Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Wed Jul 22 2020
Valid Jul 22/0000 UTC thru Jul 25/1200 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: 00Z GFS, 12Z ECMWF/CMC/ECENS
Confidence: Slightly Below Average
Biggest concern across the northern tier involves a shortwave
moving from the Great Lakes today through the
Northeast/Mid-Atlantic Friday. This impulse drives a surface wave
and cold front across the region, with a slowing or stalling of
the front possible in the Mid-Atlantic late in the week as it
becomes more parallel to the flow and moves into a strong
mid-level ridge. The NAM and GEFSmean are both strong outliers
with the amplitude of the trough D2 into D3 in the northeast, and
both appear to be due to differences in handling of a convectively
enhanced shortwave/MCV on the upstream side of the ridge causing
deeper troughing downstream. The UKMET is showing its typical
strong bias in the ridge, and is much too high with its mid-level
heights behind the cold front. Otherwise, the mass fields are well
agreed upon for the models comprising the preference. However,
there are some QPF differences with the front moving through New
England and then the Mid-Atlantic, most notably the GFS being slow
to push QPF southward. The GFS may be a bit slow, but some
uncertainty in timing is typical beyond 48 hours so the GFS can
still be included at this time.
...California/Southwest U.S...
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Preference: 00Z Non-NCEP suite
Confidence: Average
A large trough is progged to develop across much of the West
through the end of the week, including a closed mid-level low
rotating around central CA before becoming absorbed into the flow
D3. The GFS is too strong with its overall trough depth, and the
NAM appears to be mishandling northern stream features moving
across British Columbia and Alberta. The NAM being too fast with
the latter impacts the trough evolution across the West
negatively, despite only modest interaction with the longwave
trough digging into the Great Basin. The Non-NCEP models are in
pretty good agreement in both the evolution of the closed low and
the parent longwave trough, and comprise the preferred 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 end of the week.
...Easterly wave moving through the Gulf of Mexico...
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Preference: Non-CMC
Confidence: Slightly above average
A robust easterly wave will move into the central Gulf of Mexico
today and then advect slowly westward to possibly come onshore
Texas Friday. The trend of a subtly deeper/more amplified feature
continues tonight, and while the NAM remains a strong outlier,
there is a noted intensification in guidance from prior runs, and
most guidance shows a sharp trough approaching Texas, while 3 of
the models (NAM/CMC/ECMWF) close off a low at 500-700mb by 84
hours. The CMC is the only outlier in terms of position, it
outruns the consensus and is likely too fast. The UKMET may be a
bit flatter/weaker than consensus, while the NAM as noted is on
the strong edge of the envelope. A GFS/ECMWF compromise could work
well here, but did not want to completely remove the NAM as some
light weight of its depth could produce a better solution.
Also noted was a closed low at 250 mb making its way along 30N
over the waters of the western North Atlantic Ocean...approaching
the southeast U.S. coast by 24/12Z in the GFS and ECMWF. Given
the fact the low has little reflection by 500 mb...no preference
needed here although it is a feature worth probably worth watching
in subsequent runs.
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