Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Sat Mar 30 2019

Valid Mar 30/0000 UTC thru Apr 02/1200 UTC

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

00Z Model Evaluation With Preferences and Confidence
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...Central Plains to the Northeast...
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Preference: General model blend...weighted toward the 00Z GFS/ECMWF
Confidence: Above average

A southern stream shortwave currently ejecting east out across the
central High Plains will gradually become absorbed on Saturday by
a much stronger northern stream trough digging down across the
Midwest and Great Lakes region. The larger scale northern stream
height falls will then pivot across the OH Valley, Mid-Atlantic
and Northeast through Sunday and Monday while gradually taking on
a negative tilt. This will allow a strong cold front to move
through the eastern U.S. as a wave of low pressure rides northeast
along it from the mid-MS Valley to the lower Great Lakes region
and then up across the St. Lawrence River Valley. The models are
in very good agreement generally with the mass field details of
this entire system, but it has been noted that the 00Z NAM, like
with previous cycles, is probably a bit too cold with its boundary
layer temperatures immediately behind the frontal passage. A
general model blend will otherwise be preferred, but with a tad
more weighting toward the 00Z GFS and 00Z ECMWF.


...Four Corners to Southern Plains trough/closed low...
...Reaching the Gulf Coast/Southeast by Mon/Tues...
...Cyclogenesis near the Southeast Coast by Tues...
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Preference: Blend of the 00Z GFS/ECMWF
Confidence: Average

A secondary shortwave moving east from the West Coast behind the
initial wave will drift down over the Four Corners area into
Sunday underneath a closed high center that drops southeast from
southwest Canada. This trough then ejects southeast across the
southern Plains through Monday. On Tuesday, the energy will be
traversing the Gulf Coast states and moving toward the Southeast.
By the end of the period, an area of low pressure is expected to
form along a frontal zone draped from the eastern Gulf of Mexico
northeast across the FL Peninsula and up offshore the Carolinas.

The 00Z NAM is the strongest solution with the closed low/trough
that ultimately swings through the southern Plains and it hangs
onto stronger height falls as it crosses the Gulf Coast states
which helps to drive cyclogenesis by early Tuesday over the
eastern Gulf of Mexico. The NAM is also a little slower than the
global model consensus by the end of the period. The 00Z GFS and
the non-NCEP models are all a bit weaker with the energy by
comparison and tend to favor the main focus of cyclogenesis off
the east coast of the FL Peninsula. The 00Z ECMWF has trended a
bit more suppressed with its surface low evolution and is in very
good agreement with the 00Z GFS. The 00Z UKMET overall may be a
bit too suppressed and progressive by the end of the period, and
the 00Z CMC perhaps a tad too strong. Overall, the NAM is the
outlier solution, and the better deterministic clustering favors
now the GFS/ECMWF camp which is rather well supported by the 00Z
GEFS mean. Will prefer a blend of the GFS and ECMWF as a result at
this point.


...Trough/Low approaching the West Coast on Mon...
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Preference: General model blend
Confidence: Above average

The guidance depicts a fairly compact closed low approaching
northern CA by late Monday which will be gradually opening up into
a trough axis Monday night through early Tuesday while advancing
inland. There will also be a wave of low pressure focused a bit
farther north 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
has now come into sufficient agreement, albeit with some modest
depth/timing differences, such that a general model blend can be
preferred.


...Upper trough over the Northern Plains/Midwest Tues...
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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 some modest spread with the timing of
the cold front and the details of surface low pressure over
south-central Canada, but for now a general model blend will be
preferred to resolve these differences.


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

Orrison