Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 231 PM EDT Mon Jun 29 2020 Valid Jun 29/1200 UTC thru Jul 03/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low anchored over New England ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average 19Z update: The 12Z CMC trended toward the preferred blend of the ECMWF/GFS/UKMET though still have some timing issues, especially late in the day 3 period. But it's much improved and probably can be incorporated now. This leaves the 12Z NAM as the main outlier, which will still be kept out of the blend preference. ---previous discussion--- Upper level energy over New England will remain in place over the area through mid-week with really good model agreement seen from the latest 12Z guidance through about 60 hours. Beyond that, an approaching shortwave trough from southern Quebec will approach New England and help kick out and absorb the weakening closed low. The CMC and NAM are the most sluggish, holding back energy over the Northeast and New England the longest, which is out of place compared to the ensemble mean. For now, will prefer a blend that excludes the 12Z NAM and 00Z CMC. Deep upper trough/closed low across the Intermountain West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/ECMWF/UKMET Confidence: Average 19Z update: Fairly good agreement still with the 12Z guidance in the large scale sense, though the 12Z CMC remains an outlier and unfavorable as it is significantly out of phase with the other deterministic models (and ensemble means). Otherwise, no significant changes to the model blend preference incorporating the 12Z GFS, ECMWF, and UKMET. ---previous discussion--- Strong upper level low over the Intermountain West will lift northeast over the northern Rockies through tomorrow before absorbing with another approaching shortwave trough from southwest Canada, leading to a large closed low over the Pacific Northwest to northern Rockies through much of the week before retrograding back to the northwest by Thursday night/Friday as ridging builds downstream over the central US. Initially, the CMC drops out of favor with several timing issues related to individual vort lobes rounding the large scale low. For day 2/3, the large scale evolution is well agreed upon by the GFS/ECMWF/UKMET, except for the end of day 3 when a final shortwave trough moves onshore the Pacific Northwest. Here, there are some timing issues where the GFS is a bit fast and UKMET on the slower side. For now, will prefer a blend composing of the 12Z GFS, 00Z ECMWF/UKMET. MCV/Weak mid-level low over MN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average MCV and associated weak mid-level shortwave will continue to lift northward out of Minnesota through western Ontario over the next 24 hours. Model agreement is above average with very good clustering seen in the latest guidance. The only notable difference is a slight lag in the 00Z CMC compared to the rest of the deterministic guidance, but overall this should not affect much in the way of sensible weather, so a general model blend is preferred. Shortwave amplifying toward mid MS Valley by Monday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 48 hours; GFS/ECMWF/UKMET blend day 48-84 hours Confidence: Slightly below average A convectively enhanced MCV is forecast to track from the Arklatex region northeast before stalling over the Mid-MS River Valley mid-week. Virtually all of the deterministic models have this signal with relatively good agreement through 48 hours, but beyond that time frame, more notable differences are seen. The development and expansion of the northern Rockies troughing, some models allow the mid-MS MCV to be picked up and lifts northward through the Upper Midwest. Conversely, the ECMWF /CMC and the NAM to some degree, show more separation. As heights build by the end of the period, some models allow a piece of the energy to drop southeastward in a psuedo-northwest flow regime, taking the energy toward the Gulf coast. All in all, it's a low confidence forecast with several competing systems. The best consensus approach right now would favor a blend composing of the ECMWF/GFS/UKMET for now but noting the strong and potentially significant sensible weather differences for day 2/3. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor