Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1144 AM EST Sat Mar 03 2018

Valid Mar 03/1200 UTC thru Mar 07/0000 UTC

12Z model evaluation...along with model preferences and confidence
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...Powerful nor'easter pulling away from the East Coast...
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Preference: General model blend 
Confidence: Above average 
 
The models are in very good agreement in taking the strong
nor'easter away from the East Coast over the next 24 hours and out
over the open Atlantic Ocean. A general model blend will be
preferred given the minimal mass field spread.


...Deep closed low impacting the Western U.S. today...
...Negatively tilted trough approaching the Plains on Sunday...
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Preference: General model blend...through 60 hours
            06Z GEFS mean/00Z ECENS mean blend...after 60 hours
Confidence: Above average...becoming below average after 60 hours

A deep layer closed low and associated broad trough impacting the
West Coast will gradually be crossing the Intermountain region
through Sunday. The models then indicate energy lifting out of the
base of the trough by Sunday night which will allow the trough to
take on a negative tilt out across the central/northern Plains on
Monday. Expect a new mid/upper level low center to evolve as well
as the system amplifies. Surface low pressure over the Great Basin
through Sunday is expected to reorganize over the Plains on Monday
and begin lifting across the upper Midwest by Monday night. The
guidance is generally in good agreement with their timing and
depth of the trough evolution through Monday, and the spread with
the surface low details across the Plains is rather minimal.

More spread though occurs Monday and Tuesday as this system
encounters a very blocky downstream pattern over eastern North
America. Most of the models refocus their respective closed low
features more to the east over parts of the middle Mississippi
Valley and the lower Great Lakes region by the end of the period
and also show some binary interaction with a closed low farther
north over Ontario to the south of Hudson Bay. The 00Z UKMET tends
to have more energy farther north over the Great Lakes region and
takes its surface low a little north of the model consensus. The
12Z GFS is a little more suppressed with its height falls and has
more energy impacting the Ohio valley. The 00Z ECMWF is north of
the GFS with its surface low evolution on Tuesday and many of the
ECENS members are north as well in support of the ECMWF. The GEFS
members tend to have two camps of low pressure by late Tuesday
with one area of low pressure over Ohio and another one back over
Illinois. However, aloft, the GEFS mean is a bit northwest of the
deterministic GFS. The 00Z CMC and many Canadian ensemble members
attempt to split the difference latitudinally with the low
pressure wave. Confidence becomes limited by Tuesday, but the
preference will be for a general model blend through Monday with
this system, and then a compromise between the 06Z GEFS mean and
00Z ECENS mean thereafter. This would best approximate the model
consensus as well.


...Trough digging southeast across the Northeast on Monday...
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Preference: Blend of the 12Z GFS and 00Z ECMWF
Confidence: Average

The models take a portion of the trough/closed low just southwest
of Hudson Bay and slowly shift it southeast across Quebec on
Sunday and then in more of sheared fashion down across the
Northeast on Monday as the system encounters a blocking high that
is settling southwest from southern Greenland. The guidance
compared to yesterday has trended toward more energy dropping
southeast across the Northeast with a better defined closed low
feature. This energy then quickly goes southeast and offshore by
Monday. The 12Z NAM and 00Z CMC become a little slower than the
12Z GFS and 00Z ECMWF, but the 00Z UKMET does favor the slower
camp. The latest GEFS mean and ECENS mean favor the faster
solutions. Will lean toward the more progressive GFS and ECMWF
solutions for now.


...Shortwave trough over the northern High Plains Tuesday...
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Preference: General model blend
Confidence: Slightly above average

The guidance drops another shortwave trough down across the
northern High Plains by Tuesday. There is some minor depth
differences by late Tuesday over Montana with the height falls,
but will suggest a general model blend for the time being.
  
Previous model trends at www.wpc.ncep.noaa.gov/html/model2.shtml  
Previous 500 mb forecasts at  
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml  
  
Orrison