Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1232 AM EDT Thu Oct 25 2018

Valid Oct 25/0000 UTC thru Oct 28/1200 UTC

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

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

Most of the QPF during the next few days will be caused by an
evolving East Coast cyclone, and trough beginning to arrive in the
Northwest this weekend. Models are in fairly good agreement with
the big picture with respect to these two troughs, but there are
detail differences and they will matter for the WPC QPF.

For the East Coast trough, the 12Z CMC and UKMET have a notable
southward displacement of the vorticity maxima (along the Gulf
Coast) relative to the 00Z GFS and 12Z ECMWF (closer to the Mid
Atlantic). The 00Z NAM is somewhat in the middle of these
forecasts. All of these models show a coastal low developing,  but
the UKMET and CMC are weaker and further offshore. Given that a
solid majority of the ensemble distribution is north of the UKMET
and CMC, the preference is to lean toward the GFS and ECMWF. Less
weight was placed on the NAM given a colder temperature profile
and faster timing of precipitation relative to other models (which
may influence precip type). Slightly less weight was also placed
on the ECMWF, which has much heavier precipitation inland; given
the expectation of a relatively strong coastal front, the
expectation is that precipitation should be concentrated closer to
the coast which appears to be better represented by the GFS.
However, the magnitude of the GFS QPF maxima seems to be high, so
some ECMWF is incorporated.

In the northwest, the GFS shows a slightly faster arrival of the
precipitation that extends further south relative to the other
models. A blend of the GFS and ECMWF seems appropriate there. The
other notable model difference exists with a digging wave in the
Midwest this weekend. The ECMWF kicks the wave further southeast
relative to all the other deterministic models, and greater weight
was placed on the GFS in this region as well. The NAM and UKMET
seemed to be too strong with the wave (based on mid-upper level
vorticity fields aloft).


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

Lamers