Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1230 AM EDT Mon Jul 20 2020
Valid Jul 20/0000 UTC thru Jul 23/1200 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
00Z Preliminary Model Evaluation Including Preferences and
Forecast Confidence
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...Northern tier of the CONUS...
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Preference: Non-NCEP blend
Confidence: 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 NAM continues its trend
of the last several runs being too amplified and too slow with
most of these shortwaves, while the 00Z GFS has also trended a bit
stronger, especially with the feature lifting across the Northern
Plains into the Great Lakes Tuesday into Wednesday. In the
fast/more zonal flow, the weaker solutions featured by the
non-NCEP models seems more reasonable and is preferred. Note that
there is some potential for any of these shortwaves to drive MCS
development and become convectively enhanced/an MCV across the
middle of the country. The NAM is most aggressive with this
development, and while this is not preferred, it does indicate
some potential for this evolution.
...California/Southwest U.S...
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Preference: Non-CMC blend
Confidence: Slightly above average
A broad mid-level trough is likely to develop across the Southwest
beginning Tuesday, with an embedded closed low progged to move
along the central CA coast into Wednesday. Downstream of this
closed low, a secondary shortwave ridge/trough combination is
likely to amplify across the eastern Great Basin and advect to the
Four Corners by Wednesday. The models are in generally good
agreement with the overall structure, amplitude, and evolution of
this trough. However, the CMC is the notable outlier depicting
lowered heights across much of the region compared to consensus,
and also suggests greater amplification of the downstream
shortwave into the Four Corners Wednesday.
It is worth noting that this energy 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 Southwest going
through the middle of the week.
...Mid-level easterly waves impacting the southern CONUS...
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Preference: Blend of the 00Z GFS/12Z 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 NAM continues to be strong with each
individual wave, while the UKMET suppresses most of the amplitude
due to a stronger ridge to the north. However, the final wave,
which is progged to be near the central Gulf of Mexico at the end
of the forecast period, does feature more significant amplitude
from most of the globals, so the 00Z NAM could be included back
into the blend the latter half of D3.
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