Prognostic Meteorological Discussion
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000
FXUS10 KWNH 180444
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 PM EST WED DEC 17 2014

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

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

00Z NAM/GFS EVALUATION AND PRELIMINARY 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: 12Z ECMWF/CMC
CONFIDENCE: AVERAGE

THE 00Z NAM IS SLOWER THAN THE CONSENSUS WHILE THE 12Z UKMET IS A
BIT FASTER. THE 00Z GFS IS SLIGHTLY WEAKER THAN THE REMAINING
DETERMINISTIC/ENSEMBLE MODEL CONSENSUS NEAR 850 MB. THIS LEAVES
THE 12Z ECMWF/CMC AS REASONABLE ALTERNATIVES WHICH ARE CLOSEST TO
THE LATEST ENSEMBLE GUIDANCE ACROSS THE SOUTH.


MID-LEVEL TROUGH AXIS REACHING THE PLAINS FOR SUN MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z NAM...00Z GFS...12Z ECMWF
CONFIDENCE: AVERAGE

WHILE THE 12Z ECMWF IS A BIT BROADER WITH UPPER TROUGHING OVER THE
CNTRL U.S. BY 12Z SUN...WHEN BLENDED WITH THE SIMILAR TIMING AND
AMPLITUDE OF THE 00Z NAM AND 00Z GFS...A GOOD COMPROMISE IS
REACHED. THE 12Z UKMET IS A BIT MORE AMPLIFIED AND THE 12Z CMC IS
MUCH SLOWER WITH THIS FEATURE. A STRONGER UKMET TROUGH IS DUE TO
ITS MUCH LARGER RIDGE IN THE EAST PACIFIC...ON THE EDGE OF THE
LATEST ENSEMBLE SPAGHETTI PLOTS...AND NOT IN LINE WITH THE
RELATIVELY ZONAL FLOW OBSERVED ACROSS THE MID-LATITUDES IN THE
PACIFIC.


SHORTWAVES ENTERING THE NWRN U.S. THROUGH SUN MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z NAM...00Z GFS...12Z ECMWF
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...00Z GFS...12Z ECMWF ALL SHOWING A
SIMILAR DEPICTION...WHICH IS CLOSE TO THE ENSEMBLE MEANS...WHILE
THE 12Z UKMET/CMC SHOW WEAKER OR STRONGER AMPLITUDES WITH
MID-LEVEL TROUGHING AND VORTICITY ENERGY ENTERING THE PACIFIC
NORTHWEST.


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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