926  
FXUS10 KWNH 230429  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1128 PM EST WED NOV 22 2017  
 
VALID NOV 23/0000 UTC THRU NOV 26/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..UPPER TROUGH EXITING THE NORTHEAST THROUGH EARLY THANKSGIVING
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN VERY GOOD AGREEMENT WITH THE DEPARTURE OF THE  
UPPER TROUGH OVER THE NORTHEAST...SO A GENERAL MODEL BLEND WILL BE  
PREFERRED.  
 
...SLOW-MOVING UPPER LEVEL TROUGH OVER THE GULF OF MEXICO LIFTING  
ACROSS THE FL PENINSULA...  
...SURFACE LOWS OVER THE EASTERN GULF OF MEXICO/NEAR  
FLORIDA...TRACKING NORTH OVER THE WESTERN ATLANTIC THIS WEEKEND...   
..REINFORCING UPPER TROUGH OVER THE GULF OF MEXICO BY SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z ECMWF...12Z ECENS MEAN...18Z GEFS MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE MODELS GRADUALLY LIFT THE SOUTHERN STREAM UPPER TROUGH OVER  
THE EASTERN GULF OF MEXICO OFF TO THE NORTHEAST OVER THE NEXT  
COUPLE OF DAYS WITH THE ENERGY CROSSING THE FL PENINSULA AND THEN  
LIFTING OFFSHORE THE SOUTHEAST COAST OUT OVER THE WESTERN  
ATLANTIC. THE GUIDANCE IS IN RATHER GOOD AGREEMENT IN DEVELOPING A  
PAIR OF SURFACE LOWS ALONG A FRONTAL ZONE DRAPED OVER THE  
REGION...WITH ONE LOW INITIALLY OVER THE EASTERN GULF OF MEXICO  
AND THEN GRADUALLY A SECONDARY LOW OFFSHORE THE SOUTHEAST COAST AS  
THE HEIGHT FALLS BEGIN TO LIFT OFF TO THE NORTHEAST. THIS  
SECONDARY LOW WILL BECOME THE DOMINANT LOW BY SATURDAY AND THEN  
COME UNDER THE INFLUENCE OF NORTHERN STREAM TROUGHING MOVING  
TOWARD THE EAST COAST BY SATURDAY NIGHT AND SUNDAY.  
 
THE 12Z CMC OVERALL APPEARS TOO WEAK WITH ITS HEIGHT FALLS AND  
ALSO WITH ITS SURFACE REFLECTION AT LEAST THROUGH FRIDAY ACROSS  
THE EASTERN GULF OF MEXICO AND OFFSHORE THE SOUTHEAST.  
HOWEVER...THE CMC ON SATURDAY AND SUNDAY SHOWS MUCH MORE IN THE  
WAY OF INTERACTION WITH THE NORTHERN STREAM ENERGY WHICH RESULTS  
IN A MUCH STRONGER SURFACE LOW LIFTING UP OFF THE EAST COAST AND  
TOWARD NOVA SCOTIA. THE REMAINING GUIDANCE SHOWS BETTER CLUSTERING  
THROUGH FRIDAY...BUT THEN ON SATURDAY AND SUNDAY THE 00Z GFS AND  
12Z UKMET ARE WEAKER AND FASTER WITH THE EJECTING SURFACE  
LOW...WITH THE 00Z NAM AND 12Z ECMWF SLOWER AND FARTHER WEST.  
OVERALL THE CMC ENDS UP BEING FARTHEST WEST AND THE DEEPEST. THE  
LATEST 18Z GEFS MEAN AND 12Z ECENS MEAN BOTH TEND TO SUPPORT THE  
OPERATIONAL ECMWF AND SUGGEST THE GFS AND UKMET ARE TOO WEAK AND  
TOO FAR EAST. REGARDING UPSTREAM ENERGY APPROACHING THE GULF COAST  
ON SUNDAY WHICH RENEWS A TROUGH OVER THE GULF OF MEXICO...THE CMC  
APPEARS TO BE GENERALLY TOO WEAK AS THE REMAINING GUIDANCE IS  
BETTER CLUSTERED WITH THIS SYSTEM. THE ECMWF HAS THE BEST ENSEMBLE  
SUPPORT ACROSS THE REGION...AND A BLEND OF THIS MODEL WITH THE  
GEFS MEAN AND ECENS MEAN WILL BE PREFERRED.  
 
...UPPER TROUGH AXIS CROSSING THE PACIFIC NORTHWEST AND REACHING  
THE GREAT LAKES BY FRI NIGHT...   
..ASSOCIATED SURFACE LOW CROSSING SOUTHERN CANADA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A POSITIVELY-TILTED UPPER TROUGH CROSSING THE PACIFIC NORTHWEST ON  
THANKSGIVING DAY WILL QUICKLY ADVANCE EAST ACROSS SOUTHERN CANADA  
AND THEN SOUTHEAST ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST  
THROUGH FRIDAY. THIS WILL DRIVE A STRONG AREA OF LOW PRESSURE  
ACROSS SOUTHERN CANADA WITH A TRAILING COLD FRONT THAT WILL CROSS  
THE NORTHWEST AND THEN ADVANCE RAPIDLY THROUGH THE EASTERN U.S.  
THIS WEEKEND AS THE ENERGY LIFTS TOWARD SOUTHEAST CANADA THIS  
WEEKEND. THE CMC TENDS TO TRACK ITS LOW CENTER FARTHER SOUTH  
ACROSS SOUTHERN CANADA COMPARED TO THE OTHER GUIDANCE. A NON-CMC  
BLEND WILL BE PREFERRED WITH THIS SYSTEM.  
 
   
..LOW PRESSURE LIFTING UP OFF THE WEST COAST ON SATURDAY
 
   
..DEEP UPPER TROUGH OFFSHORE THE WEST COAST THROUGH SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 18Z GEFS MEAN AND 12Z ECENS MEAN  
CONFIDENCE: BELOW AVERAGE  
 
ENERGY THAT IS NEAR THE BASE OF THE POSITIVELY-TILTED UPPER TROUGH  
THAT IS NEAR AND OFFSHORE THE PACIFIC NORTHWEST WILL BREAK AWAY  
AND DRIFT SLOWLY SOUTH OVER THE NEXT COUPLE OF DAYS BEFORE THEN  
GETTING PICKED UP BY A STRONGER INTRUSION OF NORTHERN STREAM  
HEIGHT FALLS FROM THE GULF OF AK. THE SOUTHERN STREAM ENERGY WILL  
GET SLINGSHOT NORTHEAST TOWARD THE WA/OR COASTAL RANGES AND  
VANCOUVER ISLAND BY SATURDAY NIGHT AS AN AREA OF LOW PRESSURE  
DEVELOPS AND STRENGTHENS OFFSHORE THE PACIFIC NORTHWEST. THE 12Z  
UKMET AND 12Z ECMWF BOTH BECOME DEEP OUTLIERS WITH THIS LOW  
CENTER...WITH THE 12Z CMC BY FAR THE WEAKEST. THE 00Z NAM AND 00Z  
GFS SPLIT THE DIFFERENCE BETWEEN STRONG AND WEAK CAMPS. THE  
ENSEMBLE GUIDANCE IS GENERALLY MORE SUPPORTIVE OF THE OPERATIONAL  
GFS...ALTHOUGH THE GFS MAY BE A TAD TOO FAR EAST AT THE END OF THE  
PERIOD. WILL STAY AWAY FROM THE DEEPER UKMET/ECMWF CAMP FOR NOW  
AND LEAN TOWARD A BLEND OF THE ENSEMBLE MEANS AS PER THE 18Z GEFS  
MEAN AND 12Z ECENS MEAN FOR NOW. CONFIDENCE IS HIGHLY LIMITED  
GIVEN THE SPREAD IN THE AMOUNT OF DEEPENING OF THIS LOW CENTER.  
 
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ORRISON  
 

 
 
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