Prognostic Meteorological Discussion
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FXUS10 KWNH 220459

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1259 AM EDT Thu Mar 22 2018

Valid Mar 22/0000 UTC thru Mar 25/1200 UTC

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

00Z NAM?GFS evaluation...including preliminary preferences

...Departing Nor`easter from the Northeast Coast today...
Preference: General model compromise
Confidence: Above Average

The models show similarly with this system.

...Mid-level trough crossing the Great Lakes today and reaching
the Mid Atlantic on Friday while gaining some amplitude...
Preference: General model compromise
Confidence: Slightly Above Average

Only minor placement differences exist with the latest model
guidance concerning the center of the vorticity maximum within the
base of the trough axis as it crosses the East Coast late Friday.
No single model stands out enough to discount it, so a general
model blend is preferred.

...Deep Trough / Closed Low offshore the Northwest thru Friday...
...Opening up into a series of shortwaves crossing the West Coast
Friday night through Saturday night...
Preference: Non 12Z CMC Blend
Confidence: Slightly Above Average

The 12Z CMC is notably faster with the lobe of shortwave energy
forecast to cross the West coast Saturday evening. Outside of this
differences, the models are in fairly good agreement.

...Ongoing atmospheric river Event focused into California...
...Related shortwaves ejecting into the Southwest Thursday and
...Lee cyclogenesis on the Plains, consolidating into a surface
low near Kansas Friday evening and moving east toward the southern
Appalachians Saturday night...
...Surface low redevelopment off of the Mid-Atlantic coast early
Sunday morning...
Preference: 00Z GFS/12Z ECMWF blend
Confidence: Average

Differences begin to appear in the models as a shortwave reaches
the Plains on Friday, with the 00Z NAM showing a bit quicker than
the latest consensus and north with the related warm front
crossing the MS valley from northwest to southeast 00Z/24. The 00Z
NAM continues to look quicker than the model and ensemble
consensus going forward with decent agreement for a non-NAM blend
considering previous model cycles. The 12Z CMC on the other side
is a bit slower than the consensus.

As Sunday morning approaches, surface low redevelopment is
expected off of the Mid-Atlantic coast. Due to differences aloft
in the 00Z NAM over the Northeast, with a more amplified extension
of a closed low over the northern Mid-Atlantic, the NAM is not
preferred despite a relatively favorable placement with respect to
the ensemble scatter low plots. The 00Z GFS and 12Z UKMET appear
toward the southern side of the ensemble spread with these models
also a bit weaker. Through 12Z/25 at least, a 00Z GFS/12Z ECMWF
blend will suffice for this system.

Model trends at
500 mb forecasts at


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