Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 236 PM EDT Sun Apr 12 2020 Valid Apr 12/1200 UTC thru Apr 16/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 19Z Update: The 12Z CMC trended slightly stronger with the East Coast shortwave and surface low compared to its 00Z run, but is still weaker than the remainder of the 12Z model suite, and trended faster with the shortwave crossing the southwestern U.S. on Wednesday. The 12Z UKMET trended more in line with the other model guidance across the Intermountain West on Tuesday compared to its earlier run, leaving the 12Z NAM as the most amplified solution aloft. The ECMWF trended a little father east with the closed low off the West Coast by the middle of the week, and is close to the NAM in its position. Southern stream shortwave leading to intense surface low over Great Lakes ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC deterministic blend Confidence: Moderate-High The strong southern stream trough and shortwave currently over the southern Plains will rapidly track northeastward across the ArkLaTex region through this evening, and then reach the Ohio Valley and Northeast U.S. by Monday night while phasing with a northern stream disturbance over the Great Lakes region. This will lead the way for a rapidly intensifying surface low to lift northeastward across the Ohio Valley and Great Lakes, along with a strong cold front reaching the East Coast by Monday evening. It appears likely that a dual surface low structure develops, and then evolves into one main powerful and occluded low by Monday afternoon across the northern Great Lakes. The model guidance has consolidated on a general track and intensity, with the main difference being with the 00Z CMC in that it is weaker with the shortwave perturbation and not quite as strong with the intensifying low over the northern Great Lakes and Ontario. There are also some latitudinal differences noted across Michigan as the surface low consolidates, and those differences can be resolved with a non-CMC deterministic blend across that region. Amplifying upper trough over the northern U.S. through midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Wednesday, then 12Z GFS/12Z UKMET/12Z CMC Confidence: Moderate The models bring amplifying shortwave/jet energy southeastward from southwest Canada and out across the northern Rockies and northern Plains by Monday, reinforcing the longwave pattern and broad cyclonic flow aloft over much of the continental U.S. through the middle of the week, with multiple shortwaves pivoting through. Overall, the models are in good agreement with the details of the longwave trough evolution, with the exceptions of the 00Z UKMET that is a bit more amplified across the Intermountain West on Tuesday, and the ECMWF becomes more amplified with the mid-level shortwave sinking south across the northern Rockies on Wednesday. Shortwave near the Pacific Northwest by midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECENS/12Z ECMWF/12Z NAM Confidence: Limited-Moderate A closed low currently near 40N and 155W over the North Pacific will try to undercut an upper level ridge near the Gulf of Alaska through Tuesday, and then sink southward near the West Coast of the U.S. by the middle of the week. The models begin to differ on their solutions as early as 18Z Tuesday as they have difficulty handling the interactions with the existing ridge axis. The latitudinal and thus speed differences are more apparent by Wednesday, with both the 6Z and 12Z versions of the GFS faster with the closed low offshore. The 00Z CMC is on the slower side of the guidance and the ECMWF is a bit farther west with the core of the upper low. Given these differences, an ensemble mean approach with the 00Z ECENS along with some of the UKMET and NAM would yield a decent compromise. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick