Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1257 AM EDT Tue Jul 21 2020
Valid Jul 21/0000 UTC thru Jul 24/1200 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
00Z Preliminary Model Evaluation Including Preferences and
Forecast Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...Northern tier of the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend through D2
Non-GFS D3
Confidence: Slightly above average
Fast flow atop an expansive ridge will persist across the northern
tier of the CONUS going through the middle of the week. Embedded
within this flow, a series of weak to moderate shortwaves will
traverse west to east, causing at least subtle amplification of
troughs into the ridge to the south. The models are in good
agreement for most of the period, but by Thursday the 12Z GFS is a
tad stronger and faster with its shortwave evolution across the
Pacific Northwest and the energy exiting the Great Lakes and
moving into the Northeast. A general model blend should suffice
through about 48 hours, but thereafter, removing the GFS for the
better aligned GEFS mean and other global guidance seems most
reasonable.
...California/Southwest U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z NAM, 12Z ECMWF/UKMET
Confidence: Average
Through 48-60 hours, a general model blend is acceptable as the
mass fields spread is minimal. However, late D2 into D3, a complex
evolution begins as a northern stream trough digs into WA state,
while a closed low pivots near central CA, and a third vort lobe
ejects northeast from the Four Corners towards the Northern
Rockies. The GFS is likely too strong with the vort dropping into
WA, which then phases too much energy of the closed low near CA
rendering it mostly dissipated, or as just a weakness, by 72-84
hours. The CMC goes the other route with a very weak northern
stream trough, which skips any interaction whatsoever with the
closed low leaving it to linger deeper and longer than the
remaining consensus. The NAM/ECMWF/UKMET are all in reasonable
agreement with all three impulses to comprise the blend.
It is worth noting that this energy over the Southwest coupled
with an influx of deepening monsoonal moisture from northern
Mexico and Rio Grande Valley is expected to help drive an uptick
in the coverage and intensity of monsoonal convection across the
Four Corners region through the middle of the week.
...Mid-level easterly waves impacting the southern CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: NAM/GFS/ECMWF
Confidence: Slightly above 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 UKMET and CMC are both much flatter/weaker
with this wave activity, but the remaining guidance is in
reasonably good agreement in tracking this energy across the Gulf
of Mexico and into Texas. It should be noted that by Thursday the
guidance has been trending toward and coming into agreement on
there being at least a weak area of low pressure over the western
Gulf of Mexico.
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
Weiss