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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1659Z Dec 18, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EST THU DEC 18 2014

VALID DEC 18/1200 UTC THRU DEC 22/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT TO IMPACT THEIR FORECASTS.


...UPPER LOW DEPARTING NEW ENGLAND...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY SHOWS A WELL-DEFINED UPPER CYCLONE GRADUALLY
EXITING UPPER NEW ENGLAND. MUCH OF NORTHERN ME CONTINUES TO SEE A
LIGHT/MODERATE AXIS OF SNOW WITH MUCH OF THE ACTIVITY WINDING DOWN
LATER IN THE DAY. MODELS SHOW SOME VARIABILITY IN HOW QUICKLY THEY
PUSH THE UPPER LOW OFFSHORE. HOWEVER...THESE DETAILS ARE SMALL SO
A GENERAL MODEL COMPROMISE SHOULD SUFFICE.


...ELONGATED SHORTWAVE MOVING FROM MO TOWARD THE MID-ATLANTIC THIS
EVENING...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

AN ELONGATED AXIS OF VORTICITY CURRENTLY STRETCHING FROM EASTERN
KS INTO SOUTHERN IL WILL SHIFT ITS FOCUS EASTWARD IN TIME. THIS
BATCH OF SHORTWAVE ENERGY IS FORECAST TO EVENTUALLY REACH THE
MID-ATLANTIC BY 19/0600Z. MODELS AGREE WITH THE EVOLUTION OF THIS
FEATURE AS IT UNDERCUTS A SEPARATE VORTICITY MAXIMA DROPPING DOWN
FROM THE LOWER GREAT LAKES. THE GUIDANCE DO VARY WITH THE POSITION
OF THIS SECONDARY FEATURE BUT IT DOES NOT APPEAR TO BE OF MUCH
CONSEQUENCE TO THE SENSIBLE WEATHER. THEREFORE...WILL RECOMMEND A
GENERAL MODEL COMPROMISE.


...SPLIT FLOW CARRYING ENERGY THROUGH THE NORTHERN TIER AND
SOUTHERN PLAINS ON FRIDAY...
...SURFACE LOW TRACKING ALONG THE NORTHERN GULF OF MX...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z ECMWF/ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: AVERAGE

A COMPLEX/SPLIT FLOW REGIME IS IN PLACE THROUGHOUT MUCH OF THE
PERIOD. ACROSS THE NORTHERN STREAM...THE LEAD SHORTWAVE CROSSING
THE DAKOTAS IS FORECAST TO SLOWLY MIGRATE EASTWARD BEFORE LIFTING
NORTHWARD INTO MN AND EVENTUALLY FAR SOUTHWESTERN ONTARIO.
SUFFICIENT AGREEMENT IS NOTED WITH THIS SYSTEM. LOOKING AHEAD...A
PAIR OF SYSTEMS IN THE NORTHERN/SOUTHERN
STREAM...RESPECTIVELY...WILL MARCH THROUGH THE CENTER OF THE
COUNTRY ON FRIDAY. DIFFERENCES ALOFT ARE NOT TERRIBLY SIGNIFICANT
WITH MORE OF THE DETAIL DIFFERENCES CONCENTRATING AT THE SURFACE
OVER THE WESTERN GULF COAST. NOTABLE OUTLIERS ARE THE SLOWER 12Z
NAM AND TO A LESSER EXTENT THE 00Z CMC WHICH CARRIES THE SURFACE
LOW SLIGHTLY NORTH OF THE CONSENSUS. COMPARING THE PAST 4 MODEL
CYCLES OF ENSEMBLE LOW PLOTS SHOW A DECREASING NUMBER OF MEMBERS
IN EACH FUTURE RUN. THE 00Z ECMWF ENSEMBLE MEMBERS CLUSTER NICELY
ALONG THE TX/LA BORDER WHILE THE 00Z CMC ENSEMBLE MEMBERS ARE
SLIGHTLY TO THE NORTH. CHOOSE TO KEEP SOME EMPHASIS ON A LOW
CENTER IN THE FORECAST SO WILL LEAN IN THE DIRECTION OF THE 00Z
ECMWF. THE ENSEMBLE MEAN WILL BE THROWN IN TO ACCOUNT FOR THE
FORECAST UNCERTAINTY.


...SERIES OF PACIFIC SHORTWAVES MOVING TOWARD THE NORTHERN
ROCKIES...
...EVENTUAL SURFACE CYCLONE CROSSING THE DAKOTAS BY SUNDAY
EVENING...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS-PARALLEL WITH THE 00Z
ECMWF/ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AN ACTIVE PACIFIC JET WILL ALLOW A SERIES OF SYSTEMS TO TRACK
ACROSS WESTERN CANADA/PACIFIC NORTHWEST THROUGHOUT THE PERIOD. THE
INITIAL CLOSED LOW ACROSS THE NORTHEAST PACIFIC WILL ALLOW AN AXIS
OF HEIGHT FALLS TO PUSH INTO THE WA/OR COASTS BY 19/1200Z. THIS
SHORTWAVE ENERGY IS EXPECTED TO REACH THE NORTHERN ROCKIES BY
SATURDAY MORNING WITH THE 12Z NAM/00Z UKMET ON THE SLIGHTLY FASTER
SIDE OF THE SPREAD. MODELS SHOW SOME SORT OF SPLIT ACROSS THE
NORTHERN HIGH PLAINS WITH THE GUIDANCE VARYING IN WHICH WAVE THEY
FORECAST TO DOMINATE. ON ITS WINGS...A MORE IMPRESSIVE BATCH OF
VORTICITY WILL MOVE ALONG THE U.S./CANADIAN BORDER TOWARD THE HIGH
PLAINS REGION LATE IN THE PERIOD. THIS LEADS TO A RATHER STRONG
AREA OF SURFACE LOW PRESSURE ACROSS THE NORTHERN PLAINS BY SUNDAY.
THE ENSEMBLE LOW PLOTS PLACE MUCH OF THE CLUSTERING UP ALONG THE
MT/ND BORDER ON 22/0000Z WITH PREVIOUS MODEL CYCLES ALSO FAVORING
THIS LOCATION. THIS MAKES THE 12Z GFS APPEAR TOO FAR SOUTH WHILE
THE 00Z CMC SHOWS NOTHING GIVEN IT SUGGESTS A MORE ZONAL FLOW WILL
DOMINATE RELATIVE TO THE EXPECTED AMPLIFICATION IN THE MID-LEVEL
FLOW. ADDITIONALLY...NOT READY TO JUMP ON THE 00Z UKMET SOLUTION
GIVEN HOW DEEP IT IS RELATIVE TO THE OTHER MODELS. FOR NOW WILL
FAVOR THE STEADY CONSENSUS OF THE 12Z GFS-PARALLEL WITH THE 00Z
ECMWF/ECMWF ENSEMBLE MEAN.


...NEXT SOUTHERN STREAM FEATURE CROSSING NORTHERN MX LATE IN THE
WEEKEND...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z ECMWF/UKMET WITH THE 00Z
ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: BELOW AVERAGE

BY SUNDAY...THE ACTIVE SOUTHERN BRANCH OF THE JET WILL ALLOW
ANOTHER SYSTEM TO MOVE ACROSS MX AND EVENTUALLY NEARING THE
WESTERN GULF COAST BY SUNDAY EVENING. THERE ARE NUMEROUS TIMING
DIFFERENCES WITH THE 00Z ECMWF QUICKER THAN ITS ENSEMBLE MEAN
WHILE THE 00Z CMC IS DECIDEDLY SLOWER. ACTUALLY A NUMBER OF THE
DETERMINISTIC MODELS ARE QUICKER THAN THE 00Z ECMWF ENSEMBLE MEAN
INCLUDING THE 12Z NAM AND 00Z UKMET. WPC WILL CHOOSE TO SPLIT THE
DIFFERENCE BETWEEN THE MORE MIDDLE GROUND 00Z ECMWF ENSEMBLE MEAN
AND THE QUICKER DETERMINISTIC GUIDANCE. THE BLEND OF CHOICE WILL
BE A MIX OF THE 00Z ECMWF/UKMET WITH THE SLOWER 00Z ECMWF ENSEMBLE
MEAN.



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