Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
127 PM EST Sat Feb 16 2019

Valid Feb 16/1200 UTC thru Feb 20/0000 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

12Z Model Evaluation...with Preferences and Confidences
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...Overall Pattern Across the CONUS...
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Preference: General model blend
Confidence: Slightly above average

19z update: 12z non-NCEP guidance and GEFS mean continued positive
agreement trend.  The 12z CMC showed marked improvement to the
overall cluster, especially with the lead shortwave through the
Great Lakes into New England; shearing in a similar manner in
shape and timing.  This also seemed to positively affect the
upstream developing trof to match the the 12z ECMWF, both slightly
slower than the GFS/UKMET but in a more typical/favorable timing
orientation to each other to have increased confidence in a
general model blend.   With that stated, there are some QPF issues
(UKMET is a bit too wet in the NM/CO terrain) and there is modest
spread in magnitude of QPF and a slight westward shift in the
CMC/ECMWF/UKMET across the Lower MS River Valley/NE TX at the end
of the forecast period.  Still, this is good agreement in
placement to have increased confidence in a general model blend.

Large model spread remains with the compact shortwave dropping
south along the West Coast Tuesday, this continues the run to run
uncertainty/variation in speed, size and shape to have little
confidence.  Though without significant sensible weather/QPF
issues, will effectively ignore the feature in the larger CONUS
general model blend.


---Prior Discussion---
Overall model trends continue to converge on solutions
particularly in the large scale with ill-defined trof in the West,
shedding energy eastward into the Midwest/Great Lakes Sun into
Monday but also reloading a better defined positively orientated
deep trof in the Southwest.  This lead shortwave/broad closed low
into the Midwest, has the elongated deformation zone across the
Midwest into the Lower Great Lakes, eventually shearing across New
England by late Monday, only the 00z CMC seems to be out of place
with the mass fields, failing with a typical slow negative bias. 
The 12z NAM and 00z UKMET may be a bit faster shifting the
moisture/QPF axis into the Mid-Atlantic/northern Carolinas a bit
faster still the 12z GFS and 00z ECMWF support a strong enough
agreement to have fairly high confidence even though the mass
fields are generally flat with strong jet dynamics posing
mesoscale/localized QPF enhancements.

Further upstream, the digging trough also is fairly well agreed
upon especially in the Day 2, early Day 3 time frame.  By later
Tuesday, the 00z UKMET and 12z GFS show typical late-term fast
biases shifting eastward compared to slightly greater amplified
12z NAM and the slower 00z ECMWF.  This leads to some issue in
timing especially with the inner core of the wave, and therefore
QPF across the terrain of NM/CO but believe a non-CMC blend both
in timing/placement and mass field magnitudes should suffice at
average to slightly above average confidence.  Further east, the
intersection of the moisture plume/return flow through the
Southern Plains into the Lower Miss River/TN River basins, will be
of great concern with QPF/heavy rainfall impacts.  At least there
is fairly good agreement in timing/orientation of the plume to the
mass field forcing to have moderate confidence in a non-CMC blend
here as well. 

The greatest uncertainty is associated with a piece of
Pacific/Gulf of AK energy that breaks off into the Pacific NW by
the end of Tuesday.  The strong jet feature will help this wave be
fairly progressive on the back side of the larger scale trof
(ejecting eastward) but some guidance such as the 12z GFS show a
very compact likely over-amplified shortwave feature that is not
favored.  The 12z NAM is very weak, almost non-existent with the
feature; while the 00z UKMET/ECMWF are more middle-ground.  Given
this wave is not a major player in the QPF...will not favor one
piece of guidance over another, even though it does stick out in
the mass fields or any preference/blend.


Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Gallina