402  
FXUS10 KWNH 011628  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1127 AM EST MON JAN 01 2018  
 
VALID JAN 01/1200 UTC THRU JAN 05/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
COMPACT S/W ENTERING MT DROPS INTO THE LOWER MS VALLEY EARLY WED  
SPURS RAPID COASTAL CYCLOGENESIS FROM BAHAMAS LATE WED TO GULF OF  
MAINE THRU 00Z FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 03/12Z  
12Z GFS/00Z ECMWF THEREAFTER (REPS. GEFS/ECENS)  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE THROUGH 03/12Z  
SLIGHTLY BELOW AVERAGE AFTERWARD  
 
GOES-WV MOSAIC DEPICT A FAIRLY BROAD WARM SPOT ASSOCIATED WITH  
CORE OF S/W THAT DESCENDS ALONG THE ROCKIES INTO THE CENTRAL  
PLAINS TO LOWER MS VALLEY AND NORTHERN GULF THROUGH WED BECOMING  
THE LARGE BASE OF LARGE SCALE TROF AS UPSTREAM SHORTWAVE (SEE  
SECTION BELOW) CATCHES UP AND INTERACTS WITH SOME PHASING. THROUGH  
THIS TIME PERIOD THE SPREAD IS FAIRLY MILD AND A GENERAL MODEL  
BLEND CAN BE SUPPORTED...HOWEVER THE SMALL DIFFERENCES IN  
SHAPE/INTENSITY AND LOCATION (N-S) WITH RESPECT TO THIS  
INTERACTION SHOW HAVE LARGE SENSITIVITY DIFFERENCES TOWARD THE END  
RESULT OF THE EXPECTED COASTAL LOW THAT DEVELOPS LATE WED OVER THE  
N BAHAMAS AND RACES NORTH. SENSITIVITIES CAN BE TRACKED TO THREE  
SMALLER DIFFERENCES: 1) LATITUDE WHEN REACHING THE BASE OF THE  
LARGE SCALE TROF OVER THE NORTHEAST GULF 2) SPACING FROM THE  
UPSTREAM S/W AND 3) MESOSCALE OR CONVECTIVE UPSCALE ENHANCEMENT  
MAGNITUDE IN LATENT HEAT RELEASE TOWARD JET/OUTFLOW STRENGTH.  
 
THE 12Z NAM ALONG WITH THE GFS ARE NORTH WITH THE INITIAL S/W  
SHOWS EARLIER CONVECTIVE RESPONSE BUT MORE IMPORTANTLY GREATER  
CONVECTIVE/FRONTOGENETIC RESPONSE DUE TO DEEPER COLD AIR AND  
PROXIMITY TO WARMER GULF STREAM. THIS COMBINATION SHIFTS THE  
CYCLONE TO DEVELOP IN TWO CENTERS NEAR THE GA/SC GULF STREAM AS  
WELL AS NORTH AND WEST OF THE MAIN CLUSTERING SEEN IN ENSEMBLE SFC  
LOW CLUSTERS...EVENTUALLY THIS IMBALANCE IN A DUAL VORT/CENTER  
STRUCTURE LEAS IT TO BE A DEEPER AND CLOSER TO THE COAST ALSO  
DELAYING ITS NORTHWARD TREK AS A CLEAR OUTLIER. WHILE NOT  
PREFERRED DUE TO THIS OUTLIER NATURE; IT CAN BE DISMISSED AT THIS  
POINT BUT GIVEN FINER RESOLUTION IN HORIZONTAL/VERTICAL IT IS  
POSSIBLE IT MAY HAVE BETTER HANDLING OF COLD AIR/WARM GULF STREAM  
PROCESSES THAN THE COARSER RESOLUTION GUIDANCE AND BEARS WATCHING  
OVER SUBSEQUENT RUNS.  
 
THE 00Z CMC IS FURTHEST SOUTH IN LATITUDE ROUNDING THE BASE OF THE  
TROF BUT HAS MOST REDUCED INTERACTION WITH THE UPSTREAM S/W  
LEADING TO A FASTER ACCELERATION TOWARD THE SARGASSO SEA. AS SUCH  
THE SURFACE CYCLONE DEEPS ON THE NORTHERN PERIPHERY OF THE  
ENSEMBLE SUITE EVEN OUT PACING THE GFS/GEFS MEMBERS THAT DEVELOP  
THE LOW FURTHER NORTH TO START WITH. GIVEN THESE NEGATIVE ASPECTS  
WILL NOT INCLUDE IN THE PREFERENCE AT THIS TIME.  
 
THE 00Z UKMET WHILE A SOUTHERN REPRESENTATION HAS THE GREATEST  
UPSTREAM S/W INTERACTION IN FACT SHOWING A MORE BINARY INTERACTION  
WITH THE WAVE THAN A MORE PHASED/NEGATIVE TILTED ORIENTATION THAT  
IS THE DOMINANT THREAT IN THE ENSEMBLE SUITE. THIS ORIENTATION  
SUPPORTS A DEEPER/RAPID BOMBING OF THE SURFACE CYCLONE WITH THE  
MOST SIGNIFICANT 'UPPER CUT' SFC LOW TRACK THAT ARCS BACK TOWARD  
NEW ENGLAND BY 00Z FRI. AS SUCH THIS ALSO LOOKS TO BE A EXTREME  
POTENTIAL LIKE THE NAM OR CMC.  
 
THE GFS LIKE THE NAM IS A NORTHERN LATITUDE REPRESENTATIVE BUT  
WITH THE 12Z RUN SHOWS AN INCREASE IN SPACING BETWEEN THE UPSTREAM  
WAVE ALLOWING FOR SLIGHTLY NORTH AND FASTER SURFACE  
CYCLOGENESIS...YET STILL NOT AS FAST AS THE CMC. THE 12Z RUN DOES  
KEEP GOOD CONSISTENCY WITH PRIOR RUNS AND GEFS MEMBERS WHICH SHOW  
THE MOST LINEAR SFC LOW TRACK PARALLELING THE COAST WITH VERY  
LITTLE WESTWARD SHIFT TOWARD LATE THUR/FRI TO AFFECT NEW ENGLAND  
LESS.  
 
THE 00Z ECMWF IS ALSO CONSISTENT RUN TO RUN NOW BUT UNLIKE THE GFS  
IS A SOUTHERN REPRESENTATIVE WITH SIMILAR SPACING/INTERACTION WITH  
THE UPSTREAM WAVE. THE FURTHER SOUTH SFC LOW DEVELOPMENT LIKELY  
HAS A BIT MORE LATENT HEAT RELEASE/CONVECTIVE INFLUENCES ALLOWING  
FOR A DEEPER LOW BY FRIDAY THAT TURNS LEFT (CURVED TRACK) RELATIVE  
TO THE GFS.  
 
ALL IN ALL...THERE IS HIGH SENSITIVITY TO SMALL SCALE INTERACTIONS  
AND PLACEMENT OF LATENT HEAT RELEASE IN THE SYSTEM TO HAVE HIGH  
CONFIDENCE IN PICKING ONE SOLUTION OVER ANOTHER. ENSEMBLE  
SUITE/SENSITIVITY TRACKS WOULD SUPPORT SOMETHING BETWEEN THE 00Z  
ECMWF AND 12Z GFS POSSIBLY A 06Z GFS RUN MAY BE A BETTER BLEND  
THAN 12Z GFS...BUT EITHER WAY BOTH REPRESENT THE CENTER OF THE  
ENSEMBLE SUITE TO SELECT THEM AS WPC PREFERENCE AT THIS TIME.  
WHILE OVERALL CONFIDENCE IS BELOW AVERAGE...IT IS ONLY SLIGHTLY  
GIVEN THE CLUSTERING (MINUS THE NAM) IS ACTUALLY NOT BAD 3 DAYS  
OUT WITH SUCH A DYNAMIC/THERMODYNAMIC SETUP.  
 
S/W OVERTOPPING BC RIDGE TODAY DROPS INTO NORTHERN TIER/GREAT  
LAKES WITH SFC LOW/ARCTIC FRONT TUES/EARLY WED...WEAKENING THURS.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE CONFIDENCE  
 
FAST MOVING SHORTWAVE AND ASSOCIATED JET STREAK SEEN IN GOES WV  
ENTERING NW BC AT THIS TIME OVERTOPPING THE LARGE SCALE RIDGE.  
ONCE DESCENDING THE EASTERN SIDE OF THE RIDGE...THERE IS BROAD  
DIFFLUENT FLOW AND WITH UPSTREAM ARCTIC WAVE KICKING THE NORTHERN  
PORTION OF THE SHORTWAVE INTO THE GREAT LAKES...SUPPORTS A FAST  
MOVING SFC LOW THAT TAKES UP RESIDENCE OVER THE GREAT LAKES BY  
EARLY WED WHERE IT WILL ACT AS THE FULCRUM OF ROTATION OF THE  
UPSCALE EXPANSION OF THE FULL LATITUDE TROF OVER THE EASTERN THIRD  
OF THE US. OVERALL THE SYNOPTIC TO GLOBAL SCALE SPREAD IS VERY  
SMALL EVEN GIVEN THE RAPID SPEED/TIMING OF THE WAVE. AS SUCH A  
GENERAL MODEL BLEND CAN BE SUPPORTED AT SLIGHTLY ABOVE AVERAGE  
CONFIDENCE FOR AT LEAST THE NORTHERN PORTION OF THE TROF AND THE  
RESULTING SURFACE LOW/ARCTIC FRONT.  
 
THE BASE OF THE SHORTWAVE...ON THE OTHER HAND IS NOT AS SIMPLE.  
WITHIN THE DIFFLUENT FLOW THE SHORTWAVE WILL STRETCH WHILE  
ACCELERATING TOWARD THE BASE OF THE TROF THROUGH THE CENTRAL  
PLAINS/LOWER MO VALLEY...AND BY MIDDAY WED BEGIN TO INTERACT WITH  
THE DOWNSTREAM S/W...THAT SPREAD/PREFERENCE IS BETTER HANDLED IN  
SECTION ABOVE GIVEN ITS INFLUENCE ON THE DEVELOPMENT OF THE  
COASTAL LOW  
 
CLOSED LOW SW OF CA WEAKENS AS IT LIFTS NORTHEAST TOWARD CA/SW OR  
THURS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS SHOW SLIGHTLY DIFFERENT REPRESENTATIONS OF THE WEAKENING  
PROCESS OF THE CLOSED LOW WELL SW OF CA AS IT LIFTS TOWARD THE CA  
COAST LATE WED INTO THURS...HOWEVER AT LEAST THE TIMING IS QUITE  
GOOD. THE 12Z GFS/00Z ECMWF AND LESSER SO THE 00Z UKMET PRESENT A  
SMALLER MORE COMPACT WAVE CENTERED AT THE BASE OF THE TROF WHERE  
IT SPINS DOWN WHILE ENTERING THE WEST COAST. THE 12Z NAM/00Z CMC  
ARE A BIT WEAKER BUT ALSO BROADER BUT ALSO ENTER AND WEAKEN  
THROUGH NW CA. THIS DOES NOT SEEM TO LEAD TO MUCH DIFFERENCE IN  
SENSIBLE WEATHER FIELDS TO NOT SUPPORT A GENERAL MODEL BLEND YET  
THE SPREAD IS MILD ENOUGH TO HAVE SOME SMALL LOSS OF OVERALL  
CONFIDENCE (SLIGHTLY ABOVE AVERAGE).  
 
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