194  
FXUS10 KWNH 301618  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1117 AM EST SAT DEC 30 2017  
 
VALID DEC 30/1200 UTC THRU JAN 03/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
BROAD CLOSED MID-LEVEL CYCLONE OVER ONT/QUE SLIDING INTO NEW  
ENGLAND TONIGHT INCLUDING COASTAL CYCLOGENESIS SOUTH OF LONG ISLAND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z NAM/GFS ARE INITIALLY A BIT DEEPER WITH THE CENTER OF THE  
BROAD UPPER LOW ACROSS NORTHERN NEW ENGLAND TOWARD SE CANADA BY  
SUN AFTERNOON BUT NOT SIGNIFICANTLY SO. GIVEN GOOD TIMING/SHAPE  
OVERALL A GENERAL MODEL BLEND CAN BE SUPPORTED AT ABOVE AVERAGE  
CONFIDENCE.  
 
BROADENING SHORTWAVE IN WA SLIDING INTO AND BROADENING BASE OF  
LARGER SCALE TROF ACROSS THE OH/TN VALLEY LATE SUN INTO MON...WEAK  
SURFACE WAVE FRONTAL ZONE IN NORTHEAST GULF OF MX/FL MON/TUES.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
SHORTWAVE MOVING THROUGH THE MEAN GLOBAL RIDGE OVER THE WEST  
CURRENTLY SEEN IN GOES-W WV IN NE WA/N ID/NW MT WILL CONTINUE TO  
SLIDE SOUTHEAST INTO CONFLUENT FLOW ACROSS THE CENTRAL PLAINS  
TOWARD THE OH VALLEY...THIS ENERGY WILL FEED/STRENGTHEN THE JET  
ACROSS THE OHIO VALLEY TOWARD NORTHEAST COAST THROUGH THE EARLY  
WEEK AND EVENTUALLY AMPLIFY THE LARGER SCALE TROF. THE BROAD  
HEIGHT FALLS AND LINGERING FRONTAL ZONE ALONG THE GULF COAST WILL  
EVENTUALLY SPUR WEAK SURFACE CYCLOGENESIS/INVERTED TROF IN THE  
NORTHEAST GULF MON AND PRESS THE COLD FRONT SOUTH THROUGH THE FL  
PENINSULA BY TUES. SLIGHT DEPTH/TIMING DIFFERENCES EXIST AND  
IMPACTING WX APPEARS TO BE MORE IN MESOSCALE INTERACTIONS...YET  
THE SYNOPTIC SCALE MODEL EVOLUTION/TIMING/DEPTH IS SOLID AND  
CONSISTENT RUN TO RUN TO SUPPORT A GENERAL MODEL BLEND AT SLIGHTLY  
ABOVE AVERAGE (SOME LOSS OF CONFIDENCE DUE TO THE SUB-SYNOPTIC  
INFLUENCES).  
 
TRAPPED SHORTWAVE OVER NW BC BECOMES DISLODGED DESCENDING INTO N  
US ROCKIES MON...WEAKLY AMPLIFYING TO POSITIVE TROF OVER  
MID-MS/LOWER TN VALLEY BY LATE TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
CURRENT GOES-W WV DEPICTS A COMPACT VORT OVER NW BC AT THIS TIME  
AT THE APEX OF THE LARGER SCALE RIDGE. THIS KEEPS IT IN LIMITED  
FLOW BUT EVENTUALLY STARTS SLIDING SOUTHEAST INTO THE N US  
ROCKIES/HIGH PLAINS OF MT BY LATE MON UNDER KICKING INFLUENCE OF  
COMPACT WAVE OUT OF THE SOUTHERN GULF OF AK (SEE SECTION BELOW).  
THE 12Z GFS SLOWED A BIT ACCELERATING INTO THE POSITIVE TILT TROF  
ACROSS THE MO/MID-MS VALLEY AND LOWER TN VALLEY BY TUES...TO BRING  
THE AXIS OF THE TROF MORE IN LINE WITH THE 12Z NAM/00Z ECMWF AND  
00 CMC. THE ONLY SIGNIFICANT OUTLIER WAS THE 00Z UKMET WHICH  
SHOWED SOME UNREALISTIC COMPACT NATURE OF THE UPSTREAM WAVE  
ROLLING THROUGH THE MEAN RIDGE AND TAGGING ALONG THE BASE OF THE  
TROF THROUGH THE US ROCKIES...SLOWING THIS TROF. AS SUCH A  
NON-UKMET BLEND IS SUPPORTED...CONFIDENCE IS FAIRLY HIGH GIVEN THE  
SHAPE/TIMING ARE CONSOLIDATING WITHIN THE REMAINING  
GUIDANCE/ENSEMBLE SUITE.  
 
FAST MOVING COMPACT S/W FROM PACIFIC/NORTHERN BC LATE MONDAY COMES  
ACROSS UPPER MIDWEST/GREAT LAKES BY LATE TUES WITH SURFACE LOW AND  
ARCTIC COLD FRONT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
STRONG HEIGHT FALLS APPROACHING THE MEAN RIDGE ALONG THE  
US/CANADIAN WEST COAST ARE STRONG ENOUGH TO CRUSH THE TOP OF THE  
RIDGE THROUGH SE AK/YUKON AND WITH A STRONG ASSOCIATED JET STREAM  
REMAINS FAST CROSSING CENTRAL CANADA AND USHERING NW FLOW TO BRING  
THE NEXT ICE BOX PLUNGE FROM THE ARCTIC ACROSS THE NORTHERN TIER  
TUES WITH AN ASSOCIATED SURFACE WAVE REACHING LAKE SUPERIOR BY 00Z  
WED. ONCE AGAIN...THE UKMET IS THE OUTLIER AS IT SHED A BULK OF  
ENERGY THROUGH THE RIDGE FURTHER SOUTH ACROSS THE S CANADIAN  
ROCKIES LEADING IT TO CATCH THE BASE OF THE PRECEDING WAVE. THIS  
GENERALLY DELAYS THE SFC WAVE/COLD AIR ESPECIALLY FURTHER WEST  
BANKED UP AGAINST THE TERRAIN COMPARED TO ITS GLOBAL MODEL  
COUNTERPARTS. OTHERWISE...SURPRISINGLY A SLIGHTLY SLOWER 12Z GFS  
BRINGS A VERY TIGHT CLUSTERING OF THE WAVE THROUGH A DEPTH GIVEN  
ITS OVERALL SPEED AND COMPACT NATURE. ALL CONSIDERED...A  
NON-UKMET BLEND IS SUPPORTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
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