Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1235 PM EDT Fri Aug 14 2020 Valid Aug 14/1200 UTC thru Aug 18/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ...Long wave trough moving from Northern Plains into Great Lakes Sun/Mon and through to Interior Northeast Mon/Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 17.00z Non-NAM thereafter Confidence: Slightly above average Strong shortwave crossing the Northern High Plains will take the strong surface wave through the Red River Valley into Canada with very strong agreement, the model spread starts to increase with the upstream 'kicker' shortwave and associated jet streak that will help to elongate the larger scale trough more negative tilted through the Great lakes into Sunday. The UKMET/CMC/ECMWF are all very elongated having retained the main inner core to the large scale closed low over N Canada much further north. The GFS/NAM suggest a secondary compact 5 vorticity center much further south along the trof axis into NE Ontario by late Monday. This will drive height-falls dynamic forcing into New York and the Interior Northeast in greater strength, particular the NAM. Given the NAM tends to over play this by the end of Day 3, there is less confidence in its utility after 17.00z. As such, a general model blend is preferred with a non-NAM blend (mainly in mass fields) after 17.00z. Confidence is increasing to slightly above average given similar sensible weather evolution even with moderate mass field spread. ...Ill-formed long wave trough across OH/TN Valley slowly exiting Carolinas by Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/NAM and 00z CMC blend (incl 00z ECMWF at low weight for QPF) Confidence: Slightly below average Overall agreement is increasing to the larger scale pattern with a weak, ill-formed shortwave across the Lower Ohio Valley driving the broader large scale trof, especially as the subtropical wave/low exits the Carolina coast later today. The 00z UKMET continues to be a bit too weak and north with the trough as a whole but as it slides east, the new surface wave along the frontal zone appears south and weak relative to the remaining suite. The 00z ECMWF is similarly weak and generally slow to the stronger/north 12z GFS and NAM; however, the greater depth through 7H depicts a similar overall evolution to the deeper cyclone to the GFS/NAM and CMC which are further north. This makes the QPF pattern similar to be useful as a slower potential solution, yet may be less useful in a mass field blend. So will support a 12z GFS/NAM and 00z CMC blend with some spot inclusion of the ECMWF. Confidence remains slightly below average. - ...Subtropical TUTT West of California lifting north into the Pacific Northwest ahead of digging northern stream trough Sun into Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF/CMC blend Confidence: Slightly above average A strong/compact closed low with origins in the tropics (TUTT cell) resides off the West Coast of California with a solid central core and eastern quadrant elongated trof. The eastern wave will rotate toward the northern quadrant and help stretch/elongate the wave toward an approaching deep Gulf of AK gyre. As the gyre breaks down and digs with a strong shortwave on Sunday, it will draw the remaining energy northward toward the Pacific Northwest late Sunday into early Monday. Mass fields are fairly agreeable with some timing/sheared aspects to the wave. The UKMET is also drawing higher moisture/wind flow northward producing broad QPF. While this system is likely to enhance thunderstorm (likely dry) environment, the UKMET is likely too moist and is less preferable. The 12z NAM shows a bit stronger/compact solution through the lower depths of the troposphere, like the UKMET which is a negative tendency toward the late day 2, early day 3 period...so while it cannot be fully discounted there are some concerns for inclusion in a blend. The ECMWF/CMC are a tad slower than the GFS...but a compromised location/timing will quite likely verify best given all considerations available at this time. As such a 12z GFS and 00z ECMWF/CMC blend is preferred at slightly above 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 This product will terminate August 15, 2020: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Gallina