Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 243 AM EDT Sat Jul 27 2019 Valid Jul 27/0000 UTC thru Jul 30/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation along with Final Confidence/Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern Tier of the U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z ECMWF and 00Z UKMET blend Confidence: Slightly above average ...07Z update... Concerning the second shortwave and the related surface low tracking through the Upper Mississippi Valley into the Great Lakes region, the 00Z UKMET slowed down toward the consensus but the 00Z CMC shifted west and strengthened relative to its previous run. The 00Z ECMWF remained similar but with greater adjustments by Monday night into James Bay concerning the surface low. The end result is for a 00Z ECMWF/NAM/UKMET blend given their agreement to one another than the ensemble means. ...previous discussion follows... Models show that two shortwaves should skirt across the CONUS Northern Tier during the short range. The first wave is forecast to move from the Upper Midwest/Great Lakes early this morning to central Quebec Sunday afternoon with the trailing frontal boundary lingering across the north central U.S. The second shortwave and associated cold front are currently moving into western British Columbia and should reach the Northern Plains/Upper Midwest by Sunday and the Great Lakes late Monday. There remain some minor differences with the second shortwave, mainly from the 00Z GFS which affects its surface low strength/placement across the northern Great Plains Sunday morning. Better agreement exists with the non-00Z GFS guidance, but the 12Z UKMET is slightly faster than the consensus for a time on Sunday. A blend of the 00Z NAM, 12Z ECMWF and 12Z CMC agrees best with the ensemble means. ...Remainder of the CONUS including the Southwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average ...07Z update... Changes with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles were minor across the remainder of the CONUS with no change to the previous thinking concerning the preference. ...previous discussion follows... No significant mass field differences were noted with the southwestern ridge and the remainder of the U.S., with a general model blend preferred to iron out smaller scale differences. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Otto