Prognostic Meteorological Discussion
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000
FXUS10 KWNH 180638
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
138 AM EST THU DEC 18 2014

VALID DEC 18/0000 UTC THRU DEC 21/1200 UTC

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

00Z MODEL EVALUATION AND FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.


PACIFIC SHORTWAVES REACHING THE PLAINS TONIGHT
WEAK SURFACE LOW TRACKING ALONG THE GULF COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF
CONFIDENCE: AVERAGE

THE 00Z NAM IS SLOWER THAN THE CONSENSUS WHILE THE 00Z UKMET/CMC
ARE SLIGHTLY MORE AMPLIFIED AT 500 MB WHICH CAUSES THE
CORRESPONDING SURFACE LOW TO BE A BIT FARTHER NORTH IN THE
UKMET/CMC THAN THE LATEST ENSEMBLE SCATTER LOW PLOTS AND MEANS.
THE 00Z GFS IS SLIGHTLY WEAKER THAN THE REMAINING
DETERMINISTIC/ENSEMBLE MODEL CONSENSUS NEAR 850 MB. THIS LEAVES
THE 00Z ECMWF AS A REASONABLE ALTERNATIVE...WHICH IS CLOSEST TO
THE LATEST ENSEMBLE GUIDANCE ACROSS THE SOUTH. NOTE THAT THE 12Z
CMC COULD BE USED AS A SECOND OPTION ALONG WITH THE 12Z
ECMWF...THOUGH THE 12Z ECMWF WAS A TAD NORTH WITH ITS SURFACE LOW
COMPARED TO THE ENSEMBLE GUIDANCE.


MID-LEVEL TROUGH AXIS REACHING THE PLAINS FOR SUN MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z NAM...00Z GFS...00Z ECMWF
CONFIDENCE: AVERAGE

THE SIMILAR TIMING AND AMPLITUDE OF THE 00Z NAM/GFS/ECMWF
CORRESPOND TO A GOOD COMPROMISE CONCERNING A MID-LEVEL TROUGH
FORECAST TO REACH THE PLAINS BY SUN MORNING. THE 00Z UKMET TRENDED
WEAKER THAN ITS 12Z RUN BUT REMAINS SLIGHTLY MORE AMPLIFIED ACROSS
THE PLAINS WHILE THE 00Z CMC JUST HAS A DIFFERENT EVOLUTION OF
SHORTWAVES RESULTING IN AN UNSUPPORTED FLOW PATTERN BY SUN
MORNING. THE RELATIVELY ZONAL FLOW OBSERVED ACROSS THE
MID-LATITUDES IN THE PACIFIC FAVORS LESS AMPLIFICATION THAN SHOWN
BY THE LATEST 00Z UKMET...AND FAVORS THE CURRENT ENSEMBLE GUIDANCE
WHICH DOES NOT SUPPORT THE UKMET.


SHORTWAVES ENTERING THE NWRN U.S. THROUGH SUN MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC COMPROMISE
CONFIDENCE: AVERAGE

THE FAST MID FLOW ENTERING THE PACIFIC NORTHWEST AND NORTHERN CA
MAKES IDENTIFYING INDIVIDUAL SHORT WAVES IN THE FLOW DIFFICULT BY
SAT/SUN. HOWEVER...SOME OF THE LARGER SCALE DIFFERENCES CAN BE
RESOLVED...WITH THE 00Z NAM/GFS SHOWING SLIGHTLY FLATTER FLOW INTO
THE PAC NW...WITH THE 00Z ECMWF/UKMET MORE AMPLIFIED. A BLEND OF
THESE TWO CAMPS SEEMS APPROPRIATE AT THIS TIME...WHILE THE 00Z CMC
APPEARS TO BE LEAST SUPPORTED IN A WEAKER...MORE
NORTHERN...PLACEMENT OF MID-LEVEL TROUGHING AND VORTICITY ENERGY
ENTERING THE PACIFIC NORTHWEST...UNLIKE THE ENSEMBLE MEANS.


CLOSED LOW DEPARTING FROM THE NORTHEAST TODAY AND FRI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ONLY SHOW MINOR DIFFERENCES WITH THIS SYSTEM.



...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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