Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 252 PM EDT Thu Mar 29 2018 Valid Mar 29/1200 UTC thru Apr 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...Including Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough over the Lower Mississippi Valley lifting northeast in convergent flow to New England by Friday... ...Secondary shortwave over the High Plains reaching the Mid-Atlantic by Friday... ...Surface low tracking from the Lower Mississippi Valley to the Northeast by Friday and associated cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in reasonably good agreement with their mass field details concerning the evolution of the Lower Mississippi Valley shortwave trough and associated surface low evolution up across the Northeast through Friday. The guidance also is agreeable with the details of a relatively weak secondary shortwave that arrives across the Mid-Atlantic by Friday. Therefore, a general model blend will be preferred at this time. ...Shortwave over the Gulf of Alaska today, crossing the Northwest on Friday 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: 12Z GFS Confidence: Slightly above average The models bring a shortwave down from the Gulf of Alaska and across the Northwest by Friday and allow a surface low to drop southeast across Montana. This energy will then advance across the Northern Plains and Upper Mississippi Valley late Friday and early Saturday with a relatively compact and energetic low crossing the region and reaching the Great Lakes on Saturday. The low will lift across Ontario and Quebec through Sunday with a trailing cold front that will cross the Ohio Valley and Northeast. The 12Z NAM is a bit stronger than the global model consensus with the shortwave and tracks its surface low a little farther north than any other model. The 12Z UKMET is overall the slowest solution again, and is now also the farthest south. The 12Z ECMWF also is perhaps a tad on the slow side with its low evolution. The 12Z CMC is close to the 12Z GFS which collectively are just a little faster than the ECMWF. The 12Z GFS overall best reflects the model consensus and has excellent support from the 12Z GEFS mean. Given very good run to run continuity and overall ensemble support, the GFS mass fields will be preferred. ...Low-amplitude shortwave reaching the Oregon coast on Saturday, and shearing toward the High Plains by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models generally agree that a low-amplitude shortwave will be pushing through portions of the West this weekend before gradually shearing out. The models are in good agreement with this feature and so a general model blend will be preferred for the time being. ...Large scale trough digging into the Northwest by late weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM, 12Z GFS and 12Z UKMET Confidence: Average Additional height falls will be digging toward the Northwest U.S. by late in the weekend, as a strong shortwave trough over the northern Gulf of Alaska amplifies southeastward across British Columbia. The 12Z CMC and to a lesser extent the 12Z ECMWF are not as amplified with the troughing as compared to the 12Z NAM, 12Z GFS and 12Z UKMET. The latest ECMWF though did trend a bit more amplified compared to its previous run. The 12Z GEFS mean and 00Z ECENS mean tend to favor the more amplified consensus, and so will lean toward a blend of the NAM, GFS and UKMET as a result for now. ...Lingering trough and stalled surface front in the vicinity of Florida this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average The models stall out a front across the Florida Peninsula this weekend as a weak mid level trough traverses the eastern Gulf of Mexico, the Florida Keys and Cuba. The 12Z NAM overall is the strongest solution with the trough and also the slowest. The remaining models are Will prefer a non_NAM blend 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