755
FXUS10 KWNH 281846
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EST SAT DEC 28 2019
VALID DEC 28/1200 UTC THRU JAN 01/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CENTRAL PLAINS TO GREAT LAKES CLOSED LOW/SURFACE CYCLONE(S)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: WHILE THE 12Z NON-NCEP SOLUTIONS CONTINUE TO BE VERY
STRONG/CONSISTENT WITH THE INITIAL SHORTWAVE LIFTING NORTH AND
INITIAL PIVOT POINT; THERE IS A TRANSITION PARTICULAR WITH THE
ECMWF/UKMET TRENDING SLOWER, A BIT SHARPER WITH THE NEGATIVE TILT
TROF AND THEREFORE EAST TOWARD THE 12Z NAM AND CLOSER TO THE GFS.
WHILE THE 12Z GEFS DOES SUPPORT THE GFS, PREFERENCE WOULD BE
TOWARD A NON-GFS SOLUTION STILL; EVEN THOUGH THE TRENDS WERE
TOWARD IT, AS IT STILL APPEARS OUT OF TOLERANCE IN THE OVERALL
CLUSTER.
---PRIOR DISCUSSION---
GOES-WV SUITE DEPICTS WEAKENING SOUTHWEST SHORTWAVE PROGRESSING
THROUGH THE CENTRAL PLAINS WITH VERY IMPRESSIVE MID TO UPPER LEVEL
JET/ANTICYCLONIC BAROCLINIC SHIELDS EVOLVING ACROSS THE NORTHERN
PLAINS AT THIS TIME AS WELL AS THE SHARP TROF ALONG THE EASTERN
ROCKIES/HIGH PLAINS AND THE MERIDIONAL JET SLIDING SOUTH. THE
GUIDANCE APPEARS TO HAVE COME INTO COMMON AGREEMENT WITH THE
TIMING/PLACEMENT OF THE SOUTHERN STREAM WAVE AND ASSOCIATED 150KT
25H JET INTO THE DEVELOPMENT OF THE PIVOT OF THE CLOSED LOW IN SE
SD/SW MN/NW IA BY 00Z MONDAY. THE MODEL SPREAD BEGINS TO
INCREASE IN EARNEST AS THE UPSTREAM JET ROTATES AROUND THE BASE
AND THE ASSOCIATED SHORTWAVE GOES NEGATIVE TILT THROUGH THE
MISSISSIPPI VALLEY INTO THE GREAT LAKES. HERE, THE GFS HAS BEEN,
AND CONTINUES TO BE WITH THE 12Z RUN, WEAKENING THE INNER CORE IN
FAVOR OF THIS STRONGER/SHARPER NEGATIVE TILT WAVE...WHICH LEADS IT
TO BE WELL EAST WITH THE LOWER LEVEL SURFACE LOW THROUGH THE GREAT
LAKES. MAKING IT LESS FAVORABLE OVERALL. THE 12Z NAM, CONTINUES
TO BE A MIDDLE GROUND BETWEEN THE ECMWF/CMC/UKMET AND THE
GFS...BUT CONTINUES ITS TREND TOWARD THE NON-NCEP CAMP, SUGGESTING
A NON-GFS BLEND IS A SOLID SLIGHTLY ABOVE AVERAGE CONFIDENCE
PREFERENCE.
...REMAINS OF CLOSED LOW/DEVELOPMENT OF COASTAL LOW INTO NORTHEAST
MON-WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THRU 31.06Z, NON-GFS AFTER
CONFIDENCE: AVERAGE
19Z UPDATE: LIKE THE UPSTREAM CLOSED LOW, THE TREND IN THE
NON-NCEP SOLUTION WAS VERY MUCH IN LINE WITH FASTER...VERY NEAR
THE 12Z NAM, CLOSING THE GAP TO THE FASTEST GFS. SO, WHILE THE
SPREAD IS REDUCED, THERE IS STILL SOME QUESTION IN INCORPORATING
THE FASTER GFS AFTER 31.06Z. SO WILL STICK WITH INITIAL
PREFERENCE WITH 12Z UPDATES THAT DOES TREND THAT DIRECTION BUT NOT
FULLY TO THE GFS.
