Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
247 PM EDT Tue May 19 2020
Valid May 19/1200 UTC thru May 23/0000 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
12Z Model Evaluation Including Final Preferences and Confidence
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**Note that the 12Z CMC was not available for this update**
...Cut-Off Low Over Lower OH and TN River Valleys...
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Preference: non 12Z GFS blend beyond 12Z/Thursday
Confidence: Slightly above average
...19Z update...
While the 12Z ECMWF trended a little north with its closed low
Friday evening, it is within the ensemble clustering. A non 12Z
GFS blend remains for the final preference.
...previous discussion follows...
While there are some minor placement differences with the handling
of the low to mid-level closed low over the eastern U.S., the
models are in fairly good agreement through early Thursday. From
the latter half of Thursday through Friday, the 12Z GFS is faster
to progress the gradually weakening closed low toward the north
and east, away from the better deterministic/ensemble agreement.
While the GFS has been trending toward the agreeable ensemble
means, it remains displaced enough to exclude it from the
preference for the second half of Thursday through Friday evening.
By Friday afternoon, ensemble spaghetti plots show spread in the
west-east direction for the closed low, with greater support for
the western cluster of the guidance envelope, but very little
support for the farther north GFS.
...Deep upper trough/closed low over the Western U.S.
today/Wednesday...
...Secondary upper trough over the Pacific Northwest by Thursday...
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Preference: 12Z NAM/12Z ECMWF blend
Confidence: Average
...19Z update...
No significant changes were noted in the 12Z ECMWF/UKMET compared
to their previous 00Z cycles.
...previous discussion follows...
The latest guidance shows agreement for a spoke of the longwave
trough out West to lift northward into southwestern/south-central
Canada through Thursday as another spoke/shortwave moves into the
Pacific Northwest. Differences in the handling of these two pieces
of mid-level energy are evident but with greater support in place
for a 12Z NAM/00Z ECMWF blend.
The 12Z GFS ends up with less separation between the two waves,
resulting in a singular closed low over Alberta/Saskatchewan on
Friday. The only support for the 12Z GFS is the 00Z CMC which is a
near outlier with its slower handling concerning the exiting of
the first wave into Canada Wednesday night into Thursday.
Meanwhile, the 00Z CMC is also faster/weaker with the second piece
of mid-level energy over the Pacific Northwest Thursday evening
resulting in the smaller separation between the two waves Friday
morning. Better ensemble support is in place for a 12Z NAM/00Z
ECMWF blend given the 00Z UKMET appears a bit more amplified than
the consensus over the West Coast with the second wave/closed low
through Friday morning. While the amplified nature of the pattern
may allow for the slower/deeper 00Z UKMET idea at the end of the
week, current guidance does not show much support for the 00Z
UKMET.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Otto