Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1138 PM EST Wed Jan 08 2020
Valid Jan 09/0000 UTC thru Jan 12/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation with Preferences and Forecast Confidence
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...Shortwave entering OR/CA tonight, amplifying across the Four
Corners/High Plains Fri and through MS Valley into Great Lakes
late Sat into Sun...
...Deepening surface low over the Lower MS Valley Fri/Sat...
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Preference: Non-CMC blend with lower NAM influence
Confidence: Slightly above average
GOES-West WV denotes sharpening shortwave nearing SW OR at this
time, this wave digs through CA today before bottoming out over
far northern Old Mexico early Friday. Concurrently, the
ill-formed northern portion of the longer wave meridional trof
sharpens and accelerates along the S Canadian Prairies under
stronger anticyclonic jet streak crossing the Canadian Rockies,
eventually decoupling with the southern portion of the wave. The
base slowing and having a favorable jet entrance associated with
the exiting northern stream, amplify ins a closed low across the
Lower MS valley with very strong moisture flux supporting
convection that will feed the increasingly diffluent upper level
pattern (feeding back on cyclogenesis). The 00z NAM shows very
consistent but also substantially deeper solution nearly 40-60 dm
so at 5H which may be related to finer resolution of convection
and latent heat release supporting stronger jet both aloft and in
the low levels, which is a typical negative bias toward Day 3;
though the mass field placement and track of the surface cyclone
are solidly in the center of the ensemble suite...there is some
concern of stronger blending into any preference. The 00z GFS
showed the most significant change mainly in a slightly
slower/sharper base to the trof, delaying its ejection into the
Southern Plains, this brought it into very strong agreement with
the very consistent ECENS mean solution providing greater
confidence overall. The 12z ECMWF/UKMET have some very small
internal differences/placement of convection relative to the GFS,
but a blend between these 3 are best especially with timing of the
cold front pressing through the South, to account for fast/slow
biases.
The 12z CMC is much too weak and fast and with the slowing of the
GFS it is dismissed. So overall a non-CMC blend is preferred
though would weight the NAM lower in any blend, and perhaps
eliminated in some locations were thermal profile may be a bit
more compromised in precip phase. Confidence in this blend is
raised slightly above average.
...Next upper trough over the Northwest by Sat shearing into
longer wave trof over Intermountain West Sun...
...Phasing/sharpening third shortwave along BC coast into Pac NW
late Sun...
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Preference: Non-NAM (remove CMC in NW US late Sun).
Confidence: Slightly above average
In the wake of the larger meridional trof, a compact
mid-wavelength shortwave/small closed low nears Vancouver Island
into the Pacific Northwest. Downstream splitting of flow regime
of the southern and northern portion of the trof allows for
greater southern stream ridging, therefore allowing for a
broadening of the trof as a whole breaking into smaller scale
shortwave features along the periphery of the broadening trof
through the Intermountain West by Sunday. With the exception of
the 00z NAM that shows very strong/sharp shortwave energy sliding
along the western side of the ID/MT Rockies, there is strong model
agreement. So a non-NAM blend is favored through Sun.
Another shortwave phasing with a lobe of very deep Arctic cold
closed low slides down the BC Coast, here guidance is in good
agreement, with exception of the 12z CMC which bleeds a much
colder Arctic air mass through the northern Canadian Rockies
displacing the interaction...so would favor removal of the CMC in
any NW US/Western Canadian blends for Sunday.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina