Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1103 AM EST Sat Feb 24 2018 Valid Feb 24/1200 UTC thru Feb 28/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with latest model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Strong upper trough over the High Plains region today... ...Cyclogenesis over the Plains and lifting across the Midwest... ...Trailing cold front sweeping through the Eastern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The models take a strong mid/upper level trough entering the central and southern High Plains today lift it northeast across the upper Midwest by tonight as it takes on a negative tilt which will help deepen surface low pressure that will cross this region. The 12Z NAM ends up again just a tad stronger aloft than the remaining guidance as the system lifts northeast across the upper Midwest and upper Great Lakes tonight and through early Sunday. Meanwhile, a trailing cold front associated with this system will sweep east across the Eastern U.S. through Sunday and then move offshore Sunday night. Model spread with the front is rather minimal at this time, and the models overall are in rather good agreement with the secondary area of low pressure offshore New England Sunday night and early Monday. Based on the overall clustering of solutions and latest trends, a non-NAM blend will be preferred. ...Shortwave arriving over the Pacific Northwest today... ...Crossing the Four Corners/High Plains on Sunday... ...Ejecting east across the Mississippi/Ohio Valleys on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 12Z GFS/00Z UKMET/00Z ECMWF blend ...after 48 hours Confidence: Above average The next in a series of shortwaves to drop southeast down across western North America is currently arriving across the Pacific Northwest and will rapidly drop down into the Four Corners region on Sunday before rapidly ejecting east toward the mid Mississippi Valley and Ohio Valley on Monday. The energy will then cross parts of the Mid-Atlantic and Northeast by Monday night. The models are in good agreement with their mass field details of this system until Monday when the 12Z NAM and 00Z CMC become just a tad more progressive and flatter than the 12Z GFS, 00Z UKMET and 00Z ECMWF. The latest GEFS mean and ECENS mean both favor the latter camp which is also rather well clustered. Will prefer a general model blend through 48 hours, and then a GFS/UKMET and ECMWF blend thereafter. ...Shortwave arriving over the Pacific Northwest on Sunday... ...Closed low evolution over the Southwest by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 06Z GEFS mean and 00Z ECENS mean Confidence: Slightly above average The guidance brings another shortwave into the Pacific Northwest on Sunday along with a progressive cold front. The guidance is in good agreement with the arrival of the shortwave energy and the evolution of the height falls digging down across California and the Great Basin on Monday which will lead to a larger scale trough evolution aiming for the Southwest. Overall, there has been a somewhat stronger trend in the guidance with the idea of a closed mid/upper level low center evolving over the Southwest by Tuesday. Model spread is mainly noted down over southern California by Tuesday where the 00Z UKMET and 00Z ECMWF both have their respective closed lows focused a tad farther west compared to the 12Z NAM, 12Z GFS and 00Z CMC. For now, the ensemble means support their respective deterministic output with the ECENS mean farther west and the GEFS mean a little farther east. Will suggest a blend of the latest GEFS mean and ECENS mean as a compromise for now to approximate the model consensus. ...Shortwave arriving over the northern Rockies on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring another northern stream trough down from western Canada and across the northern Rockies by Tuesday. The model spread with this system is rather minimal at this time, and so a general model blend will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison