Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 131 AM EST Fri Mar 01 2019 Valid Mar 01/0000 UTC thru Mar 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Phasing across Northeast/Coastal surface cyclone Sat/Sun ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GEFS/UKMET/ECMWF/CMC blend Confidence: Average 07z update: The shift westward and slightly deeper continues in the late arriving guidance. The most significant shift was the 00z UKMET, with a deep almost convective upscale response, (similar to the GFS), while slightly east of the GFS, it is in line with the 00z GEFS mean. The 00z ECMWF shifted west but remains very close to the 12z ECENS mean, east of the UKMET/GFS, less amplified. This was further corroborated by the 00z CMC. Clearly, the trend is deeper, but do not want to go as aggressive as the GFS. As a compromise, will favor inclusion of the 00z GEFS/UKMET with the CMC/ECMWF in the blend. With some reduction of spread, there is increased confidence but only to average in this blend. ---Prior Discussion--- Complex confluence of mid-level shortwave energy fairly rapidly deepens surface cyclone off the Mid-Atlantic Coast clipping SE New England. Broadly zonal pattern over the CONUS transports shortwave energy out of the closed low in WA across the Northern Plains and Great Lakes by early Saturday. Southern shortwave and associated surface wave slide out of the TN Valley, into the Mid-Atlantic. The southern stream wave deepens the surface wave off the Mid-Atlantic coast. As the northern stream shortwave elongates to phase with the wave, difference in timing and orientation to the southern stream lead to moderate to high model spread. Ensemble spaghetti analysis depicts a fairly steady state ECMWF/ECENS solution slowly adjusting westward while other guidance has been very inconsistent but trending toward it. Clear outliers remain: the 00z NAM, which does not depict much of the northern stream energy (mainly sheared out into the zonal flow) eventually shunting the deepening surface wave well east of the cluster; the 12z CMC shows greater amplification in both streams but the southern stream is further east, having not trended like other guidance. The 12z ECMWF, like prior runs, has been on the southeast side of the ECENS cluster but is also generally slower with the northern stream wave, leading to reduced iteration initially (compared to other deterministic runs, esp. GFS). As the wave deepens, it is slowest to eject eastward and may be a bit too slow. The 00z GFS, like the 18z run, continues a sizable shift westward with a stronger/faster deepening surface wave near or just inside the benchmark receiving much of the deepening through upscale growth. While there is increased low level theta-e, this may be a bit too aggressive, especially without other guidance support. The 12z UKMET would be most middle ground and shows a similar evolution to the ECMWF, but more favorably faster than the EC. All considered, will favor the 12z UKMET and ECMWF, but with the GFS trend/upscale enhancement there is a growing uncertainty in the preference as the overall mass field setup deems the GFS/GEFS solutions remaining plausible (even if not favored), making confidence is slightly below average. ...Progressive West Coast Low (Sat), Lower Red/MS Valley by Sun and Amplifying along East Coast by Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z UKMET/CMC/ECMWF blend Confidence: Average 07z update: Further slowing was noted in the non-NCEP guidance but influence from a downstream deeper solution presses the trailing frontal zone a bit further south. This allows for the ECMWF/UKMET to shift southward relative to the 12z runs, with the UKMET nearing the GFS axis. The CMC shows similar run to run continuity but is bolstered by the ECMWF/UKMET. Some inclusion of the GFS seems appropriate, especially on Day 1 into Day 2, but as the system slides toward the East Coast and northern stream digging influences lead to slightly faster timing, would still prefer to hedge away by Monday. As such will favor a 00z ECMWF/UKMET/CMC blend at average confidence. ---Prior Discussion--- The closed low over the Northwest US will help direct progressive southern stream shortwave energy into Central/Southern CA later in the day Saturday, while shearing into increasing zonal flow across the Rockies and Northern Plains. There is fairly good agreement in the timing of the Pacific wave though the 00z NAM appears a bit too amplified, and retains the strength of the wave even though it is flat across KS into the Ohio Valley making it a bit less preferred. The remaining guidance is fairly agreeable with the shortwave progressing into the Southern Plains, but there is fairly sizable difference in the placement of the surface front and upglide/convective development in the Lower Red River/Mississippi River Valley by early Sunday. The ECMWF is furthest north with greatest vertical angle to the isentropic ascent gradient supporting a more consolidated QPF response. This seems a bit unlikely this early in the season, given displacement from the warm Gulf without great warm air advection ahead of deepening/amplifying system. The 00z GFS, on the other side of the guidance, suggests a frontal zone very close to the Gulf with a secondary QPF maxima in the deformation zone further aloft in the Ozarks. This also seems a bit too dramatic for preference, especially considering how fast the GFS gets across the southeast into the Mid-Atlantic by Monday. More middle ground, in both latitude and timing are the 12z UKMET and CMC. By late Sunday, there is some typical timing difference with greater northern stream phasing (faster) with the UKMET compared to the CMC. Still, a compromise between the two seem appropriate though moderate spread keeps confidence in this blend (especially by Day 3) to slightly below average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina