132  
FXUS10 KWNH 151834  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
133 PM EST MON JAN 15 2018  
 
VALID JAN 15/1200 UTC THRU JAN 19/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
CLOSED LOW OVER UPPER MIDWEST WITH SURFACE LOW IN LOWER CENTRAL  
GREAT LAKES TODAY/TOMORROW...UNFOLDS INTO POSITIVE TILT TROF OVER  
OH/TN VALLEYS WED WITH DEVELOPING COASTAL LOW BY NEW ENGLAND WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
THE LARGE CLOSED LOW OVER THE WESTERN GREAT LAKES WITH  
UNDERCUTTING JET STREAK THROUGH THE MID-MS VALLEY WILL BEGIN TO  
UNFOLD INTO A SHARPER POSITIVE TILT TROF BY WED AND STRETCH FROM  
THE NORTH ATLANTIC TO ARKANSAS. HERE MODEL GUIDANCE IS QUITE  
AGREEABLE...THE DIFFERENCE ARISES IN WHERE THE ELONGATION OF THE  
TROF WANTS TO RECONSOLIDATE/SEVER; WITH A KEY BEING AN ARCTIC S/W  
CURRENTLY ENTERING THE TOP OF THE WESTERN RIDE IN THE YUKON. THE  
NCEP GUIDANCE HAS BEEN MORE PROGRESSIVE WITH THIS WAVE EVENTUALLY  
LEADING TO A SHARPENING OF THE TROF AND KICKING OF THE WAVE INTO  
THE NORTHWEST ATLANTIC. IN THE PROCESS DEVELOPING A SURFACE WAVE  
THAT SKIRTS BY NEW ENGLAND WED INTO THURS. HOWEVER...THE 12Z NAM  
AND GFS BOTH DEPICT A SLIGHT SLOWING OF THIS WAVE ALLOWING FOR  
GREATER AMPLIFICATION SOUTH OF JAMES BAY BY 00Z THURS. THIS  
DELAYS THE SURFACE LOW AND TRANSLATION OF THE TROF OFFSHORE.  
HOWEVER BOTH ARE STILL MUCH FASTER THAN THE REMAINING NON-NCEP  
SUITE. ALL THREE DEPICT A MUCH SLOWER SOUTHERN STREAM OF THE TROF  
THROUGH THE TN VALLEY INTO THE MID-ATLANTIC/CAROLINAS; IN DOING SO  
THE VORTICITY STRIP IS ABLE TO CURL/CONSOLIDATE. THE 00Z CMC GOES  
TO THE EXTREME AND BECOMES SYMMETRIC AND DEVELOPS A SECONDARY  
SURFACE WAVE THAT RAPIDLY DEEPENS OFF THE MID-ATLANTIC COAST BY  
THURSDAY. THE 00Z ECMWF/ECENS MEAN HAD TRENDED AWAY FROM THIS  
SCENARIO UNFOLDING AND WHILE STILL MUCH MORE CONSOLIDATED THAN THE  
GFS... THERE IS SOME SHADES OF THE NAM MIDDAY THURS TO HAVE SOME  
INDICATION THAT GUIDANCE IS HONING IN ON A COMMON SOLUTION. THE  
00Z UKMET BUILDS CREDENCE TO THIS EVOLUTION...AS A MIDDLE GROUND  
TO THE NAM/ECMWF. AS SUCH A BLEND OF THE 00Z UKMET/ECMWF AND 12Z  
NAM IS PREFERRED YET THE RUN TO RUN VARIANCE AND MODEL SPREAD  
PROVIDE LOWER THAN AVERAGE CONFIDENCE.  
 
19Z UPDATE: THE 12Z NON-NCEP GUIDANCE ALL TRENDED TOWARD THE 12Z  
NAM...IE FASTER WITH TRANSLATING THE BASE OF THE TROF OFF THE  
COAST. WHILE THE 12Z CMC REMAINS THE SLOWEST AND MOST  
SYMMETRIC/CONSOLIDATED THROUGH DAY 3; THE UKMET/ECMWF HAVE SHOWN A  
MORE SOLID AGREEMENT WITH THE SLOWED 12Z NAM SOLUTION THOUGH  
REMAIN A BIT CLOSER TO THE COAST FOR THE INITIAL SURFACE WAVE NEAR  
NEW ENGLAND. AS SUCH WILL CONTINUE A NAM/ECMWF/UKMET PREFERENCE  
BUT INCREASE OVERALL CONFIDENCE IN THIS SOLUTION TO AVERAGE.  
 
DEEP LAYERED CYCLONE OFF PACIFIC NORTHWEST LIFTS NORTH ALONG  
CANADIAN COAST WITH SLOW EASTWARD PUSH OF FRONTAL ZONE INTO THE  
WEST EARLY TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
GOES-W WV LOOP SHOWS A BROAD UPPER LOW WITH SPOKES OF OUTER EDGE  
S/W VORT CENTERS NEARING THE PACIFIC NW COAST. THIS DEEP CYCLONE  
IS WELL HANDLED BY THE GUIDANCE WHICH SHOWS GOOD SIMILARITY IN  
TIMING/PLACEMENT OF THE MAIN FEATURES INCLUDING THE SURFACE  
LOW/TRIPLE POINT AND COLD FRONT. THE 12Z NAM JOINED THE 00Z UKMET  
SUPPORTING A SLIGHTLY ENHANCED/STRONGER TRIPLE POINT DEVELOPING  
ALONG 130W AND LIFTING NORTH...WHILE DEEPER IT CONTINUES TO MATCH  
THE TIMING/PLACEMENT IN THE INFLECTION OF THE 12Z GFS/00Z  
ECMWF/CMC TO KEEP WITHIN ANY BLEND. THE MODEL SPREAD INCREASES  
AS THE INNER CORE/MAIN ENERGY LIFT AWAY INTO TUES AND THE TAIL END  
OF UPPER LOW BEGINS TO SHARPEN INTO A NEGATIVE TILT TROF CROSSING  
THE COLUMBIA BASIN INTO SW CANADA...PLEASE SEE SECTION BELOW FOR  
FURTHER DETAILS ABOUT ITS INFLUENCE/EVOLUTION THEREAFTER.  
OTHERWISE A GENERAL MODEL BLEND CAN BE SUPPORTED AT ABOVE AVERAGE  
CONFIDENCE FOR THE DEEP LAYERED LOW AND THE FRONTAL ZONE ENTERING  
THE US TUES.  
 
19Z UPDATE: THE 12Z UKMET SHIFTED BACK TO A SLIGHTLY WEAKER TRIPLE  
POINT REFLECTION AND MELDS NICELY WITHIN THE GENERAL MODEL BLEND  
EVEN FURTHER CONSOLIDATING THE GUIDANCE...AND CONFIDENCE.  
 
TAIL END OF WESTERN LOW CROSSES US/CANADIAN ROCKIES WED BEFORE  
SLIDING THROUGH THE NORTHERN PLAINS/GREAT LAKES THURS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
THE SHARPENING TAIL END OF THE DEEP CYCLONE LIFTING OFF THE  
CANADIAN COAST WILL REACH THE MEAN RIDGE AXIS OVER THE SOUTHERN  
CANADIAN/N US ROCKIES BY EARLY WED...WITH A BULK OF THE VORTICITY  
AT THE BASE OF THE TROF TO HELP BREAK DOWN THIS RIDGE. IN DOING  
SO THE WAVE REMAINS CONSOLIDATED AS IT BOWLS THROUGH THE NORTHERN  
PLAINS INTO THE GREAT LAKES BY THURSDAY. THE 00Z CMC IS LEAST  
ALIGNED WITHIN THE GUIDANCE SUITE WITH RESPECT TO THE  
CONSOLIDATION OF THE VORT CENTER AS IT HITS THE RIDGE...AND AS  
SUCH REMAINS MORE STRUNG OUT AND SLIDES THROUGH MUCH FURTHER NORTH  
AND IN PIECES; OPPOSED TO THE TRENDS IN THE GUIDANCE. THE NAM  
WHICH HAD PARTNERED WITH THE CMC BUT THE 12Z NAM TRENDED AWAY  
'BASE-LOADING' THE TROF AND SO THE WAVE EJECTS MORE CONSOLIDATED.  
HOWEVER THE 12Z NAM ALSO REMAINED FURTHER NORTH EMERGING OVER THE  
RIDGE INTO CENTRAL CANADA AND NORTH OF THE MAIN CLUSTERING. THE  
12Z GFS CONTINUED ITS TREND OF EJECTING FASTER OUT OF THE  
WEST...THIS ALLOWED IT TO KEEP PACE AND GENERAL SHAPE WITH THE 00Z  
ECMWF THOUGH REMAINS SLIGHTLY WEAKER/SLOWER THAN THE FASTER UKMET.  
OVERALL A BLEND OF THE 12Z GFS AND 00Z ECMWF ALONG WITH A LOWER  
WEIGHTED 00Z UKMET SEEMS APPROPRIATE IN TIMING/STRENGTH AND  
LATITUDINAL PLACEMENT TO HAVE AVERAGE CONFIDENCE IN THIS BLEND.  
 
19Z UPDATE: THE 12Z CMC REMAINS FLAT AND MOST ON THE OUTER FRINGE  
OF THE SPREAD. THE 12Z UKMET TRENDED A BIT QUICKER OVER THE TOP OF  
THE RIDGE INJECTING INTO THE FLOW A BIT FURTHER NORTH AND FASTER  
THAN THE 00Z RUN INCREASING SPREAD WITH THE INITIAL PREFERENCE.  
THE 12Z ECMWF WHILE TRENDING A BIT WEAKER REMAINS VERY CLOSE TO  
THE INITIAL PREFERENCE AND GFS TO KEEP AVERAGE CONFIDENCE IN A  
BLEND OF THE 12Z GFS/ECMWF AS WPC PREFERENCE.  
 
SUBTLE PACIFIC JET/SHORTWAVE ENERGY SLIPS UNDER MEAN RIDGE IN  
ROCKIES ON TUES/WED BEFORE AMPLIFYING ACROSS TX/N OLD MEXICO THURS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/CMC/ECMWF BLEND  
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE  
 
AS THE TAIL END OF THE WESTERN LOW CROSSES THE CANADIAN  
ROCKIES...KICKER SPEED MAX/SHORTWAVES EMERGE FROM THE PACIFIC FLOW  
AND BEGIN TO SLIDE UNDER THE MEAN RIDGE THAT WAS ANCHORED THROUGH  
THE CORE OF THE NORTHERN AND NORTH CENTRAL US ROCKIES. WITH THE  
EXIT OF THE MEAN POSITIVE TILT TROF DOWNSTREAM...WEAK S/W RIDGING  
ALLOWS FOR THIS S/W ENERGY TO AMPLIFY ALONG THE SOUTHERN ROCKIES  
INTO TX AND NORTHERN COAHUILA BY EARLY THURS. THE 00Z UKMET IS A  
BIT STRONGER/TIGHT WITH THE CORE INITIALLY AND EJECTS NEARLY 6-12  
HRS EARLIER AND RACES THROUGH TO THE GULF STATES AND AWAY FROM THE  
ENSEMBLE SUITE AND OVERALL TREND TOWARD THE BROAD TROF IN IN TX BY  
00Z FRI. THE 00Z ECMWF IS OVERALL LEAST CONSOLIDATED AND BROADER  
WITH DIGGING FURTHEST SOUTH AND DRAWING TROPICAL MOISTURE FROM THE  
PACIFIC AND CARIBBEAN NORTH LATER IN THE PERIOD (THOUGH WITH  
SLIGHTLY WEAKER FLOW). THE 12Z NAM/00Z CMC ARE CENTRAL IN BOTH  
STRENGTH/CONSOLIDATION AND LOCATION OF THE INNER CORE OF THE  
BROADER TROF. THE 12Z GFS SAW MARKED CHANGES FROM THE 06Z  
RUN...LEADING TO A SHIFT TOWARD THE UKMET EVOLUTION. THIS IS  
LIKELY TO LESS SOUTHWARD INJECTION OF S/W ENERGY AS THE NORTHERN  
STREAM IS MUCH FASTER (SEE SECTION ABOVE)...AS SUCH THE REMAINING  
WEAK ENERGY IS MORE PROGRESSIVE IN MODEST FLOW COUNTER TO THE  
TREND IN THE NAM/CMC/ECMWF. GIVEN THE LARGE SHIFT WILL EXCLUDE  
THE GFS/UKMET AT THIS TIME BUT LACK OF CONFIDENCE MAY ALLOW FOR  
SOME INCLUSION IF THE CMC/ECMWF TREND THIS WAY AS WELL. SO AT  
THIS POINT A 12Z NAM AND 00Z CMC/ECMWF BLEND IS PREFERRED BUT AT  
AVERAGE TO SLIGHTLY BELOW AVERAGE CONFIDENCE.  
 
