Prognostic Meteorological Discussion
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000
FXUS10 KWNH 210653
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
153 AM EST SUN DEC 21 2014

VALID DEC 21/0000 UTC THRU DEC 24/1200 UTC

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

00Z MODEL EVALUATION AND FINAL MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS TO NOT APPEAR TO BE SUFFICIENTLY
LARGE TO IMPACT THEIR FORECASTS.


MID-UPPER LEVEL TROUGH AXIS REACHING THE APPALACHIANS BY MON A.M.
WEAK SURFACE FRONTAL WAVE OFF OF THE SOUTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS / 00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

WHILE THE 00Z GFS WAS THOUGHT TO BE SLIGHTLY FAST WITH THE UPPER
WAVE AS IT REACHES THE APPALACHIANS...THE 00Z ECMWF/UKMET/CMC HAVE
JOINED THE GFS WHICH MAKES THE 00Z NAM APPEAR SLIGHTLY SLOW.
REGARDING A WEAK COASTAL LOW FORECAST ALONG A FRONT DRAPED ALONG
THE SOUTHEAST COAST...THE GFS REMAINS SLIGHTLY EAST OF THE
CONSENSUS WHILE THE 00Z NAM REMAINS NORTH OF THE PACK. THE 00Z
ECMWF HAS TRENDED EAST IN THE DIRECTION OF THE GFS
SLIGHTLY...WHILE THE 00Z UKMET REMAINS WEST. DIFFERENCES ARE
SHRINKING GIVEN THE SHORTER TIME SCALE OF THIS SYSTEM...BUT
CURRENTLY...THE GFS/ECMWF APPEAR TO BE PLACED IN THE MIDDLE OF THE
LATEST MODEL SPREAD AND TOWARD THE ENSEMBLE MEANS.


CLOSED UPPER LOW FORMING OVER SOUTH DAKOTA BY MON EVENING
CORRESPONDING SURFACE LOW MOVING THROUGH THE DAKOTAS ON MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE

BOTH THE 00Z NAM/GFS HAVE SHOWED A SIMILAR AND CLEAR TREND TO
CLOSE OFF A MID-LEVEL LOW OVER SOUTH DAKOTA EARLIER THAN THE
ECMWF/UKMET/CMC. THE ECMWF HAS BEEN RATHER CONSISTENT BUT HAS ALSO
BEEN TRENDING TOWARD A SLOWER AND MORE AMPLIFIED SOLUTION BY
12Z/22...WITH THE 00Z ECMWF REMAINING A BIT WEAKER/NORTH COMPARED
TO THE 12Z EC MEAN. IT IS LIKELY UNWISE TO IGNORE THE NAM/GFS
TRENDS...BUT ALSO UNWISE TO JUMP ON BOARD WITH THEIR IDEAS 100
PERCENT. THEREFORE...GIVEN TRENDS SEEN IN THE LATEST 00Z MODEL
SUITE AND THE ENSEMBLE DISTRIBUTION...THE PREFERENCE IS TO GO
BETWEEN THESE EXTREMES...BEST REPRESENTED BY THE 00Z
NAM/ECMWF/UKMET. THIS 3-WAY BLEND ALSO FITS WELL WITH THE LATEST
GEFS/EC ENSEMBLE MEANS.


MID-LEVEL SHORTWAVES PASSING THROUGH SRN BRITISH COLUMBIA TODAY
DOWNSTREAM SURFACE LOW DEVELOPMENT ACROSS THE LOWER MISS VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET
CONFIDENCE: BELOW AVERAGE

GIVEN THE CONNECTION TO WHAT HAPPENS ACROSS THE DAKOTAS WITH A
CLOSED LOW REFERENCED IN THE ABOVE SECTION...IT APPEARS THIS NEXT
WAVE FOLLOWS SUIT...WITH THE 00Z GFS MORE AMPLIFIED WITH SHORTWAVE
ENERGY DIVING SWD TOWARD TEXAS...WHILE THE 12Z ECMWF IS ON THE
WEAKER SIDE...AND THE 12Z CMC IS MORE FRAGMENTED WITH THE
SHORTWAVE ENERGY DIVING EAST OF A LARGE E-PAC RIDGE.  IT APPEARS
THE 00Z GFSP IS A PREFERRED BLEND BETWEEN THE 12Z ECMWF / 00Z GFS.
THE NEW 00Z ECMWF/UKMET HAVE ADJUSTED TOWARD THE PREVIOUS
PREFERENCE...WITH MORE AMPLIFICATION AS THE SHORTWAVE DIVES DOWN
ACROSS THE ROCKIES...AND HAS SIMILARITIES TO THE GFSP. ALTHOUGH NO
SINGLE MODEL SHOWS A PREFERRED EVOLUTION AT THIS TIME...THE 00Z
ECMWF/UKMET/GFSP FORM A REASONABLE COMPROMISE FOR NOW.


SHORTWAVE REACHING THE BRITISH COLUMBIA COAST TUE MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z UKMET...00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE PRESENCE OF SUCH A STRONG RIDGE IN THE EAST PAC WOULD TEND TO
FAVOR LESS SHORTWAVE ENERGY PUSHING INTO THE RIDGE AXIS AS HAS
BEEN SEEN IN RECENT RUNS OF THE ECMWF BY TUE MORNING...ENDING WITH
THE 12Z/20 ECMWF. THE 00Z/21 ECMWF HAS TRENDED AWAY FROM THIS MORE
AGGRESSIVE IDEA AND IS MORE IN LINE WITH A GROWING MODEL
CONSENSUS. MANY MODELS ARE DEPICTING A STRONG AND COMPACT CLOSED
LOW NEARING BRITISH COLUMBIA ON TUE...WITH THE 00Z ECMWF TOWARD A
MIDDLE OF THE ROAD STRENGTH...BUT PERHAPS A BIT SLOWER THAN IDEA.
THE 12Z UKMET MATCHED CLOSER TO THE TIMING OF THE ENSEMBLE
MEANS...BUT WHEN BLENDED WITH THE 00Z ECMWF...AN ACCEPTABLE MIDDLE
GROUND IS REACHED.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...


OTTO

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