Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
307 AM EDT Tue Apr 02 2019

Valid Apr 02/0000 UTC thru Apr 05/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Shortwave trough/closed low crossing the Southeast...
...Deep surface low lifting up off the East Coast...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z GFS/UKMET/ECMWF blend
Confidence: Slightly above average

A rather compact and vigorous mid-level closed low traversing the
lower MS Valley will open up into a trough that takes on a
negative tilt across the interior of the Southeast on Tuesday
while driving strong cyclogenesis off the Southeast coastline. The
low center will lift quickly northeast up off the Mid-Atlantic
coast by Tuesday night, and then offshore New England on
Wednesday. The models reflect a very intense low center with rapid
deepening, but there is still some model spread with respect to
the low track.

The 00Z NAM remains on the western side of the model guidance at
least through about 24 hours before the coming into better
agreement with the global model consensus thereafter. As the
deepening low lifts up off the Mid-Atlantic states and offshore
New England, the 00Z GFS/CMC solutions are tad east of the 00Z
UKMET/ECMWF solutions. The 00Z NAM actually by this time basically
splits the difference. A compromise solution will be preferred
with a GFS/UKMET and ECMWF blend preferred.


...Surface low approaching the Pacific Northwest...
...Shortwave reaching the Four Corners by Wed...
...Cyclogenesis over the Southern Plains by Thurs...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend...through 60 hours
            00Z NAM/GFS/ECMWF blend...after 60 hours
Confidence: Average

The guidance depicts a progressive shortwave trough advancing
inland across northern CA on Tuesday and then moving into the Four
Corners region by Wednesday. Meanwhile, there will also be a wave
of low pressure focused a bit farther north on Tuesday that will
be approaching coastal areas of the Pacific Northwest and also
under the influence of a northern stream trough/closed low west of
Vancouver Island. The guidance overall is well clustered with the
surface low evolution, and generally speaking with the height
falls at least through about 60 hours. After 60 hours, the 00Z
ECMWF begins to lag the remaining guidance just a tad as the
energy traverses the lower MS Valley and aims for the TN Valley
and Gulf Coast states. At the surface, cyclogenesis will take
place over the southern Plains with low pressure advancing east
toward the Red River Valley through 60 hours. This wave weakens as
it approaches the lower MS Valley, but the guidance supports a
frontal zone extending downstream through the TN Valley and into
the Mid-Atlantic region by Thursday and Friday. The 00Z CMC
appears to be the most out of phase with the placement of the
front relative to the model consensus. There is better clustering
among the NAM/GFS and ECMWF solutions with this aspect of the
system. Based on the latest model spread and clustering, a general
model blend will be preferred through 60 hours, followed by a
blend of the NAM/GFS and ECMWF.


...Upper trough over the Northern Plains/Midwest Tues...
...Surface cold front crossing the Midwest...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The guidance support the intrusion of a new northern stream trough
digging down over the northern Plains and Midwest by Tuesday along
with a cold front. There is reasonably good model agreement
through Wednesday as this energy then crosses the Great Lakes and
portions of the Northeast. A general model blend will be preferred
with this energy.


...Shortwave troughs approaching the West Coast Thurs...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00Z GFS/GEFS mean/ECMWF
Confidence: Average

The models show a parade of shortwave energy/troughs approaching
the West Coast on Thursday and moving inland by Friday. This will
include a distinct southern stream trough moving into the
Southwest, and also northern stream trough moving into northern CA
and adjacent areas of the Pacific Northwest. The latest model
clustering favors a solution closest to the 00Z GFS and 00Z ECMWF.
The 00Z UKMET appears too slow with the energy coming into the
Southwest, and the 00Z CMC is notably out of phase with the global
models, including the NAM with the broad troughing and closed low
evolution well off the West Coast and south of the Gulf of AK. The
00Z GEFS mean favors the GFS/ECMWF consensus, and so will prefer a
blend of the GFS/GEFS mean and ECMWF at this point.


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

Orrison