Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1229 PM EDT Sat Aug 15 2020 Valid Aug 15/1200 UTC thru Aug 19/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ...Longwave trough expanding across the eastern CONUS into early next week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non UKMET through 17.12Z Non UKMET/GFS D3 Confidence: Slightly above average GOES-East WV suite depicts a strong block in mid-level flow across SE Ontario, south of which the remains of a weak, elongated (N-S) trof continues to press eastward across the Central/Southern Appalachians. Strong WNWly jet across the Northern Plains si pressing an elongated base of a shortwave squeezed north and south by the aforementioned block in Ontario. So while the current weak trof in the east will be replaced by the approaching wave, the flow will remain weak but generally will reduce the higher moisture associated with this slow moving trough over the Souteast out to sea. The 00z UKMET continues to be a weak solution with the exiting trof and develops the weak surface wave out of NC still south and flatter than the consensus. The 12z NAM has trended much stronger with the kicker shortwave across the Great Lakes by late Monday, and adds increased energy to the developing surface wave off the coast, eventually slowing/bending it cyclonically westward toward Nova Scotia by Tuesday. As such will not favor either the UKMET/NAM. The 12z GFS has slowed a tad and gels well with the ECMWF/CMC through day 1 and 2 to provide a slightly above average confidence in a blend of the three through 00z Tuesday. There is some typical slightly stronger, slightly faster bias noted in the later portions of Day 3 for the GFS, but this is likely to offset the typical slow bias of the ECWMF/CMC. ...Shortwave moving into the Pacific Northwest Sunday night... ...Shortwave clipping Pacific Northwest late Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend (No/limited QPF from UKMET) Confidence: Slightly above average The compact closed low west of 130W is already showing signs of opening up toward the north and the approaching/digging shortwave energy out of the S Gulf of AK. The 12z NAM and 00z UKMET continue to be the stronger solution in the overall cluster but have tempered enough that blending with the much weaker CMC will bring solid agreement to not wash out the signal. The only concern remains the slightly stronger moisture advection of the UKMET in the Pacific NW. This can be a bias of the UKMET particularly when it is on the stronger side of the guidance suite. So would suggest tempering QPF from the UKMET in any blend. The aforementioned digging trough will continue to direct moisture/flow into SE Candada, but toward the tail of the forecast period (late Monday into early Tuesday) there is solid agreement to suggest NW WA will be clipped by the base of the trof providing a very slight chance of moisture reaching the far NW tip of the Olympic Peninsula. A general model blend will continue to be favored with the evolution of this feature as well. 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