Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Sun Apr 05 2020
Valid Apr 05/1200 UTC thru Apr 09/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation with Initial Preferences and Confidence
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Overall Pattern Across the Continental U.S.
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Preference: General model blend through 12Z Tuesday, then 6Z GEFS
mean/00Z ECMWF/00Z EC mean blend beyond that.
Confidence: Moderate-High
An expansive and deep closed low near the California coast will
continue to dominate the large scale upper level pattern across
the western U.S. through the beginning of the week, along with a
strong subtropical jet streaming across northern Mexico and
extending to the Gulf Coast states. A shear axis/pair of
shortwaves are well north of the US/Canadian border, although it
will continue to extend eastward under the strong Arctic high.
This wave consolidates and clips northern New England Monday,
while broadening and maintaining northwest flow through the
remainder of the forecast period across the northeast states. The
sharp northern stream trof across southwestern Canada will quickly
progress eastward by the upstream Pacific jet, crossing Montana
and North Dakota through Monday night, sustaining a surface low
across the northern Plains. This lead shortwave will introduce
height falls to much of the north-central U.S. through Wednesday
as a second closed low in the northern stream reaches Manitoba and
Ontario. A quasi-zonal flow pattern is expected across much of
the central and eastern U.S. outside of these disturbances.
The models indicate very good overall agreement on the main
synoptic scale features through 12Z Tuesday. The 00Z CMC becomes
less amplified with the broad scale trough over the northeastern
U.S. by Tuesday afternoon, and stronger with the ridge that builds
in across southwest Canada after the shortwave/upper trough
departs the region by Wednesday morning. The 12Z GFS becomes
slightly more progressive with the main upper low reaching the
Desert Southwest by midweek, and slightly weaker with the
downstream ridge across the western High Plains. The 12Z NAM
becomes deeper with the closed low reaching south-central Canada
by Wednesday morning, and the 00Z UKMET is noted as a weaker
outlier with the surface low tracking near the Mid-Atlantic and
northeast on Wednesday, especially once that low emerges offshore.
...19Z Update...
The 05/12Z non-NCEP guidance, in general, maintained good run to
run continuity with the overall synoptic pattern. The 05/12Z
Canadian was deeper and faster than its runs over the past 24
hours with the system dropping in from the Canadian prairies
towards the western Great Lakes. While there was a general move by
the 12Z models, the Canadian became a fast outlier. The 05/12Z
UKMET and ECMWF had very good run to run continuity...which left
the UKMET slow outlier in handling the surface low tracking near
the mid-Atlantic Wednesday. Overall, there was no fundmental
change to the model preferences from the earlier Model Diagnostic
Discussion.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Hamrick/Bann