581  
FXUS10 KWNH 010403  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1203 AM EDT WED NOV 01 2017  
 
VALID NOV 01/0000 UTC THRU NOV 04/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SHORTWAVE ENTERING NORTHERN TIER LATE WED AND THROUGH GREAT LAKES  
THURS/FRI AND SOUTHEAST CANADA FRI/SAT WITH ASSOCIATED SURFACE  
LOW... SECONDARY SURFACE WAVE ALONG LEE OF ROCKIES INTO SOUTHERN  
PLAINS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
GOES-WV MOSAIC DEPICTS VERY LINEAR BUT STRONG JET ACROSS NW CANADA  
WITH LIKEWISE FAIRLY FLAT SHORTWAVE STARTING TO EMERGE IN THE LEE  
OF THE CANADIAN ROCKIES ALREADY SPURRING A 996MB SFC LOW. UNDER  
INCREASING DIFFLUENT FLOW...THE FLOW SPLITS WITH THE SHORTWAVE  
ANGLING ACROSS THE NORTHERN TIER WITH ONE SURFACE WAVE WHILE THE  
NORTHWESTERLY FLOW OVER THE ROCKIES CONTINUES TO SUPPORT ANOTHER  
LEE CYCLONE THAT WILL EVENTUALLY SETTLE AT THE TRAILING END OF THE  
FRONT ACROSS THE RED RIVER. THE NORTHERN AMPLIFICATION HAS BEEN  
GETTING BETTER AGREED UPON THOUGH THE 12Z UKMET CONTINUES TO FAVOR  
AN EASTERN STRONGER INFLECTION AT THE SURFACE THROUGH THE GREAT  
LAKES...OPPOSED BY THE 12Z CMC AND 00Z NAM WHICH HOLD BACK THE  
ENERGY IN FAVOR OF A DEEPER MAIN WAVE. THE 00Z GFS SHIFTED TOWARD  
A FASTER LEAD SHORTWAVE WITHIN THE PACKET EVEN OUTPACING THE UKMET  
A BIT. THIS LEAVES THE 12Z ECMWF AS THE MIDDLE SPLITTING THE  
DIFFERENCES WITH THE GFS/UKMET AND NAM/CMC THOUGH SHOWING  
SIMILARITIES TO BOTH. THE DIFFERENCE BETWEEN THE CMC/NAM BECOMES  
LARGEST THROUGH THE NORTHERN GREAT LAKES...WHEN THE NAM/ECMWF PAIR  
BETTER. OVERALL A NON-CMC BLEND SEEMS APPROPRIATE THROUGH WILL  
HEAVILY WEIGHT TOWARD THE EVOLUTION/TIMING OF THE ECMWF WITHIN THE  
BLEND. CONFIDENCE REMAINS AVERAGE GIVEN THE REMAINING VARIABILITY  
WITHIN FAIRLY FLAT FLOW WHERE SMALL WAVE AMPLIFICATIONS/TIMING  
DIFFERENCES CAN LEAD TO MODEST MASS DIFFERENCES.  
 
AMPLIFYING UPPER LOW NEAR VANCOUVER ISLAND BY THURSDAY AND  
SURFACE LOW JUST OFF THE PACIFIC NORTHWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS AND 12Z ECMWF/UKMET 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. SUBTLE DOWNSTREAM RIDGING IN GENERALLY  
SWLY FLOW...ALLOWS THE SHORTWAVE TO EXPLOIT THE WEAKNESS OVER THE  
PACIFIC AND WITH THE HELP OF UPSTREAM STRONG ANTICYCLONIC CURVED  
JET STREAK BEGINS TO STRETCH THE TROF SOUTHWESTWARD. SMALL TIMING  
DIFFERENCES REMAIN INITIALLY BEFORE THE STRETCHING OCCURS.  
UNCHARACTERISTICALLY THE 12Z ECMWF REMAINS SLIGHTLY FORWARD (MORE  
NEUTRAL ORIENTATION) EVEN COMPARED TO THE 12Z ECENS MEAN... WHILE  
THE 12Z CMC IS IN A TYPICAL VERY SLOW WESTWARD POSITION COMPARED  
TO THE ENSEMBLE MEANS. THE 00Z NAM HAS SHIFTED A BIT FASTER THAN  
THE PRIOR RUNS BUT STILL LAGS THE AVERAGE POSITION OF THE  
ELONGATED TROF OR SHOWING GREATER POSITIVE TILT ORIENTATION  
COMPARED TO THE 12Z UKMET/ECMWF OR THE 00Z GFS. EFFECTS TO THE  
SENSIBLE WEATHER DO NOT SEEM VERY LARGE BUT FROM A MASS STANDPOINT  
WILL FAVOR A 00Z GFS AND 12Z ECMWF/UKMET BLEND (WEIGHTING THE  
ECMWF A BIT LESS HEDGING TOWARD THE SLOWER ECENS MEAN).  
 
SOUTHERN STREAM SHORTWAVE CROSSING SOUTHWEST US INTO SOUTHERN  
PLAINS BY FRI SPURRING SURFACE LOW OUT OF RED RIVER VALLEY TOWARD  
MO ON SAT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/12Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
HIGHLY ELONGATED SHORTWAVE ACROSS S CA AND GENERAL WEAKNESS  
BETWEEN THE POLAR AND SUBTROPICAL STREAMS WILL CONTINUE TO SUPPORT  
WEAK SHORTWAVES AND MORE RANDOM WEAK VORTEX ROLL UP SOLUTIONS  
THROUGH THE SOUTHERN PLAINS INTO THE SOUTHEAST. THE MAIN CORE OF  
THE SHORTWAVE OVER S CA WILL ENHANCE/RE-CONSOLIDATE OVER THE  
SOUTHWEST INTO SOUTHERN PLAINS...HELPING TO ENHANCE THE DYING  
SURFACE WAVE/STALLED FRONT ACROSS THE RED RIVER VALLEY TO SHIFT  
NORTHEAST INTO THE LOW MO/CENTRAL MS VALLEY SAT...EVEN THOUGH THE  
SHORTWAVE SLIDES INTO THE LOWER MS AND CONTINUED SWLY FLOW  
DOMINATES FROM THE EASTERN PACIFIC THROUGH THE OHIO VALLEY BY SAT.  
WHILE THERE ARE SUBTLE DIFFERENCES IN AMPLIFICATION OF THE  
WAVE...THE 00Z NAM/UKMET A BIT WEAKER...THE CMC MORE  
AMPLIFIED/SLOWER... UKMET A BIT FASTER ACROSS THE GULF COAST BY  
FRIDAY. THE OVERALL PATTERN SUGGEST A 00Z GFS/12Z ECMWF BLEND  
GIVEN MOST CENTRAL SOLUTIONS...MORE RELIABLE VERIFICATION AND GOOD  
REPRESENTATION TO THE ENSEMBLE SOLUTIONS...THOUGH CONFIDENCE  
REMAINS AT BEST AVERAGE IN THIS BLEND.  
 
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 12Z UKMET CONTINUES TO BE 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.  
 
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