Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 116 PM EST Fri Feb 28 2020 Valid Feb 28/1200 UTC thru Mar 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12z Model Evaluation with Preferences & Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ System slowly pulling away from the Northeast through Sunday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 19z update: Little change, but still modest spread east of the CONUS, suggests the general model blend over the CONUS will suffice at slightly above average confidence. ---Prior Discussion--- Broad/elongated closed low over SW Quebec will break down a bit internally as it drifts eastward today into Sunday. Prior to the northwest to southeast oriented upper jet/shear axis advances through the Northeast later Sunday into Monday, the inner core dynamics evolve differently within the NCEP vs non-NCEP suite. The GFS/NAM both are more central and stronger with the inner core supporting a stronger surface occlusion (mainly the 06z GFS/GEFS) rotating back toward Maine; this is opposed by the ECMWF/CMC which shows a broader ring of energy (vortex breakdown) around a weak/devoid centroid hub. The 12z GFS trended more toward the ECMWF evolution and further offshore with the surface cyclone. So overall a general model blend could be employed at slightly above average confidence. System moving through southern Canada & its trailing front ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average 19z update: Sizable slowing and shifts in the 12z UKMET evolution make it more in line with the initial preference. The 12z CMC slowed also matching the 00z ECMWF, and given the 00z ECMWF showed little/no significant change; a non-NAM blend is preferred, and given higher clustering in timing/evolution will increase confidence to slightly above average ---Prior Discussion--- GOES-West WV suite depicts a compact shortwave nearing Vancouver Island at this time. This wave, particularly the leading edge of the height-falls ahead of the upstream descending branch of the jet will track across the Southern Canadian Rockies with a compact surface reflection. The 12z NAM and 00z UKMET are a faster and shifted northeast with greater shear axis through central Sask/Manitoba...leading to greater influence of Arctic shortwave energy (binary interaction). While the NAM, shows a bit tighter/compact evolution through W Ontario, the UKMET gets too fast. This is important given the associated frontal zone that slides into the northern tier as well as the deep southwesterly flow/subtropical tap or connection later in the forecast period ahead of the two trailing systems (see sections below). The 00z ECMWF shows some lagging compact evolution that retards the surface wave and frontal zone by Monday relative to the CMC/GFS and even the 00z ECENS mean, making it a bit less favorable overall. As such will support some of its inclusion, but more from the 12z GFS/06z GEFS and the 00z CMC/ECENS to help progress it a bit more in timing, of the front into the Great Lakes as well as moisture/instability flux across the Lower MS into TN river valleys by 84hrs. While the spread is fairly small, the variance along with staging the environment is critically important but also in a lower than normal predictability flow regime. Still, the agreement is solid enough to have average confidence in this blend. System dropping down the West Coast Sunday & Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend weighted toward CMC/ECWMF Confidence: Slightly above average 19z update: Fairly consistent CMC, UKMET and ECMWF 12z solutions along with slowing 12z GEFS (matching the GFS) provides increasing confidence toward the longer term trend of slowing/further south digging closed low. While the GFS/GEFS still remains well east of the best clustering, will continues to keep initial preference of non-GFS/GEFS blend weighting toward the CMC/ECMWF. ---Prior Discussion--- Strong shortwave off Vancouver island will press east, but the strong upstream energy in the upper level jet behind the main trof, will allow for the development of an closed low across N CA by Monday through anticyclonic wave break processes. This process is fairly well agreed upon in the suite through 02.00z (late Sunday evening), but this agreement beings to fade as the inner core evolves, and its interaction with the subtropical moisture stream as well, as the northern stream connections. The run to run trends in the ensemble suite appear to be favoring a slowing/further southward digging of the closed low first presented by the CMC suite, then followed by the ECMWF. The UKMET trended this way, as well as the 12z NAM, providing increased confidence, as the guidance falls into their more traditional bias spacing relative to each other. Still, the connection of the CMC to the northern stream appears to be the middle ground with best continuity and will continue to favor it as the anchor to the preference. The 00z ECMWF/ECENS mean are within tolerance as well. The UKMET is solid in the southwest into the southern Plains, but the affects of the stronger/faster northern stream (see section below) make it a bit less favorable, lower weighted (possibly having a faster stronger subtropical jet too) but still included. The 12z NAM while still a bit north/elongated into the northern stream relative to the CMC/ECMWF, looks to meet an acceptable evolution to have some lower weighted inclusion as well. The 12z GFS, much like its prior runs, continues to be faster in swinging the upstream shortwave energy around the base of the developing closed low, shifting it eastward, leading to substantial mass differences by 84hrs in the Southwest. As such will favor a CMC/ECMWF heavy, Non-GFS blend at slightly above average confidence. Fast moving shortwave through British Columbia, Northern Rockies, potentially phasing with southern stream across the Central Plains into Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend (weight to ECMWF/CMC/GFS) Confidence: Slightly above average 19z update: A slowing of the UKMET brings it much closer to the tightening cluster, though still remains the fastest timing, but is small enough to have included in the blend. The CMC was a bit deeper in amplitude across the High Plains, but matches the ECMWF well. Enough to support a general model blend, with greater weighting toward the ECMWF/CMC/GFS over the UKMET/NAM. And though the clustering is tight currently, the placement to the terrain and track still suggest there is potential for a different evolution coming to fruition, so confidence is only increased to slightly above average. ---Prior Discussion--- A very important shortwave to the eventual high hazard/flooding concern in the medium-range across the MS Valley into the TN Valley will have some impact to the very end of the short-term forecast period across the Pacific NW and northern High Plains. This wave is still well north along the Aleutian chain and is expected to track along the Alaskan peninsula, before over-topping the broad Gulf of AK ridge and dropping through the central Canadian Rockies by 12z Monday. Vortical stretching and sharp 250mb left exit, anticyclonic curvature will support compact spin up of the wave and support surface cyclogenesis through N Alberta to Saskatchewan, but still broad ascent as far south as the Central US Rockies by 03.00z. This is fairly low predictability track for precise depth/strength though there is increasingly tightening in the guidance suite. The importance of the placement is critical to the placement/timing of phasing with the southwest system lifting out, after 84hrs. The 00z CMC/ECMWF/ECENS mean have been consistent providing the centroid of initial preference. This will lead the faster UKMET (typical of bias) a bit out of tolerance. The 12z NAM is a bit slower and further north, which may have some more to do with the resolution of the terrain and the vortical spin up, showing the uncertainty/low predictability environment. The 12z GFS, however, saw sizable adjustment toward the trend and looks to be a good match at least for this system and through 84hrs. This was due to a slight adjustment north, slowing and injecting less energy from this wave toward pulling/kicking the southwest wave out into the Plains. So will prefer a 00z CMC/ECMWF and 12z GFS blend but confidence will be average given the run to run variance expected in this flow regime/cyclone track. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina