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Model Diagnostics Discussion
(Latest Discussion - Issued 1824Z Mar 21, 2019)
Version Selection
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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
224 PM EDT Thu Mar 21 2019

Valid Mar 21/1200 UTC thru Mar 25/0000 UTC

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

12Z Model Evaluation Including Preferences and Confidence

...Trough and Coastal Low in the East...
Preference: General model blend thru 23/12z
            Non-UKMET after 
Confidence: Slightly above average

19z update: 12z CMC/ECMWF like the GFS trended a bit faster,
leaving the NAM as the slowest solution.  The UKMET remains a bit
fast particularly after 48hrs, so a general model blend will
suffice up to 48hrs weighted toward the CMC/ECMWF less to
NAM/UKMET then shift to non-UKMET blend after 48hrs at slightly
above average confidence.

---Prior Discussion---
The first phasing of shortwaves into a more concentric closed low
over the Mid-Atlantic has occurred with surface deepening on going
currently.   Upstream jet/nose of jet shortwave is taking shape
over East Central Canada dropping southward.  The 00z UKMET was
already off-balance compared to observations (stronger lead wave)
to have confidence for its inclusion in an otherwise tightening
guidance suite.  The 12z GFS showed some typical negative bias,
especially at 7H with the last few runs trending a bit too fast
particularly with upstream amplification that should slow,
increase binary interaction across New England.  After the
wobble/redevelopment along coastal ME/Gulf of ME...the GFS remains
fast to exit northeast as well.  Some inclusion would be alright,
but will favor a 12z NAM and 00z ECMWF/CMC blend.  Confidence
given the higher packing is slightly above average.

...Remainder of the CONUS...
Preference: 12z ECMWF/NAM/CMC blend
Confidence: Average to slightly above average

19z update:  The UKMET remains a bit out of step, though trending
in the right direction, especially with the second shortwave into
the West/Snake River Plain 25/00z, and remains a bit too fast with
the small compact vort center lifting through the Plains into the
Great Lakes.   The 12z CMC remained very similar to the 00z run,
though the ECMWF, like the NAM shifted a bit faster with the lead
wave into the Great Lakes (with minor effects).   With a bit
better agreement with the NAM/ECMWF/CMC across the West into day
3, will suggest a removal of the weak/shearing GFS in the
preference for that wave. Confidence is slightly above average for
the lead wave and only average for the moderate spread of the
secondary wave into the Intermountain West for Day 3

---Prior Discussion---
The weakly formed closed low over UT/AZ will continue to advance
into the mean ridge over the Plains.  By early Sat, there has
become much strong guidance alignment for the base of the
elongating trof to stretch vertically crossing the Sangre de
Cristo Range of the Rockies into E CO/OK Panhandle.  The 00z UKMET
is a bit fast and north with the ejection away from the ensemble
run to run trends.   As the wave crosses the Plains, a non-UKMET
blend will suffice, but toward 84hrs the 12z GFS is first/fast to
weaken.  However, it has favorably trended to a similar
track/placement to the 12z NAM and 00z ECMWF/CMC to keep it
included at lower weighting.  

Upstream, a pair of lead shortwave troughs from the larger scale
cyclone over the southern Gulf of AK, advance to the West Coast in
the short-term.  The lead wave approaches and shears northeastward
toward the WA coast by late Fri into early Sat, weakening quickly.
 Guidance is fairly good in timing/strength, to have good
confidence in a general blend for this wave.  Quick on its heels,
a more neutral oriented shortwave crosses the OR/N CA coast late
Sat.   Here, only the 00z UKMET is showing greater amplification
and more concentric nature.  The 12z NAM/GFS are like usual,
partnered with slightly increased depth relative to the 00z
CMC/ECMWF, but all in all, even as they translate into the
Intermountain West well.  The 12z GFS weakens quickly, and the 12z
NAM/CMC are north of the ECMWF.  At this point, a non-UKMET blend
would suffice but confidence is average for this wave alone.  
Overall, non-UKMET is slightly above average as preferred blend. 

Model trends at
500 mb forecasts at