Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 334 AM EDT Mon Jul 20 2020 Valid Jul 20/0000 UTC thru Jul 23/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Final Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern tier of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF/ECENS/GEFS blend Confidence: Average 07Z Update: The UKMET has become an outlier with its height pattern, shifting shortwaves and related convection further north than the remaining guidance. The ECMWF remained in line with its previous run and its ensembles, which is also pretty well correlated with the GEFS mean. Previous Discussion: Fast flow atop an expansive ridge will persist across the northern tier of the CONUS going through the middle of the week. Embedded within this flow, a series of weak to moderate shortwaves will traverse west to east, causing at least subtle amplification of troughs into the ridge to the south. The NAM continues its trend of the last several runs being too amplified and too slow with most of these shortwaves, while the 00Z GFS has also trended a bit stronger, especially with the feature lifting across the Northern Plains into the Great Lakes Tuesday into Wednesday. In the fast/more zonal flow, the weaker solutions featured by the non-NCEP models seems more reasonable and is preferred. Note that there is some potential for any of these shortwaves to drive MCS development and become convectively enhanced/an MCV across the middle of the country. The NAM is most aggressive with this development, and while this is not preferred, it does indicate some potential for this evolution. ...California/Southwest U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC/UKMET blend Confidence: Slightly above average 07Z Update: The UKMET appears to be experiencing its common bias of being too aggressive with the ridge, leading to higher heights across the CONUS and impacting the amplitude of the trough near CA and the shortwave moving into the Four Corners. Otherwise, the 00Z ECMWF can be used while the 00Z CMC continues its concerns from 12Z. Previous Discussion: A broad mid-level trough is likely to develop across the Southwest beginning Tuesday, with an embedded closed low progged to move along the central CA coast into Wednesday. Downstream of this closed low, a secondary shortwave ridge/trough combination is likely to amplify across the eastern Great Basin and advect to the Four Corners by Wednesday. The models are in generally good agreement with the overall structure, amplitude, and evolution of this trough. However, the CMC is the notable outlier depicting lowered heights across much of the region compared to consensus, and also suggests greater amplification of the downstream shortwave into the Four Corners Wednesday. It is worth noting that this energy coupled with an influx of deepening monsoonal moisture from northern Mexico and Rio Grande Valley is expected to help drive an uptick in the coverage and intensity of monsoonal convection across the Southwest going through the middle of the week. ...Mid-level easterly waves impacting the southern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/00Z ECMWF 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 midweek. The NAM continues to be strong with each individual wave, while the UKMET suppresses most of the amplitude due to a stronger ridge to the north. However, the final wave, which is progged to be near the central Gulf of Mexico at the end of the forecast period, does feature more significant amplitude from most of the globals, so the 00Z NAM could be included back into the blend the latter half of D3. 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