Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1217 PM EDT Tue May 28 2019 Valid May 28/1200 UTC thru Jun 01/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...CONUS from Rockies eastward... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF/UKMET through 30/00z 00z ECWMF/UKMET blend Confidence: Average to slightly below average Closed low over CO Rockies is emerging today into Central Plains with jet streak just NW of the base of the trof prepped to round the base over the next 12-24 hrs maintaining broad southwesterly flow aloft through the Day 1, early Day 2 period. The 12z NAM already shows an increased depth to the wave before the approaching shortwave/jet reaches the Central Plains into Wed, this allows for a greater retrograde of an internal binary interaction. While not to the same evolution, the 00z CMC shows this retrograde with both models quickly falling out of phase with ensemble suite holding a stronger closed/concentric wave in NEB through Fri. This begs either's utility in the blend with perhaps exception of Day 1. The 12z GFS, while slowing a tad from the 00z/06z runs, still shows its typical bias too fast bias with the jet rounding the base and is the only global guidance member to not be matched in timing of this critical shortwave, as such the QPF axis is further north with increased elevated convection and a northward shift of the frontal boundary across the Lower Great Lakes. Now, the GFS and the GEFS members do support the ECMWF/UKMET solution of shifting this shortwave through the Southwesterly flow making it the dominant circulation with the remaining weakening closed low in the Central Plains, providing some confidence toward those solutions. This allows for a faster eastward shift and greater placement/phasing with the digging northern stream trof. Here instability/moisture stream would favor the southern track across the Central Mid-Atlantic (S PA toward Long Island) of the UKMET/ECMWF without digging it southward (due to limited instability/moisture to support propagation southward). Now, the 00z ECWMF did show a sizable shift in timing and may be too fast, through New England/Mid-Atlantic as it even starts to outpace the UKMET. The UKMET has its issues as well into Day 3, showing a typical but negative bias;ie very amplified negative tilt/digging trof out of the northern stream. While, the NAM lost some strength to the lingering closed low in NEB, the shortwave does progress in a favorable axis with slower timing to potentially be useful in the Northeast in combination with the UKMET/ECMWF to slow the potentially uncharacteristically fast ECWMF. Overall, the blend of the UKMET/ECWMF on Day 3 is slightly below average in confidence, but some inclusion (low weighting) of the NAM may help to account for some of this uncertainty, still the pattern with multiple phasing systems highly contingent on confluence axis and timing is generally a reduced confidence scenario. ...West Coast/Great Basin... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average In the West, with the shortwave accelerating around the base of the trough Wed, a very weak ill-defined trough/flow remains upstream positive tilt ridging into the far Pacific Northwest by Thursday allows for broad but weak closed low/trof to develop over California by Friday. Guidance, there is solid model agreement here with the evolution/timing and placement to have confidence in a general model blend at slightly above average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina