Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1237 PM EDT Sat Jul 04 2020 Valid Jul 04/1200 UTC thru Jul 08/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Trough building over the Northeast U.S. this weekend ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average Shortwave trough energy will skirt the Northeast and New England late in the weekend into early Monday. Model agreement is average to above average with the only notable difference seen coming from the 12Z NAM which is flatter and faster with the trough passage on Monday. It's quick to push through while the other models, dominated by the CMC and GFS, offer a slower and closed low solution off the Gulf of Maine. The UKMET and ECMWF are similar but a bit more open, but show similar timing to the GFS/CMC. Given these differences and how much the NAM is an outlier, a non-NAM blend is preferred. Trough over the Gulf Coast region ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS, 00Z ECMWF blend Confidence: Average After days of weakness in the upper level ridge over the lower MS valley and Southeast, some gradual building of heights is forecast over the next 3 days, though big significant changes in the flow are not expected. Remnant MCVs and convectively enhanced shortwaves will be common, tied to residual surface boundaries from earlier convection and much of the QPF and sensible weather differences are on the mesoscale level. Guidance ranges from the core of the upper level weakness to be as far east as GA (UKMET) or west over the lower MS Valley (CMC/NAM). The GFS/ECWMF offer a compromise approach and would be a good blend to go with given these differences. Troughing continues across the Pacific NW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average General troughing is expected to continue across the Pacific Northwest and northern Rockies through the forecast period with a couple different shortwave troughs moving through the flow. One currently is lifting across Montana which is expected to push through into southern Canada. Followed by brief ridging, another shortwave trough moves onshore Oregon/Washington Monday and Monday night. Overall, model agreement is fairly good, the NAM a bit deeper than the other deterministic guidance. But from a mass field perspective, a general model blend should be sufficient. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor