Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 143 PM EST Fri Feb 02 2018 Valid Feb 02/1200 UTC thru Feb 06/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...12Z model evaluation with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave crossing the Pacific Northwest today, tracking into the Rockies on Saturday and reaching the Mid-Atlantic coast late Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS / 12Z ECMWF / 12Z CMC blend Confidence: Average Somewhat minor timing differences appear with this feature after it crosses the Rockies and reaches the lower Mississippi valley. The 12Z GFS is a bit faster than the remaining deterministic consensus, but the bigger difference is with a weak surface low as seen in the 12Z NAM. The 12Z NAM is north of the deterministic/ensemble consensus with the surface low noted 12Z/04. The 12Z UKMET strengthens this low as it tracks north toward New England, with this low becoming dominant, north of the weaker NAM/GFS/ECMWF/CMC lows seen by 12Z/05. The latest ensemble scatter low plots best agree with the 12Z GFS/ECMWF/CMC blend for this low. ...Shortwave tracking from western Canada into the northern Plains and reaching the upper Great Lakes Sunday... ...Surface low tracking across the Great Lakes early Sunday morning, reaching southern Quebec early Monday morning with trailing cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z GFS blend through ~12Z/04 12Z GFS/ECMWF blend ~12Z/04 through 00Z/06 Confidence: Slightly below average The 12Z GFS is faster with the leading portion of this elongated upper wave, reaching the upper Great Lakes earlier than the remaining model consensus. While the 12Z CMC is the next fastest model, a non-12Z GFS blend is close to the ensemble mean placement with a related surface low through roughly 12Z/04. Beyond 12Z/04, a stronger shortwave begins to dominate, approaching the Ohio valley from the northwest. There are only minor timing differences with this next wave, outside of the slower/weaker 12Z CMC. Worth noting however, the 12Z NAM is on the stronger side of the guidance, noted at 850 mb with the low and extent of colder temperatures, so the NAM is considered a low probability possibility. Given some interaction with a surface low along the Mid-Atlantic coast discussed in the previous section, a 12Z GFS/12Z ECMWF is preferred as one single low begins to take shape and strengthen near Maine beyond 12Z Sunday. Confidence is a bit reduced given the complex evolution of this system and poor ensemble agreement in the scatter low plots. ...Onshore flow into the Pacific Northwest with low amplitude shortwave moving inland Sunday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 00Z CMC is out of phase with the shortwave near the Northwest noted 00Z/05 and overall flatter downstream into the interior West. Otherwise, decent model agreement exists with a non-00Z CMC blend of guidance. The 12Z CMC adjusted toward the remaining deterministic consensus with only minor adjustments noted in the 12Z UKMET/ECMWF relative to their previous 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