---PRIOR DISCUSSION---
UPSTREAM DEEP CLOSED LOW, WILL CONTINUE TO BREAK DOWN ACROSS THE
GREAT LAKES BY LATE MON INTO TUESDAY AND THE FORMER PIVOT/INNER
CORE CENTER ACCELERATES EASTWARD UNDER THE NEWER MATURE CENTER.
BY THIS TIME THE GFS IS NOT PREFERRED IN THE GREAT LAKES, HOWEVER,
THE GFS HAS DONE A SOLID JOB IN THE ORIENTATION/TIMING OF THE
RETURN ATLANTIC MOISTURE AROUND THE CURRENTLY RETROGRADING
SUBTROPICAL RIDGE, THROUGH FLORIDA, RELATIVE TO THE SLOWER ECMWF.
COMBINE THIS WITH STRONGER MOISTURE ADVECTION WITH THE ATMOSPHERIC
RIVER OUT OF THE WESTERN GULF (OVER 1000 UNITS OF IVT), THE 12Z
GFS MAY HAVE MORE UTILITY THROUGH THE INCIPIENT DEVELOPMENT OF THE
COASTAL LOW THROUGH THE PIEDMONT OF VA BY 30.18Z AND THROUGH THE
NY BIGHT BY 31.12Z, WHICH HAS A SIGNIFICANT INFLUENCE ON THE WARM
FRONT MOVING THROUGH THE MID-ATLANTIC AND NORTHEAST. SO IN
COLLABORATION WITH WPC QPF 2/3 AND WINTER WEATHER FORECASTERS,
MODEL PREFERENCE TO INCLUDE SOME OF THE 12Z GFS AT LEAST INITIALLY
TO ACCOUNT FOR THE SLOWNESS/RETURN OF THE WARM AIR/MOISTURE FLUX
INTO THE NORTHEAST WAS IMPORTANT; HOWEVER, TOWARD THE END OF DAY
3, THE GFS/GEFS APPEAR TO SHOW SOME OF TRADITIONAL FAST BIAS
ISSUES, THAT SHIFTING TOWARD THE NAM IS MORE PREFERABLE IN
WEIGHTING. SO A GENERAL MODEL BLEND IS PREFERRED THROUGH 31.06Z
BEFORE GOING NON-GFS BLEND AFTERWARDS. CONFIDENCE IS CONTINGENT
ON THERMALS WHICH ARE LESS CONGRUENT THAN THE MASS FIELDS/FRONTAL
STRUCTURE AS A WHOLE, AND AS SUCH, IS AVERAGE.
..PACIFIC SHORTWAVE DIVING ALONG THE WEST COAST SUN-TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: THE 12Z ECMWF WAS JOINED BY THE 12Z UKMET IN TRENDING
A BIT WEST OF THE OVERALL GUIDANCE PARTICULARLY AFTER PASSING CAPE
CONCEPCION AND THE CHANNEL ISLANDS. THIS IS STILL FAIRLY SMALL
AND WILL SUPPORT A GENERAL MODEL BLEND BUT CONFIDENCE REDUCES TO
SLIGHTLY ABOVE AVERAGE, PARTICULARLY AFTER 30.18Z.
---PRIOR DISCUSSION---
THE PACIFIC CONTINUES TO BE VERY ACTIVE BUT PROGRESSIVE AND WITH
AN UPSTREAM SHARP RIDGE THAT BLOCKS THE FLOW AND RAPIDLY STRETCHES
IT SOUTHWARD ALONG THE ENTIRE WEST COAST OF THE US. THERE IS
GROWING CONSENSUS IN THE TIMING AND SHAPE/EVOLUTION OF THE WAVE
INCLUDING THE TIMING OF THE WAVE AS IT CLOSES ALOFT AND SPINS UP A
SURFACE LOW NEAR SAN FRANCISCO BAY LATE SUNDAY INTO MONDAY.
OVERALL, THE GUIDANCE IS VERY STRONG THAT A GENERAL MODEL BLEND IS
SUPPORTED AT ABOVE AVERAGE CONFIDENCE. HOWEVER, AS A POINT OF
NOTE FOR MARINE AND BAJA CALIFORNIA INTERESTS, THE ECMWF'S SLOWER
NATURE ABSORBS THE TRAILING SHORTWAVE ENERGY IN THE SHEAR AXIS
MUCH TIGHTER AND COMPACT LEADING TO A SW WOBBLE EVEN COMPARED TO
THE MAJORITY OF ECENS MEMBERS...SO IT APPEARS TO BE AN OUTLIER TO
FAR SW AFTER 31.00Z (THOUGH WITH LITTLE/NO INFLUENCE IN THE
CONUS).
..ATMOSPHERIC RIVER SINKING INTO PAC NW BY LATE TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/CMC AND 00Z UKMET/ECENS MEAN BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
19Z UPDATE: THE 12Z UKMET TRENDED TOWARD A STRONGER SHORTWAVE THAT
ACTUALLY DEEPENS WITH A VERY STRONG SURFACE REFLECTION INTO
VANCOUVER ISLAND, TYPICAL OF UPSCALE GROWTH INFLUENCES THAT TEND
TO BE INCORRECTLY DIAGNOSED (THROUGH LATENT HEAT RELEASE) BY THE
UKMET, SO WOULD GO AWAY FROM THE 12Z RUN SOLUTION FOR THE NW. THE
12Z OPERATIONAL ECMWF SLOWED WITH THE SHORTWAVE/JET STREAK
APPROACHING THE WEST COAST, AND DELAYED THE SOUTHWARD SAG OF THE
MOISTURE DIRECTED INTO THE NW. THIS BRINGS IT MUCH CLOSER TO THE
INITIAL PREFERENCE (00Z ECENS). EVEN THOUGH THIS REMAINS A BIT
SOUTH OF THE OTHER DETERMINISTIC GUIDANCE, IT IS GENERALLY
PREFERRED OVER THE SLOWER/DRIER GFS/NAM SOLUTIONS, THOUGH THE CMC
OR STILL UTILIZING THE 00Z UKMET MAY HELP ACCOUNT FOR SOME
UNCERTAINTY. CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE.
---PRIOR DISCUSSION---
AFTER THE PRIOR SHORTWAVE DIGS SOUTHWARD, THE PACIFIC ENERGY
SHIFTS BACK INTO THE N GULF OF AK BUT STRONG ZONAL FLOW AND HIGH
ENERGY IN THE NORTHERN PACIFIC STREAM, DRAWS TROPICAL MOISTURE
NORTHWARD. THE MOISTURE AND ASSOCIATED JET FLOW IS RELATIVELY
WEAKER INITIALLY AND DIRECTED TOWARD CENTRAL BC BY LATE MONDAY
INTO TUESDAY. HOWEVER, THE OVERALL FLOW/HEIGHT-PACKING TIGHTENS
AND A STRONG 250MB -150KT JET ENTRANCE APPROACHES AND DIRECTS
MOISTURE FLUX TOWARD VANCOUVER ISLAND AND THEN SOUTHWARD INTO THE
PACIFIC NW BY THE END OF NEW YEAR'S EVE. THE 00Z ECMWF IS VERY
STRONG AND ALONG WITH THE UKMET SHOW A FASTER INITIAL WAVE WITH
INCREASED MOISTURE COMPARED TO THE GFS/NAM. HERE THE ECMWF/UKMET
MAY HAVE A BIT BETTER INITIAL ASSIMILATION OF THE MOISTURE
FLOW/STREAM THAN THE GFS/NAM DUE TO GREATER SATELLITE RETRIEVALS.
SO HEDGING THIS DIRECTION. HOWEVER, THE 00Z ECMWF IS VERY
DIVERGENCE IN THE ANTICYCLONIC (RIGHT EXIT) SHOWING INCREASED
DIVERGENCE ALOFT AND SUPPORTING GREATER ASCENT AND SOUTHWARD
PROPAGATION OF THE CONVERGENCE AXIS INTO THE NORTHWEST, GREATER
THAN THE VAST MAJORITY OF ECENS MEMBERS. AS SUCH WILL FAVOR THE
UKMET AND ECENS MEAN IN TIMING/ORIENTATION OF THE AR BUT AT
AVERAGE TO SLIGHTLY BELOW AVERAGE CONFIDENCE GIVEN THE SPREAD IN
MOISTURE FIELDS AND IMPORTANCE OF TIMING IN SUCH A STRONG ZONAL
FLOW.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA
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