114
FXUS10 KWNH 261840
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
139 PM EST THU DEC 26 2019
VALID DEC 26/1200 UTC THRU DEC 30/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SYSTEM MOVING FROM THE WEST INTO THE MIDWEST FRI-SUN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND HEDGING TOWARD ECMWF/ECENS
CONFIDENCE: AVERAGE
19Z UPDATE: WHILE THERE REMAIN SMALLER, BUT IMPORTANT INTERNAL
TIMING DIFFERENCE (E.G. NAM/GFS A BIT FASTER, THEREFORE A BIT
FURTHER NORTHEAST WITH THE WARM CONVEYOR INTO THE WESTERN GREAT
LAKES), THERE IS CONTINUED GROWING CONSENSUS IN THE MASS FIELDS
FOR THE DEVELOPMENT ACROSS THE CENTRAL PLAINS. SO WPC IS STILL
FAVORING THE ECMWF/ECENS/UKMET WITHIN A GENERAL MODEL BLEND.
AVERAGE CONFIDENCE REMAINS DUE TO THE REMAINING UNCERTAINTY OF THE
INTERNAL TIMING/INTERACTION OF THESE FEATURES.
---PRIOR DISCUSSION---
WELL DEFINED CLOSED LOW ENTERING SOUTHERN CALIFORNIA, WILL
CONTINUE TO TRACK EASTWARD THROUGH FRIDAY, AS THE NORTHERN STREAM
SHORTWAVE ENERGY ALONG THE EASTERN SIDE OF SHARPENING/ANTICYCLONIC
MERIDIONAL JET FROM BC TO THE GREAT BASIN CONTINUES TO SHARPEN AND
DRAW THE REMAINING CLOSED WAVE ENERGY NORTH INTO THE HIGH PLAINS
BY SAT. THE HIGH-AMPLITUDE TROF WILL BEGIN TO HAVE INTERNAL
BINARY ACTION INTO A LARGE CLOSED LOW BY 29.00Z. THERE REMAINS
SMALL TIMING DIFFERENCES THAT LEAD TO LONGITUDINAL DIFFERENCES IN
THE PLACEMENT/EVOLUTION OF THE CLOSED LOW THROUGH THE CENTRAL
PLAINS, WITH THE SLIGHTLY FASTER (BROADLY WEAKER) GFS/GEFS ALONG
WITH THE UKMET/12Z NAM FURTHER EAST WHILE THE ECMWF/ECENS MEAN AND
THE CMC ARE SLIGHTLY SLOWER WITH THE CENTER AND THEREFORE WEST
RELATIVE TO THE PACKING. STILL, A BLEND BETWEEN THE TWO CAMPS IS
STILL QUITE VIABLE UNTIL THE STRONG NORTHERN STREAM SHORTWAVE
ROTATES THROUGH THE BASE OF THE CLOSED LOW AND GOES NEGATIVE TILT
THROUGH THE MIDDLE TO LOWER MS RIVER VALLEY INTO SUNDAY. SO THE
STRONGER/MORE CONCENTRIC SOLUTIONS OF THE ECMWF/CMC ARE SLIGHTLY
FASTER KICKING THE WAVE THROUGH THE BASE WHILE THE GFS/NAM/UKMET
SHOW GREATER ELONGATION THROUGH THE NEGATIVE TILT/PRESSING THE
FRONTAL ZONE/WARM CONVEYOR THROUGH THE TN VALLEY FASTER.
CONTINUITY GOES TO THE ECMWF THOUGH IT REMAINS WEST OF THE ECENS
SOLUTIONS...SO A GENERAL MODEL BLEND IS PREFERRED BUT HEDGING
TOWARD THE ECMWF/CMC PARTICULARLY ON SUNDAY, BUT THE CHANGES OF
THE 12Z GFS/NAM ALLOW FOR GREATER WEIGHTING THERE AS WELL IN THE
TN VALLEY. CONFIDENCE REMAINS AVERAGE GIVEN SOME OF THE IMPORTANT
FEATURES REMAIN OFF THE DENSE OBSERVATION NETWORK AND TIMING OF
THE INTERACTIONS OF THE INTERNAL SHORTWAVE FEATURES WILL ALLOW FOR
CONTINUED RUN TO RUN VARIATIONS THAT ARE IMPACTFUL.
SYSTEM CLIPPING THE GREAT LAKES INTO THE NORTHEAST THU-SAT
SOUTHEAST US, MOISTURE FETCH OFF THE SOUTHEAST ATLANTIC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: BETTER OVERALL AGREEMENT NOW EXISTS, THOUGH THE
TRAILING NORTHERN STREAM SHORTWAVE STILL SHOWS TIMING DIFFERENCES
THROUGH SOUTHEAST CANADA...THOUGH WITH THE ODD PAIRING OF THE
CMC/GFS (FAST) AND THE UKMET/NAM/ECMWF SLOWER. STILL THE IMPACTS
ACROSS THE NORTHEAST REMAIN SOLID. FURTHER SOUTH, THE TROPICAL
MOISTURE PLUME CONTINUES TO TREND FURTHER WEST IN THE ECMWF TO GET
CLOSER TO THE GFS. STILL A GENERAL BLEND OF THE ORIENTATION AND
QPF MAGNITUDE STILL APPEAR APPROPRIATE.
---PRIOR DISCUSSION---
COMPACT SHORTWAVE LEAVING N MN WILL CONTINUE TO PROGRESS THROUGH
SOUTHERN CANADA WITH THE TRAILING ENERGY CLIPPING THROUGH THE
GREAT LAKES INTO NEW ENGLAND FURTHER ENFORCED BY A PROGRESSIVE
ARCTIC STREAM SHORTWAVE THAT CLIPS N MAINE BY LATE SAT. THEIR
INFLUENCES ARE WEAK, BUT THE TRAILING WARM FRONT AND BROAD
SOUTHWESTERLY FLOW ALOFT (ALONG WITH RETURN MOISTURE FEED OUT OF
THE BAHAMAS/ANTILLES ISLAND CHAIN) WILL PROVIDE SOME BROAD ASCENT
ACROSS THE AREA TO PRODUCED MIXED WINTRY PRECIP THAT HAS SOME
IMPACTS PARTICULARLY THROUGH TERRAIN INTO THE NORTHEAST... WHILE
KEEPING STRONG ATLANTIC FETCH INTO THE SOUTHEAST. MASS FIELDS ARE
SOLID ENOUGH TO SUPPORT A GENERAL MODEL BLEND AT THIS POINT. THE
UNCERTAINTY IS IN THE ACTIVITY ALONG THE BAHAMIAN ISLAND FETCH AND
STRENGTH OF CONFLUENT/CONVERGENCE EITHER INTO SE FL OR ANGLING
AROUND THE WESTERN PERIPHERY OF THE STRONG BUT RETROGRADING
SUBTROPICAL RIDGE IN THE SARGASSO SEA.
SYSTEM APPROACHING PACIFIC NORTHWEST SUNDAY MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/UKMET/ECMWF BLEND
CONFIDENCE: AVERAGE
19Z UPDATE: THE 12Z CMC BROKE FROM THE COMPACT CLUSTER SUPPORTING
FASTER/GREATER STRETCHING SOUTHWARD AND IN THIS WEAKNESS, STARTS
TO CLOSE OFF A SMALL LOW ON THE NOSE OF THE JET/DIGGING TROF.
THIS SEEMS WELL OUT OF FORM, AND THEREFORE IS REJECTED FROM THE
BLEND. THE ECMWF/UKMET BOTH TRENDED TOWARD A BIT STRONGER/BROADER
SHORTWAVE AND IN DOING SO, SPORT GREATER ELONGATION NORTH TO SOUTH
SIMILAR TO THE NAM BUT NOT TO THE EXTENT OF THE 12Z GFS. SO
WHILE, THERE WAS STRONGER AGREEMENT WITH THE 00Z SUITE, THE RUN TO
RUN VARIATION NOTED HERE, SHOWS THE AVERAGE DEGREE OF CONFIDENCE
IN A 12Z NAM/ECMWF/UKMET BLEND.
---PRIOR DISCUSSION---
THE SHARP/AMPLIFYING RIDGE OVER THE WEST COAST, WILL QUICKLY BE
SQUEEZED BY THE APPROACH OF THE NEXT STRONG SYSTEM ENTERING THE
GULF OF ALASKA. WHILE THE LEADING SHORTWAVE/HEIGHT-FALLS ARE
EXPECTED TO DRIVE THROUGH VANCOUVER ISLAND, THE BLOCKING
FLOW,ENHANCED BY THE COASTAL RANGES, WILL ALLOW FOR RAPID
CYCLOGENESIS FOR THE TRAILING KICKER SHORTWAVE BY LATE SAT INTO
EARLY SUNDAY, JUST WEST OF THE JUAN DE FUCA STRAIT EVENTUALLY
DEFLECTING SOUTHWARD. ENSEMBLES, PARTICULARLY THE ECENS SHOW A
FAIRLY LARGE SPREAD IN THE STRENGTH OF THE RIDGING/BLOCKING IN
ADVANCE OF THE CYCLONE DEVELOPMENT SUGGESTING HIGHER UNCERTAINTY
AND LOWER PREDICTABILITY. HOWEVER, THE 12Z GFS/NAM AND 00Z
NON-NCEP DETERMINISTIC GUIDANCE IS FAIRLY WELL PACKED OVERALL.
THE NON-NCEP SUITE SUGGESTS THE ENERGY OF THE CYCLONE IS A BIT
MORE COMPACT AND SMALLER IN SCALE BY THE END OF THE SHORT-RANGE
PERIOD, FOLLOWED BY THE 12Z NAM AND THEN THE GFS, WHICH IS
STRONGER, AND BEING A TAD FASTER (WITH ITS KNOWN BIAS), IS
STARTING TO ELONGATE/STRETCH SOUTHWARD ALONG THE N CA COAST. GEFS
SOLUTIONS WOULD SUGGEST IT BEING FURTHER EAST AND CLOSER TO THE
NAM/ECMWF/UKMET/CMC...SO THINKING A NON-GFS SOLUTION SEEMS
APPROPRIATE WHICH FEEDS WELL INTO THE MEDIUM RANGE FORECAST
PREFERENCES (SEE WPC PMDEPD FOR MORE DETAILS). GIVEN THE LARGE
VARIANCE IN THE ENSEMBLE SUITE, CONFIDENCE IS ONLY AVERAGE AND
WITH THE SYSTEM STILL WELL OUT IN THE PACIFIC, RUN TO RUN
VARIATION IS EXPECTED.
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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