Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1246 AM EDT Mon Mar 25 2019 Valid Mar 25/0000 UTC thru Mar 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation With Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ OH Valley low weakening towards Southeast US coast Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Weak shortwave trough pushing through portions of the mid-MS Valley will cross through the OH Valley and Southeast US through Tuesday before exiting off the SC/NC coast. Overall, there is excellent model agreement in the mass fields with this feature such that a general model blend should be sufficient. Shortwave moving through the Great Basin/C Plains to Southeast Sun-late Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend (lower weight to 12z ECMWF) Confidence: Above average Model agreement continues to improve somewhat with the evolution and timing of the shortwave trough coming out of the central Rockies late Monday into Tuesday then dropping through the Southeast US into portions of FL by Tuesday night into Wednesday. The ECMWF continues to be a southern solution, even in the early periods, and additionally it is slightly faster than the GFS/NAM and UKMET. As the wave drops into GA and FL, the ECMWF remains the most amplified compared to the rest of the guidance, though all of the guidance has trended further south in the past several model cycles. With the better agreement, the preference remains for a general model blend but with less inclusion to the ECMWF for its speed/amplification issues. Pacific Gyre's First Wave Entering Northwest Monday Sliding across Southern Canada Enhanced by Digging Northern Stream Trof Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average through 26/12z Slightly below average thereafter Large Pacific gyre will remain mostly offshore through the forecast period but one piece of energy will initially push onshore into the Pacific Northwest Monday into Tuesday. In the past couple of model cycles, there has been improving model agreement. The wave pushes across Oregon initially early Tuesday morning then races into southern Canada by later Tuesday. The upper level pattern orientation is fairly consistent among the various models, though the UKMET is titled more vertically compared to the most positive tilt from the other models. But the timing and strength appears to be fairly similar, such that a general model blend should be sufficient. Main Core of Pacific Gyre Nearing Northern CA by Late Tuesday/Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend (less weight toward the CMC by 28.00z) Confidence: Slightly below average The 00z NAM continues to be an outlier with the main gyre that is rotating off the western US coast and as the main energy moves onshore late Tuesday into Wednesday, the NAM is much faster compared to the rest of the operational guidance. Whereas the rest of the guidance is actually in fairly similar speed and strength with the main mid/upper level features. At the surface, the NAM keeps the low just offshore but not as much as the ECMWF/GFS do. The CMC actually takes the low onshore by early Wednesday, and is the furthest east/fastest of the solutions. With that in mind, will lean on a non-NAM blend for the whole period but with less inclusion of the CMC toward the end of the period. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor