Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1236 PM EDT Fri May 25 2018 Valid May 25/1200 UTC thru May 29/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS evaluation including preliminary preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Subtropical Storm Alberto... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: NHC Track The 12Z NAM and 12Z GFS start close to the consensus with the surface system near the Yucatan Peninsula Fri afternoon, and remain close to the consensus through Sun morning. After that time, the 12Z NAM becomes faster than the consensus and further west, as the ridging off the Southeast coast pushes it eastward. The 12Z GFS has also shown a westward shift in its track, for the same reasons as the 12z NAM. However, the 12Z GFS as also slowed a bit, as the mid level reflection has slowed as well. At this point, the 00z ECMWF/00z ECMWF/06Z GEFS Mean are closest to the track from NHC with Alberto. ...Shortwave and surface wave clipping New England late Fri into Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 28/00z Non-12Z NAM blend after 28/00z Confidence: Slightly above average Both the 12Z NAM/GFS are close to the consensus as they take the short wave energy over southern Manitoba Fri afternoon to a position over western Quebec by Sun morning...as it weakens. The frontal zone and surface wave weakens as they cross Quebec, and the 12Z NAM/GFS are close to the consensus with this feature as well. After 28/00Z, the 12Z NAM becomes faster with the short wave energy as it crosses northern New England. This appears to be due to the influence of short wave energy in the fast mid level flow over northern Ontario and northern Quebec, where the remainder of the guidance is slower with this packet of short wave energy. As a result, the 12Z NAM is faster with the surface wave that develops on a frontal boundary southeast of Nantucket Island MA and tracks well south of Nova Scotia. Because of this, the 12Z NAM is excluded from the preference. ...Closed low central CA coast...crossing the Great Basin Sun into Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Both the 12Z NAM/GFS are close to the consensus as they takes the closed mid level low from the central CA coast Fri afternoon to a position over NV/UT by 28/00z. After that time, the 12Z GFS becomes a bit faster than the consensus, especially toward 29/00Z (as does the 00Z UKMET). At this point, with the timing differences occurring late in the period, a general model blend is still preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes