Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
235 AM EDT Thu Aug 15 2019

Valid Aug 15/0000 UTC thru Aug 18/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z GEFS/12Z ECENS mean blend...North-Central U.S.
            Non-NAM blend...Remainder of CONUS
Confidence: Average

The upper-level pattern starts off with strong ridging across the
Southwest and northwesterly flow to its north, leading to broad
troughing across the eastern half of the nation. The ridge becomes
suppressed on Friday and into the weekend as upper-level troughing
begins to impinge upon the Northwest, leading to broad quasi-zonal
flow from the Pacific Northwest to the Northeast.

Anomalous moisture will remain in place ahead of a slow moving
front which will extend from the Mid-Atlantic region to the Gulf
Coast, while impulses in northwest flow aloft keep the central
Plains to the Midwest active with organized convection. There is
broad agreement among the global models with the synoptic scale
features across these two areas, but the 00Z NAM in general
appears to be too amplified and therefore too wet with the energy
it has digging down across the Midwest and into the Eastern U.S.
through the period. Across the Southeast and eastern Gulf Coast
region, the guidance continues to hint at a weak area of low
pressure developing along the aforementioned front. The 12Z ECMWF
in particular was a strong outlier with this feature as it
appeared to be suffering from convective gridscale feedback. The
00Z ECMWF has trended away from this solution and now appears to
be much more reasonable and in agreement with the remaining
guidance.

The guidance is reflecting some of its biggest disagreements with
the troughing/closed low energy advancing through south-central
Canada this weekend which impacts the evolution of a cold front
across the northern Plains and upper Midwest. The 00Z NAM is
notably farther north with its track of the closed low, and is
farther north with its surface low feature as a result. The NAM
leans on the slower side of the guidance with its frontal
evolution, but the 00Z CMC/UKMET and 00Z ECMWF are all also now
collectively slower. Meanwhile, the 00Z GFS is the fastest
solution with its height falls and the surface front. The 00Z GEFS
mean and 12Z ECENS mean both suggest the GFS is a fast outlier,
but they are a tad faster than the non-NCEP model consensus.
Therefore, a preference toward a blend of the ensemble means will
again be preferred as they are clustered fairly well with each
other.

Elsewhere, the models actually show reasonably good model mass
field agreement by the end of the period with respect to strong
height falls dropping down across western Canada, although the 00Z
NAM is likely a tad too strong with its closed low feature.

Based on the current guidance, a non-NAM blend will be preferred
across the CONUS, with exception to the north-central U.S. where a
blend of the 00Z GEFS mean and 12Z ECENS mean will be preferred.


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

Orrison