Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 239 AM EDT Fri Mar 30 2018 Valid Mar 30/0000 UTC thru Apr 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...Including Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low lifting northeast through New England today and associated trailing cold front down the East Coast... ...Secondary shortwave pushing from the Mid Mississippi Valley to the Mid Atlantic today behind primary cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average Overall models show a high degree of similarity with the mass fields along the East Coast today with the departing low and the cold front sweeping east. Thus, there is above average confidence in a general model blend. The one exception is the 12Z UKMET, which seems to depict a stronger secondary shortwave pushing through the Ohio Valley later today, which leads to slightly more downstream ridge amplification (higher heights) and slower cold front progression. ...Shortwave digging into the Northwest today with a surface low dropping down over Montana... ...Surface low evolution across the Upper Midwest/Great Lakes through Saturday... ...Trailing cold front sweeping across the Northeast by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Compared with the model spread even two or three model cycles ago, the models have moved into much better agreement with this system and now offer very similar forecasts. The timing of the shortwave is very close, with the primary difference coming from the 00Z NAM which has a more amplified wave. This leads to one of the deeper surface lows (albeit only by 1-2 millibars) among the operational models, and on the northwest extent of model spread. With mostly small differences remaining in the model mass fields, a general model blend is preferred. ...Low-amplitude shortwave reaching the Oregon coast on Saturday... ...Becoming increasingly sheared out toward the High Plains by Sunday and Mid Atlantic by Sunday Night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average As the shortwave arrives on the West Coast, the 12Z CMC shows substantially higher heights than other models. At 500mb, the heights are around 30m higher than the consensus of the remaining models. Otherwise, there are limited differences between the other models with this low amplitude wave that will quickly transit the CONUS. The preference is for a general blend of these remaining models, but to exclude the CMC given its large differences and lack of support from other models. ...Large scale trough digging into the Northwest by late weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF Confidence: Average Through the short term forecast period over the CONUS, there are probably the largest model differences with this system. The 00Z NAM and 12Z UKMET more aggressively dig a stronger wave further southeast into the Intermountain West by Monday morning, while the 12Z CMC is substantially flatter. Over Montana, this leads to 500mb height differences around 150-200m between the NAM/UKMET consensus and the CMC. This has additional effects in the model forecasts, with the UKMET and NAM showing a much stronger surface low in the Northern High Plains. In this case, the preference is for a blend of the 00Z GFS and 12Z ECMWF which offer an intermediate scenario in terms of trough amplitude and are very close to their ensemble means. Only one of the ECMWF+GEFS ensemble clusters could be interpreted as being reasonably close to the NAM/UKMET, and it has just 4 of the 65 total members. Therefore, there is much stronger support for the GFS and ECMWF scenario. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers