Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 132 PM EST Sat Feb 23 2019 Valid Feb 23/1200 UTC thru Feb 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Pacific Northwest/N California... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS through 26/00z 12z UKMET/CMC blend after Confidence: Slightly above average thru 26/00z Average 19z update: The 12z ECMWF/CMC and UKMET all trended toward a slower progression to the Central Pacific wave moving east and interacting with the Pacific Northwest trof on Day 3. The ECMWF still is quite amplified with the Pacific Trof allowing for slightly faster solution than the CMC or UKMET but now slower than the NAM. So with the 12z GFS a bit faster than the 06z, there is growing agreement with the GFS, UKMET/CMC. Still, the GFS may be a bit too fast still and so will continue favoring the 12z UKMET/CMC at increased confidence (Average). Remainder of CONUS: ~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 12z GFS/NAM continue the considerably better mass agreement including the coastal surface cyclone development into northeast New England late Sunday into Monday. The main model spread will exist with the fairly static Pacific Northwest trof that will start to form later today into tomorrow morning. Initially model spread is minor and tied to traditional timing differences with the GFS/NAM a bit fast shedding easterly energy into the confluent flow over the Northern High Plains on Monday...the UKMET follows suit. The amplifying Omega block in the Gulf of AK, helps to lead to slightly different distortion of the mid-level flow. As the trof, reconstitutes toward a deeper closed low again on Monday with surface cyclogenesis coming ashore in OR; the 12z GFS is an outlier, surging the shortwave in the mean trof faster through than any other guidance. This is also true with the block's anticyclone, where the GFS is much weaker and therefore tilts eastward earlier. This leads to less binary interaction with a fairly strong shortwave in the Central Pacific, late Monday into Tuesday. The run to run ensemble suite, while denoting the GFS as an earlier (fast) outlier, does show by Day 3 it is closer to the fold. It is the 00z ECMWF that is the clear outlier in the ensemble suite by the end of Day 3, with a strong, concentric and broad closed low off the coast, as it is the only guidance to absorb the Central Pacific shortwave. The 00z CMC is closer to the ECMWF, but with reduced distance between the two features, there is no collection of the wave, allowing for the Central Pacific wave to eject east into CA. This seems more realistic (especially given the ensemble suite over the last few cycles). The 00z UKMET being a bit slower initially, but also a bit weaker with the Central Pacific wave presents the most middle ground solution with some similarities to the CMC. The 12z NAM, while initially strong does not show some of the negative influences of being too fast but like the ECMWF eventually is very deep just a bit slower with the Central Pacific shortwave and is the deepest by Day 3 (typical of late term forecast bias). While the differences in mass field are small, they do impact the timing/orientation of the atmospheric river surges into coastal OR/CA. As such will initially favor a non-GFS blend through 26/00z (second surface low on Mon), but will shift to a 00z UKMET/CMC blend thereafter. Confidence is slightly above average through 26/00z but reduces to slightly below average thereafter given the modest spread and lack of "most reliable" guidance in the GFS/ECMWF. Elsewhere, broad zonal loosely packed height fields will exist with small variation with little overall consequence to sensible weather fields. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina