Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 147 PM EST Sat Feb 22 2020 Valid Feb 22/1200 UTC thru Feb 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Weak mid level shortwave and attendant front clipping the Great Lakes/northern ME Sun/Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend (weight toward 12z GFS/00z ECMWF) Confidence: Slightly above average 19z update: Little changes in 12z ECMWF/UKMET/GEFS or CMC did not make significant changes to change initial preference. ---Prior Discussion--- Shortwave currently tracking through the Canadian Rockies, amplifies across the Canadian Prairies into the Western Great lakes by late Sunday with a cold front concurrently draping through the northern tier into the Great Lakes. The 12z NAM has significantly increased depth of the evolving closed low by midday Monday relative to the other guidance; becoming out of tolerance for a blend. The 00z UKMET leans a bit faster allowing for a greater negative tilt orientation of the trof clipping the Northeast as well, but is more in line overall with the remainder of the guidance. The 12z GFS continued similar evolution to prior guidance and so the overall preference will support a Non-NAM blend but weighted more toward the ensemble means, which are well represented by the 12z GFS/00z ECMWF. Confidence is slightly above average. ...Closed mid level low reaching the Rockies Sun, weakening over the Upper MS/OH Valley Mon into Tues... ...Surface low tracking from northeast NM into Ohio Valley by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend through 25.00z; thereafter see section below Confidence: Slightly above average 19z update: The 12z ECMWF trended a bit faster and therefore north crossing the Ozarks into Ohio Valley, very close to the 06z GEFS and a similar 12z GEFS solution. The 12z UKMET trended a bit faster but retains the strength of the shortwave through the Ohio Valley a bit too much. So though it is trending the right direction providing confidence to the initial thinking, it is still not preferred to be included in the blend. The CMC did not change much and remains a significant outlier. A such will keep the Non-CMC blend through 25.00z but shift toward a 12z ECMWF/GEFS blend thereafter. ---Prior Discussion--- Closed low in the California Bight will slide through the Four Corners region and support surface cyclogenesis along the NE NM Front Range into Sunday. This low will advance across the Southern Plains into the Lower Ohio Valley by late Monday into early Tuesday with solid model agreement in timing and depth, even as the upper low begins weakening rapidly. A tapping of the deep moisture off the Gulf along the western periphery of the stubborn 7H ridge across the Southeast will allow for strong convection along/ahead of the frontal zone. There is more traditional timing differences with this feature, e.g. ECMWF slower/GFS faster, etc, but is not too bad through 25.00z (Tues); with exception to the 00z CMC which is too slow overall. It is most stark so after 24.12z depicting a very slow, even stalling of the system in deference to the upstream wave on Tuesday, making it less favorable. Model spread through the MS valley into the Ohio Valley (not necessarily the Gulf Coast into the Southeast) becomes quite broad and uncertain, driven mainly by the digging approaching shortwave out of the northern stream. So the preference after 25.00z will be very similar to the section below, but will be favoring the more consistent, slightly slower evolution of the ECMWF/ECENS mean and the 06z GEFS over the faster solutions. ...Mid-level shortwave crossing the Pacific Northwest Sunday, digging into Northern/Central Plains Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET; then 12z ECMWF/GEFS after 24.12z Confidence: Becoming Slightly below average after 24/12z. 19z update: The 12z UKMET was a bit tighter to the other guidance with the surface cyclone into the Pacific NW, and still remains just west/slow emerging from the West, so will still not prefer the UKMET throughout the short-term. The 12z ECMWF trended slightly faster emerging from the Rockies but still is much slower than the 12z GFS/NAM. The 12z GEFS continues to be consistent and fairly tight to the ECMWF versus the GFS/NAM, so will keep initial preference of non-UKMET through 24.12z and using an ECMWF/GEFS blend afterward. Confidence remains slightly below average but improving. ---Prior Discussion--- Compact closed low and associated surface low reaches Vancouver Island Sunday. Here the 00z UKMET is displaced from an otherwise very tight clustering; its slowness leads to further downstream issues out of the Rockies into the Plains, so initially a non-UKMET blend is preferred from the start. The 00z CMC being very slow and rapidly weakening with the precursory wave, results in this northern stream wave to be slow exiting the Rockies and is not preferred after cyclone landfall on Monday. The 12z NAM/GFS both are very strong/fast with the nose of the jet providing increased diffluence aloft and ascent out of the Rockies into the Central Plains and Ohio Valley by Tuesday, this allows for faster amplification/deepening of the closed low through the Central Plains, which helps to develop a surface reflection back and to the northwest across the Midwest by Day 3. The NAM's aggressive nature/over-deepening bias on Day 3, suggests this evolution is less likely, especially combined with the GFS known negative bias of being too fast. The 06z GEFS suggests a more gradual shift northward toward the northern stream system, a tad faster than the ECMWF/ECENS. Given the ECWMF/ECENS bias toward being a tad slow, but also being most consistent run to run over the last few days provides some confidence if blended with the GEFS (over the 12z GFS). Still, there is always sizable uncertainty with binary interaction between the stream and small shifts can lead to impactful differences in QPF swaths...as such confidence in the ECMWF/ECENS/GEFS blend is slightly below average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina