Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
237 AM EDT Tue Mar 17 2020
Valid Mar 17/0000 UTC thru Mar 20/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation with Latest Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...Deep upper trough/closed low impacting the West...
...Cyclogenesis over the central High Plains Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00Z GFS/ECMWF
Confidence: Average
A deep upper trough and embedded closed low along the West Coast
will begin to pivot inland into the Intermountain West by
Wednesday which will foster lee-side cyclogenesis over the central
High Plains. Shortwave/jet energy rounding the base of the trough
will eject northeast across the central Plains and toward the
Upper Midwest by late Thursday which will ultimately drive
deepening surface low pressure across this region and toward the
upper Great Lakes by early Friday. The 00Z NAM is on the stronger
and faster side of the guidance with this system, and suggests a
surface low track that is a bit farther north and west compared to
the global models. The 00Z GFS and non-NCEP models have all tended
to cluster together a bit better with this latest cycle, with the
ECMWF trending a little slower and also closer in agreement with
the GFS toward the latter part of the period as the energy
traverses the Midwest and Great Lakes. The UKMET overall does
still appear to be too slow with its height fall progression and
also ends up with a notably flatter/weaker surface wave evolution.
Based on the latest trends, a blend of the GFS and ECMWF will be
preferred through the period.
...Upper low/energy lingering over the Great Basin Friday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend
Confidence: Above average
The models indicate a portion of the Western U.S. closed low
getting left behind Thursday and Friday across the Great Basin,
with energy tending to settle southward down toward the Southwest.
The 00Z NAM is very ill-defined with the energy that gets left
behind and if anything suggests a more progressive shortwave would
be already advancing east across the southern Rockies and toward
the High Plains by Friday. The global models though all have a
closed low feature near the Southwest on Friday. Given the
reasonably good clustering of the global models at this point, a
non-NAM blend will be preferred.
...Surface low off the Mid-Atlantic/New England Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average
A wave of low pressure will be centered just off the Mid-Atlantic
coast early Tuesday which will lift northeast and cross southeast
New England late in the day before then lifting through the Gulf
of Maine Tuesday night. Some modest timing spread is seen with the
guidance, but at this point, a general model blend should suffice
for the mass fields.
...Trough crossing the Upper Midwest/Great Lakes Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average
A northern stream trough will cross the northern Plains, Upper
Midwest and Great Lakes region through Tuesday, with an
accompanying cold front that will sweep from the Midwest into the
eastern U.S. This front will sweep off the East Coast by Wednesday
as the upper trough quickly exits the Great Lakes and crosses the
Northeast. Given good model agreement, a general model blend will
be preferred.
...Trough arriving over the northern High Plains Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend
Confidence: Above average
The models bring a second northern stream trough down toward the
northern High Plains by late Wednesday. The 00Z NAM is slower and
deeper than the global models with this system. On Thursday, the
models take this energy east across the Upper Midwest where it
will be attempting to interact with the ejecting trough/closed low
shearing northeast across the central Plains. The NAM remains out
of tolerance with the global models through the period. Given
rather good clustering/agreement among the global models with this
cycle, a non-NAM blend will be preferred.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Orrison