19Z UPDATE: THE 12Z ECMWF TRENDED A BIT MORE CONSOLIDATED UNDER  
THE MEAN RIDGE AND PRESENTS A SMALL BUT MORE COMPACT INNER CORE TO  
THE BROAD TROF ACROSS TX/N COAHUILA BY 00Z FRI. THE 12Z CMC SLOWED  
A BIT WITH SOME INCREASED STRENGTH COMPARED TO THE 00Z RUN/INITIAL  
PREFERENCE BUT NOT SIGNIFICANTLY ENOUGH TO REMOVE FROM PREFERENCE.  
THE 12Z UKMET DID SLOW A BIT BUT REMAINS VERY CLOSE TO THE 12Z  
GFS WITH GREATER POSITIVE TILT TO THE LARGER SCALE TROF WHILE THE  
INNER CORE IS WELL EAST TOWARD THE LOWER MS VALLEY. AS SUCH WILL  
KEEP A 12Z NAM/ECMWF/CMC BLEND AS PREFERENCE FOR THIS WAVE.  
 
NEXT DEEP LAYERED PACIFIC CYCLONE NEARING SW CANADA WITH FRONTAL  
ZONE ENTERING NORTHWEST TO CENTRAL CA LATE WED AND THURS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE HIGHLY AMPLIFIED PATTERN CONTINUES BY WED INTO THURSDAY AS  
ANOTHER BROAD DEEP LOW TRACKS NORTHEAST...THERE REMAINS (AS  
EXPECTED) INTERNAL TIMING DIFFERENCES IN THE TIMING OF THE  
OCCLUSION AND THE EVOLUTION TO THE MAIN INNER CORE OF THE UPPER  
LOW ITSELF. THE 00Z ECMWF IS SLOWER AND LOADS A STRONGER S/W ON  
THE SOUTH AND EASTERN SIDE AS IT ADVANCES TOWARD SW CANADA LEADING  
TO A SLIGHT EASTWARD WOBBLE OF THE INNER CORE AND SURFACE LOW MORE  
THAN THE OTHER MAIN GLOBAL GUIDANCE MEMBERS. THE 12Z GFS IS AS  
EXPECTED A BIT FASTER TO OCCLUDE AND THAT MATURITY KEEPS THE INNER  
CORE WEST-MOST OF THE REMAINING GUIDANCE. THE 12Z NAM AND 00Z  
UKMET/CMC SPLIT THESE DIFFERENCES. THE ORIENTATION/STRENGTH AND  
TIMING OF THE JET CORE AND ITS INTERFACE WITH THE MOISTURE STREAM  
INTO THE PACIFIC NORTHWEST AHEAD OF THE FRONTAL ZONE LOOK  
REMARKABLY AGREEABLE THROUGH THE END OF THE DAY 3 PERIOD (00Z  
FRIDAY) TO SUPPORT A GENERAL MODEL BLEND. THE CONFIDENCE IS HIGH  
BUT GIVEN THE VARIATIONS IN THE OCCLUSION THE OVERALL CONFIDENCE  
IS ONLY SLIGHTLY ABOVE AVERAGE AS THE BLEND OF THESE MASS/INNER  
CORE DIFFERENCE WILL LIKELY NOT VERIFY BUT SLOWLY ADJUST TOWARD A  
COMMON SOLUTION AS THE SYSTEM APPROACHES.  
 
19Z UPDATE: THE ECMWF TRENDED A BIT EARLIER IN THE OCCLUSION  
PROCESS WHEN ENTERING THE CONUS DOMAIN ON WED...AS SO THE INNER  
CORE IS FURTHER WEST AND BETTER ALIGNED WITH THE MORE CENTRAL  
SOLUTIONS OF THE NAM AND CMC/UKMET (AS THEY SHOWED LITTLE RUN TO  
RUN VARIATION). THIS LEAVES THE CENTER OF THE SURFACE LOW/UPPER  
LOW FURTHER WEST FOR THE GFS...BUT NOT DRAMATICALLY SO ESPECIALLY  
AT THIS RANGE IN THE FUTURE. GIVEN THE MOISTURE/FRONTAL TIMING  
REMAINS STRONG WILL CONTINUE TO SUPPORT A GENERAL MODEL BLEND BUT  
INCREASE TO ABOVE AVERAGE CONFIDENCE GIVEN THE SMALL SPREAD ON A  
LARGE SYSTEM AT THIS TIME IN THE FORECAST PROCESS.  
 
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