Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1154 AM EST Thu Jan 25 2018

Valid Jan 25/1200 UTC thru Jan 29/0000 UTC

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

...12Z NAM/GFS evaluation along with preliminary preferences...
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...Mid-level shortwave weakening northeastward from West Texas
today/tonight...
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Preference: General model compromise
Confidence: Above average

The models show similarly with this system.


...Large upper trough moving through the western U.S. today...
...Surface low near the U.S./Canadian border moving east with
trailing cold front Friday through the weekend...
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Preference: 12Z NAM / 00Z ECMWF blend
Confidence: Average

The 12Z GFS continues to appear faster than the model consensus
with the progression of the 500 mb trough moving across the upper
Mississippi valley early Saturday morning and with energy in the
base of the trough near Kansas and Missouri. Given the 00Z UKMET
has an unfavorable interaction of vorticity centers Friday night
leading to a slower progression of the trough downstream, with
ensemble spaghetti plots supporting a non 00Z UKMET blend across
the north-central U.S., a 12Z NAM/00Z ECMWF blend appears most
favorable with this system.

This preference also applies across the Gulf Coast where the 12Z
GFS is less aggressive moisture return into the central Gulf Coast
region on Saturday. A frontal wave in the Gulf of Mexico appears
to be represented in the deterministic guidance by Sunday morning.
However, the 12Z GFS is faster with this feature and is stronger
than the remaining deterministic guidance and only weakly
supported in the ensemble data. Therefore, a 12Z NAM/00Z ECMWF
blend appears a better fit for this entire system, from Canada to
the Gulf Coast.


...Low amplitude mid-level shortwave nearing the Pacific Northwest
late Friday night with accompanying surface low...
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Preference: 12Z GFS / 00Z ECMWF blend
Confidence: Slightly above average

Ensemble scatter low plots support a 12Z GFS...00Z ECMWF...00Z CMC
blend with the surface low as it approaches the Pacific Northwest.
There is moderately good agreement in the ensemble data to support
this preference. The 12Z NAM is farther south while the 00Z UKMET
is stronger and northward.


...Large closed low approaching British Columbia late Sunday...
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Preference: Non 00Z UKMET blend
Confidence: Average

Ensemble data is reasonably clustered with this next system to
impact the West Coast, but the 00Z UKMET appears a low probability
solution given its placement on the slow edge of GEFS/ECMWF/CMC
ensemble members. Confidence is only average considering the
longer, 84 hour forecast range.


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