Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Tue Jun 23 2020 Valid Jun 23/1200 UTC thru Jun 27/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over Ontario/Quebec Trough crossing the eastern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The large closed upper low over Ontario is expected to slowly advance eastward through western Quebec over the next few days as the southward extension of a broader trough crosses through the eastern U.S. This will drive a cold front toward the Mid-Atlantic and New England Wednesday before then slowing down and only very slowly drifting offshore by Friday while the southwest tail of the front hangs up over the Southeast. Model spread at least synoptically is rather minimal, so a general model blend will be preferred. Shortwave crossing the Pacific Northwest and Plains Energy digging into the Southwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS Confidence: Average The latest guidance continues to advertise a shortwave trough crossing the Pacific Northwest on Wednesday and then amplifying through the central/northern Rockies going through Thursday. As this is occurring, some of the energy will be separating out and digging farther south into the Southwest. On Friday, the northern portion of the original trough will eject out across the central and northern Plains, with the guidance favoring a southern stream trough lingering near the Four Corners region. With the initial surge of the northern stream portion of the trough, the 12Z UKMET is now seen as being a tad more progressive/weaker with the energy. With the southern stream energy, the 12Z ECMWF and 12Z CMC both tend to hold energy back farther to the west over the Southwest compared to the 12Z NAM/GFS solutions. The 12Z UKMET with this energy is actually close to the NAM/GFS camps, but is a little weaker. Overall, the NAM/GFS camp has better ensemble support for the time being, and so a blend of these solutions will be preferred with both energy streams. Mid-level troughing over the lower MS Valley/Texas MCVs ejecting across southeast Texas and the Gulf Coast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS/ECMWF Confidence: Average A broad mid to upper-level trough is expected to become removed from the westerlies and slowly meander over the lower MS River Valley and TX over the next couple of days. In the meantime, a strong MCV over north-central TX this morning is expected to gradually settle southeastward toward the southeast TX coastal plain tonight and become an active focus for renewed convection and potentially some very heavy rainfall going through early Wednesday. This energy should then drift east through Thursday and generally shear across the Gulf Coast states. However, out ahead of this energy is an MCV which is currently over the western Gulf of Mexico, and the models agree in taking that energy northeastward and inland across southeast LA and southern MS going through early Wednesday. The 12Z non-NCEP models have come around to the stronger NAM/GFS reflections of the energy over the western Gulf of Mexico and especially the MCV and attendant low center over north-central TX. In fact, all of the models suggest a low center dropping down across southeast TX through early Wednesday which then advances eastward through LA and southern MS going through Thursday. However, there is some significant timing spread as the 12Z GFS and especially the 12Z ECMWF are slower to advance it east. The 12Z NAM though is actually only a tad faster than the GFS. The 12Z UKMET is a strong and fast outlier solution, while the the 12Z CMC is the weakest solution. By late Wednesday and early Thursday, the guidance favors some additional shortwave/MCV energy dropping southeast through TX which will help to reinforce the broader mid to upper-level trough over the region. The guidance is rather weak with this additional energy for time being. Based on the latest model guidance and clustering, a blend of the NAM/GFS and ECMWF will now be preferred and especially with the CMC/UKMET solutions being the bigger mass field outliers with the MCV/low evolution through southeast TX and downstream over the Gulf Coast region. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison