345  
FXUS10 KWNH 210501  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
101 AM EDT SAT OCT 21 2017  
 
VALID OCT 21/0000 UTC THRU OCT 24/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION ALONG WITH LATEST MODEL PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..LONGWAVE TROUGH EVOLUTION THROUGH WESTERN U.S
 
   
..EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT
 
   
..SURFACE LOW DEEPENING OVER SOUTHERN CANADA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS HAVE COME INTO GOOD AGREEMENT WITH THE TIMING AND DEPTH  
OF THIS UPPER TROUGH AS IT EJECTS ACROSS THE WESTERN U.S.  
OVERNIGHT AND THEN OUT ACROSS THE CENTRAL/NORTHERN PLAINS ON  
SATURDAY. A COLD FRONT ASSOCIATED WITH THIS TROUGH WILL ALSO EJECT  
OUT ACROSS THE PLAINS AS LOW PRESSURE DEEPENS ACROSS SOUTHERN  
CANADA. A GENERAL MODEL CONSENSUS WILL BE PREFERRED AT THIS TIME  
GIVEN THE GOOD MASS FIELD AGREEMENT.  
 
   
..SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW DEVELOPMENT BY MON
 
   
..SURFACE COLD FRONT SWEEPING ACROSS THE MS/TN VALLEYS
 
   
..SURFACE LOW DEVELOPMENT OVER THE TN VALLEY
 
   
..DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION BY TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 1/3 GFS...2/3 ECMWF BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE MODELS BREAK AWAY THE SOUTHERN PORTION OF THE LONGER WAVE  
TROUGH EJECTING OUT OF THE WEST AND INTO THE PLAINS STATES ON  
SUNDAY...WITH THIS ENERGY DIGGING SOUTHEAST INTO THE LOWER MS  
VALLEY SUNDAY NIGHT AND RESULTING IN A CLOSED LOW FORMATION BY  
MONDAY. THIS WILL STILL BE INTERACTING WITH THE SOUTHERN PORTION  
OF A N/S ORIENTED FRONTAL ZONE AND THE MODELS SUGGEST A WAVE OF  
LOW PRESSURE WILL DEVELOP ALONG THE BOUNDARY ACROSS THE TN VALLEY  
ON MONDAY.  
 
BY MONDAY NIGHT...THE LOW CENTER WILL LIKELY BEGIN TO DEEPEN MORE  
AGGRESSIVELY AND BEGIN LIFTING NORTH TOWARD THE OH VALLEY IN  
RESPONSE TO A STRONG INTRUSION OF NORTHERN STREAM SHORTWAVE ENERGY  
WHICH WILL BE AMPLIFYING SOUTHEAST ACROSS THE MIDWEST. THE  
NORTHERN STREAM TROUGH WILL AMPLIFY INTO THE OH VALLEY AND GREAT  
LAKES REGION AND SHOULD GRADUALLY PHASE WITH THE SOUTHERN STREAM  
CLOSED LOW AS IT AND BEGINS TO INTERACT AND GRADUALLY PHASE WITH  
THE CLOSED LOW ADVANCING EAST ACROSS THE GULF COAST STATES AND THE  
SOUTHERN APPALACHIANS. THE RESULT IS EXPECTED TO BE A DEEP  
LONGWAVE TROUGH MOVING INTO THE EASTERN HALF OF THE NATION ON  
TUESDAY WITH A STRONG COLD FRONT MOVING TOWARD THE APPALACHIANS  
AND A DEEPENING CYCLONE OVER THE GREAT LAKES REGION. THE 00Z NAM  
BECOMES A SLOW OUTLIER WITH THE SOUTHERN STREAM EVOLUTION OF THE  
CLOSED LOW AND WILL BE DISMISSED. THE 12Z CMC/ECMWF SOLUTIONS ARE  
FASTER TO LIFT THE SOUTHERN STREAM ENERGY NORTHEAST ACROSS THE  
TN/OH VALLEYS ALONG WITH THEIR RESPECTIVE SURFACE LOWS. THE 00Z  
GFS AND 12Z UKMET ARE SLOWER TO DO THIS AND KEEP MORE SOUTHERN  
ENERGY SUPPRESSED ACROSS THE SOUTH. CONSEQUENTLY...THE CMC AND  
ECMWF FAVORING FASTER PHASING OF STREAMS...WITH THE GFS AND UKMET  
SLOWER. GENERALLY THERE HAS BEEN A MULTI-DAY TREND TOWARD QUICKER  
PHASING AND WITH A STRONGER INTRUSION OF NORTHERN STREAM ENERGY TO  
FACILITATE THIS. MANY EURO AND CANADIAN ENSEMBLE MEMBERS FAVOR THE  
OPERATIONAL ECMWF/CMC CAMP...AND THERE ARE SOME GEFS MEMBERS WHICH  
LIKEWISE SUPPORT THIS CAMP AS WELL. THE GFS APPEARS TO BE  
STRUGGLING A BIT WITH THE TIMING OF ENERGY LIFTING UP OUT OF THE  
SOUTH BUT IS TRENDING TOWARD THE STRONGER ECMWF/CMC CAMP. FOR  
NOW...GIVEN SOME OF THE DETERMINISTIC SPREAD...THE PREFERENCE WILL  
BE TOWARD THE MORE AMPLIFIED SOLUTIONS BUT WITH SOME WEIGHT STILL  
INCORPORATED FROM THE WEAKER CAMP. THUS A BLEND OF THE ECMWF AND  
GFS...WITH MORE WEIGHTING TOWARD THE ECMWF.  
 
   
..SHORTWAVE REACHING B.C./PAC NORTHWEST ON SAT WITH WARM FRONT
 
   
..ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST SAT
 
   
..UPPER TROUGH SWEEPING ACROSS THE NORTHERN PLAINS/MIDWEST MON
 
   
..WEST COAST RIDGE/SANTA ANA WIND DEVELOPMENT MON/TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL CONSENSUS...THROUGH 60 HOURS  
NON-UKMET CONSENSUS...AFTER 60 HOURS  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT THROUGH EARLY SATURDAY WITH THE  
ARRIVAL OF AN UPPER SPEED MAX/SHORTWAVE AND ATTENDANT WARM FRONT  
ACROSS THE PACIFIC NORTHWEST AND SOUTHWEST BRITISH COLUMBIA. THIS  
ENERGY WILL ADVANCE RAPIDLY NORTHEAST INTO SOUTHWEST CANADA AND  
LEAD THE WAY FOR A LONG-FETCH ATMOSPHERIC RIVER TRAVERSING THE  
PACIFIC BASIN TO COME CRASHING INTO THE COASTAL RANGES AND  
CASCADES OF THE PACIFIC NORTHWEST THROUGH SATURDAY NIGHT AND EARLY  
SUNDAY. THE ONSHORE FLOW SHOULD THEN BEGIN TO SLACKEN BY LATER  
SUNDAY AS LARGER SCALE RIDGING BEGINS TO BUILD ALONG THE WEST  
COAST. MEANWHILE...THE INITIAL ARRIVAL OF SHORTWAVE ENERGY WILL  
THEN AMPLIFY DOWNSTREAM ACROSS THE MIDWEST AND TOWARD THE EASTERN  
U.S. LEADING THE WAY FOR A RATHER HIGH AMPLIFIED LONGWAVE PATTERN  
ACROSS THE U.S. BY TUESDAY. UNFORTUNATELY...THE DEVELOPING UPPER  
LEVEL RIDGE OVER THE WEST BY MONDAY AND TUESDAY WILL ALLOW  
STRONGER SURFACE HIGH PRESSURE TO SETTLE OVER THE GREAT BASIN AND  
LEAD TO THE DEVELOPMENT OF RATHER STRONG SANTA ANA WINDS OVER  
CALIFORNIA. WILL PREFER A GENERAL MODEL CONSENSUS THROUGH ABOUT 60  
HOURS...AND THEN A NON-UKMET CONSENSUS THEREAFTER AS THE UKMET  
APPEARS TO NOT BE AMPLIFIED ENOUGH DOWNSTREAM OVER THE NORTHERN  
PLAINS AND MIDWEST WITH THE SHORTWAVE ENERGY DIGGING SOUTHEAST  
ACROSS THESE AREAS.  
 
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