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Model Diagnostics Discussion
(Latest Discussion - Issued 1900Z Jan 19, 2020)
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Abbreviations and acronyms used in this product
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Sun Jan 19 2020

Valid Jan 19/1200 UTC thru Jan 23/0000 UTC

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

12Z Model Evaluation with latest Preferences and Forecast

...Shortwave/front clipping the Pacific Northwest by Monday...
Preference: General model blend
Confidence: Above average

The guidance is generally in good agreement with the progressive,
low-amplitude nature of this system brushing by the Pacific
Northwest on Monday. Given the very modest model mass field
spread, a general model blend will be preferred.

...Amplifying shortwave crossing the Midwest through Monday...
...Closed low evolution over the Southeast by Tuesday...
Preference: Non-NAM blend
Confidence: Above average

A progressive, but vigorous, northern stream shortwave will dig
southeast from Canada and cross the Upper Midwest tonight before
then swinging down through the OH/TN Valleys on Monday. By
Tuesday, the system will deepen into a closed low over the 
Southeast before going out to sea. Model spread with this has
decreased compared to yesterday, but after seeing the latest 12Z
cycle of guidance, the 12Z NAM has come in again as being a tad
stronger than the global model consensus as the energy crosses the
Southeast and then moves offshore. A non-NAM blend will be
preferred now as a result.

...Southern stream shortwave crossing California by Monday...
...Energy crossing the Southwest/Plains Tuesday and Wednesday...
Preference: Non-GFS blend
Confidence: Slightly above average

Southern stream shortwave energy will be crossing southern areas
of California on Monday ahead of a deep upper trough/closed low
offshore of the Pacific Northwest. This energy will then eject
quickly down across the Southwest on Tuesday and eject east across
the Plains on Wednesday. The 12Z GFS has at least trended a tad
deeper and slower with this system, and toward the already
relatively deeper/slower 12Z NAM and non-NCEP suite of guidance.
The 12Z ECMWF though came in slower compared to its previous run,
and is now overall the slowest solution. The NAM by the end of the
period may be just a tad too deep with its trough over the
southern Plains, but it is definitely not outside the broader
ensemble envelope, especially relative to the ECENS suite. On the
flip side, the GFS overall may still be a tad too progressive at
the end of the period, and there are concerns with its height
falls evolution upstream over the Pacific Northwest and the
northern High Plains. Despite the favorable GFS mass field trends
across the southern tier, the preference will still be to limit
the GFS incorporation into the model preference. So, based on
these latest trends and clustering, a non-GFS blend will be
preferred which will also help to resolve the relatively slow

...Upper trough/closed low over the Pacific Northwest by Tuesday...
...Energy ejecting out across the northern Plains Wednesday...
Preference: Blend of the 12Z NAM/CMC/ECMWF
Confidence: Slightly above average

A deep upper trough and associated closed low will arrive across
the Pacific Northwest on Tuesday, with the energy then quickly
advancing east across the northern Plains on Wednesday. The 12Z
GFS is out of tolerance with the 12Z NAM, and the entire non-NCEP
suite of guidance. It generally becomes a slower and relatively
deeper outlier as it crosses Pacific Northwest, and down toward
the High Plains. There is some modest support from the GEFS
ensemble suite for the GFS, but the ECENS/CMCE camps are in favor
of the non-NCEP consensus minus the UKMET. The UKMET trended more
progressive and is likely a progressive outlier by the end of the
period. Based on the latest trends/spread, a blend of the NAM, CMC
and ECMWF will now be preferred.

Model trends at
500 mb forecasts at