Prognostic Meteorological Discussion
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000
FXUS10 KWNH 231834
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
133 PM EST Fri Feb 23 2018

Valid Feb 23/1200 UTC thru Feb 27/0000 UTC

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

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

...Surface wave crossing the Great Lakes/northern New England...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models are in good agreement with the ejecting the surface
wave currently crossing the Great Lakes region that will clip
portions of northern New England tonight. A general model
orientation of the surface front across the South this period, and
also with the details of the surface wave lifting up across upper
Mississippi Valley and Great Lakes. A general model blend will be
preferred.


...Strong shortwave over the Four Corners region today...
...Cyclogenesis over the Plains and lifting to the Midwest...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z GFS, 12Z UKMET and 12Z ECMWF
Confidence: Slightly above average

The models take a strong shortwave trough digging down across the
Four Corners region today and eject it out across the Plains on
Saturday where well-defined cyclogenesis will occur. An upper
trough will then lift northeast across the upper Midwest by
Saturday night and take on a negative tilt which will help to
deepen surface low pressure as it lifts across the upper Great
Lakes region by early Sunday. The 12Z NAM ends up again stronger
aloft with its energy traversing the upper Midwest and places its
surface low northwest of the model consensus as it nears the upper
Midwest and upper Great Lakes. The 12Z CMC also is a bit deeper
aloft like the NAM. However, the 12Z GFS, 12Z UKMET and 12Z ECMWF
are not as strong with the height falls, but nevertheless show an
energetic and negatively tilting upper trough with a rather strong
surface low. The GFS, UKMET and ECMWF show good model clustering
and ensemble support, and so a blend of these solutions will be
preferred.


...Shortwave arriving over the Pacific Northwest on Saturday...
...Crossing the Four Corners/High Plains on Sunday...
...Ejecting east across the Mississippi/Ohio Valleys on Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The next in a series of shortwaves to drop southeast down across
western North America and into the Pacific Northwest will arrive
on Saturday and then 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 models are in
good agreement with their mass field details of this system until
Sunday when the 12Z UKMET begins to lag the model consensus just a
tad, and the 12Z GFS begins to outrun it somewhat. However, the
latest guidance including the latest CMC and ECMWF and NAM are all
clustered generally in between the UKMET and GFS with the overall
spread rather minimal at this point. Therefore, given the improved
model clustering and ensemble support, a general model blend will
be preferred.


...Shortwave arriving over the Pacific Northwest on Sunday...
...Larger scale trough evolution over the West by Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: 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. The 12Z ECMWF actually did
trend a bit stronger and suggests a mid level low center closing
off over central California by late Monday for which there is some
ensemble support. Overall, the model mass field spread is
relatively low and so a general model blend will still be
maintained for the time being.


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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