Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 416 AM EDT Sun May 31 2020 Valid May 31/0000 UTC thru Jun 3/1200 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 through 00Z Tuesday, then 00Z ECMWF/GFS/UKMET blend Confidence: Above average An amplified upper level trough will continue to build in across the eastern U.S. through the beginning of the week, with the surface cold front continuing to move farther offshore and a high quality airmass settling in across much of the region. Similar to last night, the models are in very good agreement through about 00Z Tuesday with the CMC remaining slightly weaker and a little faster with the trough. By Tuesday morning, an upper low is likely to evolve from the trough over the Nova Scotia region. A blend of the ECMWF, GFS, and UKMET should work well beyond 00Z Tuesday since there is good overall ensemble support for this. Upper level low slowly lifting from northern Mexico into the southern Plains Saturday-Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models are in generally good agreement indicating a broad upper low lifting north from northern Mexico into West Texas by Tuesday morning, before continuing northeast towards Oklahoma on Tuesday night. There is not much of a surface reflection of this in terms of the sea level pressure fields. A general model blend will suffice for this upper level low and trough. Shortwave lifting across the Pacific Northwest and then across southern Canada ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/ECMWF Confidence: Average Models remain in good agreement into early Monday as the system continues across southwest Canada. Model differences become more apparent by Tuesday morning as the system reaches Manitoba and western Ontario. As the system begins to round the top of the upper ridge, the ECMWF becomes faster than the GFS, and the other guidance tends to weaken the shortwave faster. It appears more likely that the system will maintain strength longer than the UKMET/NAM/CMC, so a blend of the GFS/ECMWF would work well as a starting point in the forecast process. Upper level trough moving from the Pacific Northwest to the northern Plains and Upper Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/EC mean Confidence: Slightly below average A second shortwave disturbance follow behind the current one across the Pacific Northwest on Monday, and the models are in generally good agreement through Monday as the system moves inland. This will sustain a surface low along a frontal boundary across the Dakotas. Differences become more apparent as the system moves downstream towards the northern Plains, with the UKMET, ECMWF and the 00Z EC Ensemble Mean becoming faster than the NCEP guidance and CMC. Ensemble spread tends to favor the faster solutions for the time being. Cut-off low developing west of Southern California early in the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Shortwave energy dropping southeast across the eastern Pacific is expected to develop a closed low off the Southern California and northern Baja coast for the early to middle part of the week. The models have improved in their depiction of the upper low evolution. The EC and its ensemble mean are still slightly to the west compared to the other guidance by Wednesday morning, while all similar in magnitude. Therefore a general model blend should suffice for this region. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick