Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Mon Apr 13 2020
Valid Apr 13/1200 UTC thru Apr 17/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Overall CONUS pattern
~~~~~~~~~~~~~~~~~~~~~~
Preference: 12z GFS/ECMWF blend (NAM inclusion, ok in West)
Confidence: Slightly above average
Average to slightly below average off West Coast Day 3
19z update: Little change, the 12z UKMET was a tad faster and
less amplified with the surface wave off the East Coast, but still
lags the main agreement of the CMC/GFS and ECMWF.
In the West, the 12z UKMET/CMC both suggest ejecting multiple
shortwaves through the ridge. Both support a strong initial wave
that is too fast compared to the initial preference with an
upstream/smaller wave; and this leads to phasing issues with the
northern stream wave that comes through the Rockies/Great Basin
remain unpreferred. The 12z ECMWF picked up a bit of pace to
match the GEFS/ECENS solutions with the offshore closed low, but
this also helped with timing through the Rockies/Great Basin.
There is sufficient evidence to suggest this ECMWF solution is
going to verify a bit better than the 12z GFS, but still think a
preference of the GFS/ECMWF for the Western US (including the
Rockies/lee cyclone/inverted trof in the Plains) is going to work
out best. As such no change in initial preference of a GFS/ECMWF
blend with similar confidence levels.
Eastern half of CONUS
-----------------------
Extremely deep surface cyclone is lifting out of the northern
Great Lakes with centroid of deeper global scale trof with it.
The extremely strong warm conveyor belt and cold front will press
through the Northeast without significant difference in the mass
fields to support a general model blend; though the trailing
frontal zone through the Southeast will become stationary by
Tuesday.
A subtle shortwave out of the West in fast moving westerly flow
will eventually support a weak surface wave in GA/SC or along the
Gulf stream by late Tues/early Wed. As the shortwave reaches the
confluent region of the eastern portion of the large scale trof,
there is some amplification as it lifts north along the Gulf
stream and eventually toward Cape Race by late Thursday. There is
sizable model differences with its timing/placement along the
front with the UKMET lagging and the NAM a bit left of ensemble
suite, enough to suggest less preference there.
In the northern stream, reinforcing shortwaves round and help to
elongate the global trof before it slides eastward through the
Great Lakes Wed before swinging through the Northeast Thursday.
The 12z NAM is a bit stronger/amplified, in line with deepening
the aforementioned offshore surface low. The 00z CMC also appears
to be very compact strong with this wave too, but also a tad
slower...so will push a bit further away from this solution too.
Western US/Rockies
--------------------
A highly amplified ridge exists in the Eastern Pacific through the
Gulf of AK... this block presents a lower predictability forecast
for a compact shortwave that will plow through the northern
portion of it on Tues before descending south just off shore.
Weak flow and small variation can lead to larger downstream
differences. This is clearly the case with the 00z UKMET, which
is smaller/more compact and slower getting through the ridge. The
CMC also is coming out in fractional pieces which doesn't look
correct as well.
A northern stream trough currently in central AK will also drop
between the ridge and the larger scale trof and enter the US
Rockies Wed. The wave in the general weakness between the larger
scale trof begins to broaden/amplify across the Great Basin by the
end of the forecast period. This will bring it closer to
interacting with the aforementioned off-shore low. The ensemble
suite is solid with the placement between the two, and the 12z GFS
(though a tad fast) and the 00z ECMWF (though a tad slow) are the
best representations within the guidance suite.
All together, will suggest a 12z GFS/00z ECMWF blend, though the
NAM maybe useful in the West/Rockies. Confidence is slightly
above average with exception to the closed low off the West coast
which is average to slightly below average.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina