Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 141 PM EST Sat Feb 03 2018 Valid Feb 03/1200 UTC thru Feb 07/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z model evaluation with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave tracking from the Rockies this morning and dissipating east of the Mississippi River early Sunday... ...Surface low near the lower Mississippi valley early on Sunday morning, reaching the Mid-Atlantic coast Sunday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/12Z GFS/12Z ECMWF blend Confidence: Average The 12Z ECMWF/UKMET/CMC have sped up some to match the faster 12Z NAM/GFS regarding the surface low crossing the lower Mississippi valley into the southeastern U.S. While the latest ensemble scatter low plots show good agreement toward the 00Z guidance, the trends in the newer 12Z guidance can not be ignored. A 12Z NAM/GFS/ECMWF blend is preferred given a blend of these three models represent the new middle ground shown in the latest guidance. ...Shortwave tracking across the Great Lakes/Ohio Valley on Sunday, East Coast on Monday... ...Surface low tracking across the Great Lakes early Sunday morning, reaching southern Quebec early Monday morning with trailing cold front... ...Consolidating surface low in the vicinity of New England Sunday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average There are some differences regarding the consolidation of two surface lows, one is described in the preceding section and the other is a reflection of a northern stream crossing the Great Lakes late Sunday. As described in the preceding section, the 12Z guidance has picked up on newer information and should be given more weight with lesser inclusion of the 00Z ECMWF/UKMET/CMC. Ensemble spread is rather large given the complex evolution of this system. There are minor timing differences worth noting as well with the 12Z GFS slightly faster than the remaining guidance, but when blending together with the remaining 12Z guidance, an acceptable timing/strength is reached. ...Weak 700 mb shortwave tracking across the central Plains into the Midwest Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Average The 00Z ECMWF is slightly faster with this feature and the 00Z UKMET slightly farther south, but all-in-all, the deterministic models show decent agreement with this system. 19Z update: The 12Z ECMWF/UKMET/CMC continue to show broad convergence toward a common timing/latitude with this feature so a general model compromise continues to be preferred. ...Onshore flow into the Pacific Northwest with low amplitude shortwave moving inland Sunday night and nearing the Four Corners region Tuesday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM / 12Z ECMWF / 00Z UKMET blend Confidence: Average There is good agreement here until around 00Z/06 when the 12Z GFS and 12Z UKMET begin to speed up relative to the agreeable ensemble means. The 00Z ECMWF was slowest of the deterministic guidance but the 12Z ECMWF has sped up to the previous preference.The 12Z CMC is mostly unchanged from its previous run so it is still considered a bit too fast with the shortwave by 00Z/07. Overall ensemble trends have been slightly slower over the past 4 cycles, but the better clustering is near the 12Z NAM, 12Z ECMWF and 00Z UKMET. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto