Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1243 AM EDT Tue Apr 28 2020 Valid Apr 28/0000 UTC thru May 1/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Departing Northeast storm system through Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High The exiting coastal low from New England will pass south of Nova Scotia through Tuesday as it consolidates into a stronger low south of Newfoundland by Tuesday night. Deterministic model spread is minimal and therefore a general model blend will continue to work well for this region. Strong storm system developing over the north-central U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z ECMWF/ECENS with lesser weighting to the 12Z UKMET Confidence: Average A northern stream shortwave trough is amplifying across Montana and the Dakotas in response to a deep layer ridge developing over the western U.S. and southwest Canada, and this will continue going through the middle of the week. A well developed closed low is forecast to evolve over the Midwest and then the southern Great Lakes by Wednesday night as a deep layer trough envelops much of the eastern U.S. by that time period. All of the models show reasonably good agreement with the upper level evolution and surface cyclogenesis going through Wednesday morning. By early Thursday, some latitudinal differences become apparent as the 00Z NAM/GFS solutions have the surface low over central Michigan, and the 12Z non-NCEP solutions tending to keep the low farther to the southeast, and with a bit better defined triple-point low over the Mid-Atlantic states at the end of the period given placement of stronger height falls focusing still a tad farther south, with the UKMET on the southern edge of the guidance spread through Wednesday evening. Pair of shortwave troughs for the Northwestern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/00Z GFS/12Z UKMET Confidence: Above average A modest and rather progressive shortwave trough from the north Pacific is expected to clip Washington state and reach southern British Columbia by late Tuesday. A weakening cold front is expected to accompany this shortwave feature as it heads into an upper level ridge axis, although the parent surface low will pass well to the north near the southeast Alaska panhandle. In terms of the latest model guidance, there is now enough model agreement to support a general model blend for this first wave. A second shortwave disturbance will track just behind it and should reach the Pacific Northwest on Thursday, with the front moving inland across portions of the West. The guidance reflects a relatively low-amplitude to this system at least through this period, with the NAM and UKMET initially a little stronger as the system approaches the coast, and the CMC is quicker with the progression of the front. Although the 00Z GFS is slightly more amplified aloft, it is in better agreement compared to earlier runs. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick