912  
FXUS10 KWNH 231823  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
122 PM EST SAT DEC 23 2017  
 
VALID DEC 23/1200 UTC THRU DEC 27/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHEARING/FILLING S/W CROSSING THE OHIO VALLEY TODAY THROUGH NEW  
ENGLAND EARLY SUN AND ASSOCIATED SURFACE LOW...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
GOES-WV MOSAIC DEPICTS A ROBUST WARM CONVEYOR OVER THE EASTERN  
THIRD OF THE US WITH THE INNER CORE OF THE UPPER LOW RAPIDLY  
LOOSING CHARACTERISTICS/FILLING ON THE WESTERN INTERFACE. THIS  
FEATURE WILL CONTINUE TO RAPIDLY ACCELERATE TOWARD THE  
MID-ATLANTIC AND NEW ENGLAND THROUGHOUT THE DAY WITH THE SURFACE  
LOW IN THE OH/TN VALLEYS SHIFTING TOWARD REDEVELOPMENT IN THE GULF  
OF MAINE/OVER DOWNEAST MAINE BY 00Z TONIGHT. GUIDANCE APPEARS TO  
HAVE LOCKED INTO A COMMON SOLUTION ESPECIALLY IN THE MASS  
FIELDS...ENOUGH SO TO BE CONFIDENT IN A GENERAL MODEL BLEND.  
SUB-SYNOPTIC SCALE INTERACTIONS/SPREADS PARTICULARLY IN THE  
THERMAL FIELDS PROVIDE ENOUGH SPREAD IN IMPACT TO REDUCE ABSOLUTE  
CONFIDENCE IN A GENERAL BLEND...AS SUCH CONFIDENCE IS SLIGHTLY  
ABOVE AVERAGE IN THE BLEND.  
 
19Z UPDATE: 12Z ECMWF/UKMET/CMC AND GEFS MEANS ONLY FURTHER  
SOLIDIFY THE CURRENT MASS FIELDS INCLUDING SOME THERMAL  
ADJUSTMENTS. ENOUGH TO HAVE ABOVE AVERAGE CONFIDENCE IN THE BLEND  
AT THIS POINT.  
 
...S/W IN PAC NW REACHING CENTRAL PLAINS SUNDAY BECOMING NEG TILT  
THROUGH OH/TN VALLEY SPURRING TWO SURFACE CYCLONES...UP THE SPINE  
OF APPALACHIANS AND COASTAL LOW COMBINING ACROSS NEW ENGLAND MON...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
GOES-W WV DEPICTS THE WARMING ASSOCIATED WITH A IMPORTANT S/W OVER  
WA. THIS WAVE WILL BECOME ENTRENCHED IN THE ANTICYCLONIC CURVED  
CONVEYOR/UPPER JET EMERGING OUT THE SWLY PACIFIC FLOW AND RAPIDLY  
ACCELERATE SE INTO THE CENTRAL PLAINS BY SUN...SUPPORTING A STRONG  
LEE CYCLONE IN CO. GUIDANCE IS QUITE AGREEABLE THROUGH THIS TIME  
PERIOD INCLUDING AS IT EXITS SE INTO TX AS THE WAVE CROSSES THE  
PLAINS INTO THE MID-MS VALLEY. AT THIS POINT THE WAVE SHOWS SOME  
INCREASED AMPLIFICATION/NEGATIVE TILT SHAPE. STRONG DOWNSTREAM  
OUTFLOW/JET STRUCTURE WITH THIS WAVE ALLOWS FOR TWO SURFACE LOWS  
TO DEVELOP IN A PSEUDO MILLER B CONFIGURATION. THE FIRST WAVE IN  
THE UPPER TN VALLEY ACTUALLY DEEPENS DUE TO THE NEGATIVE TILTING  
AND RIDES THE TERRAIN NORTH INTO NY WHILE A MID-ATLANTIC SURFACE  
LOW RAPIDLY DEVELOPS OVER NIGHT SUN INTO MON. BY MID-DAY MONDAY  
SLIGHT TIMING/PLACEMENT OF THE S/W IN THE STREAM (TOWARD THE  
COAST) DEVELOPS WITH THE 00Z UKMET SHIFTED A BIT EAST AND PERHAPS  
A TAD SLOWER. WHILE THE SPREAD AT THE SURFACE AND IN SENSIBLE WX  
FIELDS ARE NOT TOO BAD...TO STRENGTHEN ANY BLEND IT IS SUGGESTED  
LIMITING OR ELIMINATING THE UKMET FROM THE PREFERENCE. OTHERWISE  
CONFIDENCE IS FAIRLY HIGH GIVEN THE INGREDIENTS BEING IN THE  
CORRECT LOCATIONS FOR THIS MODEL/ENSEMBLE AGREEMENT. AS SUCH  
CONFIDENCE IS SLIGHTLY ABOVE AVERAGE IN A NON-UKMET BLEND.  
 
19Z UPDATE: THE 12Z UKMET TRENDED A BIT FASTER BRINGING IT INTO  
THE CLOSEST PACKING. THE 12Z ECMWF SHIFTED EAST EVER SO SLIGHTLY  
TOWARD THE GFS. THE CMC ALSO KEEPS ON TRACK...ENOUGH TO SUPPORT A  
GENERAL MODEL BLEND HOWEVER...THE INTERNAL/MESOSCALE DETAIL WILL  
KEEP CONFIDENCE SLIGHTLY ABOVE AVERAGE.  
 
...SE EDGE OF TROF SWINGING UP THE OR/WA COAST W/WEAK SURFACE WAVE  
LATE SUNDAY/EARLY MON...SHEARS/WEAKENS THROUGH NORTHERN ROCKIES  
THRU TUES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
GUIDANCE HAS BEEN TRENDING TOWARD A COMMON SOLUTION IN TIMING  
ACROSS THE PACIFIC NORTHWEST AS THE SOUTHEAST EXTENSION/PERIPHERY  
OF THE GULF OF AK TROF SWINGS THROUGH LATE SUNDAY INTO MONDAY.  
THE DIFFERENCES IN TIMING/DEPTH IS MORE RELATED TO THE STRENGTH  
AND SPEED OF THE SWLY SUBTROPICAL JET AXIS. THE UKMET ONCE AGAIN  
A BIT TOO FAST AND NEARLY SEVERS THE CONNECTION TO THE UPSTREAM  
TROF WITH STRONGER ENERGY IN THE SW FLOW MAKING A SLIGHTLY SLOWER  
AND STRONGER SFC WAVE ENTERING THE PACIFIC NORTHWEST. THE 12Z  
GFS/NAM KEPT FAIRLY CONSISTENT BUT SLIGHTLY FASTER THAN THE  
ECMWF/CMC. A COMPROMISE IN TIMING WILL FAVOR A NON-UKMET BLEND AT  
SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
19Z UPDATE: THE UKMET TRENDED A BIT SLOWER IN THE SEPARATION  
BETWEEN STREAMS ALLOWING FOR A SLIGHTLY FASTER SURFACE WAVE BRING  
IT INTO THE FOLD OF TIGHTENING SOLUTIONS. WHILE NOT AS TIGHT OF  
CLUSTERING AS SYSTEMS TO THE EAST...THERE IS ENOUGH SUPPORT FOR A  
GENERAL MODEL BLEND AS PREFERENCE AT SLIGHTLY ABOVE AVERAGE  
CONFIDENCE.  
 
PREVIOUS MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
PREVIOUS 500 MB FORECASTS AT  
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