Prognostic Meteorological Discussion
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000
FXUS10 KWNH 241603
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1103 AM 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
            12Z GFS/00Z UKMET/00Z ECMWF blend ...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 and 00Z CMC become just a tad more
progressive and flatter than the 12Z GFS, 00Z UKMET and 00Z ECMWF.
The latest GEFS mean and ECENS mean both favor the latter camp
which is also rather well clustered. Will prefer a general model
blend through 48 hours, and then a GFS/UKMET and ECMWF blend
thereafter.


...Shortwave arriving over the Pacific Northwest on Sunday...
...Closed low evolution over the Southwest by Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 06Z GEFS mean and 00Z ECENS mean
Confidence: Slightly 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.
Model spread is mainly noted down over southern California by
Tuesday where the 00Z UKMET and 00Z ECMWF both have their
respective closed lows focused a tad farther west compared to the
12Z NAM, 12Z GFS and 00Z CMC. For now, the ensemble means support
their respective deterministic output with the ECENS mean farther
west and the GEFS mean a little farther east. Will suggest a blend
of the latest GEFS mean and ECENS mean as a compromise for now to
approximate the model consensus.


...Shortwave arriving over the northern Rockies on Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models bring another northern stream trough down from western
Canada and across the northern Rockies by Tuesday. The model
spread with this system is rather minimal at this time, and so a
general model blend will be preferred.


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

Orrison

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