Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1243 PM EDT Mon May 11 2020 Valid May 11/1200 UTC thru May 15/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level trough amplifying across the Northeast with accompanying surface low through Tuesday morning... ...Shortwave moving across the Great Lakes and Northeast Tuesday and Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend, least weight on 00Z CMC Confidence: Average A lead shortwave moving through the Northeast with an attendant surface low shows relatively good agreement through Tuesday morning, but the 00Z CMC is slower and west of the remaining deterministic and ensemble means. Late Tuesday into Wednesday, a second, compact mid-level closed low is forecast to sweep across New England atop a cold and post-frontal environment. There are only minor timing and latitude differences in place with this second shortwave so a general model blend will work overall for the Northeast. ...Shortwave energy shearing across the Southern Plains Monday night and Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average A subtle shortwave will move through portions of the Desert Southwest today before crossing into the southern Plains and lower Mississippi Valley early next week. Regarding mass fields, only minor differences are noted with the latest model guidance. The differences in precipitation are driven more by mesoscale factors which fall outside the scope of this discussion. ...Upper trough/closed low along the Northwest Coast through Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-00Z CMC blend Confidence: Average The models are in fair agreement with the mean closed mid-level low position off of the Pacific Northwest through Wednesday, and as the shortwave moves inland toward the end of the week. Only the 00Z CMC differed significantly enough with the center of the closed low being displaced farther offshore compared to the good agreement noted in the remaining deterministic and ensemble guidance. ...Upper low closing off over western Canada on Tuesday before moving east through the Canadian Prairie Wednesday-Thursday... ...Surface cyclone moving trough the north-central U.S. Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 12Z GFS, 00Z CMC blend Confidence: Average A combination of shortwaves will impact the north-central U.S. from Wednesday into Thursday. The first will be relatively weak, emanating from ID/MT/WY Tuesday night. The 00Z ECMWF is weaker with this feature compared to the remaining model consensus and is noted with the 00Z ECMWF surface reflection differing from the remaining guidance. The 00Z UKMET is similar to the remaining guidance with this feature but differs up north with its handling of a shortwave moving across southwestern Canada. With a more elongated shortwave noted in the 00Z UKMET, a piece of shortwave energy is left behind near northwestern Montana compared to the remaining consensus. Overall, decent agreement is in place with the 12Z NAM, 12Z GFS and 00Z CMC overall for the north-central U.S., but aspects of the 00Z ECMWF and 00Z UKMET may be usable at times. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto