Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 317 AM EDT Wed Sep 04 2019 Valid Sep 04/0000 UTC thru Sep 07/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Final Model Evaluation, Confidence, and Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/GEFS and 12Z ECENS Confidence: Sightly Below Average 07Z Update: The spread amongst the full 00Z suite now including the Non-NCEP models has increased late on Day2 and Day3 across the west/northwest. The CMC is completely out of phase with most of the other models, while the UKMET becomes a fast outlier at the edge of the ensemble envelope. Due to low predictability and increasing spread, will update the times for the newer guidance, but keep the preferences unchanged. Previous Discussion: Broad trough across the east and ridging in the west will persist through the period, although slow break down of the ridge and decrease in mid-level thicknesses is likely to produce a more zonal flow on day 3. No less than three shortwaves will traverse from the Pacific NW through confluent flow across the northern tier and towards the Atlantic coast. The first of these deamplifies quickly tonight while racing towards the Great Lakes. Although for most of the lifespan of this feature the spread is minimal, the NAM is a clear deep outlier as it moves towards the Mid-Atlantic. The evolution of this shortwave trough will then impact the speed and position of Hurricane Dorian, but those preferences are handled below. Two other shortwaves advecting into the Pacific Northwest and then race eastward. The first of these will quickly deamplify from a closed feature off the coast Thursday to a short-wavelength ridge/trough across the Rockies and into the Plains by day 3. Immediately following this, yet another piece of energy will drop down the Pacific Coast to be a longer wave trough moving towards California late in the forecast period. There is considerable spread in the position and depth of this last trough, leading to lower than average confidence across the Northwest by late Friday. While much of the country features above average confidence due to lower spread, the difficulty of the Northwest leads to average overall confidence and suggests trending towards the means is likely best until some more detail and agreement can be ironed out. ...Hurricane Dorian... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Please refer to the official National Hurricane Center forecast track For the first 12-24 hours, much of the guidance is well clustered around the 03Z NHC advisory track. Thereafter, spread begins to increase with the NAM outracing everything as Dorian bends to the northeast towards NC, while the ECMWF begins to lag the track. The UKMET, as it has been many of the past few days, remains the closest proxy to the NHC track and should be given the highest weight, with the GEFS/ECENS mean also included to maintain the best track integrity. There has been a subtle shift SW and slowing of Dorian in the Non-NCEP guidance, which makes the best proxy a little less defined than earlier. Still, the UKMET/ECMWF/GEFS are the closest, but if NHC should slow/shift at 09Z, the UKMET would again be the guidance upon which the heaviest weight creates the best proxy. ...Tropical Storm Fernand.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Please refer to the official National Hurricane Center forecast track The GFS is closest to the 03Z NHC track, but most guidance is reasonable with diffuse and weakening surface low pressure moving subtly north of west into Northeast Mexico. A blend of all but the CMC, which is far too slow, should suffice, but the GFS is closest overall, while the NAM features the best proxy for QPF. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Weiss