746  
FXUS10 KWNH 191647  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1146 AM EST SUN NOV 19 2017  
 
VALID NOV 19/1200 UTC THRU NOV 23/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES WITH CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SYSTEM LEAVING NEW ENGLAND TODAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/GFS AND 00Z ECMWF BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 00Z UKMET IS INITIALIZED A BIT DEEPER THAN OTHER GUIDANCE AND  
ALLOWS FOR A GREATER NORTHWARD STRETCHING ACROSS SOUTHEASTERN  
CANADA AS THE SECONDARY KICKER WAVE APPROACHES MONDAY. ON THE  
OPPOSITE SIDE THE CMC IS A BIT WEAKER. THE 12Z GFS AND NAM FAVOR  
THE EVOLUTION OF THE UKMET WHILE THE ECMWF FAVORS THE CMC. WHILE  
WORTH NOTING...THESE SLIGHT DIFFERENCES ARE RELATIVELY SMALL WITH  
THE OVERALL ENSEMBLE SPREAD THAT A GENERAL MODEL BLEND COULD BE  
PREFERRED THOUGH WILL SUPPORT THE TIGHTER CLUSTERING OF THE 12Z  
GFS/NAM AND 00Z ECMWF AT ABOVE AVERAGE CONFIDENCE FOR THIS SYSTEM.  
 
SYSTEM DROPPING FROM NW CANADA TODAY INTO GREAT LAKES BY WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS AND 00Z ECMWF/CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
GOES-WV MOSAIC DEPICTS ELONGATED TROF ACROSS THE NORTHEAST PACIFIC  
INTO N BC WITH A SURFACE WAVE TRANSLATING ACROSS THE CANADIAN  
ROCKIES INTO A DEEP LEE CYCLONE THAT WILL DROP ALONG THE US/CANADA  
BORDER INTO THE NORTHWEST GREAT LAKES BY EARLY TUES. A JET STREAK  
ENHANCES OVER N BC AND SUPPORTS A RAPID SOUTHEASTERLY PUSH OF THE  
TROF KEEPING A MORE NW-SE ORIENTATION UNTIL IT REACHES THE NW  
GREAT LAKES. GUIDANCE SHOWS SOME DIFFERENCES WITH THIS EVOLUTION  
ALONG TYPICAL BIAS LINES: THE 12Z GFS REMAINS SLIGHTLY FASTER  
FRONT LOADING THE TROF WITH ENERGY; 12Z NAM WILL WIND UP AND  
BECOME MORE COMPACT EVENTUALLY LEADING TO ITS SLOWING; THE 00Z  
ECMWF/CMC ARE GENERALLY SLOW. THE 00Z UKMET IS THE ONLY NOT  
TRADITIONAL BIAS, BUT HAS BEEN PERSISTENT IN ITS SLOW EMERGENCE  
FROM THE ROCKIES...THOUGH EVEN THIS IS REDUCING. AS THE TROF  
ROUNDS THE BASED OF THE MEAN GLOBAL TROF IN THE GREAT LAKES...THE  
12Z NAM RAPIDLY BECOMES A VERY DEEP VERY SLOW OUTLIER.  
HOWEVER...THE 12Z GFS SLOWED ITS TREND FAVORING A SLOWER MORE  
AMPLIFIED SOLUTION THROUGH THE GREAT LAKES AND MORE IN LINE WITH  
THE ECMWF/CMC TREND IN FACT A BIT SLOWER THAN THE ECMWF/CMC. AS  
THE 12Z GFS AND 00Z ECMWF/CMC AS ROUND THE BASE BEGIN TO PHASE  
WITH AN AMPLIFIED SHORTWAVE EMERGING OUT OF THE GULF AND UP THE  
EAST COAST (SEE SECTION BELOW). THIS INTERACTION COMPLICATES THE  
FORECAST IN THE NORTHEAST...YET THE 12Z GFS AND 00Z ECMWF/CMC  
SEEMS TO HANDLE IT SIMILARLY PROVIDING SOME CONFIDENCE. . THE  
UKMET REMAINS SLOW THROUGH THE OHIO VALLEY BUT PACES BETTER  
THROUGH NEW ENGLAND HOWEVER THE GULF SHORTWAVE EMERGES FURTHER  
EAST AND THEREFORE HAS LESS INTERACTION WITH THIS SYSTEM. AS  
SUCH A 12Z GFS AND 00Z ECMWF/CMC BLEND IS SUPPORTED AT SLIGHTLY  
ABOVE AVERAGE CONFIDENCE.  
 
SHORTWAVE CROSSING THE GULF OF MEXICO TUES AND LIFTING UP GULF  
STREAM TO PHASE WITH NORTHERN STREAM WED WITH ASSOCIATED SURFACE  
WAVE FROM EASTERN GULF TOWARD GEORGES BANK LATE WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS AND 00Z ECMWF/CMC BLEND  
CONFIDENCE: AVERAGE  
 
A BROAD SHORTWAVE TROF CURRENTLY SEEN ALONG THE MEXICO/AZ/NM  
BORDER WILL SLIGHTLY AMPLIFY ACROSS THE GULF OF MEXICO AND SPUR A  
WEAK SURFACE INFLECTION ON THE LINGERING FRONTAL BOUNDARY DRAPED  
IN THE SOUTHERN GULF LATE TUES. THE WAVE WILL LIFT NORTHEAST  
ALONG THE GULF STREAM AND BEGIN TO PHASE WITH THE BASE OF THE  
NORTHERN STREAM TROF OVER EASTERN GREAT LAKES/OH VALLEY BY WED  
FURTHER DEEPENING THE COASTAL LOW. GIVEN THE WAVE'S EMERGENCE AND  
AMPLIFICATION IS PHASED MORE WITH THE NORTHERN STREAM WAVE THAN  
ITS OWN INTERNAL DYNAMICS...THE 12Z NAM IS MUCH TOO SLOW WHILE THE  
00Z ECMWF/CMC ARE WELL TIMED AND RELATIVELY EQUALLY AMPLIFIED.  
THE 12Z GFS HAS SHIFTED SLOWER IN THE NORTHERN STREAM AND  
THEREFORE MORE SO IN THE SOUTHERN WITH THE STRONGEST MANIFESTATION  
OF THE WAVE WITHIN THE GUIDANCE SUITE. TO TEMPER THIS THE 12Z GFS  
SHOULD BE BLENDED WITH THE FLATTER CMC/ECMWF SOLUTIONS.  
CONFIDENCE IS AVERAGE IN THIS EVOLUTION GIVEN MODEST SPREAD AND  
INFLUENCE FROM ANOTHER STREAM THAT HAS ITS OWN ISSUES/DIFFERENCES.  
 
BASE OF NORTHEAST PACIFIC TROF ENTERS PAC NW BY MON...SLIDES DOWN  
TO FILL OUT THE BASE OF THE TROF IN THE GULF OF MEX WED LEADING TO  
SURFACE AMPLIFICATION IN THE SOUTHERN GULF  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/GFS BLEND TO 21/12Z  
12Z NAM/00Z CMC BLEND THEREAFTER  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
ELONGATED TROF ACROSS NORTHEAST PACIFIC WILL CONTINUE TO DRIFT  
SOUTHEAST INTO PACIFIC NORTHWEST BY MON. AT THIS POINT...THE  
UPSTREAM SHORTWAVE RAPIDLY AMPLIFIES AND PUMPS THE LARGER SCALE  
RIDGE OVER THE TOP THE LINGERING BASE (THAT BEGINS TO LAY OUT E-W  
ALONG THE APEX OF THE RIDGE). THE 00Z ECMWF TRENDED EVEN SLOWER  
THAN PRIOR RUNS AND THEREFORE AS THE SHORTWAVE IS FURTHER  
STRETCHED OVER THE RIDGE...THE BULK OF THE WAVE REMAINS WEST OF  
THE RIDGE WHILE THE BULK OF THE REMAINING GUIDANCE WOULD SUPPORT  
THE MAJORITY OF THE WAVE TO BE AT THE APEX OR EAST DESCENDING THE  
EASTERN SIDE OF THE RIDGE INTO THE GREAT PLAINS AND EVENTUALLY  
CARVING OUT THE BASE OF THE LARGER SCALE TROF ACROSS THE WESTERN  
GULF BY MIDDAY WED INTO THURS. THE 00Z UKMET/CMC INSTEAD OF  
SHEARING THE WAVE THROUGH THE RIDGE...WITH ENHANCED UPPER LEVEL  
OUTFLOW CONSOLIDATE THE WAVE INTO A VERY SMALL SCALE REX PATTERN  
AT THE APEX OF THE LARGER SCALE RIDGE BEFORE STRETCHING TROUGH THE  
EASTERN SIDE OF THE RIDGE AND CARVING OUT THE BASE OF THE WESTERN  
GULF TROF. THE UKMET AND ITS BIAS OF COMPACT/DEEP VORT CENTERS  
GOES TOO FAR BY WED OVER TX/WESTERN GULF. THE 12Z NAM AND GFS ARE  
FLATTER IN THE APEX OF THE TROF BUT FAVOR MORE ENERGY EAST OF THE  
RIDGE. THE NAM IS A BIT FASTER AND STRONGER WITH THE LEAD PORTION  
OF THE WAVE BEGINS TO TAKE A CMC EVOLUTION...WHILE THE GFS IS  
WEAKER WITH THE LEAD WAVE FAVORING THE UPSTREAM ONE (MORE IN LINE  
WITH THE ECMWF).  
 
CONTINUITY WOULD FAVOR SOMETHING CLOSE TO THE 12Z GFS/NAM  
INITIALLY ENTERING THE PACIFIC NORTHWEST OVER THE SLOW ECMWF.  
HOWEVER...THE GFS BECOMES A BIT LESS FAVORABLE TOWARD THE END OF  
THE FORECAST...WHILE THE CMC NOT INITIALLY FAVORED DUE TO ITS  
OVERZEALOUS AMPLIFICATION AT THE APEX OF THE RIDGE...SHEARS NICELY  
THROUGH THE NW FLOW AND CARVES OUT THE BASE OF THE TROF MORE  
REASONABLY AND IN LINE WITH ECENS/CMCE MEANS (AND EVEN A BIT OF  
THE GEFS MEMBERS). AS SUCH WILL FAVOR A 12Z GFS/NAM BLEND THROUGH  
21/12Z TUES BEFORE TRENDING TOWARD 12Z NAM/00Z CMC THROUGH THE  
REMAINING SHORT-TERM FORECAST. GIVEN LOW PREDICTABILITY OF THE  
SETUP AND RUN TO RUN CONTINUED VARIATION IN SMALL DIFFERENCES IN  
TIMING/PLACEMENT... CONFIDENCE IS SLIGHTLY BELOW AVERAGE IN THIS  
BLEND.  
 
LARGE VORTEX OVER NORTHEAST PACIFIC BY LATE TUES SPITTING  
SHORTWAVES AT THE PAC NW LATE TUES AND LATE WED...ASSOCIATED  
SURFACE WAVES ALONG FAIRLY STATIONARY FRONT/SWLY ONSHORE FLOW (LEE  
ROCKIES SFC WAVE ON LATE WED -- FIRST WAVE).  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND TO 22/00Z  
12Z GFS/00Z ECMWF BLEND THEREAFTER  
CONFIDENCE: AVERAGE  
 
GOES-W WV LOOP SHOWS A STRONG COMPACT WAVE OVER BRISTOL BAY (AK)  
THAT WILL DROP SOUTHEAST GROWING IN SCALE ACROSS THE SRN GULF OF  
AK BY MONDAY. THIS WILL DRAW OUT A BULK OF THE SHORTWAVE ENERGY  
ASSOCIATED WITH ELONGATED KONA LOW CURRENTLY N OF HI. THIS KONA  
S/W AND DEEP SURFACE REFLECTION WILL LIFT NE TOWARD THE 40N140W  
BENCHMARK EARLY TUES WITH A STRONG SWLY SURGE/WARM FRONT CLIPPING  
THE WEST COAST OF OR/WA TUES INTO WED. THE TIMING HERE LOOKS VERY  
GOOD WITH SMALL VARIATION IN THE DEPTH/SPEED. THE 00Z ECMWF IS A  
BIT DEEPER/SLOWER...LEFT OF THE BEST CLUSTERING LIFTING NORTH  
WHILE THE 00Z CMC IS WEAKER AND EAST OF THE CLUSTER...BUT THE  
SPREAD IS MINOR (WITHIN THE ENSEMBLE SUITE THROUGH THIS TIME  
PERIOD TO FAVOR ONE SOLUTION OVER THE OTHER. HOWEVER BY WED...THE  
LOW WILL PIVOT WEST OF VANCOUVER ISLAND AND BECOME THE DOMINATE  
CENTER OF THE LARGER CYCLONE NEAR 50N140W. AT THIS POINT THE CMC  
FURTHER SPLITS EAST TRACKS WELL NORTH WELL AWAY FROM THE OTHER  
GUIDANCE WITH POSSIBLE EXCEPTION OF THE DEEPENING/12Z NAM THAT  
ALSO DOES NOT BECOME THE ANCHOR OF THE SYSTEM FAVORING TO LIFT  
NORTH TOWARD THE AK PANHANDLE/HAIDA GWAII. AS THE SECONDARY  
SHORTWAVE LIFTS NORTHEAST ON WED THE GFS/ECMWF FURTHER CONSOLIDATE  
WITHIN THE MIDDLE OF THE ENSEMBLE SUITE SHOWING SIMILAR  
TIMING/STRENGTH AND ORIENTATION OF THE TROF AND MOISTURE SURGE  
ALONG THE FRONTAL ZONE INTO THE PAC NW. AS SUCH A 12Z GFS AND  
00Z ECMWF BLEND IS SUPPORTED ESPECIALLY AFTER 22/00Z WED. THERE  
IS MODEST AGREEMENT FOR JUST A LARGE AND COMPLEX SYSTEM WITH  
RESPECT TO INTERNAL SHORTWAVE INTERACTIONS TO HAVE SOME CONFIDENCE  
IN THIS BLEND...BUT GIVEN THE SCALE AND LOCATION WITHIN THE DATA  
NETWORK...CONFIDENCE IS ONLY AVERAGE AT THIS TIME.  
 
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