST TOWARD THE END OF  
THE FORECAST PERIOD. THE 12Z NAM IS A CLEAR OUTLIER TO THE REGIME  
FAVORING DEVELOPMENT OF A MUCH SMALLER TIGHT STRONG CLOSED LOW AND  
DEEP SURFACE REFLECTION NEARING THE BC COAST BY 00Z THURS. THIS  
EVOLUTION IS NOT EVEN REPRESENTED IN THE OVERALL ENSEMBLE SUITE TO  
HAVE ANY CONFIDENCE IN USING IT. THE 00Z CMC IS ANOTHER  
OUTLIER...BUT AT LEAST EVOLVES A BROADER LARGER SCALE TROF OVER  
THE GULF OF AK. THE MAIN DIFFERENCE HERE IS THE INNER CORE  
EVOLVES UNCHARACTERISTICALLY FASTER THAN THE REMAINING GUIDANCE  
AND EVENTUALLY SWINGS THE INNER CORE TROF NEARLY 3-5 DEGREES  
FURTHER EAST BY 00Z THURS. THE 12Z GFS STILL ADVANCES THE LEAD  
HEIGHT FALLS OF THE EASTERN LOBE OF THE BROAD UPPER LOW AND WARM  
FRONT WELL IN ADVANCE OF THE REMAINING GUIDANCE AND THROUGH THE  
PACIFIC NORTHWEST BY WED NEARLY 12HRS IN ADVANCE OF THE  
ECMWF/UKMET AND ONLY REALLY SUPPORTED BY THE CMC. EVEN THOUGH IT  
HAS ISSUES WITH TIMING WITH RESPECT TO THE FRONT...THE REMAINING  
INNER CORE/MAIN GLOBAL SCALE TROF EVOLUTION IS WELL TIMED (PERHAPS  
A BIT SLOWER) THAN THE 00Z ECMWF/UKMET. THE ECMWF/UKMET  
SOLUTIONS ARE MORE TEMPERED AND MATCH BETTER WITH THE ENSEMBLE  
SOLUTIONS INCLUDING THE 00Z/06Z GEFS MEANS. AS SUCH WILL FAVOR  
THE 00Z ECMWF/UKMET BLEND AS PREFERENCE. GIVEN THE VAST SCALE OF  
THIS SYSTEM WITH INNER SMALLER SCALE DIFFERENCES IN  
TIMING/STRENGTH...CONFIDENCE IS AVERAGE TO SLIGHTLY BELOW AVERAGE  
EVEN THOUGH THE ECMWF/UKMET ARE GOOD REPRESENTATIONS OF CONTINUITY  
AND ENSEMBLE CLUSTER.  
 
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GALLINA  
 

 
 
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