Prognostic Meteorological Discussion
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FXUS10 KWNH 031831
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 PM EST SAT DEC 03 2016

VALID DEC 03/1200 UTC THRU DEC 07/0000 UTC

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

12Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE AMPLIFYING INTO A CLOSED LOW ACROSS NORTHERN MEXICO
SAT/SUN LIFTS INTO TX BY MON SPURRING SURFACE LOW DEVELOPMENT IN
WESTERN GULF MON LIFTING INTO LOWER MS VALLEY TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET/CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

SPREAD CONTINUES TO BE PERSISTENT MAINLY IN TIMING ISSUES THAT
APPEAR TO BE RELATED TO THE CROSSING OUT OF THE LESSER DATA
NETWORK OF NORTHERN MEXICO AND SOME TIMING DUE TO STRETCHING
CROSSING THE N SIERRA MADRE ORIENTAL.  THE 12Z NAM IS VERY QUICK
TO DEPART FASTER THAN THE SPREAD NOT WOBBLING AT THE BASE OF THE
TROF BEFORE THE TURN BACK NORTHEAST.  THIS SHOWS ONLY LIMITED
SUPPORT FROM VERY FAST ECENS MEMBERS WHICH HAVE HAD A NOTORIOUS
FAST BIAS THROUGHOUT THE LAST WEEK WITH THIS SYSTEM.  THE 00Z
ECMWF IS ALMOST AN EXTREME SLOW MEMBER OF THE 00Z ECENS MEAN BUT
HAS A VERY FAVORABLE CENTRAL LOCATION AS WELL AS KEEPING WITH WPC
PREFERENCE OVER THE PAST DAY OR SO.  THE 00Z UKMET IS MATCHED WELL
WITH THIS SOLUTION AS WELL TO BUILD FURTHER CONFIDENCE.

ALL OF THIS AS THE GFS HAS BEEN SLOWING IN TREND WITH TIME COUNTER
TO WPC PREFERENCE.  THE 12Z GFS KEEPS WITH THE GFS TREND EXITING
MX A BIT SLOWER AND THEREFORE TRACKS EASTWARD FURTHER SOUTH THAN
CONTINUITY AND PREFERENCE. HOWEVER BY DAY 3...THE GFS SHOWS
BETTER TIMING WHILE RETAINING SOME STRENGTH IN THE WAVE AS IT
WEAKENS/LIFTS THROUGH THE APPALACHIANS.  THIS IS LIKELY WHY THE
AGREEMENT WITH THE COASTAL SURFACE LOW IS MORE IN LINE WITH THE
ECMWF AND MAY BE WORTH BLENDING FULLY IN AREAS EAST OF THE
APPALACHIANS.  THE 00Z CMC IS LIKE THE GFS A BIT SLOWER INITIALLY.
 AS THE WAVE LIFTS AND WEAKENS THROUGH THE LOWER MS VALLEY...THE
CMC BREAKS FROM THE GFS AND RAPIDLY WEAKENS OUT THE WAVE.  ALL
CONSIDERED WILL FAVOR THE 00Z ECMWF/UKMET BLEND OVERALL WITH
INCLUSION OF THE 12Z GFS ALONG THE EAST COAST ONLY.  CONFIDENCE
REMAINS AVERAGE IN THIS BLEND.

19Z UPDATE: SMALL CHANGES IN THE INITIAL PREFERENCE; 12Z ECMWF
SLIGHTLY SLOWER AND 12Z UKMET A BIT SHALLOWER, KEEP HIGHER
CONFIDENCE IS THIS MIDDLE GROUND SOLUTION. THE 12Z CMC TRENDED
TOWARD BETTER AGREEMENT IN TIMING WITH BOTH THOUGH JUST A BIT
SHALLOWER THAN THE UKMET.  STILL A NON-NCEP BLEND IS PREFERABLE AT
THIS POINT.  CONFIDENCE IS SLIGHTLY ABOVE AVERAGE GIVEN ADDITIONAL
AGREEMENT FROM THE CMC BUT MORE IMPORTANTLY CONTINUITY WITH LAST
2-3 RUNS OF THE UKMET/ECMWF.


SHORTWAVE CROSSING SOUTHWEST NORTHERN PLAINS SAT...WESTERN GREAT
LAKES SUNDAY...NEW ENGLAND MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

MODELS HAVE CONTINUED TO SHOW MODERATE AGREEMENT OVERALL THOUGH
TIMING IS BETTER ALIGNED THAN SPECIFIC DEPTH.  THE 12Z NAM HAS
SHIFTED TOWARD THE BETTER ALIGNMENT IN TIMING/DEPTH OF THE
CONTINUITY THAT IS REPRESENTED BY THE 00Z ECMWF/UKMET/GFS.  THE
12Z GFS HAS A SIMILAR TIMING/EVOLUTION TO THE 00Z; KEEPING GOOD
CONFIDENCE IN THIS SET UP.  ONLY THE 00Z CMC HAS DEPARTING MASS
DIFFERENCES AND WHILE THE TIMING IS FAIRLY GOOD THE DOWNSTREAM
RIDGE A BIT WEAKER ALLOWING THE CMC TO SLIDE/SHEAR OUT ACROSS THE
NORTHEAST A BIT QUICKER.  AS SUCH A NON-CMC BLEND IS PREFERRED.
DIFFERENCES IN DEPTH LEAD TO SOME REDUCTION IN THE HIGHEST
CONFIDENCE BUT STILL IS SLIGHTLY ABOVE AVERAGE.

19Z UPDATE: THE 12Z CMC HAS SHIFTED TOWARD BETTER OVERALL
CONSENSUS OF THIS WAVE...AS SUCH A GENERAL MODEL BLEND IS
PREFERRED THOUGH SOME MINOR DEPTH ISSUES REMAIN TO NOT BE FULLY
CONFIDENT (ABOVE AVERAGE)...SO CONFIDENCE IS SLIGHTLY ABOVE
AVERAGE.


SHORTWAVE CROSSING THE PACIFIC NORTHWEST AND NORTHERN ROCKIES SUN
AND THEN NORTHERN PLAINS BY MONDAY/UPPER MS VALLEY MON NIGHT WITH
DEEPENING SURFACE LOW MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z/00Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE MODELS ARE BECOMING BETTER ALIGNED AS THE MAIN WAVE CROSSES
THROUGH THE NORTHERN CANADIAN ROCKIES WITH A TRAILING SHORTWAVE
ENTERING VANCOUVER ISLAND SUNDAY MORNING.  THE MAIN WAVE SETS UP
ACROSS THE NORTHERN PRAIRIE PROVIDENCES AND HELPS TO SWING THE
SHORTWAVE AND ASSOCIATED JET STREAK THROUGH THE NORTHERN US
ROCKIES.  THE 12Z GFS CONTINUES TO BE SLIGHTLY FASTER AND A BIT
MORE AMPLIFIED EXITING MT/WY AND ROUNDS THE SHARP BASE WITH TIGHT
HEIGHT PACKING ENOUGH TO SUPPORT RAPID DEEPENING WITH A STRONG
DEEP LOW ACROSS THE NORTHERN RED RIVER VALLEY EARLY TUESDAY
MORNING. THE 00Z ECMWF FOLLOWED CLOSELY BY THE 00Z UKMET AND 12Z
NAM ARE CLOSE BEHIND BUT GIVEN THE SLIGHTLY DELAYED ARRIVAL THE
SPIN UP IS A BIT LESS ROBUST WHILE SHOWING SIMILAR EVOLUTIONARY
PATH/TRACK.  THE 00Z UKMET`S UPPER LOW AND KICKER S/W WERE A BIT
DELAYED COMPARED TO THE NAM/ECMWF WHICH FURTHER SLOWS THE
DEVELOPMENT.  THE 00Z CMC IS WELL OUT OF PHASE/BROADER WEAKER IN
CANADA AND WELL SLOWER IN THE NORTHERN PLAINS...WITH A VERY WEAK
SURFACE LOW STAYING WELL SOUTH.  WHILE THE GFS MAY BE A SHADE TOO
FAST THERE IS MORE ENSEMBLE SUPPORT AND STRONGER PACIFIC FLOW
ALOFT TO NOT DISMISS THE POSSIBILITY.  AS SUCH WILL SUPPORT A
NON-CMC BLEND WITH HIGHER WEIGHTING TOWARD THE 00Z ECMWF.  GIVEN
THE SPREAD IN POTENTIAL IMPACT/DEPTH OF THE LOW CONFIDENCE IS A
BIT LOW BUT  AVERAGE OVERALL.

19Z UPDATE: FURTHER SLOWING IN TIMING OF THE ECMWF MAKES DEEP
SOLUTION OF THE 12Z GFS A BIT TOO MUCH TO SUGGEST MAY OCCUR.  THIS
AS THE UKMET IS SLOWER SLIGHTLY AND THE 12Z CMC TRENDED FASTER
TOWARD BETTER TIMING/STRENGTH OF THE NAM AND UKMET.  STILL WOULD
PREFER THE ECMWF AS THE MIDDLE GROUND. AS SUCH PREFERENCE IS A
12Z/00Z ECMWF BLEND AT AVERAGE CONFIDENCE.


LOW DEVELOPING OVER THE NORTHEAST PACIFIC AND MOVING JUST OFF
VANCOUVER ISLAND 12Z MON AND INTO GREAT BASIN BY TUESDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GULF OF ALASKA SHORTWAVE/UPPER LOW UNDER THE INFLUENCE OF
EXPANDING BROAD GLOBAL SCALE TROF ACROSS NW CANADA BEGINS TO SHEAR
ALONG THE BRITISH COLUMBIA COAST AND SLIDE INTO THE US PACIFIC NW
BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY AS BROADER LESS
AMPLIFIED WAVE.  GIVEN ISSUES DOWNSTREAM IN TIMING...THE 00Z CMC
HAS A SLIGHTLY DIFFERENT ORIENTATION OF THE WAVE BUT IN A GENERAL
SENSE THE TIMING/DEPTH/PLACEMENT OF THE WAVE IS IN GOOD AGREEMENT
AND THERE IS SOLID ENSEMBLE SUPPORT TO SUGGEST A GENERAL MODEL
BLEND AS PREFERENCE. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE.

19Z UPDATE: LITTLE DIFFERENCES IN THE ECMWF/UKMET WHILE THE 12Z
CMC BEING FASTER DOWNSTREAM ALLOWS FOR TIGHTER MODEL AGREEMENT FOR
THE WAVE TO KEEP A GENERAL MODEL BLEND.  SPREAD IS MODERATE ENOUGH
BY DAY 3 (ESPECIALLY WITH SPARSE DATA NETWORK UPSTREAM) THAT A
CONFIDENCE IN THIS BLEND IS SLIGHTLY ABOVE AVERAGE.

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

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

GALLINA

$$




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