Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 303 PM EDT Mon May 20 2019 Valid May 20/1200 UTC thru May 24/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation... ~~~~~~~~~~~~~~~~~~~~~~~~~~ ***Note... 12Z ECMWF not incorporated in the discussion owing to flash flood workload.*** ...Vigorous Central U.S. Cyclone... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS Confidence: Average An upper low churning over the Southwest is forecast to achieve 5 standard deviations below climatology at 500 mb as it swings into a negative tilt by Tuesday morning. This system is driving a High Risk of severe and flash flood hazards per SPC and WPC Outlook products. The mature cyclone may threaten monthly station pressure records in Kansas on Tuesday before the system lifts northward, and ultimately de-amplifies into a progressive northern stream trough crossing the Great Lakes on Thursday. The global models cluster decently well through Day 3. Among these, our preference leans toward the GFS for its consistency run to run. The ECMWF is also slightly "off" in some sense at the surface, as it places lowest pressures near the centroid of heavy rainfall over southern Kansas Tue morning. More likely, the surface low will remain tucked up under the jet in Colorado before migrating onto the Plains later in time per the GFS, UKMET. The EC also then tracks the low farther north and west from consensus across the northern Plains on Day 2. The 12Z NAM is usable, but not preferred in some of its upper air details, and for depicting a weaker surface reflection over the Plains. We note the FV3 was in lock step with the operational GFS. ...Vigorous Pacific closed low digging into the West Tuesday... ...Teleconnecting subtropical ridge over the Southeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS with support from the 00Z ECMWF Confidence: Average During Days 1 and 2 the next closed low arriving off the Pacific will drop into the base of the established longwave trough position occupying much of the Intermountain West and Southwest states. The GFS and ECMWF sit in fairly good agreement and share support from their respective ensembles. We give a slight nod to the GFS for the details, given run to run consistency and an associated preference for its handling of the downstream cyclone over the Plains. The NAM gets to be a bit faster than preferred by 23/00Z over the Southwest. ...Northeast U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS Confidence: Average In the near term a trough will pass through New England and move offshore. Model differences are minimal with this being in the first few forecast periods. This is followed by another shortwave arriving from upstream Wed-Thu. The ECMWF and ECMWF ensembles were not preferred at the surface over the Plains as discussed above. They then are quick to de-amplify this robust Great Plains system as it moves eastward, becoming an open wave. We prefer the GFS / GEFS which keep a bit more depth. The 00Z UKMET and 12Z NAM are reasonably similar to the GFS with the upper wave, but the GFS fits better with the ensemble support at surface and aloft. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Burke