Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 225 AM EDT Wed Apr 08 2020 Valid Apr 08/0000 UTC thru Apr 11/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface wave moving through the Great Lakes tonight, then sliding offshore along 40N Wed/Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 07z update: The 00z UKMET, CMC and ECMWF all shifted slightly faster to further tighten the spread; enough to support a general model blend at above average confidence. ---Prior Discussion--- The 00z GFS did slow and slide south with the developing offshore surface low, bringing it closer to the overall suite. While the 12z ECMWF/CMC and lastly UKMET are slower and therefore and more south of 40N; the closeness and tightening of solutions supports a general model blend at slightly above average confidence. ...Upper Trough Digging Across Great Lakes; Strong Surface Low Developing Off New England Coast Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average to above average 07z update: Frontal timing and strength/placement of triple point development across the Northeast continue to match solidly to continue a support of a general model blend (after assessing the 00z GEFS/CMC/UKMET and ECMWF). Smaller scale/mesoscale features are even now coming into agreement, which is impressive this far out. Still, there remains some important latitudinal/depth differences to not have full confidence in a general model blend but it is very close. ---Prior Discussion--- The overall model suite continues to tighten overall. The 00z NAM/GFS though are a tad weaker becoming elongated more than the concentric ECMWF/CMC. Still, the mass fields, timing and location of the surface low(s), including the rapid deepening through Southern New England/Gulf of Maine look on track to support a general model blend at slightly above average confidence. ...Slow moving southern stream (S CA/Desert Southwest) closed low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/ECMWF/CMC/GEFS and 12z ECENS mean blend Confidence: Average 07z update: The 00z CMC and GEFS both trended westward, while the ECMWF is less fractured/west compared to the 12z ECENS suite, so confidence is increasing toward further slowing down the low, and so will incorporate more ECMWF and less GFS (replaced with the GEFS). So a 00z NAM/ECMWF/CMC blend with the 00z GEFS and 12z ECENS is preferred at average confidence. ---Prior Discussion--- The 00z NAM and GFS both shifted slower and wobbled more centrally than say the 12z UKMET/ECMWF which continue to break down the inner core of the larger scale and wobble much further west. This will also allow for greater tapping of the offshore moisture stream for increased QPF threat. While not out of the realm of possibility (given the longer term trends of slowing) the UKMET/ECMWF remain on the far western side of the ensemble suite. This while the 00z NAM/GFS and 12z CMC are more representative of the suite as a whole (including the CMCE and ECENS members). As such, will support a 00z NAM/GFS and 12z CMC blend to represent the greater probabilities and knowing the negative biases of the ECMWF/UKMET...which seem to be manifesting with each run. Confidence remains average. ...Upper trough and related surface cold front reaching MT/ND on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: The CMC shifted north (stronger/slower) and while it is still a tad south of the growing consensus and small adjustment faster/east/south of the UKMET/ECMWF helps to encompass the CMC in the overall spread well, to support a general model blend at slightly above average confidence. ---Prior Discussion--- Shortwave along the south coast of AK will progress eastward into the Yukon territory and with the accelerating/exiting jet, the upstream ridge will break down and allow for greater propagation east and then southward across Central Canada. The height-falls will over spread the lee of the Canadian Rockies into the US northern High Plains and support a cold front to drop southward. The guidance is remarkably tight with the exception of the 00z CMC which is uncharacteristically fast, and there fore south within the overall suite. The 00z NAM/GFS continued solid continuity and agreement to keep with a non-CMC blend at slightly above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina