Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
224 PM EDT Fri Jul 03 2020
Valid Jul 03/1200 UTC thru Jul 07/0000 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
12Z Model Evaluation Including Preferences and Forecast Confidence
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19Z update: No significant changes noted with the rest of the 12Z
guidance and no changes needed to the model blend preference.
Trough over the Northeast U.S.
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Preference: General model blend day 1/2; GFS/ECMWF blend day 3
Confidence: Above average
A pair of shortwave troughs are expected to move through the
Northeast over the next few days, the first arriving late tonight
into Saturday. A weak and quick moving shortwave trough pushes out
of the longwave trough over eastern Canada, and dives across New
York state. Timing and position is relatively good through 24-36
hours in the global deterministic models, the main differences
being some spatial spread seen by 12Z Saturday, where the ECMWF is
a bit further north while the UKMET and the NAM to some degree are
a bit further south/southwest. Nonetheless, a general model blend
for mass field purposes is sufficient. A second shortwave trough
then arrives later in the period, during day 3, and is expected to
clip the northern areas of the Northeast and across New England.
Here, more timing differences are noted where the GFS is faster
and the ECMWF/UKMET are slower. The UKMET is also more amplified
while the GFS is a flatter. Looking at the ensemble means, a blend
of the GFS/ECMWF would be a good consensus approach for day 3.
Trough over the Gulf Coast region
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Preference: GFS/ECMWF blend
Confidence: Average
A slight weakness in the upper level ridge anchored over the
central/southern Plains expands further during the course of the
period as several convectively enhanced MCVs settle over the lower
MS river valley and Gulf Coast region (while the ridge upstream
retreats to the southwest US). The synoptic pattern is largely
agreeable though the CMC/UKMET take the shortwave energy further
south into the moisture/thermal ridge along the Gulf Coast
compared to the NAM/ECMWF/GFS. The latter makes more sense given
the higher moisture in place which should help suppress its
southward movement. Therefore a blend of the GFS/ECWMF is
preferred.
Deep upper trough/closed low across the Pacific Northwest and
western Canada
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Preference: GFS/ECMWF blend
Confidence: Moderate
Shortwave troughing over the Pacific Northwest lifts northeast
into the Canadian Rockies during the day 1/2 period. The GFS and
UKMET are slower with the shortwave and also more amplified while
the NAM/ECMWF/CMC are flatter and faster. Then on day 3, another
shortwave drops from western Canada toward the Pacific NW. Here
more typical model biases are seen, with the GFS faster than the
other deterministic guidance while the UKMET is slower/amplified.
As a compromise and consensus, a blend of the GFS/ECMWF is
preferred.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Taylor