198  
FXUS10 KWNH 041830  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 PM EST TUE FEB 04 2020  
 
VALID FEB 04/1200 UTC THRU FEB 08/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~  
   
..EVOLVING FULL LATITUDE TROUGH OVER THE CENTRAL US THROUGH THU
 
   
..SURFACE WAVE DEVELOPING OVER THE LOWER MS VALLEY
 
MOVING INTO  
THE INTERIOR MID ATLANTIC LATE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~  
PREFERENCE: 12Z ECMWF/UKMET/CMC/GEFS AND 00Z ECENS MEAN  
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE  
 
07Z UPDATE: THE 12Z UKMET SLOWED A BIT, WHILE KEEPING A VERY  
SIMILAR EVOLUTION (PARTICULARLY, THE STRONGER COMPACT SHORTWAVE  
ROUNDING THE BASE OF THE MAIN TROF THURS/FRI). THE 12Z CMC AND  
ECMWF CONTINUE TO BE SLOWER ALLOWING FOR A MUCH SHARPER SOUTHERN  
PORTION OF THE TROF AS A WHOLE. THIS CONTINUES TO BE FAVORED BY  
THE ENSEMBLES THROUGH THE GEFS WAS EVEN SLOWER THAN THE ECENS  
MEAN. AS SUCH WILL CONTINUE TO FAVOR A UKMET/ECMWF/CMC BLEND WITH  
INCORPORATION OF THE 12Z GEFS/00Z ECENS MEAN. WHILE THE LARGE  
SCALE PATTERN/SYSTEM IS AGREED THE DIFFERENCES IN THE TIMING LEAD  
TO THE AVERAGE TO SLIGHTLY BELOW AVERAGE CONFIDENCE IN THE  
PREDICTABILITY AT THIS POINT.  
 
---PRIOR DISCUSSION---  
GOES-EAST WV DEPICTS THE FULL LATITUDE TROUGH ACROSS THE CENTER TO  
SOUTHWESTERN PORTION OF THE CONUS. THE NORTHERN STREAM SHORTWAVE  
IS ALREADY DEPARTING/SEVERING CONNECTION TO THE MAIN ELONGATED  
UPPER LEVEL TROF. AS SUCH THE SURFACE PATTERN DEPICTS A WELL  
DEFINED BUT STATIONARY FRONT FROM THE EASTERN GREAT LAKES TOWARD  
THE SOUTHERN PLAINS AND HIGH PLAINS OVER NEW MEXICO. THE  
SHORTWAVE AT THE BASE OF THE ELONGATED TROF WILL EMERGE LATER  
TODAY AND ALONG WITH INSTABILITY OFF THE WESTERN GULF, WILL  
SUPPORT A SURFACE WAVE THAT LIFTS THROUGH THE LOWER MS VALLEY  
TOMORROW (WED) AND THROUGH THE UPPER OHIO VALLEY BY THURSDAY  
MORNING. THIS EVOLUTION IS FAIRLY WELL AGREED UPON, WITH  
EXCEPTION OF THE 12Z GFS, WHICH CONTINUES FAVOR STRONGER INFLUENCE  
OF THE CENTRAL US SHORTWAVE ENERGY OVER THE BASE ENERGY ROTATING  
NORTH, LEADING TO GREATER RIDGING ACROSS THE OHIO VALLEY AND  
THEREFORE GREATER INSTABILITY/MOISTURE FLUX ACROSS THE CUMBERLAND  
PLATEAU.  
 
THIS MAY BE KEYED ON THE APPROACH/INTERACTION WITH THE LEADING  
SHORTWAVE EMERGING FROM THE STRONG PACIFIC FLOW OVER-TOPPING THE  
PACIFIC/WEST COAST RIDGE. THE GFS AND LESSER SO 12Z NAM, BOTH  
SUGGEST SLIGHTLY FASTER AND MORE ELONGATED JET EXIT REGION AND  
MID-LEVEL STRETCHING INTO THE WESTERN SIDE OF THE FULL-LATITUDE  
TROF. THE 06Z GEFS THOUGH IS MORE IN-LINE WITH THE ECENS MEAN,  
UKMET, CMC AND OPERATIONAL ECMWF, SO WOULD CONTINUE TO FAVOR THIS  
DIRECTION, THOUGH THE SPREAD IS STILL FAIRLY SMALL.  
 
IT IS AFTER THIS SHORTWAVE ENTERS THE BASE OF THE MAIN TROF, LATE  
THURSDAY, THAT THE SPREAD SIGNIFICANTLY CHANGES, MAINLY ON THE  
SHAPE, TIMING OF THE WAVE AND ASSOCIATED JET STREAK ROUNDING THE  
BASE. HERE, THE 00Z UKMET IS MOST COMPACT AND VERY STRONG WITH  
THE JET AND TYPICAL OF ITS BIAS IS FASTER MOVING THROUGH AND  
LIFTING ACROSS THE SOUTHEAST INTO THE CENTRAL EAST COAST FRI  
(THOUGH STILL SLOWER THAN THE 12Z GFS). THE ECMWF/ECENS MEAN AND  
CMC ARE SLOWEST TO ENTER THE BASE AND DIG A BIT FURTHER SOUTH THAN  
THE OTHER GUIDANCE, THIS IS SIMILAR TO THE 12Z NAM AND HOW IT  
BROKE FROM THE GFS. OVERALL, THERE IS SIZABLE SPREAD/UNCERTAINTY  
BUT WILL CONTINUE A NON-GFS BLEND FAVORING THE ECMWF/ECENS MEAN  
AND GEFS MEAN. SO AVERAGE TO SLIGHTLY BELOW AVERAGE AFTER FRIDAY  
12Z.  
 
   
..PULSES ALONG ATMOSPHERIC RIVER WED-FRI INTO PACIFIC NW
 
 
...APPROACHING RAPIDLY DEEPENING CYCLONE TOWARD PACIFIC NW BY END  
OF DAY 3...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~  
PREFERENCE: 12Z ECMWF/UKMET/NAM BLEND  
CONFIDENCE: AVERAGE  
 
07Z UPDATE: THE 12Z ECMWF/UKMET BOTH TRENDED MUCH FASTER, BOTH  
CONTINUE TO BE MORE VERTICALLY STACKED AND COMPACT, BUT HAVE  
REDUCED THE SPREAD OVERALL PARTICULARLY WITH THE GFS/NAM. THE CMC  
TRENDED EVEN FURTHER EAST THAN THE GFS/NAM, TO MAKE IT STAND OUT.  
AT THIS POINT WILL CONTINUE TO FAVOR THE STRONGER, MORE COMPACT  
SOLUTIONS OF THE UKMET/ECMWF BUT HAVE SOME INCORPORATION OF THE  
NAM TO ACCOUNT FOR THE SLIGHTLY WEAKER SOLUTIONS WHICH MATCH THE  
GEFS/ECENS MEAN CLUSTERS BETTER THAN THE FASTEST CMC/GFS.  
 
---PRIOR DISCUSSION---  
UPSTREAM, THE WESTERN RIDGE REMAINS DOMINANT THROUGH THE FORECAST  
PERIOD, WITH STRONG SUPERGEOSTROPHIC FLOW OVER THE RIDGE DIRECTING  
A WEAKER BUT STILL SLIGHTLY ABOVE AVERAGE MOISTURE STREAM/AR  
ACROSS THE PACIFIC NW INTO THE SNAKE RIVER VALLEY AND CENTRAL  
ROCKIES THURS-FRI. THIS IS FINALLY DISRUPTED BY THE STRONG  
SHORTWAVE ENERGY AT THE BASE OF THE BERING SEA CLOSED LOW, THAT  
RAPIDLY EVOLVES/OCCLUDES LATE FRIDAY. THE UNCERTAINTY, HERE IS  
THE PLACEMENT AND JUST LIKE FURTHER EAST THE GFS IS FURTHER EAST  
HAVING A LESS AMPLIFIED RIDGE ACROSS BRITISH COLUMBIA. THE NAM IS  
SIMILAR BUT WITH GREATER RIDGING AND TYPICAL LATE DAY 3  
AMPLIFICATION BIAS, IT SLOWS AND MATCHES THE 06Z GEFS MEAN AND  
CMC. THE 00Z ECMWF SHOWS MUCH GREATER AMPLIFICATION OF THE RIDGE  
ALLOWING FOR A DEEPER VERTICALLY STACKED LOW WHICH IS MUCH SLOWER.  
INTERESTINGLY, THE ECENS SOLUTIONS SUGGEST THIS MAY BE A BIT  
FASTER THAN THE BULK OF ENSEMBLE SOLUTIONS. THE UKMET IS CLEARLY  
THE SLOWEST/GREATEST AMPLIFIED AND STICKS OUT SIGNIFICANTLY FROM  
THE ENSEMBLES TO HAVE MUCH CONFIDENCE IN IT. AS SUCH WILL FAVOR  
AN ECMWF/CMC/NAM BLEND FOR THIS SYSTEM, THOUGH THE AR/MOISTURE  
TRANSPORT INTO THE PACIFIC NW PRIOR TO THIS SYSTEM MAY BE BEST  
SUITED WITH A NON-GFS BLEND.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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