Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed Jul 01 2020 Valid Jul 01/1200 UTC thru Jul 05/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Final Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low exiting New England Thursday and back door front diving through late Friday... ...Developing trough near the Gulf Coast Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through Friday Non UKMET/CMC Saturday /D3/ Confidence: Above average through Friday, average Saturday 19Z Update: No changes to the preferred blend with the 12Z non-NCEP suite. The CMC has backed off a bit on the amplitude of the trough/closed low near the Gulf Coast, trending more towards the prior preferred consensus. Previous Discussion: Guidance is in excellent agreement with little spread in both the spatial and temporal evolution of the closed low dropping E/SE away from New England late in the week. By Friday the closed low opens and is well removed from the East Coast, and a general blend is acceptable through D2. Thereafter, as a ridge tries to blossom northeast from the middle of the country, a trough digs back into New England, while a secondary trough develops beneath the ridge axis across the Gulf Coast. In New England, a back door front digging southward Friday night into Saturday features similar timing, although the GFS may be a bit too fast to drive the front southwest as it encounters a ridge and may get hung up by interaction with mid-level impulses. The ECMWF on the other hand is the wettest of the guidance and features the subtly strongest shortwave. A blend of these features should get something close to reality, and is closer to the ensemble means. Across the Gulf Coast, the UKMET shows no evidence of a trough as it bulges the ridge too quickly from the W/SW, while the CMC is a strong outlier with the intensity of the trough, closing it off near the central Gulf Coast. Removing these two features from the blend leaves a good general consensus among the rest of the global models in a broad positively tilted trough lingering near the Gulf Coast Saturday. It should be noted, however, that this trough develops in response to residual MCVs diving through the MS VLY earlier in the forecast period. The position and intensity of these features are notoriously difficult to place, especially by D3, so uncertainty in the blend and the evolution becomes much greater by the weekend. ...Deep upper trough/closed low across the Inter-mountain West... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through Friday Non NAM/UKMET Saturday /D3/ Confidence: Average 19Z Update: No significant changes with the preferences after examination of the 12Z non-NCEP suite. Previous Discussion: Expansive closed low meandering across far western Canada and the Pacific Northwest will linger through Friday as multiple vort centers rotate around themselves and within the larger gyre. Slowly, this feature is likely to generally lift northeast into Canada, leaving just a weak trough across the PacNW by Friday. The guidance does feature subtle differences in the intensity and position of the individual vort centers, but the general mass field shows good agreement through 60 hours. Thereafter, the NAM and UKMET both dive a stronger shortwave near the OR coast for D3, amplifying the trough once again, becoming outliers compared to the global consensus. While QPF looks minimal across the NW during this time, a deeper trough and a more SW to NE oriented jet streak in response could provide more significant ascent locally D3. The remaining guidance including the ensemble means show a flatter depiction of the trough by this time with a more zonal jet streak, and this is preferred for the region at the end of the forecast period. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss