Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Wed May 13 2020 Valid May 13/1200 UTC thru May 17/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low over Alberta tracking to the Upper Great Lakes Thu...then across Northern New England Fri... ...Surface low moving from the north central US tonight into Northern New England Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/12Z ECMWF blend Confidence: Average The 12Z NAM/GFS are close to the consensus with the short wave energy swinging out of southern Alberta across the Upper Great Lakes by 15/12Z. After that time, the 12Z GFS becoming slower than the consensus (as it has been for the past three model cycles) with the short wave crossing Northern New England after 16/12Z. By contrast, the 12Z NAM maintains continuity with itself and the consensus with the timing of the short wave. The 12Z CMC remain close to the consensus timing, but remains flat with the short wave as it crosses Northern New England. The biggest change was with the 12Z UKMET, which sped up its short wave timing, becoming the easternmost member of the ensemble guidance. The 12Z GFS also remains slower with the surface wave as it exits the ME coast after 16/12Z, with the remainder of the guidance forming a fairly tight cluster with the surface low as it passes south of Nova Scotia. Given the slowness of the GFS, and the weakness of the 12Z CMC short wave and change in the 12Z UKMET, forecast confidence remains average through this period. ....Closed mid level low off the Pacific Northwest coast Thu...moving to the Northern Plains Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Both the 12Z NAM/GFS are close to the consensus taking the closed mid level low off the Pacific Northwest coast Thu and tracking it across the Northern Rockies before reaching the Northern Plains by 17/00Z. In fact, there is generally good clustering with this feature, so a general model blend is preferred with slightly above average forecast confidence. ...Mid level trough over northern Mexico Thu...moving into central TX Sat... ...Surface low over eastern NM/west TX Fri...crossing into central TX Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-12Z ECMWF model blend Confidence: Average The 12Z NAM/GFS are close to the model consensus developing a long wave trough over northern Mexico Thu...then tracking it eastward across NM into central TX Sat. While there are some minor differences in the placement/strength of the mid level system in central TX, there is a good clustering here, as it the surface system. The 12Z ECMWF now seems to be too far north with the mid level system over the Red River Valley, with enough change to remove it from the preference. Given the change with the 12Z ECMWF, forecast average has dropped to average. ...Low pressure developing near the Bahamas Fri night into Sat ... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF/12Z GEFS mean/00Z ECMWF mean blend Confidence: Average The 12Z GFS has backed off on its westward depiction of the surface wave closer to the FL east coast late Fri night, before moving the wave north of the Bahamas Sat. The eastward movement brings it closer to the 12Z GEFS mean/00Z ECMWF mean with the placement of the surface wave by 17/00Z. The 12Z ECMWF brought the surface wave back toward the 12Z GFS, enough so that it was introduced to the preferred blend. In contrast, the 12Z NAM/12Z UKMET look too far east with the system from Fri night into Sat, while the 12Z CMC has returned to a more western solution, as its mid level system tries to take of a negative tilt. Since the 12Z ECMWF has come back closer to the the 12Z GFS/ensemble cluster, forecast confidence has increased, but still remains average with this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes