Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1247 PM EDT Mon May 04 2020 Valid May 04/1200 UTC thru May 08/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Initial Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Series of impulses on a mid-level shortwave tracking across the northern/central Great Plains and the Ohio Valley through Tuesday night... ...These waves consolidate over the Mid-Atlantic Wednesday and track off New England... Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend...less weight for 12Z GFS/NAM and 00Z CMC Days 2/3 Confidence: Average The broad area of convection driven by mid-level impulses (as well as creating new ones) across the north-central portion of the CONUS is ahead of a mid-level wave over the central Great Plains which will be reinforced by energy coming from a low over the western Canadian Prairies. A surface low will develop over the Mid-South tonight ahead of the central Plains trough. Given the convective nature there are inherit differences with the global models. However, the overall pattern of the surface low track is in decent agreement among global guidance across the southern Appalachians and Carolinas and a general model blend is preferred through Tuesday/Day 1. As a surface low organizes off the Mid-Atlantic on Wednesday, there are essentially two camps; a farther east 00Z UKMET/ECMWF which agree with the 00Z ECENS mean, and a farther west from the 12Z GFS/NAM and 00Z CMC along with the 06Z GEFS mean. As the NAM and GFS have trended this way and the difference is not too great, will include them in the preference for now and see what the 12Z CMC/UKMET/ECMWF do in terms of surface low track. The impact is to QPF in southeast New England which would be heavier in a farther west track. ...Shortwave trough brushing Pacific Northwest coast tonight... ...Mid-level shortwave moving from Pacific Northwest Coast Tuesday night across the northern Rockies Wednesday night and the northern Plains Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF Confidence: Slightly Above Average A shortwave trough will pivot around a broad upper level gyre over the Gulf of Alaska and clip the Pacific Northwest coast tonight. There are no outliers with this feature. The next shortwave trough is much stronger/amplified as it crosses the WA/OR coast Tuesday night and the ID/MT Rockies Wednesday night. There is little difference among guidance here as the trough takes on a negative tilt and closes off into a low over MT. The 00Z ECMWF/ECENS mean and the 12Z GFS are in excellent agreement (along with their Day 2/3 QPF), so they are preferred. Notes about this low evolution are that the rest of the guidance is south, the 12Z NAM and 00Z UKMET are slightly south and the 00Z CMC is farther south. The 00Z UKMET/CMC also slightly weaker with less of a closed low. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson