Prognostic Meteorological Discussion
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000
FXUS10 KWNH 051652
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1251 PM EDT SAT SEP 05 2015

VALID SEP 05/1200 UTC THRU SEP 09/0000 UTC

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

12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


MAIN UPPER LOW LIFTING INTO SOUTH CENTRAL CANADA AND ASSOCIATED
COLD FRONT CROSSING THE UPPER MIDWEST/GREAT LAKES/NEW ENGLAND
DRAPING BACK THROUGH THE CENTRAL PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: ABOVE AVERAGE

STRONG AGREEMENT EXISTS WITH THE OPERATIONAL MODEL SUITE THROUGH
07/00Z MONDAY WITH A `Y-PATTERN` SEEN IN THE SURFACE FIELDS AND
STRONG CLUSTERING OF ALL 3 LOWS AND THE TRIPLE POINT IN THE MN
BOUNDARY WATERS.  AFTER THIS TIME PERIOD...DIFFERENCES BEGIN TO
OCCUR IN THE MASS FIELDS WITH THE 00Z CMC MOVING OUT OF PHASE
BECOMING FASTER WITH THE UPPER LOW AND EVENTUALLY DIGGING AN
OVERALL POSITIVELY TILTED TROF ACROSS MANITOBA INTO THE NORTHERN
RED RIVER VALLEY AND MOVING THE FRONT FASTER AND FURTHER SOUTHEAST
ACROSS THE GREAT LAKES BY DAY 3 AS WELL AS BRAKING OUT QPF UNDER
THE DEEPER UPPER TROF/LOW IN MN. THIS SOLUTION HAS LITTLE SUPPORT
FROM OTHER GUIDANCE. OTHERWISE DIFFERENCES IN MASS FIELDS APPEAR
TO BE LIMITED NORTH OF THE BORDER IN CANADA... WITH THE 12Z NAM
REMAINING A BIT FAST AND NORTHEAST OF THE MAIN CLUSTER.  THE 12Z
GFS IS BETWEEN THE NAM AND THE SLOWER 00Z ECMWF/UKMET LOCATIONS
WHILE EACH ENSEMBLE MEAN (GEFS AND ECMWF) FOLLOWING SUPPORTING ITS
OPERATIONAL RUN.  OF NOTE FOR THE 12Z GFS RUN:  THE KICKER
SHORTWAVE RAPIDLY ACCELERATING OUT OF THE TOP OF THE GULF OF
ALASKA RIDGE IMPACTING THE NORTHWEST COAST BY MONDAY AND EJECTING
OUT OF WY BY TUESDAY APPEARS OVER AMPLIFIED AND TO BE EXPECTED A
BIT SLOWER COMPARED TO THE 12Z NAM/00Z ECMWF.  THIS FEATURE
APPEARS TO NOT AFFECT MUCH OF THE SENSIBLE WEATHER ANY MORE THAN
ANY OTHER FAVORED MODEL.  SO WITH REMARKABLE AGREEMENT IN THE 12Z
NAM/GFS AND 00Z ECMWF/UKMET SOUTH OF THE BOARDER IN PLACEMENT OF
THE FRONT AND QPF...A NON-CMC BLEND IS PREFERRED WITH ABOVE
AVERAGE CONFIDENCE.


STRONG/CONSOLIDATED WAVE ENTERING WESTERN CANADA TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z NAM/00Z ECMWF
CONFIDENCE: AVERAGE

A SHORTWAVE CURRENTLY OVER THE EASTERN BERING SEA IS FORECAST TO
TRANSVERSE SOUTHERN AK AND IMPACT CENTRAL BC EARLY TUESDAY WITH A
GOOD FETCH OF WESTERLY MOIST FLOW FOR INCREASED QPF ACROSS
SOUTHERN BC, THE OLYMPICS AND WA CASCADES THROUGH THE END OF THE
PERIOD.  THE SYSTEM APPEARS WELL HANDLED IN MAGNITUDE BUT
SIGNIFICANT DIFFERENCES APPEAR TO BE SPREAD IN THE TIMING.  THE
00Z UKMET IS FASTEST PER ITS USUAL BIAS COMPARED TO THE REST OF
THE OPERATIONAL MODELS AND ENSEMBLE SUITE.  THE 12Z NAM IS A
MIDDLE GROUND RESOLVING A BIT STRONGER BUT SLOWER THAN THE 00Z
ECMWF.  THE 12Z GFS HAS SHIFTED NOTICEABLY SLOWER THROUGH 08/06Z
TUES...BEFORE CATCHING UP IN PACE BY THE END OF THE FORECAST
PERIOD MORE IN LINE WITH THE 06Z GEFS/09Z SREF.   THE 00Z CMC IS
ALSO SLOW BUT ALSO MUCH BROADER OF A WAVELENGTH MAKING IT AN
OUTLIER.   STILL REDUCING SPREAD IN THE ENSEMBLE SPAGHETTI CHARTS
WITH A GENERAL TROF BEST REPRESENTED BY THE 00Z ECMWF AND 12Z NAM
SHOWS SOME CONFIDENCE IN THESE MIDDLE SOLUTIONS. AS SUCH A 12Z
NAM/00Z ECMWF IS PREFERRED AT AVERAGE CONFIDENCE GIVEN GOOD
AGREEMENT IN TIMING WITH ENSEMBLE MEANS (00Z ECMWF/06Z GEFS/09Z
SREF).


WEAK RETROGRADING UPPER LEVEL TROF ACROSS SOUTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: OPERATIONAL MODEL BLEND WITH HIGHER WEIGHTING TOWARD
00Z ECMWF
CONFIDENCE: ABOVE AVERAGE

THERE IS VERY GOOD AGREEMENT WITHIN THE MODEL GUIDANCE CONCERNING
THE EVOLUTION OF THE UPPER LEVEL TROF DRIFTING SOUTHWEST ACROSS
THE U.S. SOUTHEAST INTO THE CENTRAL GULF BY DAY 3. THOUGH THE 12Z
NAM (IN LINE WITH ITS KNOWN BIAS) IS A BIT STRONG AND THE GFS IS
FAST...THE 00Z ECMWF IS CENTRAL TO THE OPERATIONAL MODEL PACKING
AND IS MOST REPRESENTATIVE TO THE 00Z ENSEMBLE MEANS...GIVING A
GREATER WEIGHTING AND CONFIDENCE IN ITS PARTICULAR SOLUTION.
HOWEVER...OVERALL SPREAD IS MINIMAL ENOUGH TO GENERALLY PREFER A
BLEND OF THE OPERATIONAL MODELS WITH HIGHER WEIGHTING TOWARD THE
00Z ECMWF AT ABOVE AVERAGE CONFIDENCE


...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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