024  
FXUS10 KWNH 161845  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
143 PM EST TUE JAN 16 2018  
 
VALID JAN 16/1200 UTC THRU JAN 20/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
PLEASE REFER TO THE WPC QPFPFD PRECIPITATION FORECAST DISCUSSION  
FOR DETAILS ON MODEL PREFERENCES AND SYSTEM TIMING UNTIL THE NEXT  
PMDHMD IS ISSUED AT 1645 UTC.  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
EASTERN US TROF AND COASTAL SURFACE LOW PASSING NEW ENGLAND WED  
INTO EARLY THURS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/GFS/ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODEL SPREAD CONTINUES TO REDUCE THOUGH GIVEN PROXIMITY TO TIME  
T=0 THE SPREAD REMAINS MODEST. THE IMPORTANT ARCTIC SHORTWAVE  
CURRENTLY NEAR NUNAVUT WILL AMPLIFY AND HELP KICK THE NORTHERN  
PORTION OF THE CURRENT SHARPENING POSITIVE TILTED TROF OVER THE  
EASTERN US. THE COMBINATION WILL DEVELOP A SURFACE WAVE OFF THE  
MID-ATLANTIC BY EARLY WED THAT WILL GLIDE PAST NEW ENGLAND DURING  
THE DAY. MODELS SEEM TO HAVE SETTLED ON MUCH OF THE MASS  
SPREAD/DIFFERENCE FOR THIS WAVE THOUGH THE SLIGHTLY FASTER BUT  
LESS AMPLIFIED 00Z UKMET ALLOWS FOR A CLOSER TO COAST SFC  
TRACK...AND THE 00Z CMC REMAINS SLOW. HOWEVER AFTER THIS TIME  
PERIOD AS THE REMAINING BASE OF THE TROF SLIDES EASTWARD...THE 06Z  
GFS AND A BULK OF GEFS MEMBERS CONTINUES TO BE VERY ARCHED/SHARP  
WITH THE WAVE WHILE THE SLIGHTLY SLOWER GUIDANCE PRESENTED BY THE  
12Z NAM/00Z ECMWF ALLOW FOR INCREASED BREADTH OF THE TROF. THE 12Z  
GFS HOWEVER HAS SHIFTED SLOWER TOWARD THE NAM/ECMWF PROVIDING  
GREATER CONFIDENCE . THE LARGER MORE CONSOLIDATED WAVE SOLUTIONS  
ALLOW FOR A POTENTIAL SECONDARY SURFACE LOW ALONG THE COLD FRONT  
NEAR THE GULF STREAM/EAST OF THE OUTER BANKS WITH THE 00Z  
UKMET/CMC MOST AGGRESSIVE WITH THIS SCENARIO. GIVEN THE SLOWING  
OF THE 12Z GFS AND AGREEMENT WITH THE 12Z NAM/00Z ECMWF WILL  
PREFER THIS BLEND ESPECIALLY GIVEN A LESS AMPLIFIED SECOND WAVE.  
CONFIDENCE IS INCREASED TO SLIGHTLY ABOVE AVERAGE.  
 
19Z UPDATE: LITTLE NUDGES SLOWER WERE NOTED IN THE 12Z  
ECMWF...PARTICULARLY WITH RESPECT TO THE SECOND DEVELOPING SFC LOW  
ON THE TRAILING COLD FRONT THURSDAY AND MATCH THE 00Z ECENS MEAN.  
THE 12Z UKMET AND CMC BOTH TRENDED A BIT FASTER BUT REMAIN WELL  
SPREAD FROM THE NAM/GFS. AS SUCH WILL KEEP INITIAL PREFERENCE OF  
A NAM/GFS/ECMWF BLEND.  
 
NORTHWEST US SHORTWAVE ROLLING THROUGH NORTHERN PLAINS LATE WED  
INTO GREAT LAKES THURS AND NEW ENGLAND BY FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
GOES-WV LOOP DENOTES SHORTWAVE NEAR THE OLYMPIC PENINSULA  
EXTENDING SE ACROSS WA/OR ATTM WITH DOWNSTREAM RIDGE OVER THE  
ROCKIES. THIS WAVE WILL CONTINUE TO LIFT OVER THE RIDGE AND IN  
DOING SO CONSOLIDATE AND ROLL RAPIDLY EASTWARD ALONG THE NORTHERN  
TIER INTO THE GREAT LAKES. MODELS CONTINUE TO STRUGGLE IN  
CONSOLIDATE IN TIMING WITH RESPECT TO WHEN THE WAVE WILL OVER-TOP  
THE RIDGE AND AT WHICH LATITUDE IT WILL EJECT TO. THE 00Z UKMET  
REMAINS FAIRLY CONSISTENT RUN TO RUN BUT HAS BEEN A FASTER  
SOLUTION THROUGHOUT THE LAST FEW MODEL CYCLES (ESPECIALLY COMPARED  
TO ENSEMBLE MEMBERS)...HOWEVER...THE 00Z CMC HAS TRENDED A BIT  
FASTER AND GENERALLY MATCHED THE LATITUDE. LIKEWISE...THE 00Z  
ECMWF HAS BEEN CONSISTENT OVER THE LAST 2-3 RUNS BUT IS A BIT  
SLOWER INJECTING TO THE MEAN FLOW AND IS DELAYED RELATIVE TO THE  
UKMET/CMC BUT APPEARS BEST CENTERED IN THE ENSEMBLE SUITE. THE  
12Z NAM HAS SHIFTED FASTER THAN EARLIER RUNS AND EVEN OUTPACES THE  
UKMET/CMC. THE 12Z GFS HAVING RESOLVED THE DOWNSTREAM SHORTWAVE  
RIDGING THAT SLOWED ITS EMERGENCE OVER THE RIDGE LATE WED AS SEEN  
IN THE GEFS AND 06Z GFS RUN...SPLITS THE DIFFERENCE IN TIMING WITH  
THE ECMWF AND CMC/UKMET...AND IS AT A MORE MIDDLE GROUND/PREFERRED  
LATITUDE OF THE NAM/ECMWF. BELIEVE A BLEND OF THE 12Z GFS WITH  
THE CONTINUITY OF THE 00Z ECMWF/ECENS MEAN WILL PROVIDE THE BEST  
SOLUTION GOING FORWARD YET THE SPREAD BEING HIGHLY CONTINGENT ON  
TIMING/LATITUDE EMERGING OVER THE RIDGE LEAVES ENOUGH UNCERTAINTY  
IN THIS BLEND TO HAVE ONLY AVERAGE CONFIDENCE OVERALL.  
 
19Z UPDATE: THE 12Z ECMWF TRENDED FASTER AND MATCHES VERY WELL  
WITH STRENGTH/TIMING AND LATITUDE OF THE 12Z GFS... ADDITIONALLY  
THE 12Z UKMET SLOWED TO MATCH WELL TOO. THE 12Z CMC SLOWED BUT  
ALSO REMAINS A BIT FURTHER NORTH IN THE CLUSTER BUT LIKELY MORE  
USEFUL THAN THE NAM AT THIS POINT. STILL CONFIDENCE IS ONLY  
AVERAGE GIVEN THE INITIAL SETUP VARIATION THAT REMAINS MOVING  
THROUGH THE RIDGE...BUT WILL INCLUDE THE 12Z UKMET TO A 12Z  
GFS/ECMWF BLEND.  
 
SHORTWAVE DEVELOPING ACROSS TX BY EARLY THURS...SLIDING EAST ALONG  
NW GULF COAST BY LATE FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/CMC/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
00Z ENSEMBLE SPAGHETTI ANALYSIS CONTINUE TO SHOW TWO DISTINCT  
CAMPS WITH RESPECT TO THE EVOLUTION OF WEAK SHORTWAVE ENERGY  
EMERGING THROUGH THE BASE OF THE MEAN RIDGE AXIS OVER THE NORTHERN  
US ROCKIES WED. INITIALLY THE GUIDANCE IS CLEAR ON THE FORMATION  
OF A BROAD SLIGHTLY POSITIVE TILT TROF ACROSS TX BY  
THURS...HOWEVER THE DIFFERENCE EXISTS THEREAFTER WITH SPECIFIC  
RELATIONSHIP TO THE TIMING/TRACK OF THE INNER CORE/VORT CENTER.  
THE 12Z GFS/NAM AND 00Z UKMET REMAIN MORE PROGRESSIVE ALLOWING THE  
WAVE TO DRIFT EASTWARD BY LATE THURS/EARLY FRI AND MARCH TOWARD  
THE MOUTH OF THE MS RIVER FRI WITH THE BASE OF THE BROAD TROF  
LINGERING ACROSS NE MEXICO IN A POSITIVE TILT ORIENTATION. THE  
00Z ECMWF/CMC IN THE OTHER CAMP DO NOT ALLOW THE INNER VORT TO  
ADVECT EASTWARD AND REMAIN CENTERED TO THE BASE OF THE TROF AS IT  
DRIFTS SOUTHEAST INTO NORTHERN MEXICO. THE SPREAD IN THE WIND  
FIELDS/QPF ARE MINOR BUT DUE TO SLIGHTLY STRONGER SOUTHERLY FLOW  
WITH A DEEPER WAVE ALLOWS FOR INCREASED FETCH FROM THE SW GULF/BAY  
OF CAMPECHE FOR THE ECMWF/CMC. WILL FAVOR THE GFS/NAM/UKMET FOR  
NOW GIVEN STRENGTH OF MEAN STEERING FLOW CURRENTLY THOUGH  
UNCERTAINTY REIGNS AND MAY NOT SETTLE UNTIL ENERGY EMERGES THROUGH  
THE TERRAIN.  
 
19Z UPDATE; THE 12Z ECMWF/CMC NO LONGER DELAY THE EASTWARD  
RESPONSE THE MEAN FLOW AND HAVE SHIFTED FURTHER EAST THOUGH REMAIN  
WELL SLOWER THAN THE 12Z NAM/GFS. HOWEVER...THE 00Z UKMET HAS  
SLOWED ENOUGH TO BE MORE ALIGNED WITH THE ECMWF/CMC. THIS  
SHIFT/CHANGE IS MORE IN THE DIRECTION OF ORIGINAL THINKING BUT  
WITHOUT REPRESENTING GUIDANCE. AS SUCH AVERAGE CONFIDENCE IS  
GIVEN TO A SLIGHT SHIFT EASTWARD WITH A 12Z ECMWF/UKMET/CMC BLEND  
OVER THE NAM/GFS.  
 
DEEP LAYERED TROF APPROACHING VANCOUVER ISLAND BY LATE WED/EARLY  
THURS WITH COLD FRONT SINKING SOUTH THROUGH FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
BRITISH COLUMBIA/SE AK PREFERENCE (FRI): 12Z CMC/ECMWF  
CONFIDENCE: ABOVE AVERAGE  
 
A MATURE DEEP LAYERED CYCLONE EMERGES FROM THE CENTRAL PACIFIC BY  
EARLY WED AND BEGINS TO SLOW EASTWARD PROGRESSION TOWARD THE EAST  
SETTLING BETWEEN VANCOUVER ISLAND AND THE QUEEN CHARLOTTE ISLANDS.  
WHILE SLOWING THE LOW IS GENERALLY FILLING WITH STRONG SSWLY  
MOISTURE FLUX AHEAD OF A SLOWLY SOUTHWARD DRIFTING FRONTAL ZONE  
FROM THE PACIFIC NORTHWEST LATE WED INTO THURS INTO CENTRAL CA BY  
FRIDAY. MODELS HAVE BEEN HANDLING THE SSWLY FLOW WELL WITH  
CONSISTENT MST FLUX AND TIMING AS IT DRIFTS SOUTH. SOME SMALL  
MODEL SPREAD EXISTS WITH THE INNER CORE OF THE UPPER LOW AND THE  
SURFACE RESPONSE TO IT WITH THE 00Z UKMET SHOWING A SOUTHWARD  
PREFERENCE COMPARED TO AN OTHERWISE STRONG SFC LOW CLUSTER. AS  
THE LOW FURTHER BREAKS DOWN THE 12Z NAM/12Z GFS AND 00Z CMC DRIFT  
THE WEAKENING SFC LOW SOUTHEAST ALONG VANCOUVER ISLAND WHILE THE  
00Z ECMWF REMAINS STUBBORN WITH THE LOW UP NEAR MORESBY ISLAND.  
WOULD FAVOR THE SLIGHTLY FASTER NAM/GFS ON THIS TIME FRAME BUT  
RELEVANT TO THE U.S. NORTHWEST A NON-UKMET BLEND WILL LIKELY  
SUFFICE THROUGHOUT. PLEASE SEE BOTH SECTIONS BELOW FOR DIFFERENT  
SHORTWAVE PIECES OF THE DEEP CYCLONE HAS IT BREAKS DOWN ENTERING  
THE CONTINENT.  
 
19Z UPDATE: THE UKMET NO LONGER HAS THE OVER DEVELOPED CENTER VORT  
SHIFTING THE SURFACE LOW SOUTH OF THE MAIN CLUSTER AND AS SUCH THE  
GUIDANCE HAS COME TO MUCH STRONGER AGREEMENT THROUGH THE MATURE  
AND EARLY DECAY PHASE OF THIS DEEP LOW. THIS ALLOWS FOR  
INCREASED SCRUTINY OF FINAL FULL DECAYING STAGE AFTER 00Z FRIDAY.  
THE GFS REMAINS MORE CONCENTRIC AND DEEPER BUT ALSO SLIDES SOUTH  
WITH THE NAM. THE OTHER NON-NCEP SOLUTIONS BEGIN TO FEEL THE  
UPSTREAM MATURING CYCLONE AND LIFT NORTH INTO THE QUEEN CHARLOTTE  
ISLANDS...THOUGH THE UKMET MAY GO A BIT TOO EAST/FAST WITH THE  
UPSTREAM WAVE TO DRIVE THE REMAINING LOW WELL NORTH OF THE SFC  
CLUSTER BY THE END OF THE FORECAST PERIOD. WOULD FAVOR A MORE  
CENTRAL SOLUTION HERE FOR THIS AREA OF THE ECMWF/CMC. WITH THAT  
STATED...PLACEMENT/TIMING OF THE TRIPLE POINT/MOISTURE STREAM AND  
SOUTHWARD PUSH OF THE COLD FRONT THURS/FRI IN THE LOWER 48 LOOK  
STRONG ENOUGH TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE  
CONFIDENCE.  
 
LEAD SHORTWAVE ENERGY FROM DEEP LAYERED TROF INTERACTS WITH ARCTIC  
STREAM TO PRODUCE BROAD TROF SPURRING SURFACE CYCLONE ACROSS  
CENTRAL CANADA CLIPPING THE NORTHERN TIER LATE THURS INTO FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 1/2 12Z UKMET & 1/2 12Z ECMWF/CMC BLEND  
CONFIDENCE: BELOW AVERAGE  
 
AS THE DEEP LAYERED CYCLONE BREAKS DOWN LATE THURS INTO  
FRIDAY...THE LEADING SHORTWAVE ENERGY NEAR THE TRIPLE POINT  
(INTERSECTION OF SSWLY FLOW AND TROWAL BACK TO THE NW) PRESSES  
NORTHEAST INTO THE SOUTHERN CANADIAN ROCKIES. COMBINATION FROM  
DOWNSTREAM LINGERING ENERGY FROM THE PREVIOUS TROF AS WELL AS  
DESCENDING SHORTWAVE OUT OF THE ARCTIC FLOW WILL PRODUCE A BROADLY  
CYCLONIC SHORTWAVE INTERACTION ACROSS CENTRAL CANADA INTO FRIDAY.  
THE AMOUNT OF BINARY INTERACTION WITH THE ARCTIC FLOW AND THE  
ANGLE AT WHICH THEY DO INTERACT LEAD TO A VERY LARGE SPREAD AND  
BROAD SURFACE LOW BY 00Z SAT. THE 12Z NAM IS MOST CONSOLIDATED  
AND STRONGEST OVERALL BUT ALSO IS A BIT SLOWER THAN THE MORE  
LOOSELY INTERACTING 12Z GFS AND 00Z ECMWF/CMC. THE 00Z UKMET IS  
VERY FAST IN SHIFTING THE LEAD HEIGHT-FALLS FROM THE PACIFIC  
EASTWARD ON FRIDAY WITH LESS INTERACTION FROM THE ARCTIC STREAM  
LEADING TO A MUCH LONGER/STRUNG OUT POSITIVE TILT TROF CONNECTING  
BACK TO ENERGY IN THE NORTHERN US ROCKIES. GIVEN THE MOVING  
PIECES (MULTIPLE STREAMS) TIMING INTERACTIONS ETC...THERE IS VERY  
LOW CONFIDENCE IN THE EVOLUTION OF THIS DEVELOPING  
WAVE/AMALGAMATED SHORTWAVES...BUT WILL GO TO A MIDDLE GROUND  
PREFERENCE INCLUDING THE 12Z GFS AND 00Z ECMWF/CMC AT THIS POINT.  
 
19Z UPDATE: ENTERING THE PACIFIC NORTHWEST REMAINS WELL  
TIMED...HOWEVER THE 12Z ECMWF/CMC HAVE SHIFTED FASTER WITH THE  
LEAD SHORTWAVE INTO SOUTHERN CANADA AND ACCELERATE WITH THE  
INTERACTION WITH THE ARCTIC STREAM S/W. THIS MATCHES THE 00Z  
UKMET AND WITH THE 12Z UKMET A BIT SLOWER THE 12Z UKMET IS NOW  
MOST CENTRAL IN THE OVERALL LARGE SPREAD. THIS WOULD SUGGEST A  
PREFERENCE TOWARD THE 12Z UKMET THOUGH WOULD INCLUDE SOME  
WEIGHTING TO THE 12Z ECMWF/CMC. STILL CONFIDENCE REMAIN WELL  
BELOW AVERAGE GIVEN THE HIGH SENSITIVITY OF THE PIECES THAT ARE  
CONTINGENT EARLIER DOWNSTREAM EVOLUTION.  
 
BASE OF DEEP LAYERED CYCLONE CROSSING INTERMOUNTAIN WEST LEADING  
TO LEE CYCLONE BY LATE FRI IN SE COLORADO  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AS THE DEEP LAYERED CYCLONE BREAKS DOWN LATE THURS INTO  
FRIDAY...THE BASE OF THE TROF BEGINS TO FOLD SLIGHTLY SHARPENING  
THE TROF ENTERING CENTRAL CA AND SLIDING SOUTH. AS ALLUDED TO TWO  
SECTIONS ABOVE...THE GUIDANCE IS FAIRLY WELL HANDLED ACROSS THE  
EARLY PERIOD WITH GOOD TIMING OF THE FRONTAL ZONE AND MOISTURE  
STREAM SLOWLY SAGGING SOUTH. THIS TRANSLATES FAIRLY WELL ACROSS  
THE GREAT BASIN/JACKSON RANGE/YELLOWSTONE VICINITY. THIS ALSO  
SUPPORTS AN ENVIRONMENT OF HEIGHT FALLS ACROSS THE CENTRAL  
ROCKIES AS WELL AND BY 00Z SAT...LEE CYCLOGENESIS BEGINS IN SE CO  
AND IS FAIRLY TIGHTLY CLUSTERED. THE ONLY EXCEPTION BEING THE  
UKMET A BIT OFF IN PLACES...THIS MAY OR MAY NOT WARRANT ITS  
COMPLETE ELIMINATION FROM A PREFERRED BLEND BUT AT LEAST SUPPORTS  
A LOWER WEIGHTING. CONFIDENCE IS ABOVE AVERAGE IN A GENERAL MODEL  
BLEND OR NON-UKMET BLEND.  
 
19Z UPDATE: THE 12Z UKMET SHIFTED A BIT SLOWER AND MORE AMPLIFIED  
IN THE BASE OF THE TROF LEADING TO FURTHER DISCONNECTION TO AN  
OTHERWISE FAIRLY TIGHT CLUSTER THROUGH SOUTHERN  
CALIFORNIA/INTERMOUNTAIN WEST AND LEE CYCLONE DEVELOPMENT INTO  
LATE FRIDAY. AS SUCH A NON-UKMET BLEND IS SUPPORTED AT SLIGHTLY  
ABOVE AVERAGE CONFIDENCE.  
 
PREVIOUS MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
PREVIOUS 500 MB FORECASTS AT  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
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