Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 327 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 Final Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Series of impulses on a pair of mid-level shortwaves 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: Non-NAM General Model Blend...less weight for 12Z GFS on Day 2 and the 12Z ECMWF on Day 3 Confidence: Average Convective complexes over Missouri are 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 as the features shift to the Ohio Valley through Tuesday night. A surface low will develop from the Missouri complex over the Mid-South tonight and track east southern Appalachians Tuesday before a coastal low develops along the Carolina Coast Tuesday night. The overall pattern of the surface low track and coastal development is in decent agreement and a general model blend is preferred through Tuesday/Day 1. As a surface low develops and shifts north off the Mid-Atlantic Wednesday differences in track arise. The 12Z ECMWF remains farthest east, particularly Wednesday night and on while the 12Z UKMET/CMC shifted west and are a good compromise between the ECMWF and the farther west 12Z GFS. The 12Z GFS is the quickest to develop, closing off at 500mb Tuesday night which allows a farther north track that comes into better alignment by Wednesday night. The 12Z NAM, however, tracks farther south from the Carolinas and is slower to develop/weaker and is enough of an outlier to be dismissed from the preference. ...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/ECMWF/UKMET 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 12Z ECMWF/GFS are in excellent agreement (along with their Day 2/3 QPF), so they are preferred. The 12Z UKMET inched north and into agreement with the ECMWF/GFS. The 12Z NAM is slightly south and the 12Z CMC remains even farther south. The 12Z UKMET remains slightly weaker with less of a closed low, but the track agreement warrants its inclusion in the preference. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson