Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
101 AM EDT Fri Jul 31 2020
Valid Jul 31/0000 UTC thru Aug 03/1200 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
00Z Model Evaluation Including Preferences and Forecast Confidence
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...Mid-upper level troughing over the OH Valley/Northeast
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Preference: General model blend
Confidence: Above average
The models all show reasonably good agreement with the details of
the current trough over the OH Valley and Northeast that will be
gradually exiting the region going through Saturday. A general
model blend will again be preferred with this energy.
...Mid-level trough digging across the Mid-MS/TN/OH Valleys...
...Northern stream trough dropping though the Great Lakes...
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Preference: Blend of the 00Z NAM/12Z ECMWF/12Z ECENS/18Z GEFS
Confidence: Average
Mid-level energy digging southeast across the mid-MS Valley will
drive a trough in across much of the TN/OH Valley going through
the weekend. This will be reinforced by Sunday by an intrusion of
northern stream troughing dropping down across the Great Lakes
region. On the synoptic scale, the models are in good agreement
with timing and depth of the height falls. However, there are some
differences with respect to shortwave energy lifting northeast out
of the trough across the OH Valley and lower Great Lakes region
Sunday into Monday along with a wave of surface low pressure. The
12Z UKMET suggests a stronger/slower evolution of shortwave energy
along with gradually a slower and deeper surface low over the
lower Great Lakes. The 12Z CMC was the weakest and most
progressive with the energy aloft and at the surface. The 00Z GFS
is generally slower and a bit stronger, but not quite to the
extent of the UKMET. The 00Z NAM and 12Z ECMWF were a bit weaker
and more progressive, but not to the extent of the CMC. Ensemble
clustering suggests more support for the NAM/ECMWF camp at this
point as both the 18Z GEFS mean and 12Z ECENS mean suggest the
UKMET/GFS are too slow/strong with its shortwave energy/low
center. Will prefer a NAM/ECMWF/GEFS/ECENS blend as a result.
...Hurricane Isaias...
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Preference: See NHC special 04Z advisory
Best model proxy: General model blend...through 60 hours
18Z GEFS mean...after 60 hours
Isaias was upgraded to a hurricane in a special 04Z NHC advisory
package. The 00Z NAM/12Z UKMET and 12Z ECMWF overall are all
rather tightly clustered with their tracks of Isaias through 84
hours, and gradually end up a solid 6 to 12 hours slower than the
official NHC forecast track by the end of the period. Of this
cluster, the UKMET is a tad farther south and west of the model
consensus. However, the 00Z GFS is again a progressive outlier and
ends up notably faster than the NHC track from 60 hours onward.
The 12Z CMC is a weaker and westward tracking outlier compared to
NHC and the remaining model suite. Overall, the NHC track is close
to a general model blend through 60 hours, and then closer to the
18Z GEFS mean after 60 hours which ends up in between the faster
GFS and slower NAM/UKMET/ECMWF camps.
...Cold front moving through the north-central U.S. Friday and
Saturday...
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Preference: General model blend
Confidence: Above average
This cold front is related to the intrusion of northern stream
troughing mentioned before that drops down across the Great Lakes
region this weekend. Timing differences are modest with the front,
so a general model blend will be preferred.
...Upper low/trough approaching the Pacific Northwest...
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Preference: Non-CMC blend
Confidence: Slightly above average
The models bring a relatively strong upper trough for this time of
the year into the Pacific Northwest by early Monday. The 12Z CMC
is a bit weaker and faster with the energy. The remaining model
suite is in fairly good agreement with some modest timing/depth
differences. So, a non-CMC blend will be preferred.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
This product will terminate August 15, 2020:
www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination.
pdf
Orrison