Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
137 PM EST Wed Dec 25 2019
Valid Dec 25/1200 UTC thru Dec 29/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation with Preference and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: 12z ECMWF/12z UKMET blend
Confidence: Slightly below average
There is good model agreement in the short term (through about
27/12z), with the 12z NAM/GFS close to the consensus bringing the
closed mid level low from the CA coast into AZ. After that time,
there is an increasing model spread concerning how the mid level
system as it crosses the Southern Rockies on its way to the
Central Plains and Upper MS Valley.
Both the 12z NAM/GFS are stronger and faster with a northern
stream short wave that tracks from 49N 149W this afternoon into
the northern Rockies by 28/00z. The stronger northern stream spins
up surface low pressure over eastern CO more quickly that the
non-NCEP guidance, resulting in an eastward displacement in the
axis of heaviest QPF. By contrast, the non-NCEP guidance is slower
with the short wave energy in the northern stream, allowing it to
drop into the developing long wave trough. This results in a
westward displacement with the track of the surface low, and
westward placement of the axis of heaviest QPF.
There have been some changes in the the placement of the surface
low in the non-NCEP guidance, which has shown an overall faster
solution for the 12z cycle. This appears to be due to how these
solutions handle the abovementioned short wave energy. The
non-NCEP solutions still drop the northern stream shortwave into
to the developing long wave trough , but now drive the short wave
energy east across the Southern Plains, resulting in an eastward
displacement of the surface low. Interestingly, despite the
eastward trend of the non-NCEP model solution, the placement of
the QPF did not change much (though the magnitude did increase a
bit, possibly owing to better difluence and increases low level
flow).
In spite of the changes with the 12z non-NCEP guidance, the model
preference did not change much. A blend of the 12z ECMWF/UKMET
still form a fairly solid consensus, which is supported by the 12z
GEFS mean/00z ECMWF ensemble mean. However, given the model
spread, forecast confidence remains slightly below normal.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Hayes