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The Weather Prediction Center

Model Diagnostic Discussion

[Abbreviations and acronyms used in this product]
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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Sat Oct 20 2018

Valid Oct 20/1200 UTC thru Oct 24/0000 UTC

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

12Z model evaluation...with final preferences and confidence

...Overall Pattern Across the CONUS...
Preference: General model blend of the 12z guidance
Confidence: Slightly above average

19z Update: The 12z ECMWF/UKMET/CMC showed no major differences to
their previous runs or the other 12z guidance with respect to the
large scale pattern over the CONUS during the period. As such, a
general multi-model blend is preferred for this cycle, with some
higher weight toward the 12z ECMWF.

---previous discussion---
The synoptic pattern across the CONUS featured a digging trough
over the Great Lakes region with a quasi-rex block over the
western US. A subtropical ridge continued across south Florida
westward into southern Texas and Mexico, where two tropical
systems were in the far eastern Pacific waters.

Through the next 24-36 hours, the strong shortwave trough over the
Upper Midwest will continue pushing southeast, sweeping across the
Mid-Atlantic and Northeast US through early Sunday. This will
usher in seasonably cold air for mid-October with sprawling
Canadian high pressure building behind. Another shortwave trough
will sweep across the Upper Midwest Monday into Tuesday.

For the western US, ridging is expected to build and hold across
the Intermoutain West while a closed upper level low and trough
will slowly push into the northwest US and Canadian BC province
areas by Tuesday-Wednesday. A stalled frontal boundary along the
southern Texas Gulf Coast may loosely organize into an area of low
pressure early next week. The models vary with placement and
strength of the surface features, which has a noticeable
difference in the placement of QPF. Confidence here is lower.
Finally, current Tropical Storm Willa is expected to slowly turn
north then northeast, approaching mainland Mexico by the
middle/latter portions of next week.

Overall, the 12z GFS/NAM were in similar agreement to its previous
runs and other 00z guidance. With the approach of the shortwave on
Monday/Tuesday across the Upper Midwest, the GFS/NAM are both
stronger/deeper with the trough axis compared to the 00z
ECMWF/CMC/UKMET solutions. By Tuesday, the GFS/NAM are faster as
well. The models are in reasonable agreement with the approach of
the shortwave energy in the Northwest US, with the GFS/NAM a bit
faster compared to other models and the ensemble means.

Overall, a general model blend including the 12z GFS and the 00z
ECMWF/UKMET/CMC is preferred.

...Tropical Storm Willa...

Toward the end of the forecast period, the NAM is considerably
faster with the remains of Willa pushing into Mexico by Tuesday
while the GFS is also faster compared to the model consensus (and
official NHC track). For the latest information, see the official
NHC advisory.

Model trends at
500 mb forecasts at


Last Updated: 249 PM EDT Sat Oct 20 2018