Prognostic Meteorological Discussion
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000
FXUS10 KWNH 020450
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1150 PM EST THU DEC 01 2016

VALID DEC 02/0000 UTC THRU DEC 05/1200 UTC

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

00Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE AMPLIFYING IN THE SOUTHWEST FRI WITH A CLOSED LOW
FORMING AND MOVING ACROSS NORTHERN MEXICO SAT/SUN SPURRING SURFACE
LOW ACROSS NEAR S TX/NE MEXICO SUN

PREFERENCE: BLEND OF 12Z ECMWF/00Z GFS/00Z UKMET
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THERE REMAINS A MODERATE TO HIGH SPREAD IN THE MODEL/ENSEMBLE
SOLUTIONS. THE 12Z ECMWF/UKMET AND THE ECMWF ENSEMBLE CLUSTER WITH
A FASTER MOTION.  THE GFS/GEFS CLUSTER WITH A MOTION SEVERAL HOURS
SLOWER...AND THE 12Z CANADIAN/00Z NAM/21Z SREF THE SLOWEST
CLUSTER.
THE SLOWEST CLUSTER APPEARS THE LEAST LIKELY GIVEN HEIGHT FALLS IN
THE NORTHEAST PACIFIC AND UPPER JET MAXIMA COMING ONSHORE INTO
OR/NORTHERN CA TO ACT TO EJECT THE WAVE.

THOSE SOLUTIONS THAT ARE SLOWER BUILD A STRONG 500 MB RIDGE NORTH
OF THE LOW IN NV/UT.  THE FASTER SOLUTION LIKE THE ECMWF HAVE A
LOWER AMPLITUDE RIDGE AND LESS BUILDING OF THAT RIDGE NORTH OF THE
CLOSED LOW...SO WHICH WAY THE STRENGTH OF THE WEST-EAST WILL HELP
DETERMINE WHICH CLUSTER IS MORE CORRECT...AS CLOSED LOWS MOVE MORE
SLOWLY ONCE A DEEP LAYER RIDGE BUILDS NORTH OF THEM IN A REX BLOCK
CONFIGURATION.

CONFIDENCE REMAINS ON THE LOWER SIDE OF AVERAGE GIVEN THE
REMAINING SPREAD. THE CURRENT PREFERENCE IS TO USE AN INTERMEDIATE
SOLUTION SOMEWHERE BETWEEN THE 12Z ECMWF/UKMET AND 00Z GFS/18Z
GEFS CAMPS.


SHORTWAVE CROSSING SOUTHWEST CANADA FRI...NORTHERN PLAINS SAT AND
WESTERN GREAT LAKES SUNDAY

PREFERENCE: NAM/GFS/CMC BLEND
CONFIDENCE: AVERAGE

A STRONG 150+ KT JET STREAK APPROACHES AND REACHES VANCOUVER
ISLAND ON SAT.  THE WAVE DOWNSTREAM FROM THE JET MAX WILL BEGIN TO
AMPLIFY ACROSS THE SOUTHERN CANADIAN/NORTHERN U.S. ROCKIES AND
SUPPORT A WEAK SURFACE DEVELOPMENT IN THE LEE ACROSS SW
SASKATCHEWAN BY SAT EVENING.
THERE IS GOOD AGREEMENT AMONG THE NAM/ECMWF/UKMET/GFS ON THE 700
MB WAVE TRACKING FROM EASTERN MT/WY 12Z SAT ACROSS THE DAKOTAS TO
THE MN BORDER BY 12Z SUN. DIFFERENCES DEVELOP AS THE OVERALL TREND
IS TOWARDS DEAMPLIFICATION OF THE WAVE...WITH TYPICAL TIMING AND
DIFFERENCES DEVELOPING SUN NIGHT TO EARLY MON.

THE SREF TIMING AND PHASING OUT OF SYNC WITH THE OTHER
MODELS/ENSEMBLE MEANS...AS THE ARW CORE STARTED WITH A WEAKER
700-500 MB WAVE SAT INTO SUN AND HAS A MEAN RIDGE IN THE LAKES SUN
WHERE THE OPERATIONAL MODELS HAVE A MEAN TROUGH.

PREFER A BLEND OF THE 00Z GFS/12Z/12Z ECMWF/00Z NAM TO MITIGATE
TIMING AND AMPLITUDE ISSUES.



SHORTWAVE CROSSING SOUTHWEST CANADA TO THE NORTHERN ROCKIES AND
THEN NORTHERN PLAINS BY SUN NIGHT

PREFERENCE: 00Z GFS/UKMET AND ECMWF BLEND
CONFIDENCE: AVERAGE

THE MODELS START TO BUCKLE THE WESTERLY ONSHORE FLOW WITH A LOW
AMPLITUDE WAVE CROSSING THE NORTHEAST PACIFIC TO PACIFIC NORTHWEST
SUN.  ON SUN NIGHT A LEE LOW FORMS EAST OF THE ROCKIES IN EASTERN
MT/WY...AND MOVES EAST INTO THE DAKOTAS BY 12Z MON...WHEN THE 18Z
GEFS MEAN AND 00Z NAM HAVE THE LOW FURTHER NORTH IN ND THAN THE
12Z ECMWF/UKMET/GFS...WHICH HAVE THE LOW IN SD...AND CLUSTER WELL.

THE 21Z SREF MEAN AGAIN IS LESS AMPLIFIED WITH THE 700 MB WAVE
THAN THE OPERATIONAL RUNS DUE TO DIFFERING BEHAVIORS AMONG THE
NMMB AND ARW CORES THAT RESULT IN A SMEARED SIGNAL IN THE MEAN.

WE WILL FAVOR THE NICELY DEFINED CLUSTER OF THE 00Z GFS/12Z
ECMWF/12Z-00Z UKMET.  THE ECMWF ENSEMBLE MEAN IS ALSO CLOSE TO
THESE 3 SOLUTIONS.


...LOW DEVELOPING OVER THE NORTHEAST PACIFIC AND MOVING TOWARDS
VANCOUVER ISLAND 12Z MON...

PREFERENCE: 00Z GFS/00Z UKMET AND 12Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE 12Z UKMET FORMED A CLOSED LOW OVER THE NORTHEAST PACIFIC THAT
WAS A FEW HOURS FASTER WITH THE SURFACE LOW A FEW MB DEEPER AND
SLIGHTLY SOUTHEAST OF THE GFS AND ECMWF.
THE 00Z UKMET IS SHOWING THE LOW FURTHER NORTHWEST ON 00Z MON AND
NOW CLUSTERS BETTER WITH THE OTHER MODELS. CONSEQUENTLY...A BLEND
OF THE 00Z UKMET/GFS/12Z ECMWF SHOULD SUFFICE.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

PETERSEN

$$





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