Prognostic Meteorological Discussion
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000
FXUS10 KWNH 040722
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM EST SUN DEC 4 2016

VALID DEC 4/0000 UTC THRU DEC 7/1200 UTC

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

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

WESTERN MEXICO CLOSED LOW EJECTING NORTHEASTWARD
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET/CMC BLEND
CONFIDENCE: NEAR AVERAGE

A LARGE AND ANOMALOUS UPPER LEVEL LOW OVER WESTERN MEXICO AT THE
BEGINNING OF THE PERIOD IS FORECAST TO TRACK EASTWARD ACROSS
MEXICO AND REACH TEXAS BY MONDAY.  BEYOND THIS TIME, THIS FEATURE
IS PROGGED TO GRADUALLY TRANSITION INTO AN OPEN WAVE ACROSS THE
EASTERN U.S. BEFORE BECOMING ABSORBED INTO THE OVERALL FLOW.

OVERALL MODEL AGREEMENT IS GOOD THROUGH 12Z MONDAY WITH THE UPPER
LOW TRACKING ACROSS NORTHERN MEXICO.  BY THE TIME THE LOW ENTERS
TEXAS, THE 00Z NAM BECOMES FARTHER NORTH THAN THE MODEL CONSENSUS
AND THE GFS MORE AMPLIFIED AND SLOWER WITH THE TROUGH AXIS
CROSSING THE DEEP SOUTH THROUGH 12Z TUESDAY.  THERE ARE MINOR
TIMING DIFFERENCES AMONG THE MODELS AS THIS FEATURE DAMPENS OUT,
BUT NO MAJOR OUTLIERS ARE IMMEDIATELY APPARENT.


NORTHERN U.S. SHORTWAVE REACHING NEW ENGLAND BY MONDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A PROGRESSIVE NORTHERN STREAM SHORTWAVE TROUGH OVER THE CENTRAL
AND NORTHERN PLAINS SUNDAY MORNING IS FORECAST TO TRACK RAPIDLY
EASTWARD ACROSS THE GREAT LAKES WHILE ACQUIRING NEGATIVE TILT,
WITH AN UPPER LEVEL RIDGE DIRECTLY AHEAD OF IT.  BY THE TIME IT
REACHES NEW ENGLAND, IT IS EXPECTED TO SHEAR OUT AND BECOMING MORE
ZONALLY ORIENTED.

MODELS HAVE CONTINUED TO SHOW DECENT AGREEMENT OVERALL WITH
RESPECT TO TIMING.  THE UKMET IS NOW CLOSER TO THE MODEL CONSENSUS
SO A MODEL COMPROMISE CAN BE INCORPORATED.


SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW DEVELOPMENT OVER
NORTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~
PREFERENCE: 12Z ECMWF/GFS COMPROMISE
CONFIDENCE: AVERAGE

PACIFIC SHORTWAVE ENERGY TRAVERSING THE U.S./CANADIAN BORDER EARLY
IN THE PERIOD IS FORECAST TO JOIN FORCES WITH AN UPPER LEVEL LOW
OVER SOUTH CENTRAL CANADA BY TUESDAY.  THE DIFFLUENT REGION ALOFT
IN ASSOCIATION WITH THIS FEATURE WILL ALLOW FOR SURFACE LOW
DEVELOPMENT OVER THE NORTHERN PLAINS.

THE NAM IS A STRONG SOUTHERN OUTLIER WITH THE 500MB LOW THROUGH
00Z TUESDAY.  THE 00Z CMC IS CONSIDERABLY MORE AMPLIFIED WITH THE
UPPER LEVEL TROUGH AND IS AN OUTLIER SOLUTION.  THE ECWMF AND GFS
CONTINUE TO BE CLOSE TO THE MODEL CONSENSUS AND THUS ARE THE
PREFERRED CHOICES FOR THIS SYSTEM.


SHORTWAVE TROUGH REACHING THE INTERMOUNTAIN WEST BY TUESDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GULF OF ALASKA UPPER LOW UNDER THE INFLUENCE OF A LARGER
GLOBAL SCALE TROUGH ACROSS NORTHWESTERN CANADA BEGINS TO SHEAR OUT
ALONG THE BRITISH COLUMBIA COAST ON MONDAY.  THE SHORTWAVE ENERGY
ASSOCIATED WITH THIS IS EXPECTED TO CROSS THE PACIFIC NORTHWEST
BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY AS A BROADER AND
LESS AMPLIFIED WAVE.

THE 00Z CMC HAS A DIFFERENT ORIENTATION OF THE WAVE THAT IS LIKELY
RELATED TO THE OVER AMPLIFICATION DOWNSTREAM.  THE OTHER MODEL
SOLUTIONS ARE RELATIVELY WELL CLUSTERED AND CONFIDENCE 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...

HAMRICK

$$




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