Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
241 PM EDT Sun Jul 19 2020
Valid Jul 19/1200 UTC thru Jul 23/0000 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
12Z Model Evaluation Including Preferences and Forecast Confidence
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...Northern tier of the CONUS...
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Preference: Non-NAM blend
Confidence: Slightly above average
No major changes to the previous thinking across the northern tier
of the CONUS going through the middle of the week. Generally fast
mid-level flow with a series of shortwaves will be traversing the
north side of the mid-level subtropical ridge covering much of the
central and southern U.S.
The 12Z NAM again tends to be on the strong side with the
evolution of the shortwave energy, and especially the shortwave
that amplifies a bit over the northern Plains and Midwest late
Monday through Tuesday in the wake of the current shortwave over
that region today. Upstream a new shortwave will arrive across the
Pacific Northwest by Wednesday, and the models are at least in
rather good agreement with that energy. Overall, a non-NAM blend
will still be preferred, and with particular focus on the energy
Monday and Tuesday impacting the northern Plains and Midwest.
...MCV activity over the central High Plains/lower MO Valley...
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Preference: Blend of the 12Z GFS/HREF
Confidence: Average
There is evidence if a weak mid-level vort center over areas of
southern CO and northern NM currently as seen in the latest
GOES-16 Airmass RGB imagery. This energy is forecast to drift east
this evening and overnight while becoming convectively active with
time. Some subtle height falls associated with arriving shortwave
energy farther north should generally drive this convectively
enhanced vort energy off to the east and through the lower MO
Valley and gradually the mid-MS Valley late Monday through early
Tuesday. The 12Z NAM overall appears too aggressive with its vort
center, but there is some belief that the non-NCEP models from
even the latest 12Z cycle are all too weak with this. The 12Z GFS
and consensus of the 12Z HREF guidance suggests a relative robust
MCV evolving, but just not to the degree of the NAM. So, based on
this, a blend of the 12Z GFS and 12Z HREF will be preferred for
the MCV details.
...California/Southwest U.S...
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Preference: Non-CMC blend
Confidence: Slightly above average
A broad mid-level trough along and just offshore of
northern/central CA on Monday and Tuesday will gradually drift
east and inland by Wednesday with an embedded closed low that is
forecast to cross central CA by the end of the period. A separate
smaller scale shortwave trough is expected to meanwhile be
concentrating over areas of the Southwest involving southern NV,
southwest CA, western UT and northwest AZ by late Tuesday. This
energy coupled with an influx of deepening monsoonal moisture from
northern Mexico and Rio Grande Valley is expected to help drive a
notable uptick in the coverage and intensity of monsoonal
convection across the Southwest going through the middle of the
week. The models are mostly in good agreement with the mass field
details for the time being, but the 12Z CMC trended stronger with
its vort energy/troughing over AZ by the end of the period, and
spatially is more out of tolerance relative to the other models in
this region. So a non-CMC blend will now be preferred with the
upper low evolution for CA and the shortwave energy just to its
east over the broader Southwest.
...Mid-level easterly waves impacting the southern CONUS...
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Preference: Blend of the 12Z GFS/CMC/ECMWF
Confidence: Average
A series of mid-level troughs/easterly waves with at least a
modest surface reflection will move across the Gulf Coast region
through midweek. The 12Z NAM still overall looks a tad too strong
with its energy propagation, with the 12Z UKMET too weak. A blend
of the better clustered 12Z GFS, 12Z CMC and 12Z ECMWF 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
This product will terminate August 15, 2020:
www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination.
pdf
Orrison