Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1257 AM EDT Sun Jul 19 2020 Valid Jul 19/0000 UTC thru Jul 22/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Preliminary Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern tier of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM Confidence: Average The northern tier of the CONUS will remain active with fast flow atop an expansive mid-level ridge covering much of the central and southern U.S. A pair of shortwave troughs though will be advancing across the northern Plains and upper Midwest going through early next week. The most important of these shortwaves will drop out of the Pac NW today and race into the Northern Plains. As this feature interacts with a surface baroclinic gradient along a stationary boundary, it is likely to become convectively enhanced and dig into the expansive ridge to cause height falls across the Central Plains. There exists considerable spread in the amplitude of the shortwave, with the NAM possibly suffering from some convective feedback due to its strength, while the ECMWF is on the other end of the envelope with a very flat, broad trough late Monday. While the NAM is likely too strong, it does have some support from the GFS and GEFS mean, and the pattern appears favorable for an MCS/convective enhancement of the shortwave. Including the GEFS/GFS with the non-NCEP suite will produce better amplification of the mid-level height field D2 into D3, but not as robust as shown by the NAM. ...California/Southwest U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM/CMC Confidence: Average A closed low developing within a larger trough across the Southwest will meander near the coast of CA Monday into Tuesday. The NAM is the slowest to develop the cutoff, while the CMC is much weaker than the global consensus showing little height falls off CA at all. The trend over the past few runs of the globals has been for a deeper solution, with the closed low moving onshore CA during D3. A blend of the non-NAM/CMC is reasonable due to good clustering, with most weight on the ECMWF/ECENS due to good continuity. ...Mid-level easterly waves impacting the southern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM, little UKMET D3 Confidence: Average A series of mid-level troughs/easterly waves with at least a modest surface reflection will move across the Gulf Coast region through Tuesday. The NAM remains strong with the 700mb amplitude of these features compared to consensus, and is also slow with the westward progression. The UKMET is a tad north with these features, especially the secondary wave lifting near FL on D3 when its weight in the blend should be very conservative. The other globals are well clustered and generally weak/flat with these waves as they push towards the TX/LA coast and into FL. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Weiss