Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 229 AM EDT Thu Apr 12 2018 Valid Apr 12/0000 UTC thru Apr 15/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large-scale trough moving across the West... ...Amplifying across Plains by Friday and Saturday... ...Associated strong surface low in the Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z UKMET, 00Z ECMWF and 00Z GEFS mean Confidence: Average The models agree in bringing a large scale trough in across the West through Thursday and then amplifying the height falls over the Plains Friday and Saturday as a strong closed low evolves. This will drive a rather intense area of low pressure over the central High Plains by late Thursday which is expected to gradually move east across the middle Mississippi Valley through Saturday and then the Ohio Valley on Sunday. The model spread is minimal as the energy traverses the West, but as the energy crosses the Plains and especially the middle Mississippi Valley, the 00Z NAM begins to lag the global model consensus. The NAM also tends to take its surface low a bit farther south compared to the global models. The 00Z GFS this run has trended a little slower compared to its previous run and is now just a little faster than a consensus of the 00Z UKMET and 00Z ECMWF. The 00Z CMC ends up still being somewhat of a weaker outlier by the end of the period, but it has trended a bit slower and its low placement is close to that of the model consensus. Collectively, the global models have trended slower with the 00Z cycle, and even the 00Z GEFS mean has trended slower as well. Given that the latest GEFS mean is slower than the deterministic GFS and is a bit more aligned with the UKMET and ECMWF, the preference will be to swap out the GFS for the GEFS mean for this latest update. Thus a blend of the UKMET, ECMWF and GEFS mean will be preferred. ...Low amplitude northern stream wave crossing the Great Lakes/Northeast through Thursday Night... ...Associated weak surface low following a similar path... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The models are generally in good agreement with the details of this shortwave, however, the 00Z CMC is a little flat with it compared to the model consensus. Consequently, the CMC eventually ends up just a tad weaker with its surface reflection. A non-CMC consensus will be preferred. ...Deep trough and upper level low slowly dropping toward the Pacific Northwest by this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average A relatively stationary closed upper low over the Gulf of Alaska is expected to begin to devolve and dig southeast as an amplified trough toward the Pacific Northwest this weekend. The models still show some subtle differences but overall are in quite good agreement with the larger scale pattern, so a general model blend is preferred at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison