Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 238 PM EDT Mon Jul 20 2020 Valid Jul 20/1200 UTC thru Jul 24/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern tier of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 12Z ECMWF/GEFS and 00Z ECENS blend...after 48 hours Confidence: Slightly above average 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 models are in good agreement for most of the period, but by Thursday the 12Z GFS is a tad stronger and faster with its shortwave evolution across the Pacific Northwest and the energy exiting the Great Lakes and moving into the Northeast. Also the 12Z UKMET appears to be a tad too strong and too far south with its surface low crossing areas of the lower Great Lakes and Northeast Wednesday and Thursday. A general model blend should suffice through about 48 hours, but thereafter, a solution weighted toward the 12Z ECMWF/GEFS mean and 00Z ECENS mean will be preferred given better model clustering. The 12Z NAM and 12Z CMC are also at least close to this consensus. ...California/Southwest U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average A mid-level trough and embedded closed low is expected to advance toward the central CA coast by Tuesday and then move inland by late Wednesday. Meanwhile, ahead of this energy, there will be a separate mid-level trough axis and a more compact closed low circulation that evolves by Tuesday over the lower CO River Valley. This will then lift north and northeast with time through the eastern Great Basin and then the central Rockies going through Wednesday and Thursday. The models are in good agreement with the broader mass field evolution of both features of interest, however the 12Z GFS does appear to be a tad too progressive. The 00Z ECENS mean did favor the slightly slower consensus, although the new 12Z GEFS mean is a bit more progressive like the GFS. For now, a non-GFS blend will be preferred with both systems. It is worth noting that this energy over the Southwest 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 Four Corners region through the middle of the week. ...Mid-level easterly waves impacting the southern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above 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. Outside of the weaker 12Z UKMET with this wave activity, the remaining guidance is in reasonably good agreement in tracking this energy across the Gulf of Mexico and into Texas. It should be noted that by Thursday the guidance has been trending toward and coming into agreement on there being at least a weak area of low pressure over the western Gulf of Mexico. Based on the latest model clustering and spread, a non-UKMET blend will be preferred. 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 Orrison