Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 236 PM EDT Thu May 14 2020 Valid May 14/1200 UTC thru May 18/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low over the Northern Plains and Upper Great Lakes tonight...crossing Northern New England Fri... ...Surface low moving from the Northern Plains tonight into Northern New England Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-12Z NAM blend Confidence: Slightly above average The 12Z NAM/GFS are close to the consensus with the short wave energy tracking from the International border of ND across the Upper Great lakes today into early tonight. After that time, the 12Z NAM becomes faster and deeper with the short wave crossing ME and Nova Scotia Fri. In response to the short wave, the 12Z NAM also appears to be too deep/too far north with the surface low crossing northern New England Fri. The 12Z GFS is closer to the consensus throughout the period with the short wave, but may be a tad slow with the surface low crossing ME (as it has been for the past few model cycles). At this point, with fairly good clustering (outside of the NAM), a non-12Z NAM was the preferred blended with increasing forecast confidence. ....Closed mid level low off the Pacific Northwest today...moving to the Northern Plains Sat and the upper Great Lakes Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/12Z ECMWF/12Z UKMET blend Confidence: Slightly below average The 12Z NAM/GFS are close to the consensus taking the closed mid level low from just off the Pacific Northwest coast this afternoon across the Northern Plains Sat. After that time, the 12Z GFS slows with the mid level system, and drops it southwest of the consensus (in a position nearly identical to the 12Z CMC) by 18/00Z. As a result of the mid level system slowing, the 12Z GFS looks a bit slow with the surface low position by that time. In contrast, the 12Z NAM remains close to the loose consensus (which includes the 12Z ECMWF/00Z ECMWF mean/12Z GEFS mean) taking the closed mid level low over WI/MI by the end of the period. Fortunately, the 12Z ECMWF has come into better agreement with the surface low and associated front. At this point, the preferred blend is the 12Z NAM/12Z ECMWF (with ensemble support), though the 12Z GFS solution is not unusable, especially with the surface systems. Due to the spread not only at the surface but in the mid levels, forecast confidence is slightly below average. ...Developing long wave trough moving from northern Mexico into central TX Sat...then into the Lower MS Valley Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-12Z NAM blend Confidence: Average Both the 12Z NAM/GFS are close to the consensus taking a developing long wave trough out of northern Mexico tonight and Fri into central TX Sat. From this point, the 12Z NAM slows with a closing mid level low hanging back over east TX Sun. The 12Z GFS is closer to the remainder of the guidance taking the long wave trough across the Lower MS Valley late Sat into Sun. The 12Z UKMET sped up its solution with the long wave trough, leaving only the 12Z NAM on the slow side of the guidance envelope. With no obvious mechanism for closing the mid level system off over east TX, at this point the 12Z NAM looks too slow with its depiction of the mid level system. Overall, a non-12Z NAM blend is preferred with this system. Given the spread still in place with this system (as well as the overall trend of slowing the long wave trough), forecast confidence has increased to average. ...Low pressure developing near the Bahamas Fri night into Sat ... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF/00Z ECMWF mean blend Confidence: Slightly above average The 12Z NAM/GFS are close with the developing surface low as it tracks from southeast FL Fri/Fri night to a position north of the Bahamas by 18/00Z. By that time, the 12Z NAM bit further east that the 12Z GFS/12Z ECMWF/00Z ECMWF ensemble mean, while the 12Z CMC remains further west of that position. Only the 12Z UKMET seems to be too far from the consensus, taking this system much further east (as has been its trend the past three cycles). However, based on consistency of the GFS/ECMWF/ECMWF ensemble mean over the past three model cycles, the 12Z GFS/12Z ECMWF/00Z ECMWF mean comprise the preferred blend. With only the 12Z UKMET straying from the tightening model cluster with this system, forecast confidence is slightly above average. ...Large closed mid level low drifting toward the Pacific Northwest Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average There is generally good model agreement taking a closed mid level low from 48N 161W this afternoon and tracking it to a position of the southern OR/northern CA coast by 18/00z. Given the impressive model clustering, a general model blend is preferred with above average forecast confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes