Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Fri Oct 05 2018

Valid Oct 05/0000 UTC thru Oct 08/1200 UTC

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

00Z Model Evaluation...with latest preferences and confidence
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...Overall Pattern Across the CONUS...
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Preference: 00Z GFS/ECMWF blend...through 72 hrs
            00Z ECMWF/12Z ECENS mean/00Z GEFS mean...after 72 hrs
Confidence: Slightly above average

The guidance indicates a northern stream shortwave crossing the
Pacific Northwest over the next couple of days, with the energy
quickly crossing the northern Plains and upper MS Valley Friday
through Saturday. This will drive a wave of low pressure across
the Midwest and Great Lakes region and then across northern New
England on Sunday as the shortwave energy traverses southeast
Canada. A cold front will cross all of these areas, but the front
will then stall out by Sunday back to the southwest across the
middle MS Valley and the central Plains region. The guidance is
generally in agreement with this scenario, but the 00Z NAM with
the initial shortwave trough is seen as being perhaps a tad too
strong. Also, the 00Z CMC appears to be a bit too slow with its
surface low crossing the Great Lakes.

In the wake of the initial northern stream shortwave, a secondary
shortwave will cross the Pacific Northwest by late Friday and then
amplify sharply down across the Great Basin this weekend, which
will lead to a highly amplified large scale pattern across the
CONUS Sunday and Monday. This will feature a strong longwave
trough over the Western U.S. and a strong subtropical ridge across
the Eastern U.S., and this will be a major reason for the
aforementioned front becoming stalled out over the central Plains
and Midwest. Unfortunately, this will also set the stage for a
multi-day and high-impact rainfall event across this part of the
country.

The models agree very well with the details of the large scale
pattern by the end of the period, although the NAM tends to drop
its height falls a bit farther south over the Four Corners region
compared to the global models. The NAM also tends to be a little
stronger than the global models with a northern stream shortwave
by Monday clipping the northern Plains. Additionally, there are
some concerns also that the NAM may be a bit too robust with a
surface wave and associated mid level shortwave impulse lifting
northeast up across the Midwest by Monday with the deep layer
southwest flow across the region.

Based on the latest model clustering and ensemble guidance, a 00Z
GFS/ECMWF blend will be preferred for the mass fields across the
CONUS out through 72 hours. After 72 hours, the GFS looks as
though it may be a tad too strong and too far north with the
surface low pressure over the central High Plains. The ECMWF, and
the latest ensemble means as per the 00Z GEFS mean and 12Z ECENS
mean will be favored as a cluster thereafter for the remaining
portion of the short range period.


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

Orrison