Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 246 AM EDT Mon Jun 1 2020 Valid Jun 1/0000 UTC thru Jun 4/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper level trough and cold front across the Eastern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate-High A pronounced upper level trough by early June standards will be in place across the eastern U.S. to begin the week with a pristine airmass in place, courtesy of a Canadian surface high. By Tuesday, warm air advection begins in earnest as a warm front surges eastward with the upper trough departing. Although there are some minor differences once the trough reaches eastern Canada, there is excellent agreement for the Northeast U.S. through Tuesday before the trough lifts out, so a general model blend can be recommended. Upper level low slowly lifting from northern Mexico into the southern Plains early this week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate-High A broad upper low currently situated over north-central Mexico will slowly lift northward across Texas through Tuesday evening, and then weakens as it enters the broad upper ridge axis across the Mid-South by Wednesday. The models are in close enough agreement on the main features to merit the use of a multi-deterministic model blend. Slow cut-off low developing west of Southern California through midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/NAM Confidence: Moderate-High With the flow pattern amplifying off the West Coast over the next few days, an upper level low is forecast to become pinched off from the westerlies farther north, and then remain nearly stationary through the end of the week, trapped by an upper ridge to its east. The models overall are improving with the evolution of this low, with the ECMWF/ECENS only slightly displaced to the west of the other guidance. Most of the ensemble spread is currently among the GEFS members, and overall the ensemble plots indicate the best support for the UKMET solution, and some of the ECENS can also be incorporated. With the arrival of the 00Z non-NCEP guidance, it appears that the GFS and the GEFS mean are slightly farther to east, whereas the other guidance is more clustered with the EC mean. Active flow pattern near the U.S./Canada border ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/00Z NAM/12Z ECENS mean Confidence: Moderate The westerlies on the northern periphery of the central U.S. ridge are expected to be rather active with three well defined shortwave disturbances tracking eastward near the U.S./Canada border through Wednesday. The first shortwave, currently near Alberta, will track eastward to western Ontario by Tuesday morning and weaken. This will be quickly followed by another disturbance that is currently near the Pacific Northwest coast and follow a similar path across south-central Canada. A third system will likely impinge upon the Pacific Northwest by Tuesday night and then rapidly track eastward along the International border. Given the quasi-zonal and progressive flow pattern in place across the region, this is where the greatest model differences currently exist. The 12Z CMC becomes slower with the first system by as early as 18Z Monday and then quickens dampens the trough, whereas the 00Z CMC has trended closer to the consensus there. The 00Z GFS is noted as a stronger solution for the second and third shortwaves moving through, and also suppresses the central U.S. ridge more compared to the other guidance. The 12 UKMET also becomes more amplified with the second system crossing the northern Great Lakes on Wednesday, and farther north with the surface low associated with the third system. The 00Z UKMET trended a little slower with this shortwave. Not much has changed with the 00Z ECMWF solution over this region. Taking all of these factors into account, blending the 12Z ECMWF/12Z ECENS/00Z NAM would work well as a starting point in the forecast process. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick