Prognostic Meteorological Discussion
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FXUS10 KWNH 191718
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 PM EST SUN FEB 19 2017

VALID FEB 19/1200 UTC THRU FEB 23/0000 UTC

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

12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


DEEPENING TROUGH/CLOSED LOW DEVELOPMENT NEAR NORTHERN NEW ENGLAND
  AND NOVA SCOTIA THROUGH MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM THROUGH TUE MORNING
WITH ANY SIGNIFICANT DIFFERENCES NOT SHOWING UP UNTIL AFTER THE
SYSTEM HAS MOVED WELL OFFSHORE.


SHORTWAVE/SURFACE LOW APPROACHING THE PACIFIC NORTHWEST TODAY
UPPER TROUGH EJECTING OUT OF THE SOUTHWEST INTO THE PLAINS SUN-MON
  REACHING THE UPPER MIDWEST MON NIGHT
SURFACE LOW PRESSURE/COLD FRONT CROSSING THE PLAINS/MIDWEST MON-TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF/00Z UKMET THROUGH 00Z/21
            NEAR THE 12Z GFS AFTER 00Z/21
CONFIDENCE: AVERAGE...BECOMING BELOW AVERAGE

ENSEMBLE SPAGHETTI PLOTS CONTINUE TO SHOW THE 00Z CMC AS FLATTER
WITH THE NRN PORTION OF THIS WAVE ACROSS THE N-CNTRL U.S. ON MON.
THIS DIFFERENCE IN THE 00Z CMC CARRIES OVER THROUGH TUE MORNING
ACROSS THE UPPER MIDWEST. THE ECMWF HAS STEADILY TRENDED FASTER
TOWARD THE RELATIVELY CONSISTENT 12Z GFS VALID 00Z/21 ACROSS THE
N-CNTRL CONUS. THE 12Z NAM REMAINS A TAD FLATTER BUT IT TOO HAS
BEEN TRENDING TOWARD THE 12Z GFS THROUGH 00Z/21.

BEYOND 00Z/21...THE 00Z UKMET EDGES FASTEST WITH THE TROUGH AND
WEAKENING COLD FRONT INTO THE NORTHEAST AND THE 00Z ECMWF SLOWS
RELATIVE TO THE 00Z UKMET AND 12Z GFS. GIVEN A MORE FAVORABLE
UPPER TROUGH DEPICTION IN THE 12Z GFS OVER THE 12Z NAM...WILL EDGE
THE PREFERENCE TOWARD THE 12Z GFS BEYOND 00Z/21.


SHORTWAVE/SURFACE LOW APPROACHING THE WEST COAST EARLY MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND
CONFIDENCE: AVERAGE

THE 12Z NAM IS A TAD FLATTER/SLOWER WITH THE SHORTWAVE/SURFACE LOW
COMPARED TO THE REMAINING GUIDANCE...BUT IT IS WITHIN REASON GIVEN
ENSEMBLE SCATTER LOW PLOTS SUPPORT THE NAM AS A REASONABLE
SOLUTION. DESPITE THE SHORT TIME FRAME...MODERATE ENSEMBLE SPREAD
REMAINS WITH THE LOW PLACEMENT...WITH THE 00Z ECMWF FARTHEST SOUTH
AND THE 00Z UKMET STRONGEST. HOWEVER...THESE DIFFERENCES ARE
SOMEWHAT MINOR AND ONLY THE 00Z CMC IS OUTSIDE OF THE RELATIVELY
GOOD DETERMINISTIC CONSENSUS WITH A FLATTER SHORTWAVE APPROACHING
THE NORTHWEST COAST TONIGHT/EARLY MONDAY. THEREFORE...A NON 00Z
CMC BLEND OF GUIDANCE IS RECOMMENDED WITH THIS SYSTEM.


SHORTWAVE/SFC LOW APPROACHING THE WEST COAST MON NIGHT/TUE MORNING
SURFACE LOW REACHING THE NRN PLAINS TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET
CONFIDENCE: BELOW AVERAGE

THE 12Z GFS CONTINUES LIKE PREVIOUS RUNS TO BE FASTER WITH THE
LEADING EDGE OF AN UPPER TROUGH REACHING THE WEST COAST TUE
MORNING WHICH SHOWS UP IN THE ENSEMBLE SPAGHETTI HEIGHTS. ON THE
FLIP SIDE...THE 00Z CMC IS SHOWING SLOWER TO BRING THE TROUGH
INLAND. WITH THE SURFACE LOW...THE 00Z ECMWF/UKMET APPEAR TO BE A
CLOSER MATCH TO THE BETTER ENSEMBLE CLUSTERING. THIS IS ALSO THE
CASE DOWNSTREAM ACROSS THE N-CNTRL U.S. AT LEAST WITH THE ENSEMBLE
SCATTER LOW PLOTS SHOWING MORE SUPPORT FOR A MORE SRN TRACK THAN
SHOWN BY THE 12Z GFS...NEARER TO THAT OF THE 00Z ECMWF/UKMET.
CONFIDENCE IS LOW GIVEN ROOM FOR ADJUSTMENTS IN THE ENSEMBLE
GUIDANCE IN THE FAST/LOW AMPLITUDE FLOW AND THE FACT THAT NO
DETERMINISTIC MODEL IS AN OUTLIER.


LONGWAVE TROUGH FINALLY REACHING THE WEST COAST BY WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: AVERAGE

THE MIDDLE OF THE ENSEMBLE SPREAD SHOWS CLOSEST TO THE 00Z ECMWF
AND 12Z GFS WITH THE REMAINING DETERMINISTIC MODELS ON EITHER SIDE
OF THE GFS/ECMWF COMBO. ENSEMBLE SPREAD IS NOT TOO LARGE WITH THE
LARGE SCALE PLACEMENT OF THE TROUGH BUT INDIVIDUAL SHORTWAVE
IMPULSES HAVE LOWER CONFIDENCE.


SOUTHERN STREAM TROUGH/CLOSED LOW DEVELOPMENT NEAR THE WESTERN
GULF
  COAST TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/00Z UKMET AND 12Z/18 ECMWF
CONFIDENCE: BELOW AVERAGE

THE TREND HERE HAS BEEN FOR MORE ENERGY TO BE INJECTED INTO THE
BASE OF THE TROUGH AND WHILE THE 12Z/18 RUN OF THE ECMWF SHOWS
THIS IDEA...THE NEXT CYCLE...00Z/19...WENT BACK TO A FASTER
PROGRESSION. ENSEMBLE SPAGHETTI HEIGHTS FROM THE EC ENSEMBLE
SUPPORT A WIDE VARIETY OF SOLUTIONS...BUT THERE IS GROWING
CONFIDENCE IN THE GFS/NAM/UKMET/CMC AND THEIR ENSEMBLES FOR A
SLOWER PROGRESSION THAN DEPICTED BY THE 00Z/19 ECMWF. THE 12Z GFS
AND 00Z UKMET AGREE WITH THE PREFERRED TRENDS AND MIDDLE GROUND
ALONG WITH THE BIAS-CORRECTED NAEFS MEAN 500 MB TRACK OF THE SRN
PORTION OF THE LOW/TROUGH INTO THE WRN GULF OF MEXICO FOR TUE/WED.


www.wpc.ncep.noaa.gov/html/model2.shtml...

www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

OTTO

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