Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Sat May 09 2020 Valid May 09/0000 UTC thru May 12/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Final Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deepening surface low moving along the Northeast Coast... ...Dual Shortwaves moving out of Canada and around periphery of Eastern North American Low ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average Flow over North America is expected to feature an omega block with lows near 45N/145W and over the Northeast U.S. and adjacent portions of Canada...with a ridge extending from the Western U.S. northward across western Canada as far north as the Yukon and Northwest Territories. The models have a decent handle on the large-scale pattern. The agreement persists as far down into the details of the Northeast U.S. low being anomalously deep (by nearly 4 standardized anomalies greater than climatology) and magnitude of an anomalously strong mid- and upper-level jet will be supporting the low. The 09/00Z NCEP guidance remained in good agreement with the 08/12Z ECMWF and UKMET with respect to the low as well as in regards to two shortwaves that drop out of Canada in succession within northerly flow between the ridge to the west and the low to the east...and then rotating around the periphery of the broader circulation of the low on Sunday and Monday as it makes its way toward Labrador. There are some difference with respect to timing and the degree to which the shortwaves can interact and sharpen a broader trough. In this case, think a non-Canadian blend will work to minimize some of the timing differences. A second shortwave which initially begins north of Hudson Bay on Sunday may be too strong at 500 mb in the 09/00Z ECMWF by the time it reaches the northern Great Lakes late Monday. ...Shortwave energy crossing southern CA by Sun morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A weak shortwave lifting onshore southern CA Saturday will weaken as it shifts eastward into the Desert Southwest on Sunday. The overall envelope of solutions remains minimal..and a general model blend should minimize what differences in timing and magnitude there are. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Bann