Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1217 AM EDT Fri Apr 24 2020 Valid Apr 24/0000 UTC thru Apr 27/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Evaluation with Initial Model Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Low pressure crossing Mid-Atlantic on Friday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/00Z NAM/00Z GFS Confidence: Moderate-High The southern stream storm system with surface low initially over the central Appalachians will continue tracking east across the Mid-Atlantic on Friday, with a secondary low likely developing southeast of New England by Friday evening that becomes the main low passing south of Nova Scotia. The 12Z CMC is a little bit weaker with the accompanying 500mb shortwave, and once the system emerges offshore, the UKMET becomes slightly slower with the consolidated surface low. Low pressure tracking from Texas to the Ohio Valley ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z EC mean/00Z GFS Confidence: Limited-Moderate A somewhat complicated upper level pattern evolution across the north-central U.S. with broad northwest flow will be in place to end the week. A stronger lead trough will be followed by a more subtle secondary trough, tracking from the northern Rockies to the Midwest states, and eventually consolidate into one main upper level trough and then closed low over the Northeast U.S. by the end of the forecast period Monday morning. A surface low will become better organized across the southern plains and then cross the mid-south and Ohio Valley by Saturday night, followed by likely secondary cyclogenesis near New England as a potential nor'easter for early next week. In terms of the models, the 00Z NAM appears slightly slower with the track of the low, the 12Z UKMET a little weaker and south of the model consensus, and the CMC a bit more amplified with the upper trough crossing the mid-south on Saturday. Much of this will depend on the shortwave energy rounding the apparent trough axis and therefore influence the timing of precipitation as well. The energy diving south from Canada into portions of North Dakota and into Minnesota seem to be weaker and slower with the ECMWF. For Day 3, the NAM seems slightly slower with the upper level low, and the UKMET a bit more suppressed with the surface low. The 00Z GFS is reasonably well clustered with the low near the Northeast coast albeit a little faster, although the 18Z GEFS mean is displaced some to the north.  Pair of troughs affecting the northwestern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General blend for first trough, and 00Z GFS/00Z NAM/12Z EC mean for second trough Confidence: Moderate The upper level ridge that is currently in place across the West Coast region will begin to be eroded by a moderately strong storm system approaching British Columbia on Saturday with a cold front reaching the Pacific Northwest coast. There will be a brief break before a second and potentially stronger system approaches from the northeast Pacific Sunday night into Monday morning with another frontal passage. For the first system, there is enough deterministic model agreement to merit the use of a general blend. For the second system, the 12Z UKMET is a bit faster with the surface low and front, and the ECMWF becomes slightly stronger with the shortwave by Monday morning. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick