933  
FXUS10 KWNH 241858  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
257 PM EDT TUE APR 24 2018  
 
VALID APR 24/1200 UTC THRU APR 28/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...CLOSED LOW OVER THE OH/TN VALLEY TODAY, GRADUALLY OPENING INTO  
A TROUGH AND LIFTING INTO THE MID ATLANTIC AND NORTHEAST, PHASING  
WITH NORTHERN-STREAM SHORTWAVE CLOSING OFF THROUGH THE GREAT LAKES  
LATE WEDNESDAY BEFORE LIFTING INTO THE NORTHEAST THURSDAY...  
...WEAK SURFACE LOW OVER THE INTERIOR SOUTHEAST TRANSITION TO  
CAROLINAS WEDNESDAY/THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE  
 
THE MODELS CONTINUE TO ADVERTISE THE PHASING OF SOUTHERN STREAM  
TROUGHING/CLOSED LOW ENERGY OVER THE OH/TN VALLEY REGION WITH THE  
ARRIVAL OF A NORTHERN STREAM SHORTWAVE DROPPING SOUTHEAST ACROSS  
THE GREAT LAKES REGION. DIFFERENCES WITH THE SOUTHERN STREAM  
ENERGY ARE QUITE SMALL AS THE ENERGY LIFTS OFF TO THE NORTHEAST  
OVER THE NEXT 24 TO 36 HOURS. HOWEVER, THE 12Z NAM AND 12Z GFS ARE  
A BIT FASTER TO ADVANCE THE NORTHERN STREAM ENERGY OFF TO THE EAST  
THROUGH WEDNESDAY, WHICH ALLOWS FOR PHASING TO OCCUR A BIT FARTHER  
EAST OVER NEW ENGLAND WEDNESDAY NIGHT AND THURSDAY. THE 12Z CMC,  
12Z ECMWF AND ESPECIALLY THE 12Z UKMET ARE ALL SLOWER, AND  
CONSEQUENTLY ALLOW FOR PHASED LOW PRESSURE TO LINGER A BIT FARTHER  
BACK TO THE WEST OVER THE INTERIOR OF THE NORTHEAST. THE GFS AND  
ECMWF TEND TO SHOW THE STRONGEST PHASING AND ACTUALLY BY THURSDAY  
NIGHT TEND TO COME INTO SOMEWHAT BETTER SPATIAL/TIMING AGREEMENT  
ALONG WITH THE CMC SOLUTION, BUT THE UKMET REMAINS A SLOW OUTLIER  
POST-PHASING. FOR NOW, AN ATTEMPT TO COMPROMISE BETWEEN CAMPS WILL  
BE PREFERRED GIVEN THE ENSEMBLE SPREAD, WHILE ALSO ATTEMPTING TO  
APPROXIMATE THE MODEL CONSENSUS. THUS A GFS/ECMWF BLEND WILL BE  
PREFERRED FOR NOW.  
 
...ELONGATED TROUGH WITH EMBEDDED SHORTWAVES CROSSING THE  
ROCKIES/BLACK HILLS...  
...ENERGY DROPPING SOUTHEAST TO THE LOWER MS VALLEY THURSDAY  
BEFORE WEAKENING THROUGH THE SOUTHEAST BY FRIDAY...   
..LOW PRESSURE NEAR THE MID-ATLANTIC BY LATE FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM, 12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE...BECOMING BELOW AVERAGE  
 
ENERGY CROSSING THE NORTHERN ROCKIES AND HIGH PLAINS WILL DROP  
SOUTHEAST OVER THE NEXT COUPLE OF DAYS AND DIG IN TOWARD THE  
SOUTHEAST U.S. BY FRIDAY. THE 12Z UKMET BECOMES GENERALLY A WEAKER  
AND FASTER OUTLIER IN DIGGING THE ENERGY ACROSS THE SOUTH, WITH  
THE BEST MODEL CLUSTERING GENERALLY RESIDING WITH THE 12Z NAM, 12Z  
GFS AND 12Z ECMWF. ALL OF THIS ENERGY IS EXPECTED TO DRIVE AN AREA  
OF LOW PRESSURE ACROSS THE INTERIOR SOUTHEAST BY THURSDAY AND THEN  
NORTHEAST UP TOWARD THE MID-ATLANTIC REGION BY FRIDAY. HOWEVER,  
THERE IS SOME NOTABLE SPREAD WITH RESPECT TO THE PLACEMENT OF LOW  
PRESSURE AT THE END OF THE PERIOD AS THE GUIDANCE DIFFERS WITH  
DEGREE OF POSSIBLE NORTHERN STREAM INTERACTION AT THAT TIME. THE  
NAM AND GFS SHOW MORE NORTHERN STREAM INTERACTION AND FOCUS LOW  
PRESSURE MORE OVER THE INTERIOR OF THE MID-ATLANTIC ON FRIDAY. THE  
UKMET, CMC AND ECMWF ARE FARTHER EAST ALTHOUGH THERE HAS BEEN SOME  
TREND TO FOCUS THE LOW PRESSURE AT LEAST CLOSER TO THE  
MID-ATLANTIC COASTAL PLAIN BY THE END OF THE PERIOD. THE  
PREFERENCE FOR NOW IS TO LEAN TOWARD A COMPROMISE SOLUTION THAT IS  
CLOSE TO A BLEND OF THE NAM, GFS AND ECMWF, WHICH IS ALSO  
GENERALLY FAVORED BY THE 12Z GEFS MEAN.  
 
...NORTHERN STREAM PORTION OF GULF OF ALASKA TROUGH BREAKING OFF  
AND SLIDING SOUTHEAST THROUGH NORTHERN ROCKIES EARLY THURSDAY THEN  
STARTING TO ANCHOR THE GLOBAL SCALE TROUGH FROM THE GREAT LAKES TO  
THE LOWER MS VALLEY LATE FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
ENERGY EMANATING FROM THE NORTHERN GULF OF ALASKA WILL CROSS  
THROUGH WESTERN CANADA AND DROP SOUTHEAST THROUGH THE NORTHERN  
ROCKIES AND PLAINS STATES THROUGH THURSDAY AND HELP LEAD THE WAY  
FOR MORE OF A LONGER WAVE TROUGH EVOLUTION OVER THE EASTERN U.S.  
BY LATE FRIDAY. THE GUIDANCE TENDS TO AGREE ON THE LARGER SCALE  
WITH THE DETAILS OF THE HEIGHT FALLS EVOLUTION AND AGREE WITH  
FOCUSING THE BULK OF THE ENERGY FARTHER NORTH CLOSER TO THE GREAT  
LAKES ON FRIDAY ALONG WITH AN AREA OF LOW PRESSURE. HOWEVER, THERE  
REMAINS SOME MODEST SPREAD TOWARD THE BASE OF THE TROUGH WITH THE  
DETAILS OF HOW MUCH ENERGY SEPARATION OCCURS AND THE TIMING OF IT.  
MOST OF THE MODELS ARE HINTING AT AT LEAST A WEAK CLOSED LOW BY  
FRIDAY OVER THE GULF COAST STATES, BUT THE UKMET TENDS TO BE THE  
MOST EMPHATIC WITH THIS AT THIS TIME. BASED ON THE LATEST SPREAD  
OF GUIDANCE AND THE ENSEMBLE MEANS, A GENERAL MODEL BLEND WILL BE  
PREFERRED WITH ALL THE DETAILS OF THIS HEIGHT FALL EVOLUTION.  
 
   
..CLOSED LOW EVOLUTION TOWARD THE WEST COAST BY FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE SOUTHERN PORTION OF AN ELONGATED TROUGH AXIS OFFSHORE THE WEST  
COAST AND EXTENDING NORTH THROUGH THE GULF OF ALASKA WILL SEPARATE  
OUT AND ADVANCE EAST TOWARD THE WEST COAST BY FRIDAY AS A  
WELL-DEFINED CLOSED LOW. ON THE LARGER SCALE THE MODEL DIFFERENCES  
ARE RATHER SMALL WITH RESPECT TO TIMING AND DEPTH, AND SO A  
GENERAL MODEL BLEND WILL BE PREFERRED FOR NOW.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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