Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 137 PM EST Sat Mar 03 2018 Valid Mar 03/1200 UTC thru Mar 07/0000 UTC 12Z model evaluation...along with model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Powerful nor'easter pulling away from the East Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement in taking the strong nor'easter away from the East Coast over the next 24 hours and out over the open Atlantic Ocean. A general model blend will be preferred given the minimal mass field spread. ...Deep closed low impacting the Western U.S. today... ...Negatively tilted trough approaching the Plains on Sunday... ...Impacting the Midwest through Monday/Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z UKMET/12Z ECMWF blend...through 60 hours 12Z GFS/12Z ECMWF blend...after 60 hours Confidence: Above average...becoming average after 60 hours A deep layer closed low and associated broad trough impacting the West Coast will gradually be crossing the Intermountain region through Sunday. The models then indicate energy lifting out of the base of the trough by Sunday night which will allow the trough to take on a negative tilt out across the central/northern Plains on Monday. Expect a new mid/upper level low center to evolve as well as the system amplifies. Surface low pressure over the Great Basin through Sunday is expected to reorganize over the Plains on Monday and begin lifting across the upper Midwest by Monday night. The guidance is generally in good agreement with their timing and depth of the trough evolution through Monday, and the spread with the surface low details across the Plains is rather minimal. However, the 12Z CMC does tend to track its height falls and surface low a bit farther south compared to the other models. More spread though occurs Monday night and Tuesday as this system encounters a very blocky downstream pattern over eastern North America. However, with the 12Z cycle of guidance, there has been some consolidation of the solutions as the 12Z UKMET and more so the 12Z ECMWF have trended toward the 12Z GFS solution which had a height fall evolution a tad more suppressed over the greater Midwest and toward the Ohio Valley later in the period. The 12Z NAM now sort of sticks out as a somewhat stronger outlier aloft by the end of the period, and its dominant surface low is also a bit north of the model consensus. The UKMET also tends to have its surface low a bit farther north like the NAM, but aloft it has trended toward the GFS solution. Based on the latest model clustering and trends, will suggest a GFS, UKMET and ECMWF blend through Monday, and then a straight up GFS and ECMWF blend thereafter which is supported also by the latest GEFS mean. ...Trough digging southeast across the Northeast on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Average The models take a portion of the trough/closed low just southwest of Hudson Bay and slowly shift it southeast across Quebec on Sunday and then in more of sheared fashion down across the Northeast on Monday as the system encounters a blocking high that is settling southwest from southern Greenland. The guidance compared to yesterday has trended toward more energy dropping southeast across the Northeast with a better defined closed low feature. This energy then quickly goes southeast and offshore by Monday. The 12Z NAM and 12Z CMC become a little slower than the 12Z GFS and 12Z ECMWF, but the 12Z UKMET trended a bit more progressive and is now closer to the faster GFS/ECMWF camp. The latest GEFS mean and ECENS mean favor the faster solutions and thus will continue to support a blend of the GFS and ECMWF solutions. ...Shortwave trough over the northern High Plains Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The guidance drops another shortwave trough down across the northern High Plains by Tuesday. There is some very minor depth differences by late Tuesday over Montana with the height falls, but will a general model blend should suffice for the time being. Previous model trends at www.wpc.ncep.noaa.gov/html/model2.shtml Previous 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison