Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1233 AM EDT Tue Mar 12 2019
Valid Mar 12/0000 UTC thru Mar 15/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z NAM/GFS Evaluation Including Preliminary Preferences and
Confidence
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...Upper trough crossing the Pacific Northwest Tuesday...
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Preference: General model blend
Confidence: Above average
The models continue to be in good agreement as this system moves
inland through Tuesday night. During the day on Wednesday, the
mid-upper level trough axis merges with an existing closed low and
associated negatively tilted trough axis discussed below. Through
Wednesday morning, a general model blend is recommended across the
West with this system.
...Closed low/negatively tilted mid-level trough axis crossing the
Southwest Tuesday/Tuesday night...
...Large Great Plains closed low Wed-Thu with associated deep
surface low tracking toward the Great Lakes late Thursday...
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Preference: 00Z GFS/12Z ECMWF blend
Confidence: Slightly above average
Differences in the model fields begin to appear around 12Z/13 with
the 12Z CMC/UKMET a bit weaker with the shortwave amplifying into
the back of the closed low/negatively tilted shortwave trough axis
into Kansas and Oklahoma. The 12Z CMC is slowest with the main
shortwave ejecting out into the Great Plains with the 12Z UKMET
between the agreeable 00Z NAM, 00Z GFS and 12Z ECMWF. Overall, the
12Z CMC appears to be the model with the lowest likelihood of
verifying.
By 00Z/14, the 00Z NAM and 12Z UKMET are noted to be weaker with
the surface low and displaced slightly east of the better ensemble
consensus which trended slightly back to the west with the 12Z/11
cycle. The 00Z GFS/12Z ECMWF show some minor differences but are
better aligned well with the latest GEFS/ECMWF mean positions at
500 mb and at the surface. Run to run continuity has been decent
from the GFS and ECMWF but future minor wobbles in position and
timing can be expected, just not likely deviating far from the 00Z
GFS and 12Z ECMWF blend.
...Upper trough approaching CA late Thursday...
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Preference: 00Z NAM/GFS and 12Z CMC blend
Confidence: Slightly below average
The models bring another shortwave trough toward CA on Thursday
but this one is of much lower amplitude than the one currently
near the Southwest and Pacific Northwest. Ensemble spread is
fairly large with this next system but trends have been toward a
more amplified system. The 12Z UKMET/ECMWF represent the slowest
of the deterministic guidance, the 00Z NAM/GFS are fastest while
the 12Z CMC is slightly slower/weaker than the 00Z NAM/GFS. The
ensemble means show greater support for the middle to faster side
of the model spread with a little more amplitude than seen in the
12Z ECMWF/UKMET. Therefore, will recommend a blend of the 00Z
NAM/GFS and 12Z CMC at this time.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto