Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 238 AM EDT Wed May 30 2018 Valid May 30/0000 UTC thru Jun 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...System moving across Plains Tonight to the upper Great Lakes Thu. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average Upper low over W SD currently will shift northeast through the upper Midwest eventually absorbing the remains of Alberto north of the Great Lakes into Thursday, this is fairly well handled by the guidance, though the 00z GFS shows some faster timing issues translating the bulk of this feature slightly faster than Alberto. The remaining guidance is a bit more steadfast of either greater phasing or even slightly delaying the shortwave. The 00z NAM and 12z UKMET are more in line with the ECMWF/CMC with respect to surface and mid-level phasing, however, the ECMWF/CMC both being a bit slower typically fall into line, enhancing a stronger trough and frontal zone through the Great Lakes. While this may be a bit aggressive of the ECMWF/CMC would hedge to a compromise of the two remaining camps and suggest a non-GFS blend at Average confidence. The remaining energy will slide SE into weaker flow and potentially lead to a stationary trof or even closed low by the weekend, please see below 3 sections for more details. 07z update: Little change in the Non-NCEP guidance, so will continue initial preference of non-GFS blend at Slightly above average confidence. ...Alberto... ~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 12z UKMET remains quite strong almost 2-4 mb deeper through the Great Lakes than even now, though it tracks well with a tight surface low cluster. The ECMWF is generally more favored as it retains a bit more depth (but not to the extent of the UKMET) but matches well the GFS/NAM to support a Non-UKMET blend before it merges with the shortwave described in section above. Confidence is above average. 07z update: The 00z UKMET remains a bit deeper at the surface but only a MB or 2 lower than the ECMWF which it matches in track very well. Given the ECMWF has not varied much, will support a general model blend at above average confidence. ...Shortwave entering S AZ and associated MCS across KS Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/UKMET/ECMWF blend Confidence: Average Goes-WV suite, depicts a dry but very compact shortwave feature exiting the northern portion of the Sea of Cortez into AZ. This is already slightly outpacing global guidance with the stronger 12z UKMET/CMC and ECMWF a bit more resolved than the 00z NAM/GFS. This seems to resolve itself due to mesoscale forcing convection and accelerating the wave a bit more. It is noted the CMC is a bit further north than one would expect (especially given current boundaries/rainfall swaths. The NAM seems to retain a stronger wave into the mid-MS valley which is likely part of a later time frame negative NAM bias. The UKMET is a bit further south overall. All considered the 00z GFS and 12z UKMET/ECMWF blend will be favored but given QPF/convection please refer to WPC QPFPFD for additional model preference information. 07z update: The ECMWF/UKMET both remain a bit south but are both now a bit weaker crossing the Central Plains while the CMC continued to be north. No change in preference/confidence. ...Combination of Multiple shortwaves into loosely formed Close Low/Stalled Trof over Mid-Atlantic into Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/UKMET/ECMWF blend Confidence: Below average Lingering energy from the northern stream trof (described in first section above as well as the shortwave/MCS energy crossing out of the MS River Valley on Thurs into Friday and some lingering influence of Warm conveyor off the East Coast/Gulf Stream will lead to a very complex/convoluted interaction to build a loosely defined broad trough or even rounded closed low over the Mid-Atlantic by late Fri into Sat. Cycle to Cycle spaghetti ensemble analysis is not very helpful with exception that the deeper 00z GFS and 12z CMC solutions with more of a closed low feature are generally not preferred. However, given the 'Frankenstein's Monster' approach of development of this feature with convective boundaries/upscale influences there is extremely low confidence in the mass field preference solution. Here the evolution of the 12z ECMWF/UKMET and 00z NAM seem to match the ECENS mean and placement of the frontal zone (with the NAM a bit faster toward the southeast). 07z update: The 00z ECMWF trended a bit faster with the wave descending through the Great Lakes toward the Mid-Atlantic while this is a trend toward the 00z NAM. The 00z UKMET also shifted in this direction providing greater confidence in the NAM solution. The 00z CMC is even stronger/symmetric with the developing closed low. While, the models in the preference remain the same, the overall preference shifts faster/slightly stronger with the NAM/UKMET/ECMWF blend, with slightly increased confidence, it still remains below average given the overall spread/ensemble uncertainties. ...Amplified trough moving into the West Thursday, ejecting into the Plains with surface waves in the Northern High Plains/Dakotas & E CO/KS late Fri into Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECMWF/CMC blend Confidence: Average As lead shortwave over S BC lifts away...strong upstream jet energy over-tops the Pacific ridge and further amplifies the lingering trof off the West Coast. This will make it much more progressive, especially in the middle section from WA to central CA and translate it into the Intermountain West toward Friday. By this time, the 00z NAM is much stronger and faster, while the UKMET becomes quick but also much more compact shedding much of the lower middle and base of the trof through the Four Corners region. The 00z GFS and 12z ECMWF have been more consistent and slower overall and as well as more gentle through the length of the trof with timing, yet retaining strong mid-level cyclogenesis over the southern Canadian Rockies as well as a well defined lee surface trof in the MT High Plain into the Dakotas on Friday evening as well as the lee cyclone over the central CO Rockies. This matches continuity and ensemble suite enough to support a 00z GFS/12z ECMWF blend. Spread and precise placement of where to focus fastest flow/best focus in the length of the trof provides some lower confidence and lower overall predictability, so confidence is just average in this blend. 07z update: The 00z UKMET continues to be very fast and wrapped up in the northern stream, away from initial preference or continuity. The CMC trended toward the GFS and ECMWF, which showed small internal trof changes but not significant to depart from initial preference. As such a 00z GFS/CMC/ECMWF blend is preferred at Average confidence. ...Base of amplified trof into Desert SW potentially closes off late Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECMWF/CMC blend Confidence: Average Subtropical shortwave in southwesterly flow in advance of the base of digging northern stream trof will have reduced flow and timing issues, given placement in the larger scale environment. The 00z NAM being much to fast further north, cuts the tail off into a compact closed low into AZ by late Fri into Sat, and is much too strong/north compared to the ensemble suite. The UKMET, also fast in the northern stream, lead to wave break further west, allowing for a slower development but eventual strong closed low SW of southern CA by 12z Sat, also a bit too out of phase with ensembles. The 12z ECMWF depicts a stronger subtropical shortwave, like the 00z GFS and the interaction with the base of the trof eventually develops into a stronger more compact vort center by the end of the forecast period. Its difference with the GFS, is related to traditional timing differences...as the GFS is faster, more north with the interaction, while the ECMWF is slower and southwest. The CMC shows an earlier severing from the base of the progressive northern trof, and allows for more of a binary interaction into a more compact vort center earlier than the GFS/ECMWF but at least on par with latitude and timing toward the Baja CA coast by Sat. Confidence is slightly below average given the importance of when and how much interaction with the subtropical wave as well as when the northern stream breaks...but a blend of the 00z GFS and 12z ECMWF/CMC should be close to some run to run ensemble suite agreement. 07z update: All three non-NCEP guidance members remained fairly similar to their 12z solutions, so there is no change in initial preference or confidence. ...Shortwave/eastern extent of Eastern Gulf of AK Closed Low clips Pacific NW on Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Slightly above average The next shortwave crossing the ridge in the southern Gulf of AK will tamp down the ridge and rotate closer to the closed low developing a fairly strong occlusion by Fri into Sat. This shortwave is fairly well timed with depth, but the 00z CMC is a bit weaker with the inner core of the upper low and therefore presses the shortwave further SE as well as the triple point low. The 00z GFS is equally fast and nudged SE compared to the ECMWF/NAM and UKMET but not significantly as it still is within the moderately broad ensemble suite (at the end of day 3). As such mass fields would favor a non-CMC blend at this point at slightly above average confidence. 07z update: The 00z CMC trended toward the growing consensus with respect to the depth/timing of the upper low and occluded surface low enough to support a general model blend, though there is enough variation and possibility for changes to have only 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