Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 134 PM EST Sat Feb 15 2020 Valid Feb 15/1200 UTC thru Feb 19/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model evaluation with preferences & confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large scale pattern over the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/GFS blend Exception: Remove GFS for NAM/UKMET along Gulf Coast Sun/Mon) Confidence: Slightly above average 19z update: The 12z ECMWF trended a bit weaker/faster and therefore a bit south through the Great Lakes, very near the 12z GFS, combine this with the 12z CMC trending back toward the GFS...there is some growing confidence through Day 3 across the Central Plains into the Great Lakes. These slight shifts, highlighted the slowness of the UKMET, which remained similar to the 00z run, making it a bit less favorable in a blend. The CMC still has an issue being too far north with the QPF axis (well north of the expected coastal boundary) across the south on Tuesday, still favoring the ECMWF/GFS axis/orientation overall. As such to best encompass both the mass fields as well as QPF, will support a stronger 12z ECMWF/GFS blend with some minor incorporation of the CMC (Great Lakes) and UKMET Central/Southern Plains and Gulf Coast region (less GFS along Gulf on Sun/Mon). ---Prior Discussion--- A fairly zonal pattern currently exists across the CONUS with some broad cyclonic curvature centered around the Central Plains as Pacific air replaces the Arctic sourced air that dominates the eastern third of the US (with due exception to the subtropical ridge over the eastern Gulf of Mexico/Florida). A stronger shortwave exists well into Canada with some moderate influence for QPF/snows across the Great Lakes today through Sunday. Guidance is quite agreeable with this system even as it clips the Interior Northeast late Sunday into Monday. Additionally, return moisture around the subtropical ridge along the coastal front appears to be set best with a NAM/UKMET/ECMWF blend as the GFS appears to be well south of the coastal front/well offshore. The zonal pattern will usher in another Pacific shortwave into the Pacific Northwest later today into Sunday and will spread across the Northern Rockies into the Central Plains by Monday morning. The elongated shortwave will start to split with the trailing edge amplifying across the Central Rockies, while the leading edge will start to shift east into the Great Lakes under influence/direction from sharpening Arctic shortwave dropping out of central Canada into Tuesday. As typical small variation in wave length/spacing between the features leads to the difference in timing/orientation of the surface mass fields, moisture flux and therefore QPF axes. The guidance is fairly agreed upon with the timing of the Pacific feature, with exception of the CMC which is a bit further south and uncharacteristically faster, otherwise; the main spread is in the timing of the Arctic wave. The GFS is very fast but weaker narrowing the spread with the Pacific wave, which leads to slightly faster advection and track of the surface wave along the frontal zone into the Great Lakes. This is opposed by the slightly slower ECMWF/UKMET and ECENS ensemble solutions that favor a bit greater spacing and therefore stronger/slower amplification of the surface wave. The 12z NAM is more in this slower camp, but is much further west and compact with the Arctic wave that doesn't bare much support in the overall larger scale flow. As such will favor a non-NAM, non-CMC solution with this wave, surface cyclone and QPF pattern. Weighting toward the ECMWF/UKMET QPF/surface pattern is higher in the blend but while a bit fast, the evolution of the GFS/GEFS seems plausible given the fast overall flow initially. Confidence is slightly above average in this blend Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina