Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 223 AM EDT Fri Apr 05 2019 Valid Apr 05/0000 UTC thru Apr 08/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave/surface low crossing the Ohio Valley Fri/East Coast Sat... ...Potential surface low developing along the Southeast coast Fri night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: The 00z UKMET/CMC/ECMWF depicted little significant change to continue a general model blend solution as preference. ---Prior Discussion--- Both the 00z NAM/GFS are a bit more amplified across the Ohio River Valley, directly sampling the current observations. This does not significantly affect later evolution of the wave and surface low along the Southeast Coast later tonight. As such a general model blend can be employed at slightly above average confidence. ...Active Pacific upper-level jet reaching the West Coast with series of embedded shortwaves... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average 07z update: By early Sunday, the CMC is generally slower and flatter with this wave, and in turn becomes much more amplified with the subsequent wave toward 00z Monday nearly perfectly out of phase with the GFS/NAM and lesser so flatter, UKMET/ECMWF solutions. This also leads to some downstream issues across N Central Canada. The ECMWF/UKMET continue to show similarity in timing to support a blend with the NAM/GFS throughout the period, yet the magnitude of the waves continue vary run to run and within this blend to keep only an average confidence in predictability. ---Prior Discussion--- Models continue to show larger scale consistency with placement/timing of the deep closed low across the NE Gulf of Alaska. Models also show fairly good agreement in the multiple outer bands/shortwave troughs quickly rotating through the Northwest Pacific states, while run to run consistency in precise depth of each wave continues to be eluded, the timing is suffice to have confidence overall. QPF-wise, the intersection of the base of each trof and the deep moisture stream provide higher confidence in the placement of the highest moisture flux across S OR/N CA. As such, a general model blend is preferred, mostly to tamp out some of the most amplified waves (ie, 00z GFS early Sat, or 00z NAM/12z UKMET early Sunday), but keep the strong moisture flux and focus. However, this would reduced confidence in any specific wave, though fairly high in the overall pattern; so average overall. ...Southern stream shortwave crossing the Southwest Fri and reaching the central U.S. Sun/Mon... ...Connection to northern stream wave entering Southern Prairies into Northern Plains by early Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/CMC blend with 00z GFS at lower weight Confidence: Slightly below average 07z update: The UKMET continues to be very fast in the northern stream and with less interaction with the southern stream, allows for a stronger, yet faster closed low in the Lower MS Valley by 12z Monday. Both the 00z ECMWF/CMC trended toward a faster northern stream too, with much less phasing than the NAM/GFS. This is an atypical timing orientation with the ECMWF/CMC outpacing both the NAM/GFS, leading to reduced confidence in the slower solutions. Still the GFS is somewhat closer and with the amount of uncertainty in a lower predictability flow regime, confidence remains slightly below average in a ECMWF/CMC blend (for both streams) with some inclusion of the 00z GFS at lower weighting to account for some slower possibilities. ---Prior Discussion--- At the start of the period, an ill-defined base of shortwave energy crosses through the Southwest, amplifying/stretching (vertically) slightly after crossing into the Plains on Sat, additional southern peripheral shortwave energy from the energetic Pacific, reinforce and broaden the southern trough by Sunday. Strong jet crossing from the atmospheric river into the Northern Rockies, will aid the left rotor to the jet circulation across the Southern Prairies by Sunday as well, leading to two cyclones north and south, respectfully of the strong SSW flat jet. Interestingly, the 00z NAM is broader with the 250mb jet, and retards the westward progression of the deformation zone between the cyclones relative to the GFS/ECMWF. While the 00z GFS did strengthen the northern stream and shift the jet axis slightly north it did not affect the overall evolution too much relative to the 18z run or 12z ECMWF solution. It does, delay the southern stream solution and help support a more rounded cyclone through the southern Red River Valley. This trends away from the 12z CMC which has been a bit faster than the GFS/ECMWF in the southern stream, but also significantly amplifies the northern rotor cyclone across Ontario by 84hrs. The UKMET is and has been out of phase with the ensemble suite. Overall, this is a very low predictability pattern, given the importance of many weak shortwave trough placement relative to each other, as well as influence of Pacific jet orientation. This leads to lower confidence overall in any particular blend. Still, will favor a blend of the GFS/ECMWF at slightly below average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina