Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Thu Jun 13 2019

Valid Jun 13/0000 UTC thru Jun 16/1200 UTC

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

00Z Final Model Evaluation...with Confidence and Preferences
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...Great Lakes/Ohio Valley/East Coast...
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Preference: 12Z.12 ECMWF/ECENSmean and 00Z.13 GEFSmean/UKMET
Confidence: Slightly Below Average

07Z Update: The 00Z.13 CMC looked very similar to the previous run
until day 3 when it became faster and stronger with the trough
digging into the Ohio Valley/Great Lakes, producing a more
southeast push to the heavy rainfall for the weekend. The UKMET
appears usable through day 2 as it did before, but it also has
become notably stronger/faster/wetter with the trough and
front/QPF by day 3, trending towards the GFS, and actually now
further southeast with the heavy qpf by the end of this discussion
period. This represents a pretty significant change and am
hesitant to adjust the preferred blend based on a jump. Instead,
felt adding the GEFS mean as a compromise and lowering the
confidence was the best course of action for this update.

Note, the 00Z.13 ECMWF is not available due to delayed
dissemination and was not considered for this issuance.

Previous Discussion:
Uncertainty abounds even early on day 2 /Friday/ due to spatial
and temporal discrepancies in the interaction of energy shedding
from a vortex over eastern Canada and a trough digging through the
Great Lakes/Northeast CONUS. There appears to be two distinct
pieces of energy which will rotate around the CONUS trough, with
the guidance differing on which will be the primary, leading to
timing differences of the eastern translation of the trough. The
NAM/CMC suggest the lagging shortwave will dominate which suggests
a slower progression of the trough and associated surface front,
while the GFS/ECMWF/UKMET favor the leading shortwave and a faster
solution. Although the ridge downstream is amplified, it has a
very short wavelength and expect the faster solutions will verify,
especially as most guidance has been too slow with ongoing
evolution early this morning. Although the GFS is usable D1-D2, by
D3 renewed troughing digs in from central Canada, and the GFS is
much stronger /lower heights/ across the Plains and Great Lakes
than the global consensus. As this is the new FV3/GFS, there is
little to discern as far as trends, so as it is a strong outlier
would be hesitant to include much of it by day 3, and favor the
more consistent and clustered UKMET/ECMWF which also match with
the heaviest QPF across the Ohio Valley by the end of the period.


...Western and Southern U.S...
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Preference: Non-ECMWF Day 1, Non-NAM Days 2-3
Confidence: Average

07Z Update: Recent runs of the CMC/UKMET continue a somewhat
drier/faster trend with QPF and shortwave energy across the
Central Plains D1-D2, leading to lowered confidence as there are
two distinct camps between the NCEP and Non-NCEP guidance at this
point. The new UKMET appears more reasonable and consistent than
the CMC so can be included in day 1, but with less weigh than the
NAM/GFS/GEFSmean. Later in the period the differences become even
more pronounced due to timing and intensity differences of
mesoscale features moving through the mean and weakly cyclonic
flow. A general Non-NAM blend should still be acceptable for
D2-D3, despite some washing out of details by the weekend due to
the larger guidance envelope.

Note, the 00Z.13 ECMWF is not available due to delayed
dissemination and was not considered for this issuance.

Previous Discussion:
The flow across the West and South becomes generally zonal as the
eastern trough lifts away Friday before developing broad cyclonic
flow into the weekend. During day 1, the most significant
variation involves a shortwave moving across the Southwest into
Texas. While nearly all the guidance has this feature, the ECMWF
is very quick to dissipate into a downstream shortwave ridge, and
produces little to no QPF across the Panhandle of Texas. This is
an outlier and is not included in the preferred blend. Thereafter,
many of the features across the west and south are related to
mesoscale impulses moving through the flow, with a more
substantial longwave trough developing the latter half of this
discussion period. Timing and Spatial extent of these small scale
features are difficult to discern beyond near-term time scales, so
other than the NAM which is notably stronger with several impulses
translating eastward, a general model blend should suffice.


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

Weiss