486  
FXUS10 KWNH 240457  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1157 PM EST THU JAN 23 2020  
 
VALID JAN 24/0000 UTC THRU JAN 27/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND FORECAST  
CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE TROUGH MOVING FROM THE PACIFIC NORTHWEST TO THE  
MISSOURI VALLEY BY SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM OR UKMET BLEND  
CONFIDENCE: AVERAGE  
 
SHORTWAVE LIFTING ONSHORE THE PACIFIC NORTHWEST FRIDAY MORNING  
WILL MOVE INTO THE NORTHERN PLAINS SATURDAY AND THEN DIG SOUTHEAST  
AROUND A BIG CLOSED LOW OVER NEW ENGLAND BY SUNDAY. THE GUIDANCE  
IS NEARLY UNANIMOUS IS INTENSIFYING THIS FEATURE AS IT SHIFTS OUT  
OF THE PLAINS, BUT DIFFER CONSIDERABLY WITH TIMING AND STRENGTH.  
THE NAM IS SHOWING A GENERAL STRONG BIAS ACROSS THE CONUS WITH ITS  
00Z/24 RUN, INCLUDING THIS SHORTWAVE CLOSING OFF PRIOR TO THE  
GLOBAL CONSENSUS. IT ALSO SHIFTS THIS FEATURE VERY QUICKLY INTO A  
SHORT-WAVELENGTH BUT HIGH AMPLITUDE SHORTWAVE RIDGE WHICH DEVELOPS  
UPWIND OF THE CLOSE LOW OVER NEW ENGLAND. THIS SEEMS UNLIKELY DUE  
TO THE STRENGTH OF THIS LATTER FEATURE. THE UKMET LOOKS REASONABLE  
AND IS WITHIN THE CONSENSUS ENVELOPE THROUGH 48 HOURS, BUT THEN  
RACES THE SHORTWAVE OFF TO THE SOUTHEAST SUCH THAT BY D3 IS IT  
NEARLY 5 DEGREES OF LONGITUDE EAST OF PREFERRED CONSENSUS, SO IS  
NOT USABLE AT THE EXTENDED TIMERANGE.  
 
   
..NEXT SHORTWAVE TROUGH MOVING ONSHORE THE WEST COAST SUN
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/12Z ECENS AND LIMITED WEIGHT ON 12Z ECMWF  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
A VORTICITY LOBE SHEDDING EASTWARD AROUND A DEEP TROUGH IN THE  
GULF OF ALASKA WILL SHIFT ONSHORE SUNDAY AND THEN DIVE TOWARDS THE  
FOUR CORNERS SUNDAY NIGHT WHILE AMPLIFYING. THE DEGREE OF THIS  
AMPLIFICATION IS THE BIGGEST QUESTION MARK AS FAR AS THE GUIDANCE,  
SINCE THE POSITIONING AND SPEED AT WHICH THE SHORTWAVE ADVECTS  
EASTWARD IS WELL SUPPORTED BY THE GLOBAL CONSENSUS. THE INTENSITY  
OF THIS SHORTWAVE THEN CREATES DIFFERENCES IN THE PLACEMENT OF THE  
ATTENDANT SURFACE LOW, ESPECIALLY JUST BEYOND THIS FORECAST  
PERIOD. THE GFS AND ECENS MEAN ARE IN GOOD AGREEMENT, WHILE THE  
ECMWF HAS SHOWN LESS RUN-TO-RUN CONTINUITY.  
 
...CLOSED MID LEVEL LOW TRACKING FROM THE CENTRAL PLAINS ACROSS  
OHIO VALLEY SAT INTO THE NORTHEAST SUN...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM OR CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE GLOBAL MODELS HAVE COME INTO MUCH BETTER AGREEMENT BOTH WITH  
THE EVOLUTION OF THE LARGE CLOSED LOW, AS WELL AS TIMING AND  
POSITION OF VORTICITY IMPULSES ROTATING AROUND IT. THE MID-LEVEL  
FEATURE SHOULD BE OVER EASTERN MO FRIDAY MORNING, NW OHIO BY  
SATURDAY MORNING, AND THEN LIFTING ACROSS UPSTATE NEW YORK SUNDAY  
MORNING. WAVES OF VORTICITY ROTATING AROUND THIS FEATURE WILL  
PRODUCE SWATHS OF SNOWFALL AND QPF IN THE OHIO VALLEY AND GREAT  
LAKES, BUT MORE SIGNIFICANT QPF WILL BE ASSOCIATED WITH THE  
LEADING SHORTWAVE ABOVE A TRIPLE POINT IN THE MID-ATLANTIC WHICH  
WILL SPAWN SECONDARY SURFACE LOW CYCLOGENESIS SATURDAY. THE  
BIGGEST DIFFERENCES IN THE GUIDANCE INVOLVE THESE MORE SUBTLE  
FEATURES, AND NOT THE PRIMARY MID-LEVEL CYCLONE.  
 
THE NAM IS GENERALLY A BIT NW OF THE CONSENSUS, AND ALSO SWINGS A  
ROBUST VORTICITY IMPULSE ATOP THE CHICAGO AREA, WHILE THE  
REMAINING GUIDANCE FOCUSES THIS ENERGY FURTHER NORTH. FURTHER TO  
THE EAST, THE CMC SWINGS THE VORT LOBE RESPONSIBLE FOR SECONDARY  
SURFACE LOW DEVELOPMENT FURTHER EAST AND FASTER THAN THE REMAINING  
GUIDANCE. FROM A MASS FIELDS PERSPECTIVE, THESE ARE THE ONLY TWO  
NOTABLE DIFFERENCES. HOWEVER, THE GFS HAS A QPF MAXIMA THAT IS NOT  
REPRESENTATIVE OF THE CONSENSUS, WITH HIGH VALUES ACROSS THE  
MID-ATLANTIC THAT ARE OUTSIDE THE ENVELOPE AND SEEM TOO ROBUST  
BASED ON THE SPEED OF THE FEATURE. THIS SUGGESTS A  
UKMET/EC/ECENS/GEFS SOLUTION IS MOST REASONABLE FOR D2 AND BEYOND.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
WEISS  
 

 
 
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