Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 117 PM EDT Wed Jul 22 2020 Valid Jul 22/1200 UTC thru Jul 26/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Broad Great Lakes trough axis and corresponding cold front impacting the OH Valley, Northeast and Mid-Atlantic into Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 12Z GFS and 00Z ECMWF blend Confidence: Average Timing differences regarding the eastward tracking Great Lakes trough show up late Thursday with the 00Z UKMET slowing relative to the remaining deterministic/ensemble consensus. The 00Z UKMET also shows the strongest depiction of the central CONUS ridge which may have impacts on downstream troughing across the Northeast over the weekend. Meanwhile, the 00Z CMC stands out with greater amplification of the trough axis near the East Coast Saturday morning with ensemble spaghetti plots of the 500 mb 588 dam height contour supporting greater clustering around the 12Z NAM, 12Z GFS and 00Z ECMWF models. The 06Z GEFS mean continues to stand out with greater amplification of the mid-level trough over the East Coast as well. Therefore, the preference centers around greater ensemble/deterministic support and staying clear of outliers since trends over the past four 12/00Z cycles seem to support the middle ground. ...Mid-upper level troughing impacting the Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average After the departure of a shortwave trough over Washington (Thursday morning), the southern portion of a second trough is expected to pass over the Northwest on Friday/Saturday before advancing eastward toward the northern High Plains for Saturday evening. The 12Z NAM/GFS are slightly faster and stronger with the second trough axis affecting the Northwest on Saturday compared to the 00Z ECMWF/UKMET/CMC. However, the ensemble means appear to split the difference with a general model blend likely best across the northwestern U.S. ...California/Southwest U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average A series of systems will impact the southwestern U.S. over the next few days. First, a negatively tilted mid-level trough axis will track from UT this morning into the northern High Plains for Thursday evening. Minor timing differences here, with the 00Z ECMWF slightly faster and 00Z CMC slightly slower. Second, a closed low over central CA is expected to weaken with an eastward or southeastward progression into interior portions of the West. After the departure of the closed low from CA, another disturbance (weaker than the previous low) will reach the CA coast late on Saturday. The models all show decent agreement with all of these features with no single model differing enough to exclude it from the preference. ...Easterly wave moving through the Gulf of Mexico... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 12Z GFS, 00Z ECMWF blend Confidence: Slightly below average All of the models show a similar depiction regarding a low to mid-level trough axis/low advancing westward across the Gulf of Mexico through Saturday, reaching the Texas Coast sometime Friday night or Saturday morning. The 00Z UKMET is the strongest of the latest model guidance, followed next by the 00Z CMC. The NAM/GFS/ECMWF show varying degrees of strength but similar position and timing over the next couple of days. The 12Z GFS is a bit weaker and the 00Z ECMWF stalls the system near the Middle Texas Coast on Saturday which is not supported in a majority of the available ensemble guidance. The 12Z NAM is also a bit weaker but splits the difference in strength between the weaker 12Z GFS and stronger 00Z ECMWF. The National Hurricane Center is monitoring this area for tropical cyclone formation, showing a 50 percent chance of development over the next 5 days. It should be noted that scatter low ensemble plot spread is moderate and both deterministic and ensemble guidance has shown a unanimous trend to be slower with the westward progression of the low level wave compared to model runs from yesterday. 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 Otto