Prognostic Meteorological Discussion
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000
FXUS10 KWNH 251903
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
202 PM EST Sun Feb 25 2018

Valid Feb 25/1200 UTC thru Mar 01/0000 UTC

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

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

...Deep surface low lifting northeast across Ontario today...
...Trailing cold front sweeping through the Eastern U.S...
...Surface wave developing just offshore southern New England...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models take a deep surface low away from the upper Great Lakes
region today and up across Ontario. This low will advance up
across Quebec tonight through early Monday. A trailing cold front
meanwhile will be sweeping across the Eastern U.S., although the
guidance agrees in hanging up the front a bit along the central
and western Gulf Coast region. Additionally, there will a wave of
low pressure developing just offshore southern New England later
today that will lift northeast up toward the Canadian maritimes on
Monday. All of the models show good agreement generally with the
mass field evolution of these features and so a general model
blend will be preferred.


...Shortwave ejecting across the Four Corners/High Plains...
...Ejecting east across the Mississippi/Ohio Valleys on Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

A shortwave will cross the Four Corners region today and then
rapidly eject east toward the 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 and as a result a
general model blend will be preferred.


...Shortwave arriving over the Pacific Northwest today...
...Closed low evolution over the Southwest by Monday...
...Advancing east toward the southern High Plains by Wednesday...
...Surface low development over the central Plains...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Preference: Blend of the 12Z GFS and 12Z ECMWF
Confidence: Average

The next in a series of western North American shortwaves will dig
into the Pacific Northwest today along with a progressive cold
front. The guidance is in good agreement with this energy digging
sharply south down across California on Monday which will lead to
the development of a compact and rather robust mid level low
center that drops down along the coast of central and southern
California before then pivoting east over areas of the Desert
Southwest by Tuesday. The guidance is in good agreement on the
mass field evolution of this system through Monday, but then
begins to show spread thereafter over broader areas of the
Southwest and toward the southern High Plains. The 12Z NAM becomes
a slower and deeper outlier as the height falls cross especially
southern California and areas farther east through Tuesday and
Wednesday reaching toward the southern High Plains. The 12Z GFS is
the most progressive solution, but also now has strong support
from the 12Z ECMWF which trended faster with this cycle. The 12Z
UKMET and 12Z CMC are just a little slower than the GFS and ECMWF,
but it was noted that the CMC also becomes rather weak and flat as
the energy reaches the southern Plains which results in a more
progressive surface wave evolution. As the energy approaches the
southern High Plains, all of the guidance agrees on developing low
pressure over the central Plains along a front. Based on the
latest model trends and clustering, a blend of the GFS and ECMWF
will be preferred surface and aloft which has good support from
the latest GEFS mean.


...Shortwaves over the northern Rockies/Plains through Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models bring another northern stream shortwave down from
western Canada and across the northern Rockies Monday and Tuesday,
followed by another one through Wednesday with all of the energy
ultimately ejecting east out across the northern Plains. Spread
with the initial shortwave is quite minimal, but there is some
modest spread mainly with the depth of the second shortwave by
Wednesday as it traverses the northern Plains. Will prefer a
general model blend at this time with both shortwaves.


...Strong upper trough offshore the Pacific Northwest Wednesday...
...Strengthening surface low approaching Vancouver Island...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Preference: Blend of the 12Z GFS, 12Z UKMET and 12Z ECMWF
Confidence: Average

The guidance agrees in dropping another shortwave trough south
from the Gulf of Alaska on Tuesday which amplifies sharply into a
strong and larger scale trough near British Columbia and
approaching the Pacific Northwest by Wednesday. A deepening
surface low will be approaching Vancouver Island with a trailing
cold focused offshore the Washington and Oregon coastal ranges by
the end of the period. The stronger model clustering at this point
resides with the 12Z GFS, 12Z UKMET and 12Z ECMWF which have
better ensemble support as well. The 12Z NAM tends to be less
robust with the height falls/surface low deepening, and the 12Z
CMC now appears to be the model that is a bit too slow. Will
prefer a GFS/UKMET/ECMWF blend.


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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