947  
FXUS10 KWNH 141836  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
235 PM EDT SUN JUN 14 2020  
 
VALID JUN 14/1200 UTC THRU JUN 18/0000 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..CLOSED LOW DEVELOPING IN SOUTHERN APPALACHIANS MON/TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH TUESDAY NIGHT  
NON-NAM WEDNESDAY  
CONFIDENCE: ABOVE AVERAGE  
 
19Z UPDATE: THE UKMET DID SLOW DOWN A BIT MORE TOWARDS THE PRIOR  
PREFERENCES, SO IT CAN BE ADDED BACK INTO THE BLEND FOR THE ENTIRE  
FORECAST TIME PERIOD. OTHERWISE, LITTLE CHANGE IN THE SPREAD WITH  
ONLY THE NAM BEING A WESTERN OUTLIER D3.  
 
PREVIOUS DISCUSSION:  
THROUGH 60 HOURS, THERE IS LITTLE DISAGREEMENT IN THE GUIDANCE  
EVOLUTION OF A CLOSED LOW DROPPING ACROSS THE SOUTHERN  
APPALACHIANS AND INTO GA/SC WHERE IT WILL STALL AND SLOWLY FILL. A  
GENERAL BLEND IS ACCEPTABLE THROUGH TUESDAY. ON WEDNESDAY, SOME  
DIVERGENCE IN THE SOLUTIONS BEGINS AS THE NAM SENDS A POTENT VORT  
LOBE WESTWARD, DRAGGING THE WEAKENING LOW CENTER WITH IT, WHILE  
BEING FORCED IN THAT DIRECTION AS WELL BUT STRONGER MID-LEVEL  
RIDGING TO THE N/NW. THE UKMET DOES JUST THE OPPOSITE, LIFTING THE  
WEAKENING LOW QUICKLY TO THE NORTH, AND WHILE A SLOW NORTHWARD  
MOTION IS LIKELY, SOMETHING AS FAST AS THE UKMET SEEMS UNLIKELY  
SINCE THE SYSTEM IS COMPLETELY REMOVED FROM THE MEAN FLOW AND  
BLOCKED BY RIDGING TO THE NORTH. THIS LEAVES THE ECMWF/GFS/CMC AS  
THE BEST CONSENSUS, WHICH ALSO HAS SUPPORT FROM THE ECENS AND GEFS  
MEANS. DESPITE THE COMPARABLE MASS FIELDS, QPF DISCREPANCIES DO  
EXIST, ESPECIALLY BY D3, AS THE ECMWF WANTS TO SPREAD HEAVIER  
RAINFALL FURTHER INLAND INTO THE CAROLINAS/VIRGINIA THAN THE  
CMC/GFS. THERE HAS BEEN LITTLE CONSISTENCY IN THE HEAVIEST QPF  
AXIS RECENTLY, BUT NOTE A SUBTLY STRONGER JET MAX AND LFQ ROTATING  
NORTHWARD AND OFFSHORE D3. THIS COULD ALLOW FOR SOME HEAVIER  
QPF/SUBTLY DEEPER SURFACE PRESSURE FALLS NEAR THE COAST TO LIFT  
INLAND, SO THE ECMWF SOLUTION CANNOT BE RULED OUT. WILL MAINTAIN  
THE PREFERENCES HOWEVER, BUT NOTE THAT THIS BLEND WOULD WASH OUT  
SOME OF THE HEAVIER QPF POTENTIAL BY D3.  
 
...INTERACTION OF SHORTWAVE LIFTING THROUGH SW CANADA WITH A  
CLOSED LOW ADVECTING ONSHORE WASHINGTON SUNDAY...   
..SECONDARY CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC THROUGH 17/00Z  
12Z GFS/12Z ECMWF THEREAFTER  
CONFIDENCE: ABOVE AVERAGE THROUGH D2, AVERAGE D3  
 
INTERACTION OF A SHORTWAVE LIFTING INTO SASKATCHEWAN AND A CLOSED  
LOW MOVING ONSHORE WASHINGTON STATE DRIVES THE BLEND THROUGH  
17/00Z. THE GUIDANCE IS VERY WELL CLUSTERED WITH THESE FEATURES  
INITIALLY, WITH ONLY THE CMC BECOMING AN OUTLIER ON D2 AS IT SENDS  
THE LEADING SHORTWAVE TOO FAR TO THE EAST COMPARED TO CONSENSUS.  
THIS LEAVES LESS BINARY INTERACTION BETWEEN IT AND THE APPROACHING  
BUT WEAKENING CLOSED LOW, AND ALLOWS THE NEWLY FORMING GYRE/TROUGH  
AXIS TO BE DISPLACED FURTHER WEST. OTHERWISE, SENSIBLE DIFFERENCES  
ARE MINIMAL AT THIS TIME.  
 
BEYOND 17/00Z, SPREAD BEGINS TO EXPAND. AS ANOTHER CLOSED LOW  
DROPS OUT OF THE GULF OF ALASKA AND ONSHORE WASHINGTON TUESDAY, A  
LARGE GYRE WILL FORM ACROSS WESTERN CANADA/NORTHWEST CONUS. ENERGY  
SHEDDING AROUND THE APPROACHING CLOSED LOW WILL LIFT ONSHORE PRIOR  
TO THE CLOSED LOW, AND THE UKMET IS MUCH TOO FAST WITH THIS FIRST  
VORT LOBE. THIS ENERGY MOVING TOO QUICKLY EAST CAUSES THE  
INTERACTION OF THE APPROACHING LOW AND THE PREVIOUS ONE TO BE  
STRETCHED/SHEARED TOO FAR TO THE SOUTHEAST, AND OUT OF TOLERANCE  
WITH THE OTHER GUIDANCE WHICH DUMBBELL THE VORT MAXES N/S AROUND  
EACH OTHER. OTHERWISE, THE NAM/GFS/ECMWF ARE ALL QUITE SIMILAR  
BOTH WITH THE INTERACTION, AND WITH THE INTENSIFICATION OF THE  
SHORTWAVE AS IT TILTS NEGATIVELY INTO MONTANA D3. THE NAM DOES  
BEGIN TO LAG LATE D3, LIKELY IN RESPONSE TO SUBTLY STRONGER LFQ  
JET DYNAMICS AS A JET STREAK PIVOTS AROUND THE CLOSED FEATURE, AND  
FOR SLIGHTLY HIGHER HEIGHTS BLOCKING TO THE EAST. WHILE THE  
GFS/ECMWF ARE FASTER THAN THE NAM SHIFTING THIS FEATURE EASTWARD,  
IMPRESSIVE DYNAMICS SHOULD BE ABLE TO DRIVE HEIGHT FALLS INTO THE  
RIDGE AS THE SHORTWAVE PIVOTS E/NE, AND THE AGREEMENT COMBINED  
WITH THE ENSEMBLE MEANS PRODUCES THE SUGGESTED BLEND FOR D3.  
 
WEISS  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 

 
 
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