455  
FXUS10 KWNH 311649  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1248 PM EDT TUE OCT 31 2017  
 
VALID OCT 31/1200 UTC THRU NOV 04/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
PRELIMINARY 12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SHORTWAVE OVER WESTERN TEXAS AND BECOMING SHEARED OUT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A COMPACT MID LEVEL LOW CENTER AND ASSOCIATED TROUGH OVER WESTERN  
TEXAS WILL TRACK EASTWARD AND GRADUALLY SHEAR OUT THROUGH TUESDAY  
NIGHT AS IT ENCOUNTERS LARGER SCALE CONFLUENT FLOW ALOFT. THIS  
DRAWS MOISTURE INLAND FOR SOME SHOWERS AND STORMS ACROSS SOUTHERN  
AND EASTERN TEXAS INTO THE LOWER MS VALLEY WEDNESDAY AND THURSDAY.  
LITTLE CHANGE IN THE 12Z NAM/GFS KEEPS STRONG CONTINUITY AND  
ALLOWS FOR A GENERAL MODEL BLEND PREFERENCE.  
 
SURFACE LOW TRACKING ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: NEAR AVERAGE  
 
A SHORTWAVE WILL LEAD TO A MID LEVEL TROUGH EVOLUTION ACROSS THE  
NORTHERN PLAINS AND UPPER MIDWEST THROUGH WEDNESDAY BEFORE THE  
ENERGY THEN CROSSES THE GREAT LAKES BEFORE EXITING ACROSS ONTARIO.  
A SUB-1000MB SURFACE LOW ACCOMPANYING THE SHORTWAVE ENERGY WILL  
SLIDE SOUTHEAST DOWN THE EAST SIDE OF THE CANADIAN ROCKIES AND  
CROSS THE NORTHERN PLAINS AND UPPER MIDWEST AS A TRAILING COLD  
FRONT GRADUALLY SETTLES DOWN TOWARD THE SOUTHERN PLAINS. SIMILAR  
TO THE EARLIER MODEL PREFERENCE, THE UKMET STRAYS FROM THE MODEL  
CONSENSUS WITH A MORE AMPLIFIED AND PROGRESSIVE UPPER LEVEL  
PATTERN.  
 
AMPLIFYING UPPER LOW NEAR VANCOUVER ISLAND BY THURSDAY AND SURFACE  
LOW JUST OFF THE PACIFIC NORTHWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GFS/ECMWF/CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A POTENT DISTURBANCE IN AMPLIFIED NORTHERLY FLOW OVER BRITISH  
COLUMBIA EVOLVES INTO A CLOSED MID-LEVEL LOW BY FRIDAY NEAR THE  
PACIFIC NORTHWEST COAST. IT IS EXPECTED TO BECOME MORE OF AN  
ELONGATED TROUGH BY THE END OF THE FORECAST PERIOD, WITH A SURFACE  
LOW AND SHARP FRONTAL BOUNDARY NORTH OF IT. THERE IS DECENT MODEL  
AGREEMENT OVERALL WITH THIS FEATURE, WITH THE 00Z UKMET SLIGHTLY  
NORTH OF THE MODEL CONSENSUS. BY FRIDAY NIGHT, THE NAM IS SLOWER  
WITH THE PROGRESSION OF THE TROUGH AXIS. THEREFORE A BLEND OF THE  
ECWMF, GFS, AND CMC SEEMS PRUDENT.  
 
SOUTHERN STREAM SHORTWAVE CROSSING SOUTHERN PLAINS ALONG WITH  
SURFACE LOW DEVELOPMENT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/00Z ECMWF/00Z CMC BLEND  
CONFIDENCE: NEAR AVERAGE  
 
LEE CYCLOGENESIS OVER WYOMING ON WEDNESDAY IS EXPECTED TO RESULT  
IN A SURFACE LOW THAT TRACKS SOUTHEAST TO A POSITION OVER OKLAHOMA  
BY THURSDAY EVENING IN RESPONSE TO A SOUTHERN STREAM SHORTWAVE.  
THIS WILL DEVELOP ALONG A STRONG COLD FRONT THAT WILL SINK SOUTH  
ACROSS THE PLAINS. THE 00Z UKMET APPEARS MORE AMPLIFIED WITH THIS  
LOW AND FARTHER SOUTH. THE NAM IS SLIGHTLY MORE AMPLIFIED WITH  
THE 500MB PATTERN. THERE IS GOOD AGREEMENT AMONG THE GFS, ECMWF,  
AND CMC FOR THIS LOW.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
HAMRICK  
 

 
 
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