Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1243 PM EDT Sat Mar 31 2018

Valid Mar 31/1200 UTC thru Apr 04/0000 UTC

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

12Z Model Evaluation...Including Model Preferences and Confidence
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...Surface low pushing through the Great Lakes today with trailing
cold front sweeping across the Northeast by Sunday...
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Preference: Blend of the 12Z GFS and 00Z ECMWF
Confidence: Slightly above average

Overall, the model spread is rather modest, but the 12Z NAM tracks
its surface low a tad north and west of the model consensus over
the next 12 to 24 hours as it exits the Great Lakes region. The
00Z UKMET also appears to be just a tad too slow. Will favor the
better model clustering led by the 12Z GFS and 00Z ECMWF which
best approximates the model consensus.


...Shortwave crossing Oregon today...
...Shearing downwind toward the High Plains by Sunday and Mid
Atlantic by Sunday Night...
...Weak surface low impacting the central
Appalachians/Mid-Atlantic...
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Preference: Non-NAM blend
Confidence: Slightly above average

The models are in good agreement in taking a weak Pacific
shortwave inland across Oregon today which then quickly begins to
shear downstream across the High Plains on Sunday and then toward
the central Appalachians and Mid-Atlantic region Sunday night. The
energy should allow a weak area of low pressure to develop along a
front over the Tennessee Valley Sunday evening, with the low then
quickly advancing east-northeast and crossing the Mid-Atlantic
region by early Monday. The model spread is rather modest with the
shortwave itself and the surface wave evolution, but the 12Z NAM
is just slightly farther north with its low track compared to the
global models and is also a tad stronger with its 700 mb
reflection that crosses the central Appalachians and Mid-Atlantic.
This correspondingly is allowing the NAM to be a bit wetter than
the global models. Will suggest a non-NAM blend at this time.


...Upper level trough digging into the Northwest by late weekend...
...Surface cyclogenesis over the Plains Monday into Tuesday...
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Preference: Blend of the 12Z GFS, 06Z GEFS mean and 00Z UKMET
Confidence: Slightly below average

There is good agreement in the large scale with the details of a
robust trough digging down across the Northwest U.S. through
Sunday night and then ejecting out across the northern/central
Plains through Monday while cyclogenesis takes place in the lee of
the Rockies. By Tuesday, the trough along with the well-developed
area of low pressure will take aim on the upper Midwest and Great
Lakes region. The 12Z NAM becomes of a bit of a stronger and
faster solution aloft with the trough, and this yields an
extension of low pressure farther to the north up across the
northern Plains and upper Midwest compared to the global models
Monday through Monday night. By late Tuesday, the NAM ends up
being the fastest with low pressure going through lower Michigan.
On the other hand, the 00Z ECMWF begins to gradually lag the
remaining models beginning Monday and through Tuesday with its
trough evolution which yields a slower surface low that is also a
tad more suppressed. The 12Z GFS and 00Z UKMET tend to split the
timing difference between the NAM and ECMWF, but the GFS is
certainly the strongest solution with the surface low as it
crosses the Midwest. The 00Z CMC is a bit slower than the GFS, but
faster than the ECMWF. It however is generally the weakest
solution. Based on all of this, will suggest a blend of the GFS
and UKMET, along with incorporation of the 06Z GEFS mean which
will temper the stronger deterministic GFS solution while still
favoring the GFS low track. Confidence is somewhat limited at this
time.


...Lingering trough and stalled surface front in the vicinity of
Florida this weekend...
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Preference: General model blend
Confidence: Above average

There is sufficient mass field agreement for a general model blend
with these features going through Sunday.


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

Orrison