Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
241 PM EDT Tue Jul 03 2018

Valid Jul 03/1200 UTC thru Jul 07/0000 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

12Z Model Evaluation...with Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Model Assessment over the CONUS...

Preference: General model blend
Confidence: Slightly above average

---18Z UPDATE---
No substantial changes to the model preference or reasoning as
stated in the preliminary discussion. One noteworthy trend is that
many of the 12Z models have trended a bit slower with the
developing Canadian low, closer to the UKMET, and slower than the
00Z ECMWF Ensemble Mean. Given the number of models exhibiting
this trend, a trend in the forecast in this direction would also
be reasonable.

---PRELIMINARY DISCUSSION---
Broadly speaking, over the next several days, models are in very
good agreement with their mass fields over most of the CONUS. One
such product that is illustrative of this is the ECMWF Ensemble
normalized standard deviation for MSLP, 850mb T, and 500mb Z
relative to the forecasts over the last 30 days. In general, these
values are around or less than 1 over most of the CONUS in the
next few days, suggestive of forecast uncertainty near or less
than normal. Some areas of slightly higher uncertainty appear to
be along the Gulf Coast, and with the cyclone developing from the
Canadian Prairies to Quebec.

The Canadian low will largely be lifting north of the CONUS, with
greater model agreement on the timing and position of the trailing
surface cold front. However, with the low there are some timing
differences. The 00Z UKMET and 00Z CMC appear slower than the
other models initially. Therefore, the preference in this specific
area would be to lean more toward the GFS, NAM, and ECMWF, which
together are clustered relatively close to the ECMWF Ensemble Mean.

Along the Gulf Coast states, some weak shortwaves or upper level
lows should be embedded in the easterly flow on the south side of
the broad anticyclone over much of the CONUS. Some of these waves
are likely to be influenced by daily convective trends, which
itself introduces some uncertainty. There also appear to be some
general timing differences. By 05.12Z there is fairly good
agreement on a broad low near the Florida Panhandle, and another
wave near Deep South Texas. However, the GFS and NAM appear to
progress the wave faster into Mexico, while the other models are
several degrees of longitude further east. The preference in this
area may be to trend toward the slower non-NCEP models given the
overall weak flow pattern.

Given the agreement on the large scale pattern, confidence is
above average on the placement and timing of broader precipitation
patterns. However, typical summertime uncertainty exists as a
result of convective processes, making it difficult to assess the
model placement of specific QPF maxima. Therefore, the overall
confidence is rated as slightly above average.


Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Lamers