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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1832Z Feb 24, 2018)
 
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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
132 PM EST Sat Feb 24 2018

Valid Feb 24/1200 UTC thru Feb 28/0000 UTC

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

12Z model evaluation...with latest model preferences and confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Strong upper trough over the High Plains region today...
...Cyclogenesis over the Plains and lifting across the Midwest...
...Trailing cold front sweeping through the Eastern U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend
Confidence: Above average

The models take a strong mid/upper level trough entering the
central and southern High Plains today lift it northeast across
the upper Midwest by tonight as it takes on a negative tilt which
will help deepen surface low pressure that will cross this region.
The 12Z NAM ends up again just a tad stronger aloft than the
remaining guidance as the system lifts northeast across the upper
Midwest and upper Great Lakes tonight and through early Sunday.
Meanwhile, a trailing cold front associated with this system will
sweep east across the Eastern U.S. through Sunday and then move
offshore Sunday night. Model spread with the front is rather
minimal at this time, and the models overall are in rather good
agreement with the secondary area of low pressure offshore New
England Sunday night and early Monday. Based on the overall
clustering of solutions and latest trends, a non-NAM blend will be
preferred.


...Shortwave arriving over the Pacific Northwest today...
...Crossing the Four Corners/High Plains on Sunday...
...Ejecting east across the Mississippi/Ohio Valleys on Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend...through 48 hours
            Blend of the 12Z GFS and 12Z ECMWF...after 48 hours
Confidence: Above average

The next in a series of shortwaves to drop southeast down across
western North America is currently arriving across the Pacific
Northwest and will rapidly drop down into the Four Corners region
on Sunday before rapidly ejecting east toward the mid Mississippi
Valley and Ohio Valley on Monday. The energy will then cross parts
of the Mid-Atlantic and Northeast by Monday night. The models are
in good agreement with their mass field details of this system
until Monday when the 12Z NAM, 12Z CMC and 12Z UKMET become just a
tad more progressive and flatter than the 12Z GFS and 12Z ECMWF.
The latest GEFS mean and ECENS mean both favor the latter camp
which is also well clustered. Will prefer a general model blend
through 48 hours, and then a GFS/ECMWF blend thereafter.


...Shortwave arriving over the Pacific Northwest on Sunday...
...Closed low evolution over the Southwest by Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The guidance brings another shortwave into the Pacific Northwest
on Sunday along with a progressive cold front. The guidance is in
good agreement with the arrival of the shortwave energy and the
evolution of the height falls digging down across California and
the Great Basin on Monday which will lead to a larger scale trough
evolution aiming for the Southwest. Overall, there has been a
somewhat stronger trend in the guidance with the idea of a closed
mid/upper level low center evolving over the Southwest by Tuesday.
The 12Z guidance has come into better agreement with placement of
this closed low over southern California by Tuesday as the latest
UKMET and ECMWF have shifted a little farther east to be in good
agreement with the NAM, GFS and CMC solutions. Given the model
mass field agreement, a general model blend will now be preferred.


...Shortwave arriving over the northern Rockies on Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-CMC blend
Confidence: Above average

The models bring another northern stream trough down from western
Canada and across the northern Rockies by Tuesday. The 12Z CMC is
tad slower and deeper than the remaining models which are
reasonably well clustered. Will suggest a non-CMC blend as a
result 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

Orrison