Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 234 PM EDT Thu May 21 2020 Valid May 21/1200 UTC thru May 25/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cut-Off Low Over Lower OH and TN River Valleys, exiting Mid-Atlantic late Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 19z update: No significant change was noted with the 12z UKMET, CMC, ECMWF or GEFS to break from initial thinking. The spread of the surface low due to the anticyclonic loop between Long Island and Bermuda. ---Prior Discussion--- There continues to be near-term solid agreement through about 48hrs (23.12z) as the closed low starts to be picked up into the northern stream and move through the Mid-Atlantic. The 12z NAM/GFS continue to be slightly outward from the center of anticyclonic looping and further into the northern stream as the surface wave develops along the Hudson Canyon/New York Bight region of the NW Atlantic. The CMC/ECMWF are much tighter to the anticyclonic loop and therefore south and west especially by Sunday. Ensemble suite/trends would support this tighter rotation solution but the GFS/NAM remain close enough to be viable in a general model blend throughout the short-term forecast period. Confidence is above average. ...Deep upper trough/closed low over the northern High Plains... ...Secondary upper digging underneath across Northern Rockies, ejecting into Northern Plains by late Sat/early Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 19z update: The 12z ECMWF trended much slower, in fact, moving to one of the slowest members with the shortwave emerging out of the north-central Rockies and so the surface evolution is now in line with the remainder of the guidance, and it makes the GFS look more normal being a bit too fast and with the shift of the GEFS further south, a general model blend is supported throughout the short-term forecast, with no increase of weighting desired, as such will have slightly above average confidence throughout the remainder of the forecast period as well. ---Prior Discussion--- GOES-WV suite denotes a closed low currently in eastern MT is lifting into Canada, with a replacement closed low/shortwave across SW BC/Vancouver Island starting to undercut the larger low. This wave will elongate the larger scale trof into the Central Rockies by Sat. Uncharacteristically, the 00z ECMWF is a bit too fast bottoming out further west in SE ID, while the UKMET/NAM/CMC suggest a small closed low in N UT/SW WY. This leads to an earlier and northward surface wave development through the Northern Plains. The 06z GEFS and 00z ECENS mean, support this northern solution to a point but are generally washed out with solid amounts of uncertainty. The NAM/CMC/UKMET all generally much further south and slower to develop; the UKMET may be a bit off in timing given its downstream weakness. The 12z GFS further slowed and moved toward the fringe of the GEFS solutions but nearer the NAM/CMC/UKMET evolution. There is sufficient uncertainty and given the GFS trend, is a bit concerning moving away from more reliable/statistically preferable solutions; however, observations, broad ensemble spread and the ECMWF in an uncharacteristic position relative to the remainder of the suite (not to mention importance of mesoscale processes feeding back to the synoptic scale. After 72hrs, the UKMET is weak, the CMC is faster and shifts northeast while the GFS/NAM are more middle ground so will adjust weighting preferences accordingly across the Northern Plains. There may be enough to support using a non-ECMWF blend, hedging weighting toward the 12z GFS as middle-ground compromise. Confidence is initially slightly above average but decreases after 60hrs as the ECMWF moves too fast relative to the suite, becoming slightly below average ...Shortwave lifting northeast across the Midwest by late Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above average 19z update: 12z UKMET is a bit stronger but remains too weak to include in the blend, as such a non-UKMET blend remains preferred for this system. ---Prior Discussion--- A shortwave over the Southern Rockies is emerging into the Central Plains tonight (Friday morning), setting off some convective development and upscale enhancement of the wave. The magnitude and placement of the latent heat release and upscale growth is key to future evolution. The 12z GFS and NAM continue to be a bit stronger and more compact (the NAM more broad, the GFS a bit more compact). The 00z UKMET is very weak and generally faster with the wave while the CMC/ECMWF are weaker than the GFS/NAM but generally better timed than the faster UKMET. This is key to the downstream evolution through the upper-Midwest and depending on the strength of the mid-level wave, how great it shears as it over-tops the ridge in the Great Lakes on Sunday. So in general, the UKMET is not favored given the current environmental setup in the Plains, suggesting the GFS/NAM/ECMWF/CMC are more aligned. Within this non-UKMET a preference toward a compromise in timing/placement of the GFS/ECMWF are preferred. Given the importance of the upscale enhancement of the wave to the overall evolution, yet there is solid agreement in the synoptic evolution to have this slightly above average confidence in the blend. ...Southern Plains shortwave developing Sun into Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF blend Confidence: Below average 19z update: The 12z ECMWF trended a bit deeper and east pushing it a bit closer to the GFS, while the UKMET and CMC continue to be very similar to their prior solutions. As such will keep a GFS/ECMWF blend preference at below average confidence given the importance of convective features, outflow and return moisture that are very hard to delineate at due to the chaotic nature of convectively induced boundaries and cloud cover messing with instability in the nearest term. ---Prior Discussion--- The base of the elongated western large scale trof will bring broad southwesterly flow and periphery of jet energy to intersect the return Gulf moisture through the Pecos River Valley into the Rio Grande. As such a convective complex will help to support a shortwave/MCV development by early Sunday across TX with the potential for a Pacific stream shortwave to re-energize the base of the western trof. The 12z NAM is a clear outlier early given a very strong response/with unrealistic convective feedback, likely some grid-scale feedback, but more importantly much further north. The GFS seems good in timing/placement along with the CMC and UKMET; however, the UKMET and CMC show very strong convective response nearer the Gulf on late Sunday. While plausible, their convective complex magnitudes/upscale feedback may be in the same realm as the unfavored NAM. The 12z ECMWF is slower and weaker with the upscale development but is also a tad slower having a slightly stronger Pacific stream, base of the large scale Western trof late Sunday. Still, this seems more sensible given the uncertainty/importance of convective upscale...will support a 12z GFS and 00z ECMWF blend but at below average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina