518  
FXUS10 KWNH 290456  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1155 PM EST TUE JAN 28 2020  
 
VALID JAN 29/0000 UTC THRU FEB 01/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SPLIT FLOW TROUGH CROSSING THE GREAT PLAINS TODAY AND REACHING  
THE SOUTHEAST WEDNESDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
THE LATEST NUMERICAL GUIDANCE REMAINS IN DECENT AGREEMENT WITH THE  
EVOLUTION OF A SHORTWAVE WHICH WAS OVER THE SOUTHERN PLAINS AT  
29/00Z. AS THE WAVE TRACKS EAST, THE 29/00Z NAM WAS SLIGHTLY  
FASTER THAN THE 28/12Z RUNS AND WELL WITHIN THE CLUSTERING OF  
OTHER MODEL GUIDANCE. A GENERAL MODEL BLEND SHOULD LOOK VERY  
SIMILAR TO ANY OF THE INDIVIDUAL MODEL RUNS WHILE DAMPENING THE  
MINOR DIFFERENCES IN AMPLITUDE AND SPEED OF PROPAGATION.  
 
...SPLIT FLOW TROUGH IN NORTHERN STREAM FROM THE UPPER MIDWEST TO  
THE MID-ATLANTIC THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 28/12Z UKMET BLEND  
CONFIDENCE: AVERAGE  
 
THE NUMERICAL GUIDANCE GOT INTO BETTER AGREEMENT WITH RESPECT TO  
THE ENERGY IN THE NORTHERN STREAM DURING THE 28/12Z MODEL RUNS.  
THERE WERE A COUPLE OF MINOR RUN TO RUN DIFFERENCES IN THE NAM AND  
GFS...BUT THE OVERALL SOLUTION CHANGED LITTLE. THAT LEAVES THE  
28/12Z UKMET BEING A MORE AMPLIFIED SOLUTION WITH THE WAVE THAT  
MAKES ITS WAY ACROSS PARTS OF THE GREAT LAKES AND OHIO VALLEY. NO  
REASON TO CHANGE PREFERENCES BASED ON THE 29/00Z GUIDANCE.  
 
...MID-LEVEL TROUGH OVER THE PACIFIC NORTHWEST TODAY AND  
AMPLIFYING INTO THE DESERT SOUTHWEST WEDNESDAY, REACHING THE  
SOUTHERN PLAINS THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 29/00Z GFS AND 28/12Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
BOTH THE 29/00Z GFS AND 28/12Z OPERATIONAL ECMWF SHOWED SHORTWAVE  
ENERGY DROPPING SOUTH AND FORMING A CLOSED LOW WHICH DROPS INTO  
NORTHERN MEXICO...AN IDEA THAT WAS SUPPORTED BY THE ECMWF  
ENSEMBLES...WHILE THE NAM AND UKMET WERE BOTH HEDGING TOWARDS A  
FASTER SOLUTION WITHOUT THE DEPTH OF THE ECMWF/GFS. WILL NOT MAKE  
ANY CHANGES TO THE EARLIER PREFERENCE FOR THE GFS/ECMWF BLEND.  
 
...MID-LEVEL TROUGH ENTERING BRITISH COLUMBIA ON WEDNESDAY AND  
AMPLIFYING SOUTHWARD INTO THE GREAT PLAINS BY FRIDAY MORNING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 28/12Z ECMWF AND 28/12Z CMC HYBRID  
CONFIDENCE: BELOW AVERAGE  
 
UNCERTAINTY REMAINED HIGH AS THE MODELS STRUGGLE WITH THE SOUTHERN  
END OF A SHORTWAVE TROUGH AND HOW IT EVOLVES ONCE IT CROSSES  
THROUGH A RIDGE CENTERED OVER SOUTHWESTERN CANADA AND THE  
NORTHWESTERN U.S.. NEITHER THE NAM OR GFS HAD VERY GOOD RUN TO  
RUN CONSISTENCY. THE GFS AND CANADIAN HAVE BOTH BEEN INDICATING A  
COMPACT CLOSED LOW SHOULD FORM SOMEWHERE OVER THE UPPER MIDWEST OR  
CENTRAL PLAINS THAT THEN HEADS EASTWARD INTO THE OHIO VALLEY LATER  
IN THE DAY. THE 29/00Z NAM WAS NOT INCLUDED IN THE MODEL  
PREFERENCES GIVEN ITS LACK OF SUPPORT FROM ANY OF THE OTHER  
OPERATIONAL OR ENSEMBLE RUNS. THE QUESTION THEN REVOLVES AROUND  
THE PREFERENCE OF THE DEEP, BROAD OPEN TROUGH LIKE THE ECMWF OR  
THE SOLUTIONS INCLUDING A LOW. THINKING IS THAT THE OVERALL  
ANSWER MAY INVOLVE A WEAK AND MORE POORLY DEFINED LOW CLOSER TO  
THE H5 LOW SHOWN BY THE 28/12Z CMC WITHIN A BROADER FLOW PATTERN  
CLOSER TO THE ECMWF IDEA. CONFIDENCE IS BELOW AVERAGE.  
 
...LEADING EDGE OF LONGWAVE TROUGH, OFFSHORE OF THE WEST COAST OF  
CANADA FRIDAY EVENING AND DOWNSTREAM ATMOSPHERIC RIVER INTO THE  
PACIFIC NORTHWEST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
AFTER THE PASSAGE OF A SHORTWAVE AND ACCOMPANYING COLD FRONT INTO  
BRITISH COLUMBIA ON THE 30TH, INITIALLY ZONAL FLOW INTO WESTERN  
CANADA WILL BEGIN TO AMPLIFY AS RIDGING INCREASES AHEAD OF AN  
UPSTREAM SHORTWAVE NEAR 40N 145W BY 01/00Z. ENSEMBLE MEANS AND THE  
REMAINING DETERMINISTIC CONSENSUS SUGGEST THAT THE 29/00Z GFS AND  
29/12Z CMC MAY BE A BIT TOO QUICK WITH THE SHORTWAVE...SO A BLEND  
OF THE 29/00Z NAM AND 28/12Z ECMWF/UKMET REMAINS CLOSEST TO THE  
RELATIVELY AGREEABLE ENSEMBLE MEAN'S POSITION AND THE DOWNSTREAM  
ATMOSPHERIC RIVER MOVING INTO THE PACIFIC NORTHWEST.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
BANN  
 

 
 
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