Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1223 PM EDT Thu Mar 21 2019 Valid Mar 21/1200 UTC thru Mar 25/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough and Coastal Low in the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM and 00z ECMWF/CMC (weight to EC/NAM). Confidence: Slightly above average The first phasing of shortwaves into a more concentric closed low over the Mid-Atlantic has occurred with surface deepening on going currently. Upstream jet/nose of jet shortwave is taking shape over East Central Canada dropping southward. The 00z UKMET was already off-balance compared to observations (stronger lead wave) to have confidence for its inclusion in an otherwise tightening guidance suite. The 12z GFS showed some typical negative bias, especially at 7H with the last few runs trending a bit too fast particularly with upstream amplification that should slow, increase binary interaction across New England. After the wobble/redevelopment along coastal ME/Gulf of ME...the GFS remains fast to exit northeast as well. Some inclusion would be alright, but will favor a 12z NAM and 00z ECMWF/CMC blend. Confidence given the higher packing is slightly above average. ...Remainder of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Average to slightly above average The weakly formed closed low over UT/AZ will continue to advance into the mean ridge over the Plains. By early Sat, there has become much strong guidance alignment for the base of the elongating trof to stretch vertically crossing the Sangre de Cristo Range of the Rockies into E CO/OK Panhandle. The 00z UKMET is a bit fast and north with the ejection away from the ensemble run to run trends. As the wave crosses the Plains, a non-UKMET blend will suffice, but toward 84hrs the 12z GFS is first/fast to weaken. However, it has favorably trended to a similar track/placement to the 12z NAM and 00z ECMWF/CMC to keep it included at lower weighting. Upstream, a pair of lead shortwave troughs from the larger scale cyclone over the southern Gulf of AK, advance to the West Coast in the short-term. The lead wave approaches and shears northeastward toward the WA coast by late Fri into early Sat, weakening quickly. Guidance is fairly good in timing/strength, to have good confidence in a general blend for this wave. Quick on its heels, a more neutral oriented shortwave crosses the OR/N CA coast late Sat. Here, only the 00z UKMET is showing greater amplification and more concentric nature. The 12z NAM/GFS are like usual, partnered with slightly increased depth relative to the 00z CMC/ECMWF, but all in all, even as they translate into the Intermountain West well. The 12z GFS weakens quickly, and the 12z NAM/CMC are north of the ECMWF. At this point, a non-UKMET blend would suffice but confidence is average for this wave alone. Overall, non-UKMET is slightly above average as preferred blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina