Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1225 AM EDT Mon Apr 08 2019 Valid Apr 08/0000 UTC thru Apr 11/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Exclusions: No ECMWF in Pac NW on Day 3 Confidence: Slightly above average Deterministic guidance along with ensemble suite depict an increasingly convergent evolution in most streams/systems through the short-term forecast period out to Thurs 11/12z. Only the 12z CMC is a clear outlier in nearly all systems...and as such a preference of Non-CMC blend is preferred. However, to be expected, there is minor timing differences that will be discussed per system below, with deeper weighting/confidence information. ...Great Lakes/New England (northern stream shortwaves)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GOES WV suite denotes a nice dynamic depiction of a highly arched shortwave trof with strong zonal jet beginning to bisect the wave, developing rotors circulations. Timing, which had been a small issue seems to have resolved given better sampling of the atmospheric river jet from the Pacific. As such, guidance comes into agreement even with the left rotor stalling over Western Ontario through Tuesday before swinging through the Great Lakes into New England by Wed. Here only the CMC, retards the shortwave too much and allows it to languish over Manitoba in the mid to upper levels (7H-3H). Its importance to the QPF, is limited with exception of enhancing the DPVA across New England relative to the other guidance. So while, a non-CMC blend is preferred, the alternative solution does not have much difference...so a non-CMC blend is preferred at above average confidence for this stream/systems. ...Southeast (southern stream closed low)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GOES WV suite depicts mature deep cyclone over E TX advancing eastward. Guidance has come into much stronger agreement with slow stretching of the cyclone across the Lower MS Valley into Central Appalachians late Tues into Wed under influence of digging northern stream trof and increasingly progressive flow across the CONUS in the higher upper-levels. Here, the CMC stands out, being closed a bit further south than the remaining guidance/ensembles...as such shows less stretching into the northern stream and drops further south into the Gulf. While, the 12z UKMET also is a bit less hesitant to shear, this appears to be more in line with a typical bias resulting from greater upscale latent heat enhancement to the upper-low and results in a deeper (~4mb) surface low difference than the remaining guidance; however, the timing is more favorable and could be included in the non-CMC blend at lower weighting than the 00z GFS/NAM or 12z ECMWF/Ensemble mass solutions. Confidence is slightly above average for this system. ...Approaching Western trof Mon/Tues, amplifying through Intermountain West by Wed spurring deep Plains cyclone, Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Guidance continues to show very good agreement in the timing of the shortwave that brings the end to the prolonged AR event across OR/N CA by midday Tuesday. As the shortwave, translates southeast, the ECMWF/CMC are generally a bit weaker though the CMC is a tad stronger further north than other guidance, which negatively plays into its evolution thereafter but does not affect the ECMWF evolution as much. The lingering shortwave in Manitoba also further draws the closed low/surface low further north and so is not preferred in the blend for this system too. The 00z NAM/GFS and UKMET all, in line with their bias, are a bit faster and earlier aloft to amplify the wave late Wed. The 00z NAM trended a bit further north with some of the upscale feedback from initial QPF near the Black Hills. This leads to an offset that surges the main core of the shortwave northward, away from the growing consensus (as well as a bit stronger). While, this is not dramatically out of place in timing, there is much stronger agreement with the GFS/UKMET in timing/strength and placement and therefore is preferred to reduce the weighting of the NAM after 10/18z. The ECMWF is slower which initially leads to a further south QPF axis across NEB/SD. Still, a Non-CMC blend is preferred at slightly above average confidence. ...Wed/Thurs Closed Low entering Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over the Northern Gulf of AK has been consistently progressive though with ensemble trends toward a stronger downstream ridge (concentric as well). Additionally, the approach of the next very strong jet further suggests a flattening/shearing of the shortwave energy through coastal BC into the Pacific Northwest by late Wed into early Thursday. Only the 12z ECMWF appears to be opposed to the magnitude of shearing, retaining a stronger/more concentric mid-level shortwave under-cutting the ridge. This allows it to be a bit further south with the QPF axis as well by the end of Day 3. While the 12z CMC is not favored elsewhere, it is a middle ground between the highly sheared (faster) GFS and UKMET and the ECMWF. So would also exclude the ECMWF in this blend as well as the CMC (or retain a very small weight of the CMC to account for the mild spread. Confidence is average in this GFS/UKMET and NAM blend. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina