Skip Navigation Links 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center



Follow the Weather Prediction Center on Facebook Follow the Weather Prediction Center on Twitter
NCEP Quarterly Newsletter
WPC Home
Analyses and Forecasts
   National High & Low
   WPC Discussions
   Surface Analysis
   Days ½-2½ CONUS
   Days 3-7 CONUS
   Days 4-8 Alaska
   Flood Outlook
   Winter Weather
   Storm Summaries
   Heat Index
   Tropical Products
   Daily Weather Map
   GIS Products
Current Watches/

Satellite and Radar Imagery
  GOES-East Satellite
  GOES-West Satellite
  National Radar
Product Archive
WPC Verification
   Medium Range
   Model Diagnostics
   Event Reviews
   Winter Weather
International Desks
Development and Training
WPC Overview
   About the WPC
   WPC History
   Other Sites
Meteorological Calculators
Contact Us
   About Our Site is the U.S. Government's official web portal to all federal, state, and local government web resources and services.
Model Diagnostics Discussion
(Caution: Version displayed is not the latest version. - Issued 1841Z Jul 18, 2018)
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
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
241 PM EDT Wed Jul 18 2018

Valid Jul 18/1200 UTC thru Jul 22/0000 UTC

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

12Z model evaluation including preference and forecast confidence
Preference in Eastern US: 12z UKMET/ECMWF blend
Confidence: Slightly below average

Preference in Pacific NW US: Non-UKMET blend
Confidence: Average

...Overall Model Analysis for the CONUS...

19z Update: The higher uncertainty has resolved somewhat with the
UKMET/ECMWF trending faster across the Midwest as presented by the
NAM/GFS initially, yet both remain slower than the NAM/GFS.   The
CMC is the clear outlier and is much further north.  This change
in transition has shifted the timing of the Gulf to East Coast
wave further west, but the GFS is a clear outlier fast and west
while the UKMET/CMC and ECMWF still lag the NAM.  Would favor
something closer to the ECMWF for this coastal wave and close to
the UKMET/ECMWF and perhaps some GFS for the Ohio Valley.

As for the west coast, the ECMWF is a bit less sheared and more
progressive than the GFS and paired with the 12z CMC fairly well. 
Only the UKMET is more compact and faster, as such would shy away
from the UKMET.  Confidence

Models continue to show the greatest differences with a trough
digging into the Upper Midwest by late in the week, with the NAM
standing out from the main deterministic suite, being faster and
closing off a new upper level center in the Ohio Valley by Sat
into Sun.  The GFS and UKMET trend this direction (GFS faster)
while the ECMWF/CMC slide more eastward as the older center
broadens over the Central Great Lakes.  If you will, a typical
timing orientation only exacerbated by the larger spreads.  This
timing/strengthening also draws the warm conveyor belt and
associated shortwave out of the eastern Gulf of Mexico, with
moderate spread.  The NAM/GFS are quick and tucked further west to
the coast compared to the ECMWF/UKMET and CMC.  The further
eastward shift, allows the CMC to be quite amplified due to
orientation with the upper jet/divergence maxima, making it a bit
less desired at this point.   The catalyst for the model spread
appear to be related to the strength/magnitude of upscale feedback
from convection development this evening over the Mid-Missouri
River valley.  The NAM develops a complex that digs
south-southeast across NEB toward the Low MO-Valley today, with a
stronger 3H jet rounding the base of the trof earlier.  This is
followed by the GFS and so on... the Hi-res CAMs would suggest
that the NAM is an outlier but modest spread including within the
HREF mean/NBM (at least in QPF fields) suggest a compromise
between the UKMET and ECMWF may be a good suggestion, but at lower
(slightly below average confidence).

Further west, the closed low in the Gulf of AK reaches central BC
by late Fri with good agreement, the spread begins to increase
based mainly on if/how far east the main inner core before it
breaks down a bit and stretches in the ridge weakness over the
west coast (in the larger scale).  Timing, once again, becomes the
main difference though compact/vort centers, manifest as well. 
The NAM is fast and the UKMET is very compact with the trailing
shortwave.  The CMC is slow to stretch, while the ECMWF/GFS are
more inline with each other and the ensemble suite (trends in the
day to day ensemble suite) that would suggest a better overall
blend.  Confidence is average for this area.

Model trends at
500 mb forecasts at