The Weather Prediction Center

Model Diagnostic Discussion

[Abbreviations and acronyms used in this product]
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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Sun May 31 2020

Valid May 31/0000 UTC thru Jun 3/1200 UTC

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

00Z Model Evaluation Including Final Preferences and Confidence

Upper level trough and cold front across the Eastern U.S.
Preference: General model blend through 00Z Tuesday, then 00Z
Confidence: Above average

An amplified upper level trough will continue to build in across
the eastern U.S. through the beginning of the week, with the
surface cold front continuing to move farther offshore and a high
quality airmass settling in across much of the region.  Similar to
last night, the models are in very good agreement through about
00Z Tuesday with the CMC remaining slightly weaker and a little
faster with the trough.  By Tuesday morning, an upper low is
likely to evolve from the trough over the Nova Scotia region.  A
blend of the ECMWF, GFS, and UKMET should work well beyond 00Z
Tuesday since there is good overall ensemble support for this.

Upper level low slowly lifting from northern Mexico into the
southern Plains Saturday-Tuesday
Preference: General model blend
Confidence: Average

The models are in generally good agreement indicating a broad
upper low lifting north from northern Mexico into West Texas by
Tuesday morning, before continuing northeast towards Oklahoma on
Tuesday night.  There is not much of a surface reflection of this
in terms of the sea level pressure fields.  A general model blend
will suffice for this upper level low and trough.

Shortwave lifting across the Pacific Northwest and then across
southern Canada
Preference: 00Z GFS/ECMWF
Confidence: Average

Models remain in good agreement into early Monday as the system
continues across southwest Canada.  Model differences become more
apparent by Tuesday morning as the system reaches Manitoba and
western Ontario.  As the system begins to round the top of the
upper ridge, the ECMWF becomes faster than the GFS, and the other
guidance tends to weaken the shortwave faster.  It appears more
likely that the system will maintain strength longer than the
UKMET/NAM/CMC, so a blend of the GFS/ECMWF would work well as a
starting point in the forecast process.

Upper level trough moving from the Pacific Northwest to the
northern Plains and Upper Midwest
Preference: 00Z ECMWF/UKMET/EC mean
Confidence: Slightly below average

A second shortwave disturbance follow behind the current one
across the Pacific Northwest on Monday, and the models are in
generally good agreement through Monday as the system moves
inland.  This will sustain a surface low along a frontal boundary
across the Dakotas.  Differences become more apparent as the
system moves downstream towards the northern Plains, with the
UKMET, ECMWF and the 00Z EC Ensemble Mean becoming faster than the
NCEP guidance and CMC.  Ensemble spread tends to favor the faster
solutions for the time being.

Cut-off low developing west of Southern California early in the
Preference: General model blend
Confidence: Slightly above average

Shortwave energy dropping southeast across the eastern Pacific is
expected to develop a closed low off the Southern California and
northern Baja coast for the early to middle part of the week.  The
models have improved in their depiction of the upper low
evolution.  The EC and its ensemble mean are still slightly to the
west compared to the other guidance by Wednesday morning, while
all similar in magnitude.  Therefore a general model blend should
suffice for this region.

Model trends at
500 mb forecasts at


Last Updated: 416 AM EDT Sun May 31 2020