Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1222 AM EDT Sat Nov 02 2019 Valid Nov 02/0000 UTC thru Nov 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CONUS through 84hrs (05/12Z) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z UKMET blend Confidence: Average A very broad global scale trough dominates the current CONUS weather pattern with a sizable ridge (becomes closed 582dm anticyclone later today) over the northeast Pacific. Orientation of the trough will allow for persistent northwesterly flow opening up the central CONUS to colder Arctic source air though the short-term forecast with each internal smaller scale shortwave features moving through it. So from a large scale perspective there is very good agreement. Currently, a dip in the core of the trough the Great Lakes today is well handled in the guidance, as it slides through the Northeast Sunday with little fanfare beside Lake Effect snow bands in the Great Lakes. The next small scale wave, does have some uncertainty and model spread. The 12z ECWMF breaks from consensus including the bulk of ECENS members supporting increased shortwave ridging ahead of the next wave that drops out of western Canada on Sunday. This allows for further southward press of the wave and delay compared to the ensemble suite and in particular the 00z GFS and 12z UKMET. The CMC is also in line with the GFS/UKMET for this wave. The 00z NAM however, is very strong with the polar jet shortwave even tamping down the ridge in the Pacific, which does not appear meteorologically sound, given the strength of the ridge and may be in line with typical negative NAM over-amplification bias. While the differences show smaller effects across the Great Lakes by Monday, there is enough to support a preference toward the GFS/UKMET and CMC. The set up/timing with the aforementioned wave leads to timing issues with the next shortwave in the northwest flow. This wave is more out of the Arctic stream acting as the kicker to the prior one, and there is a larger uncertainty to its initialization as well as evolution as it dips into NW Ontario by 5.00z. The ECMWF being slower with the initial wave is very compact/strong with this kicker. The compact nature is a outlier in the ECENS member suite and so is not favored at this time. While, the leading wave into the Great Lakes is handled well by the CMC, this Arctic wave is resolved as very compact/strong and therefore very slow to roll southward, and given the larger scale pattern, this seems unlikely as well. The UKMET/GFS show some amplification/strength to this wave, but are weaker/broader and more in line to a typical pattern. As such the WPC preference is a 00z GFS/UKMET blend throughout the forecast period with some inclusion of the CMC early. While the impacts to sensible weather are not large, the spread and evolution uncertainty is moderate to high and so confidence is average in the GFS/UKMET blend through the short-term forecast period. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina