Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1200 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 NAM/GFS evaluation with preliminary 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/00Z ECMWF blend Confidence: Slightly below average The 12Z NAM/GFS are quicker than the 00Z ECMWF/UKMET/CMC 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 newer 12Z NAM/GFS may be picking up on newer information and will be incorporated as a blend with the 00Z ECMWF given the ECMWF is better tied to the previous consensus. ...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: 12Z NAM/12Z GFS/00Z ECMWF blend Confidence: Slightly below 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 newer 12Z NAM/GFS may be picking up on newer information and should be given more weight with lesser inclusion of the 00Z ECMWF. 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 12Z NAM and 00Z ECMWF, 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. ...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 / 00Z UKMET blend Confidence: Average There is good agreement here until around 00Z/06 when the 12Z GFS and 00Z CMC begin to speed up relative to the agreeable ensemble means. The 00Z ECMWF is slowest of the deterministic guidance. The 12Z NAM and 00Z UKMET are in the middle of the deterministic and ensemble spread, which will be leaned upon for the preference at this time. Overall ensemble trends have been slightly slower over the past 4 cycles. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto