Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 232 PM EDT Sun May 10 2020 Valid May 10/1200 UTC thru May 14/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low moving from Great Lakes to New England through Tuesday... ...Energy amplifying from the OH Valley to the Northeast Mon and Tues... ...Shortwave moving across the Great Lakes and Northeast Tuesday and Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12.12Z; followed by a ECMWF/ECENS blend Confidence: Average 19Z update: With the 12Z models now all available, there remains some spread in the progression, depth, and track of the shortwave feature over the Northeast and New England in the Day 2/3 time frame. The 12Z UKMET trended deeper, slower while now the GFS/NAM solutions are clearly a faster/weaker set of solutions. The ECMWF remains stable and in between, similar to the CMC. For the reasons, will continue to prefer a ECMWF-based blend with incorporation of the CMC given the 12z update. ---previous discussion--- Large cyclonic flow will persist over the Great Lakes and eastern US through early next week with large height anomalies centered over the Hudson Bay region. A pair of compact shortwaves will work through base of the large scale closed low, the first of which moves from the Upper Mississippi River Valley today toward the Northeast early next week. A deepening surface low will track from near Chicago to the Gulf of Maine. Through about 36 hours, the low track and depth is well agreed upon by the latest guidance but then diverges as the system exits the coast off Maine. The GFS has a northern track and the NAM also is on the northern side of the spread. The non-NCEP guidance shows fairly good clustering on the southern side of the spread. Looking at the ensembles, the ECMWF/ECENS are nearly identical while the GEFS mean leans toward the ECMWF/ECENS solution, putting the deterministic GFS as the outlier. For this reason, a non-GFS solution is recommended after 12.12Z. A secondary, compact shortwave is then forecast to wrap behind the initial system over the northern/interior New England states Tuesday/Tuesday night. Here, model agreement is relatively stable, though the CMC and UKMET seem to have some timing/depth issues. The UKMET is on the faster side of the model guidance while the CMC is a bit too deep as the shortwave pivots over New England. For these reasons, a general model blend should be sufficient through about 12.12Z but beyond that, given the issues with the initial and secondary shortwaves/lows, a blend utilizing primarily the ECMWF/ECENS mean is preferred. ...Shortwave energy crossing the Southwest on Sunday... ...Energy shearing across the southern Plains by Tue... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average 19Z update: No significant updates with the rest of the 12Z guidance now available to change the previous general model blend preference. ---previous discussion--- A subtle shortwave will move through portions of the Desert Southwest today before crossing into the southern Plains and lower Mississippi Valley early next week. In the large scale sense, there are very little differences seen in the latest model guidance and a general model blend should more than suffice for mass field purposes. As the system ejects into the Plains, there are some magnitude differences in QPF but these should be resolved on a smaller scale than the synoptic pattern. ...Upper trough/closed low lifting along the Northwest Coast Mon-Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12.12Z; non-NAM thereafter Confidence: Average 19Z update: No significant updates with the rest of the 12Z guidance now available. The NAM continues to progress the shortwave energy faster inland compared to the rest of the models, so will keep the previous model blend preference. ---previous discussion--- A longwave trough and closed low approaches the Pacific Northwest early next week. As the system approaches the coast, it will slow/stall thanks to stubborn ridging inland. The closed low will then wobble/meander through the end of the period. Pieces of the energy will separate and move inland, interacting with another piece of shortwave energy over the southern Canadian Rockies. Through about 48 hours, a general model blend should be sufficient as there is little spread seen in the latest guidance. Beyond that time frame, the NAM becomes less usable as it appears to be too quick to absorb more of the energy into the Rockies system. The more reliable ECMWF/GFS/UKMET in the 48-84 hour range show the closed low lingering longer, which fits the pattern and teleconnections. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor