Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
242 AM EDT Tue Oct 30 2018

Valid Oct 30/0000 UTC thru Nov 02/1200 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: Non-NAM blend weighted most toward 00Z GFS
Confidence: Average

---07Z UPDATE---
No change to the preliminary preference.

---PREVIOUS DISCUSSION---
The most notable model differences in the next few days occur with
the digging trough into the Southern Plains as it begins to kick
northeast and eject through the Ohio River Valley. Model spread
begins to increase between 31/00Z and 01/00Z (Wednesday) as the
wave digs through the Four Corners region. The deterministic 12Z
ECMWF and a notable number of ECMWF ensemble members show a
deeper, stronger, and slower wave which has implications on the
QPF fields east of the Mississippi River on Thursday and Thursday
Night.

Despite fairly good support of the ECMWF by its ensemble members,
most other deterministic models and NAEFS ensemble members kick
the wave out faster. The preference in this case is to lean toward
the other models, and WPC QPF in the Eastern US by Days 2 and 3
leaned most closely to the 00Z GFS. This model preference also
provides consistency with the WPC preference from the previous
model cycle.

In the West, a general model blend was preferred. Model agreement
was better early in the period, but more spread develops by
Thursday when another slug of moisture is expected to reach the
Pacific Northwest. The 00Z NAM and GFS show a stronger wave
offshore and a more amplified downstream ridge, and thus the
heaviest QPF is shifted generally north into British Columbia. The
other models show a flatter pattern overall. Given that the wave
in question will be pushing into a relatively amplified ridge
along the West Coast, a flatter wave may be more likely.
Therefore, there may be a slight preference for the 12Z CMC, UKMET
and ECMWF, but the GFS/NAM scenario cannot be completely ruled out.

In the Midwest, another digging wave on the back of the amplified
trough should lead to a clipper-like low track from the Canadian
Prairies into the Upper Midwest. The 00Z NAM is much stronger with
the wave aloft, and places the QPF further northeast as compared
to the other deterministic models. This more notable difference,
combined with other smaller differences in the rest of the CONUS,
led to the NAM generally being weighted less in this forecast.


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

Lamers