819  
FXUS10 KWNH 161622  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1121 AM 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 AND 00Z 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.  
 
NORTHWEST US SHORTWAVE ROLLING THROUGH NORTHERN PLAINS LATE WED  
INTO GREAT LAKES THURS AND NEW ENGLAND BY FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/00Z ECMWF 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.  
 
SHORTWAVE DEVELOPING ACROSS TX BY EARLY THURS...SLIDING EAST ALONG  
NW GULF COAST BY LATE FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/NAM AND 00Z UKMET BLEND  
CONFIDENCE: SLIGHTLY BELOW 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.  
 
DEEP LAYERED TROF APPROACHING VANCOUVER ISLAND BY LATE WED/EARLY  
THURS WITH COLD FRONT SINKING SOUTH THROUGH FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
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.  
 
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: 12Z GFS AND 00Z 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.  
 
BASE OF DEEP LAYERED CYCLONE CROSSING INTERMOUNTAIN WEST LEADING  
TO LEE CYCLONE BY LATE FRI IN SE COLORADO  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET OR LOW WEIGHTED UKMET WITHIN A GENERAL MODEL  
BLEND  
CONFIDENCE: 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.  
 
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