Prognostic Meteorological Discussion
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FXUS10 KWNH 190453
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1152 PM EST THU DEC 18 2014

VALID DEC 19/0000 UTC THRU DEC 22/1200 UTC

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

00Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT TO IMPACT THEIR FORECASTS.


SPLIT FLOW ACROSS THE NORTHERN TIER AND SOUTHERN PLAINS TODAY
WEAK SURFACE LOW TRACKING ALONG THE NORTHERN GULF OF MX
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z NAM...00Z GFS AND 12Z ECWMF
CONFIDENCE: A LITTLE ABOVE AVERAGE

THE MAJORITY OF MODEL TRENDS HAVE BEEN FLATTER WITH A 500 MB
SHORTWAVE TROUGH TO TRACK ACROSS THE SRN PLAINS TODAY...RESULTING
IN A SLIGHT SRN SHIFT WITH A WEAK SURFACE LOW ALONG THE CNTRL GULF
COAST BY SAT MORNING. THE 00Z NAM...00Z GFS AND 12Z ECWMF SHOW
SIMILAR TIMING AND PLACEMENT ALONG WITH THE LATEST SREF/GEFS/EC
MEANS REGARDING THE LOW-MID LEVEL SHORTWAVE AND CORRESPONDING
SURFACE LOW...WHILE THE 12Z UKMET/CMC ARE SLIGHTLY AHEAD OF THE
REMAINING MODEL CONSENSUS.


WEAKENING NRN STREAM SHORTWAVE ENTERING THE PAC NW TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

MODELS SHOW SIMILARLY WITH THIS SYSTEM.


SERIES OF PACIFIC SHORTWAVES MOVING TOWARD THE NORTHERN ROCKIES
EVENTUAL SURFACE CYCLONE CROSSING THE DAKOTAS BY SUNDAY EVENING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF / 00Z GFS BLEND
CONFIDENCE: A LITTLE BELOW AVERAGE

INITIALLY...THE 00Z NAM...00Z GFS AND 12Z ECMWF SHOW THE BEST
AGREEMENT WITH SHORTWAVE ENERGY ENTERING THE PACIFIC
NORTHWEST...WHILE THE UKMET IS A BIT DEEPER/SOUTH AND CMC A BIT
WEAKER/NORTH. DIFFERENCES ARISE AS TROUGH AMPLIFICATION BEGINS
ACROSS THE PLAINS DOWNSTREAM OF AN ANOMALOUS EAST-PACIFIC RIDGE.
THE ECMWF HAS BEEN QUITE CONSISTENT AND IS CURRENTLY IN THE MIDDLE
OF THE LATEST ENSEMBLE SCATTER LOW PLOTS BY 12Z/22...AND IN LINE
WITH THE LATEST GEFS/EC MEANS. HOWEVER...THE 12Z ECMWF COULD BE A
LITTLE WEAK WITH ITS LOW LEVEL LOW...BUT WHEN BLENDED WITH THE 00Z
GFS...A BETTER COMPROMISE IN STRENGTH IS REACHED. THE 00Z GFS IS
THE NEXT CLOSEST MODEL TO THE ECMWF...BUT POSITION-WISE...COULD BE
A BIT SOUTH WITH THE DEVELOPING SURFACE LOW ACROSS THE MIDWEST TUE
MORNING. LARGE ENSEMBLE SPREAD AND A SENSITIVE FLOW REGIME ACROSS
THE PACIFIC LOWERS CONFIDENCE A LITTLE BELOW AVERAGE.


MID-UPPER LEVEL TROUGH REACHING THE SRN PLAINS SUN MORNING AND
WEAKENING EWD INTO THE APPALACHIANS BY MON MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE

A GFS/ECWMF COMBO FITS BEST WITHIN THE MIDDLE OF THE LATEST MODEL
SPREAD AND FITS CLOSEST TO THE ENSEMBLE MEANS. RUN TO RUN
CONTINUITY HAS BEEN DECENT WITH THE GFS/ECMWF AND WORST WITH THE
CMC...ENDING WITH ITS 12Z/18 RUN. CURRENTLY...THE 00Z NAM IS
FASTER WITH THIS FEATURE WHILE THE UKMET REMAINS MORE AMPLIFIED.


...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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