699  
FXUS10 KWNH 300413  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1212 AM EDT MON OCT 30 2017  
 
VALID OCT 30/0000 UTC THRU NOV 02/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...NEGATIVE TILT SHORTWAVE EJECTING UP THE EAST COAST WITH DEEP  
SFC LOW ENTERING HUDSON VALLEY...HANDLING OF THE MERGER WITH TC  
PHILIPPE REMNANTS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM/GFS BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS HAVE COME TO A FAIRLY STRONG CONSENSUS ON THE HANDLING OF  
THE NORTHERN STREAM/SYNOPTIC SCALE NEGATIVE TILT TROF LIFTING UP  
THE EAST COAST WITH THE ASSOCIATED DEEP (980MB CURRENTLY) SURFACE  
LOW...WITH ONE EXCEPTION WHICH IS A SLOWER AND MUCH MORE TORQUED  
12Z UKMET SOLUTION THAT WOULD HAVE A 969MB LOW MAKING LANDFALL IN  
LONG ISLAND LIKELY WITH CONTRIBUTION FROM REMNANTS OF TROPICAL  
CYCLONE PHILIPPE. THE 12Z ECMWF ALSO STRUGGLED WITH THE AMPLITUDE  
OF PHILIPPE AND WHILE NOT AS AGGRESSIVE MERGING THE SYSTEMS  
SIMULTANEOUSLY NEAR NYC AS THE UKMET DOES...THE ECMWF KEPT A VERY  
DEEP AND SEPARATE PHILIPPE LOW NEARING CAPE COD TOWARD 12Z TODAY.  
CURRENT OBSERVATIONS FROM SATELLITE/BUOYS AND SHIPS AVAILABLE DO  
NOT SUPPORT THIS WITH THE WAVE OF PHILIPPE ALREADY SHOWN TO HAVE  
SHEARED SUBSTANTIALLY IN THE LOWER LEVELS/SURFACE PRESSING FURTHER  
EASTWARD THAN EITHER WOULD SUGGEST. THE OVERALL CONSEQUENCES  
CONTINUE TO FAVOR REMOVAL OF BOTH SOLUTIONS.  
 
THE 00Z NAM SEEMS MUCH MORE SENSIBLE WITH THE HANDLING OF  
PHILIPPE'S ENERGY SHOWING GREATER SHEARING/STRETCHING THOUGH THE  
LOWER ATMOSPHERE (YET STILL INDICATING THE WAVE. THE 00Z GFS IS A  
BIT MORE FLAT OVERALL HAVING SHEARED THE BULK OF ENERGY OF  
PHILIPPE THROUGH THE TROF AS A WHOLE...PERHAPS A BIT TOO MUCH  
BASED ON CURRENT OBSERVATIONS. OVERALL THE ECENS MEAN/GEFS MEANS  
BOTH SUPPORT THE NAM/GFS OVER THE ECMWF/UKMET. OVERALL THIS SEEMS  
TO BE SPLITTING HAIRS...BUT THE 00Z NAM IS FAVORED OVER THE 00Z  
GFS IN WEIGHTING WITHIN A 00Z NAM/GFS BLEND PERHAPS 60/40 OR 66/33  
WEIGHTS. SUPPLEMENTING RAPID REFRESH SOLUTIONS OR HI-RES CAMS MAY  
BE EVEN MORE SUITABLE AS 00Z-01Z RAP FIELDS/NAM-CONEST LOOK  
SIMILAR/SENSIBLE TOO THOUGH NOTE THE HRRR LOOKS GREAT IN TIMING  
AND INDICATING TREND TO SLIGHT DEEPENING WITH THE REMAINING  
WAVE...BUT APPEARS A BIT TOO AGGRESSIVE WITH THE ACTUAL MAGNITUDE  
OF THE DEPTH NEARING CAPE COD TOWARD 09Z AND ITS DOWNSTREAM  
EVOLUTION INTO MAINE/SE CANADA. CONFIDENCE REMAINS FAIRLY HIGH  
(SLIGHTLY ABOVE AVERAGE) IN BLEND OF THE 00Z NAM/GFS  
 
   
..DIGGING TROUGH INTO NORTHERN PLAINS TODAY
 
PUSHING INTO GREAT  
LAKES ON MONDAY AND PHASING WITH EAST COAST CYCLONE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
DESPITE COMPLEXITIES WITH THE PHASING OF TWO STRONG WAVES/LOWS  
ALOFT AND EMBEDDED SHORTWAVES IN THE FLOW...THE MODELS ARE IN  
QUITE GOOD AGREEMENT WITH HOW THIS PROCESS UNFOLDS. THERE ARE SOME  
SLIGHT DIFFERENCES IN THE EXACT PLACEMENT OF HEIGHT AND  
TEMPERATURE FIELDS...BUT THERE IS NOT A SUFFICIENT BIAS TO EXCLUDE  
ANY MODEL FROM THE PREFERENCE FOR THIS SYSTEM. THIS IS CONTINUED  
WITH THE 18Z GEFS MEAN AND THE 00Z NAM AND GFS RUNS...THEREFORE  
WILL CONTINUE A GENERAL BLEND AT ABOVE AVERAGE CONFIDENCE  
 
SHORTWAVE ENTERING SOUTHWEST TODAY WEAKENING INTO CONFLUENT FLOW  
IN SOUTHERN PLAINS BY WED...ASSOCIATED WESTERN GULF MST  
SURGE/INVERTED SURFACE TROF IN TX WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
SYMMETRIC BOWLING BALL VORT IS ROLLING INTO SW CA ATTM AND IS  
EXPECTED UNDER HIGH SUPPORT FROM MODEL SUITE TO PROGRESS THROUGH  
SOUTHERN AZ/NM THOUGH TUESDAY BEFORE WEAKENING/SHEARING INTO THE  
CONFLUENT FLOW ACROSS THE SOUTH CENTRAL PLAINS ON WED.  
HOWEVER...THE WEAK HEIGHT FALLS ARE SUFFICIENT TO DRAW WESTERN  
GULF MOISTURE NORTH AND RIDING OVER THE LINGERING FRONTAL BOUNDARY  
THAT CONTINUES TO SLIDE SOUTHWARD BEFORE ERODING UNDER THIS  
WESTERN GULF FLOW REGIME. THE 00Z NAM SEEMS TO RETAIN A BIT MORE  
VIGOR TO THE WAVE AS IT SHEARS INTO THE LOWER MS VALLEY...LEADING  
THE FOCUS FOR MOISTURE/ASCENT CLOSER IN PROXIMITY THAN THE  
REMAINING DETERMINISTIC GUIDANCE. PLEASE REFER TO WPC QPFPFD FOR  
ADDITIONAL PREFERENCE WITH RESPECT TO QPF. BUT GIVEN THE MASS IS  
NOT TOO FAR OFF WILL FAVOR A GENERAL MODEL BLEND OR LOWER WEIGHTED  
NAM SOLUTION WITHIN TH BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
...SHORTWAVE AT TOP OF TROF BREAKING DOWN WESTERN US/CANADA RIDGE  
EVENTUALLY SETTLING INTO THE BASE OF THE GLOBAL SCALE TROF IN THE  
DAKOTAS ON WED...ACCOMPANYING DEEP/BROAD SURFACE WAVE SLIDING DOWN  
CANADIAN ROCKIES TUES THROUGH THE NORTHERN TIER INTO WESTERN GREAT  
LAKES BY THURS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
GOES-W WV SUITE SHOWS VERY STRONG UPPER LOW OVER BRISTOL BAY  
(NORTH OF AK PENINSULA) ROLLING OVER THE TOP OF VERY STRONG RIDGE  
IN S GULF OF AK...STRONG LOW LEVEL TEMPERATURE GRADIENT (COLD AIR  
FILTERING ACROSS THE ARCTIC INTO N CANADA) WILL HELP BUILD VERY  
STRONG LONG SUPERGEOSTROPIC JET WHICH WILL STRETCH THE SHORTWAVE  
FLATTENING THE DOWNSTREAM RIDGE SUPPORTING A VERY FLAT LAMINAR  
FLOW ACROSS THE ROCKIES. THOUGH WITH GREAT UPPER LEVEL  
STRENGTH...LEE SURFACE CYCLOGENESIS WILL OCCUR AND SLIDE DOWN THE  
CANADIAN ROCKIES INTO THE NORTHERN TIER AND EVENTUALLY WESTERN  
GREAT LAKES...WHILE ALOFT THE WAVE GOES FROM FLAT TO MORE  
AMPLIFIED BY THURSDAY. GIVEN STRENGTH OF FLOW AND PRECISE  
LOCATION OF COLD/WARM AIR FOR THERMAL WIND ACROSS COMPLEX  
TERRAIN...GUIDANCE IS LIKELY TO HAVE A DIFFICULT TIME LATCHING  
ONTO A COMMON SOLUTION IN THE LOWER SCALES. IN THE LARGER  
SCALE...HOWEVER...THE GUIDANCE IS FAIRLY WELL TIMED/SITUATED WITH  
THE MAJOR FEATURES.  
 
THE 12Z CMC SHOWS A BIT OF INCREASED ROUNDNESS TO THE FLOW EARLIER  
AND CONTINUES TO SHOW A FASTER EASTWARD PROGRESSION...VERY  
ATYPICAL OF THE CMC. THE 12Z UKMET HOWEVER...ALSO SHOWS AN  
EASTWARD/FAST BIAS THOUGH THIS IS IN LINE WITH ITS KNOWN  
BIAS...ITS SPEED ALLOWS FOR A SURGE FURTHER SOUTHEAST AND  
THEREFORE A SURFACE DEEPENING ON THURSDAY WELL SOUTHEAST OF THE  
BEST ENSEMBLE CLUSTERING. THE 00Z NAM SHOWS ITS BIAS BEING A BIT  
DEEPER (POSSIBLY HANDLING THE COMPLEX TERRAIN BETTER?) MAKING IT A  
BIT SLOW INITIALLY AND EVENTUALLY A BIT NORTH WITHIN THE  
CLUSTER...BUT STILL WELL WITHIN THE ENSEMBLE CLUSTER TO HAVE SOME  
CONFIDENCE IN ITS UTILITY IN A BLEND. THE 00Z GFS CONTINUES TO  
HAVE A SOUTHERN BIAS WITH RESPECT TO THE SURFACE WAVE AND GREATER  
AMPLIFICATION THROUGH THE WAVE AS A WHOLE. THIS LEAVES THE 12Z  
ECMWF WHICH IS MORE SUBDUED/FLATTER OVERALL WITH THE WAVE AND  
SHOWS VERY STRONG RESEMBLANCE TO THE FAIRLY TIGHT ENSEMBLE SUITE  
(INCLUDING THE 18Z GEFS MEAN/21Z SREF MEAN AND OF COURSE THE 12Z  
ECENS MEAN). AS SUCH WILL FAVOR THE 12Z ECMWF AS PREFERENCE TO  
REPRESENT THE ENSEMBLES. CONFIDENCE IS AVERAGE.  
 
...WESTERN TAIL END OF THE TROF IN COMBINATION WITH AMPLIFIED  
ARCTIC SHORTWAVE THE HUGS THE N BC COAST WED NIGHT BEFORE  
AMPLIFYING INTO THE PACIFIC NORTHWEST THURS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
BY WED...THE TRAILING WESTERN TAIL END OF THE SHORTWAVE CONTINUES  
TO STRETCH ACROSS THE NORTHWEST INTO THE SOUTHEAST GULF OF AK; A  
STRONG COMPACT SHORTWAVE WILL EMERGE FROM ALASKAN ARCTIC OCEAN  
DROPPING DUE SOUTH FURTHER AMPLIFYING THE REMAINING SHORTWAVE  
ACROSS SOUTHERN BC. BOTH THE 12Z CMC/UKMET ARE MUCH SLOWER AND  
STRONGER FURTHER WEST WITH THE TAIL END OF THE TROF...BOTH  
SUGGESTING A CLOSED OR NEARLY CLOSED WAVE OVER THE SOUTHERN GULF  
OF AK BY THURS...WHICH ALSO APPEARS TO DELAY THE ARCTIC SHORTWAVE  
(WHICH IS VERY WOUND UP IN THE UKMET). THE 00Z GFS SHOWS A TYPICAL  
SLIGHTLY FASTER EVOLUTION THOUGH SHOW GOOD TIMING/DEPTH  
COMPARISONS TO THE 00Z NAM AND 12Z ECMWF WHICH ARE CENTRAL TO THE  
ENSEMBLE SUITE AND OVERALL TREND TO A GREATER AMPLIFICATION  
ENTERING THE PAC NORTHWEST THURSDAY. AS SUCH A 00Z NAM/GFS AND  
12Z ECMWF BLEND IS SUPPORTED. CONFIDENCE REMAINS AVERAGE GIVEN  
THE MODEST SPREAD AND THE FEATURES ARE WITHIN TRADITIONALLY POORLY  
OBSERVED LOCATIONS POTENTIALLY LEADING TO SMALL BUT LIKELY TO  
COMPOUND INITIALIZATION ERRORS.  
 
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