Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1242 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 NAM/GFS Evaluation Including Initial 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/00Z ECMWF/00Z UKMET 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 00Z CMC is close to the consensus timing, but remains flat with the short wave as it crosses Northern New England. 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 00Z CMC short wave, forecast confidence is climbing, but 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: General model blend Confidence: Slightly above 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 00Z ECMWF may be a bit on the weak side with the mid level system, and a bit further northeast with the surface low Sat, but at this point the differences are small enough to favor a general model blend with slightly above average confidence. ...Low pressure developing near the Bahamas Fri night into Sat ... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z GEFS mean/00Z ECMWF mean 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 00Z GEFS mean/00Z ECMWF mean with the placement of the surface wave by 17/00Z. In contrast, the 12Z NAM/00Z ECMWF look too far east with the system from Fri night into Sat, while the 00Z CMC is in between the two camps. From this vantage point, the consensus led by the 12Z GFS was favored with this system. However, there is still a fair amount of uncertainty here, for forecast confidence is average at best. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes