Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1133 AM EST Sun Jan 28 2018

Valid Jan 28/1200 UTC thru Feb 1/0000 UTC

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

12Z initial model evaluation with preferences/confidence
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Model initialization errors appear negligible

***Evolving long wave trough over the Eastern U.S. by Tuesday***
***Surface low evolution offshore the Mid-Atlantic/New England***
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Preference: Blend of the 12Z GFS/00Z ECMWF/ensemble means
Confidence: Slightly below average

A relatively weak southern stream shortwave currently crossing the
northern Gulf of Mexico is supporting a developing surface low
south of the Florida Panhandle, along with an inverted surface
trough extending northward across the southeast states.  Farther
to the north, there will be an intrusion of northern stream
shortwave energy crossing the Midwest that will be digging
southeast across the Ohio and Tennessee Valleys through Monday. 
These two features will attempt to phase along the East Coast on
Monday and will likely lead to the development of a long wave
trough over the Eastern U.S. that will take on a neutral to
slightly negative tilt.  The surface low over the Gulf of Mexico
is forecast to lift northeast and undergo intensification near the
southeast U.S. coast Sunday night and then move offshore the
Delmarva before then intensifying southeast of New England Monday
night.

This is the feature with the greatest amount of model spread
during the short term forecast period.  Part of this is owing to
differences in the amount of phasing that will take place with
shortwave energy aloft.  These differences become apparent as
early as Monday evening east of the Mid-Atlantic coast, with the
00Z UKMET being much slower than the model consensus and lacking
ensemble support.  The CMC and ECMWF are also a little slower,
with the ECMWF depicting a second wave of low pressure along the
front.  The GFS and the main surface low from the ECMWF are in
best agreement with the ensemble means, so a blend of these along
with some of the means seems prudent.


***Central U.S. storm system Tuesday and Wednesday***
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Preference: Blend of the 12Z GFS and 00Z ECMWF
Confidence: Above average

Shortwave energy crossing southwest Canada on Tuesday is forecast
to result in the development of a partially closed upper low over
south-central Canada by midweek with a sheared shortwave axis to
the south.  A strong surface low is expected just to the east of
the upper level trough and north of the Canadian border with a
strong cold front extending southward across the central and
northern Plains, along with a secondary surface low near western
Kansas. 

The 00Z UKMET appears to be slightly progressive with the track of
the main surface low over Manitoba but otherwise agrees well with
cold front timing, and the ECMWF slightly slower.  The 12Z NAM and
GFS appear to take the lead on the arrival of the front, with the
NAM showing a faster progression than yesterday.  A compromise of
the 12Z GFS and 00Z ECMWF best approximate the model consensus and
a blend of these two solutions should suffice.


***Shortwave approaching the Pacific Northwest late Tuesday***
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Preference: General model compromise
Confidence: Above average

A large low pressure gyre near 50 degrees north begins to approach
the coastal waters of northern British Columbia by Monday night
along with a deeply occluded surface low that is expected to
slowly fill as it gets closer to land.  A lobe of shortwave energy
aloft accompanied by a surface cold front is expected to pivot
around the southern periphery of the large upper low and affect
the Pacific Northwest by Monday night and into early Tuesday,
along with falling heights aloft.  A sheared axis of upper level
energy is likely to remain over Washington state going into the
middle of the week.

In terms of model solutions, there is good overall agreement with
the placement of the main upper low approaching the BC coast, with
the 00Z CMC slightly to the north of the model consensus. 
Regarding the shortwave impulse tracking towards Washington state,
the NAM is now in better agreement with the model consensus
compared to yesterday, and the models are close enough to merit a
general model compromise.


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

D. Hamrick