Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 243 PM EDT Mon Mar 30 2020 Valid Mar 30/1200 UTC thru Apr 3/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over Northeast U.S. and offshore surface low early this week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High A broad upper level low over New England, with shortwave energy pivoting around it, will continue to support offshore surface low development with a secondary cold front exiting the East Coast later today. There is enough model agreement here to merit a deterministic multi-model blend. No changes to the model preference after the arrival of the 12Z non-NCEP guidance. Central Plains shortwave and southern U.S. surface low ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF Confidence: Moderate-High A strong southern stream shortwave exiting the Rockies and emerging over the central Plains will sustain a well developed surface low across the southern tier states through Tuesday evening. The low then emerges over the western Atlantic and then tracks to a position just north of Bermuda by Wednesday evening. There is good overall synoptic scale agreement as the system tracks eastward across the Gulf Coast region. The 00Z UKMET is farther south with the offshore track, and the 00Z CMC becomes a slower solution. Both the GFS and ECMWF have good ensemble support, and thus a blend of these two models is good. The 12Z UKMET trended closer to the model consensus while the 12Z CMC is still slightly slower. Broad upper level gyre over Northwest with northern tier cold front ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z GFS/00Z EC mean Confidence: Slightly below average An upper level low initially near the British Columbia coast will gradually reform over Alberta and remain nearly anchored in place for the next few days, with a couple of shortwaves pivoting around it. This will support a surface low just north of the Canadian border, and a second low over the Dakotas. Overall deterministic trends since yesterday show greater definition with these shortwaves tracking across the Northwest. The ensemble means show relatively good agreement with these features, with the NAM slightly faster to bring mid-level height falls to the region, and the 00Z UKMET not quite as amplified as the other models with the 500mb pattern. The 12Z UKMET trended more amplified over North Dakota by Wednesday evening with the shortwave trough, and the GFS is now among the deeper solutions by the end of the forecast period across southern Canada. Southwest shortwave and High Plains cyclogenesis midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z CMC/00Z EC mean Confidence: Moderate A broad southern stream trough pivoting eastward around the upper level gyre over southwest Canada will cross the southern Rockies and support lee surface cyclogenesis over eastern Colorado, with a frontal boundary extending westward across the Intermountain West. The main model differences noted here is the faster GFS and a northward displacement of the 6Z GEFS mean with the surface low over the western High Plains. The 12Z GEFS mean trended closer to the other deterministic guidance with respect to the surface low. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick