149  
FXUS10 KWNH 071837  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
136 PM EST WED FEB 07 2018  
 
VALID FEB 07/1200 UTC THRU FEB 11/0000 UTC  
 
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z MODEL EVALUATION WITH FINAL PREFERENCES/CONFIDENCE
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...GRADUALLY DEVELOPING CYCLONE MOVING QUICKLY NORTHEAST TO NEAR  
LABRADOR BY THURSDAY, WITH TRAILING COLD FRONT SWEEPING THROUGH  
THE EAST COAST OF THE US...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
---18Z UPDATE---  
THE 12Z CMC HAS MOVED INTO MUCH BETTER AGREEMENT WITH THE OTHER  
MODELS, AND A GENERAL MODEL BLEND IS NOW PREFERRED.  
 
---PREV. DISCUSSION---  
MODELS ARE GENERALLY IN GOOD AGREEMENT WITH THIS SYSTEM THROUGH  
THE NEXT 36 HOURS, AT WHICH POINT ITS RELATED IMPACTS SHOULD HAVE  
SPREAD OFFSHORE OF THE EASTERN US. THERE ARE MINOR DIFFERENCES IN  
THE MASS FIELDS, BUT THESE DO NOT APPEAR TO BE SUBSTANTIAL OR  
COHERENT ENOUGH TO PREFER ONE MODEL OVER ANOTHER ON THE SYNOPTIC  
SCALE. THE 00Z CMC IS A SLIGHT EXCEPTION, AS IT SHOWS HIGHER  
HEIGHTS ALOFT THROUGH MUCH OF THE EASTERN US TROUGH THAN OTHER  
MODELS, AND AS A RESULT HAS A WEAKER SURFACE LOW. THEREFORE, THE  
PREFERENCE IS FOR A GENERAL BLEND THAT EXCLUDES THE 00Z CMC.  
 
...GRADUAL DEEPENING OF A BROAD TROUGH WITH SEVERAL DIGGING WAVES  
ACROSS THE NORTHERN TIER OF STATES THURSDAY TO SATURDAY...   
..SOUTHWARD PROGRESSION OF AN ARCTIC HIGH INTO NORTHERN PLAINS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
---18Z UPDATE---  
THE 12Z CMC HAS FLIPPED THE BIAS FROM THE PREVIOUS RUN, AND NOW  
SHOWS HIGHER HEIGHTS THROUGH THE TROUGH ACROSS THE WESTERN AND  
CENTRAL US, MORE THAN OTHER AVAILABLE MODELS. WHILE IT IS OVERALL  
IN BETTER AGREEMENT, WILL CONTINUE TO EXCLUDE IT FROM THE  
PREFERENCE AS IT IS SHOWING RUN-TO-RUN INCONSISTENCY. OTHER MODELS  
REMAINED FAIRLY WELL CLUSTERED.  
 
---PREV. DISCUSSION---  
OVER THE PAST COUPLE MODEL CYCLES, MODELS HAVE COME INTO BETTER  
AGREEMENT WITH THE SLOWLY EVOLVING TROUGH OVER THE CONUS. IT  
CONTINUES TO LOOK LIKE THIS WILL HAPPEN AS THE RESULT OF SEVERAL  
DIGGING SHORTWAVES AROUND THE BACK SIDE OF THE LARGE MID-UPPER  
LEVEL LOW NEAR HUDSON BAY. ONE WILL SHIFT ACROSS THE GREAT LAKES  
ON FRIDAY, SPREADING A BAND OF PRECIPITATION ACROSS THE REGION,  
WHILE THE OTHER WILL DIG THROUGH THE INTERMOUNTAIN WEST. THE 00Z  
CMC SHOWS LOWER HEIGHTS THROUGH MUCH OF THE WEST IN THE EARLY  
HOURS OF ITS FORECAST, EVENTUALLY SHOWING A MUCH SHARPER AND MORE  
AMPLIFIED (POSITIVE TILT) TROUGH ACROSS THE WEST. THE PREFERENCE  
IS TO LEAN AWAY FROM THIS SOLUTION AS IT SEEMS TO HAVE AN INITIAL  
BIAS AND IS NOT SUPPORTED BY OTHER MODELS. OTHERWISE, MODEL  
AGREEMENT IS FAIRLY GOOD. THERE ARE SLIGHT DIFFERENCES -- FOR  
EXAMPLE, WITH THE GREAT LAKES SHORTWAVE THE 12Z NAM AND GFS SHOW A  
LITTLE MORE AMPLIFICATION OF THE TROUGH AND SLOWER TIMING THAN THE  
00Z ECMWF AND UKMET. HOWEVER, THESE ARE SMALL DIFFERENCES OVERALL,  
AND SOME OF THE DIFFERENCES COULD REPRESENT A NEW TREND ON THE 12Z  
CYCLE. THEREFORE, A GENERAL BLEND IS PREFERRED WITH THE EXCLUSION  
OF THE 00Z CMC.  
 
...DEVELOPING FRONT FROM THE GULF COAST STATES NORTHEASTWARD TO  
THE NORTHEAST COAST ON SATURDAY AND SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS/NAM, 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
---18Z UPDATE---  
NO CHANGE TO THE PRELIMINARY PREFERENCE. THE 12Z UKMET HAS  
SLIGHTLY BACKED OFF ITS DEPICTION OF A SHARPER SURFACE TROUGH AND  
LOWER PRESSURES ASSOCIATED WITH THE FRONT, BUT CONTINUES TO BE THE  
STRONGEST IN THAT REGARD.  
 
---PREV. DISCUSSION---  
AS THE BROAD TROUGH SLOWLY TAKES SHAPE IN THE CENTRAL US, AN  
ASSOCIATED LOW-LEVEL FRONT IS EXPECTED TO DEVELOP IN ADVANCE OF  
THE UPPER LEVEL TROUGH. GIVEN THE INITIAL HEIGHT FIELD BIASES IN  
THE 00Z CMC, DESCRIBED IN THE DISCUSSIONS FOR OTHER SYSTEMS,  
CONFIDENCE IS LOW IN INCORPORATING THAT HERE. THE 00Z UKMET IS  
MORE SIMILAR TO THE OTHER MODELS WITH ITS HEIGHT FIELDS ALOFT, BUT  
SHARPENS THE SURFACE TROUGH MUCH FASTER WITH LOWER PRESSURES THAN  
OTHER AVAILABLE MODELS. GIVEN THE LACK OF A SHARP TROUGH ALOFT, OR  
POTENT SHORTWAVE EJECTING IN THE FLOW AROUND THE TROUGH, THE  
OVERALL EVOLUTION OF THE FRONT IS EXPECTED TO BE MORE GRADUAL, AND  
THUS THE PREFERENCE WOULD BE TOWARD THE 12Z GFS/NAM AND 00Z ECMWF  
WHICH ARE REASONABLY SIMILAR.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page