Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1225 PM EDT Wed Oct 24 2018

Valid Oct 24/1200 UTC thru Oct 28/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Overall Preference: Blend of 00Z ECMWF/UKMET, 12z GFS
Confidence: Average

A more amplified pattern is expected to evolve over the CONUS
through this weekend as a couple of digging shortwave troughs over
the central US help sharpen a longwave tough over the eastern US
while ridging begins to build over the southwestern US. The
Northwest US will see the beginnings of an active pattern as a
series of weather system push into the region.

Currently, one shortwave trough existed over New England while
another mid-level wave was noted over New Mexico. A stronger wave
was well off the western US coast and finally a compact shortwave
was analyzed across southern Alberta Canada. Over the next few
days, a remnant low over the Gulf Coast will advance toward the
Southeast US then lift/deepen along the eastern seaboard. This is
response to the diving shortwave from the central US.

The biggest differences among the deterministic models lie
generally with the timing and strength of the Alberta shortwave as
it moves into the central Plains. Its speed will influence the
sharpness of the developing longwave trough and also the surface
low that will track up the East Coast, having considerable
sensible weather effects for this weekend. The GFS continues to be
the stronger/faster outlier compared to the ECMWF/UKMET, dropping
the shortwave nearly 12 hours faster than the ECMWF. The CMC is
also an outlier, considerably further south with the shortwave.
The ECMWF/UKMET solutions are similar and are a bit
slower/flatter. Compared to previous runs, those models are
beginning to trend slightly toward the GFS, though not nearly as
amplified. Behind that system, toward the end of the forecast
period/day 3, another shortwave is forecast to drop into Montana
and the Dakotas. The deterministic models all have this feature
represented but with the expected timing/placement differences.

At the surface, the NAM is too fast with the progression of the
low up the East Coast. The rest of the deterministic models are
reasonably aligned, taking the low up the Carolina coast then just
off the Northeast / New England coast. With the potential for
more/less phasing due to the mid/upper level, model QPF
differences are higher than normal across the mid-Atlantic.

Across the Pacific Northwest, a couple waves of low pressure will
push into Canada bringing a fetch of moisture into portions of
Washington State. Differences between the deterministic models
were relatively minor with most of the spread on day 3 with the
speed of the shortwave moving onshore.

With this in mind, a blend of the 00z ECMWF/UKMET with the 12z GFS
seems like a good consensus approach for the CONUS at this time.


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

Taylor