Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1211 AM EDT Mon Jun 15 2020 Valid Jun 15/0000 UTC thru Jun 18/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low developing in Southern Appalachians Mon/Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through Tuesday night Non-NAM Wednesday Confidence: Above average The forecast, prolonged, stationary closed low is starting to take up general residency across the Central to Southern Appalachians with the inner core vorticity center continuing to SC by 48hrs. There is very strong agreement with this evolution and placement. Its influence along with easterly low level flow off the unstable Gulf Stream will support a low level wave to retrograde across the Coastal Plain over Tues/Wed. The 00z NAM continues to show a very strong convective response and builds the MCV/deeper shortwave allowing a mature cyclone to retrograde further away from the persistent instability source. Given the inflow will likely support back-building to the well of Gulf Stream warm waters; the NAM evolution looks a bit over-played as it moves away from otherwise solid consensus by Wed. As such a Non-NAM blend is supported after 48hrs 17.00z at above average confidence. The potential for stationary convective bands and high rainfall rates/totals needs to monitored closely (please see excessive rainfall discussions for further details), as the UKMET/ECMWF/GFS suggest similar bands just not to the magnitude and upscale influence as the NAM. ...Interaction of shortwave lifting through SW Canada with a closed low advecting onshore Washington Sunday... ...Secondary closed low moving into the Northwest Tuesday... ...Northern Plains surface lows/N-S frontal zone... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend until 17.18z then Non-GFS/NAM blend thereafter Confidence: Above average through 17.00z, average thereafter Interaction of a shortwave lifting into Saskatchewan and a closed low moving onshore Washington state drives the blend through 17/00Z. Given the uncertainty of the leading shortwave has come to reality, the interaction between the two in the larger global scale closed low/gyre across the West is becoming much better aligned, especially through 48hrs. Afterwards, as the nose/exit of the jet crosses the Northern Rockies, the resultant surface low across MT into the Dakotas will have some spread. The 00z GFS is once again faster with this wave and even outpaces the bulk/majority of the GEFS members to be an outlier. The GEFS mean is more inline with the ECENS mean and other global guidance, providing greater confidence in this slower evolution. The 00z NAM is more aligned synoptically, but the convective elements once again allow for greater amplification/deepening that is such a negative bias of the later hours of the NAM runs to start moving it out of the preference as well at 72hrs. So a 18z GEFS and 12z ECMWF/ECENS/CMC/UKMET blend is preferred by the end of the forecast period, but the 00z NAM could be added at lower weight from 17.00z to 18.00z if finer resolution/details are desired in the blend. Gallina Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml