Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Sat May 02 2020 Valid May 02/0000 UTC thru May 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave/surface low tracking near the U.S./Canadian border through Sunday, frontal zone through Ohio Valley; Northeast reinforcement/surface redevelopment Sunday to Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/ECMWF/CMC blend Confidence: Average ...07Z update... No significant changes noted in the 00Z ECMWF/CMC compared to their 12Z cycles, but the 00Z UKMET did make some faster adjustments to the timing of the northern portion of the shortwave trough reaching the Northeast Sunday night. The 00Z GFS continues to look too fast overall though with a 00Z NAM/ECMWF/CMC blend appearing best for this part of the country. ...previous discussion follows... The models are in fair agreement with timing, but the 00Z GFS becomes faster with the shortwave as it nears the Northeast. This is reflected in ensemble spaghetti plots and comparisons of the 00Z GFS to the latest deterministic consensus. While there are some differences with frontal placement across the MS Valley and to the west...with the 12Z UKMET slower in the Southern Plains, a non-00Z GFS blend of guidance appears reasonable at this point in time. ...Deep trough offshore the West Coast today with remnant shortwave energy moving through the Northern Rockies Sunday morning, northern High Plains surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/CMC/12Z ECMWF mean Confidence: Below average ...07Z update... There appears to be some better agreement with model convergence based on adjustments in the 00Z ECMWF/UKMET/CMC compared to their previous cycles. The 00Z ECMWF adjusted toward the consistent UKMET/CMC with the remnant shortwave across southern Alberta and Saskatchewan and all three models (ECMWF/UKMET/CMC) look better with vorticity in the zonal flow running from the Intermountain West into the Great Plains. Will continue to favor against the 00Z NAM/GFS given the latest available guidance. ...previous discussion follows... Large spread and poor run to run consistency make for below average forecast confidence. Initially, there is good agreement with the upper trough axis reaching Washington and Oregon but differences grow through Sunday with the remnant shortwave as it moves inland across the Northern Rockies and southwestern Canada. There are also embedded shortwaves within zonal flow across the Intermountain West with poor model agreement. The preference is to stay near the middle, away from outliers, while considering trends. This takes out the 00Z NAM and 00Z GFS which are faster with the upper trough into southern Alberta/Saskatchewan. The 12Z ECMWF is slightly more elongated with the trough axis toward the east by Monday morning, but the 12Z ECMWF mean is more in line with a middle ground. The 12Z UKMET is also middle ground but it lacks a more robust shortwave to the south as seen in the ensembles. The 12Z CMC is also a reasonable solution near the ECMWF and its mean. ...Next embedded shortwave in Gulf of AK gyre, clipping NW Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly below average ...07Z update... Adjustments from the 00Z ECMWF/UKMET/CMC favored a slower and more westward placement to the shortwave trough clipping the Pacific Northwest Monday night. The 00Z GEFS mean and 12Z ECMWF mean now are in general agreement with the 00Z deterministic model suite, with the 00Z UKMET/CMC remaining a bit more aggressive/faster with the shortwave trough axis compared to the 00Z NAM/GFS/ECMWF. ...previous discussion follows... Ensemble spaghetti heights show the 12Z UKMET as a fast outlier with the trough axis clipping the Pacific Northwest Monday night. The 12Z CMC also appears a bit fast while the 00Z NAM/GFS appear slow. Overall trends in the ensembles over their past four 12/00Z cycles support some slowing valid Tuesday morning which would leave the faster guidance out of the preference. While there is some potential for further slowing, prefer to stay toward the middle or the 12Z ECMWF/ECMWF mean. This solution is also consistent with other systems downstream across the CONUS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto