Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 108 AM EDT Wed May 27 2020 Valid May 27/0000 UTC thru May 30/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Reloading northern stream trough over northern Plains by Wednesday Crossing the Upper Midwest and Great Lakes Thursday/Friday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z ECMWF Confidence: Above average The models show a new northern stream trough amplifying over southern Canada and the northern Plains going through Wednesday. This energy should then move across the upper Midwest by Thursday and the Great Lakes by Friday. This will drive surface low pressure across southern Canada with a trailing cold front that will be crossing the northern Plains and Midwest, and reaching the East Coast by the end of the period. The model spread with the global models is relatively modest, but the bigger concern is with the 00Z NAM which is a bit slower with the overall trough progression, and also an outlier with its strong shortwave digging across the OH Valley Friday night and early Saturday. The better global model clustering and ensemble support would favor a blend of the 00Z GFS and 12Z ECMWF, and so a blend of these solutions will be preferred. Deep closed low over the southern Plains and lower MS Valley Weakening toward the OH/TN Valleys by Friday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models all agree in taking the cut-off upper low centered over the Red River of the South gradually off to the east through the Arklatex early Wednesday and adjacent areas of the lower MS Valley going through early Thursday. However, by late Thursday the system should weaken into an open wave and lift east-northeast toward the lower OH/TN Valleys and then become absorbed early Friday by the stronger northern stream troughing arriving across the Great Lakes. Model spread is minimal with this, so a general model blend will be preferred. Mid-level trough and surface low impacting the Southeast Energy reaching the southern/central Appalachians and Mid-Atlantic ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-ECMWF blend Confidence: Average A mid-level trough will be lifting north across the interior of the Southeast and through the southern Appalachians on Wednesday, with weakening remnants of this then reaching the central Appalachians and Mid-Atlantic by early Thursday. The 00Z NAM and 00Z GFS are again a tad more progressive in bringing this energy northward, with the non-NCEP models all a little slower. Meanwhile, at the surface, a low pressure center off the east coast of FL is expected to lift north and move inland across the Carolinas by late Wednesday. The 00Z NAM and 00Z GFS are also faster than the non-NCEP models with this, however the 12Z ECMWF is a left-moving outlier with its low track across central and northern GA. The 12Z CMC/UKMET models at least follow the 00Z NAM/GFS camp, but are a bit slower. Based on where the current low center, a compromise between slower faster camps is suggested, which will allow for the low to cross central to northeast coastal areas of SC and then lift north through central NC going through Wednesday night. So, from a mass field perspective considering the mid-level trough and the surface low situation, a non-ECMWF blend will be preferred. Subtropical closed low reaching central CA by Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models take a large upper low over the subtropical Pacific centered near 25.5N and 131.5W off to the northeast over the next few days, and bring it toward central CA by Saturday in response to stronger northern stream troughing impinging on it from upstream over the eastern Pacific. The models are in good agreement with the depth and timing of this system, so a general model blend will be preferred. Deep trough/closed low over the northeast Pacific ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average The models gradually drive a deep upper trough and associated closed low in across the northeast Pacific with an emphasis on the Gulf of AK by Saturday. The southern extension of the trough will be influencing the aforementioned upper low lifting northeast out of the subtropics, but will also be encroaching on the Pacific Northwest by Saturday. The 12Z UKMET is most out of phase with the height fall evolution and suggests a faster arrival of shortwave energy over the Pacific Northwest which the remaining models are well clustered in keeping offshore at least for this period. So, a non-UKMET blend will be preferred with the energy over the northeast Pacific basin for the time being for this period. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison