Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
139 AM EST Tue Mar 05 2019
Valid Mar 05/0000 UTC thru Mar 08/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preference and Confidence
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...Deep trough over the Great Lakes/Northeast...
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Preference: General model blend
Confidence: Above average
The 00z GFS/NAM continue with high continuity for the remaining
deep trough through the Great Lakes into the Northeast. Even
smaller scale timing/wave depths have coalesced over the last few
cycles to keep an above average confidence in a general model
blend.
...Deep closed low center near 32N 143W...
...Arriving across CA by Wed...
...Shearing downstream across the central Plains on Thurs...
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Preference: General model blend...through 60 hours (7/12z)
12z UKMET/ECMWF and 00z GFS afterward
Confidence: Above average before 60hrs becoming
Slightly above average thereafter
07z update: There was little significant shift with the 00z
non-NCEP guidance, with a slight exception to the 00z UKMET
shifting a hair northeast with the QPF axis and increasing in
magnitude...closer to overall preference of outcome initially. As
such will not change the initial preference with a slight
exception to increase weighting in UKMET ever so slightly after
7/12z. Confidence remains slightly above average though after
07/12z in the GFS/UKMET/ECMWF blend.
---Prior Discussion---
GOES-17 WV detects a deep compact closed low near 32N139W with a
broad downstream warm conveyor belt extending from the subtropics
before broadening east of 130W at this time. Models have become
much more consistent in the track, maintenance of the strength of
the wave through Wed, with only the UKMET showing some low to
mid-level northward adjustment; being a bit more aggressive with
the faster timing of binary interaction in closed low SW of
Vancouver Island).
By 00z Wed, a secondary northern stream jet streak/vort center
rotates around the base early Wed to enhance heavy rainfall and
snows across the terrain in the Intermountain West and Central
Rockies. This warm conveyor is fairly well agreed upon too to
have fairly good confidence through the Day 2 period. As the warm
advection moves into the Central Plains, Thursday, the 00z NAM and
GFS appear to have strongest upglide (shortwave). However, the
00z GFS has trended weaker shearing through the larger scale ridge
into the Ohio River Valley by Fri. The ECMWF/CMC are faster to
weakening the warm advection and eventually focus on intersection
of the return moisture coming out of the Gulf into the Ozarks to W
TN Valley by the end of the forecast. Here a compromise is
suggested favoring weaker/sheared flow through the ridge but
holding onto some of the intensity given the overall strength of
the warm conveyor. As such a blend of the 00z UKMET/ECMWF with
the weaker 00z GFS seems a good compromise both in placement of
the QPF swath as well a magnitude after 60hrs (07/12z). Given
model sensitivity is moderately high for slight differences in
moisture flux/depth of the 5H wave; though models are fairly
agreeable in placement/timing; confidence is slightly above
average after 60hrs.
...Deep closed low near the Pacific Northwest...
...Undercutting shortwave trough approaching CA on Thurs...
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Preference: 00z GFS/ECMWF/CMC blend
Confidence: Average
07z update: The 00z ECMWF trended a bit faster in the northern
stream in day 3 to increase elongation, while it is still west of
the GFS, this shift allowed for slowing of the southern stream to
something closer to initial preference (and the GFS). The UKMET
is slower with the upper low elongation/orientation across the
Pacific Northwest which seems to affect the southern wave, which
was broader unlike any other guidance. As such will suggest a
00z ECMWF/GFS and CMC blend at average confidence.
---Prior Discussion---
The initial binary interaction with the two compact vort centers
near (SW) of Vancouver Island continues to come into some good
agreement, the 12z UKMET is a bit faster, digging south
interacting with the first southern stream closed low on Wed with
limited overall model differences becoming a fairly concentric
closed low again centered near the mouth of the Strait of Juan de
Fuca by 72hrs. Another strong progressive closed low will
advance toward the Pacific Coast (reach 130W) around the same
time. Here differences start to manifest, as the upper low
breaks down a bit, with the upper low becoming a bit less
unbalanced. The 00z GFS and 12z CMC suggest very strong leading
wave/closed feature into Alberta by 84hrs while the 12z
UKMET/ECMWF favor the western portion of the low, maintaining
something more concentric. Interestingly, this leads the ECMWF
to tighten the flow along the southern side accelerating the
progressive Pacific low into the West faster than most ensemble
solutions. Interestingly, the CMC does the same thing with a bit
of increased phasing with the western side of the off-balanced
WA/Alberta closed low. Both becoming increasingly sheared
elongated through the Great Basin by 84hrs. The 00z GFS/NAM are
both uncharacteristically slower, NAM more so and a bit stronger
too.
Ensembles would suggest the ECMWF may be a bit too fast and the
UKMET a bit slow, but there seems to be be more cycle to cycle
vacillation than a consistent trending toward a common solution.
This suggests support toward a general model blend, weighted
toward the CMC/GFS as more central solutions even though a blend
like this spreads out the fields and weakens the meteorological
signal. As such confidence is average in the blend.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina