Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Tue May 08 2018 Valid May 08/1200 UTC thru May 12/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ===== 12Z Model Evaluation with Preferences and Confidence ===== ***Please note: 12z CMC was not evaluated for this product*** ...Eastern U.S. trough, consolidating and lifting from the Southeast into the Mid Atlantic... ...Weak surface low off the East Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Filling closed low over Carolinas with SW-NE offshore frontal zone/Sub-tropical moisture plume detected well in satellite derived product suite, with northern stream influence starting to deform the trof slightly toward greater elongation. This pattern continues to slowly evolve with upstream influences starting to manifest/influence increased shearing toward Thursday. Models show fairly good agreement in the placement/timing with the responding surface wave lifting through offshore waters of the East Coast with some exceptions. The 00z UKMET and CMC remain a tad deeper (with the CMC slower initially) than the general consensus. Issues with faster/earlier weakening of the wave lifting north with earlier runs of the GFS have significantly backed off with the 12z run. The 12z GFS translates its surface reflection more to the left (toward coast) and closer to the growing consensus...but may have overshot the consensus with this iteration. Still, there should be high confidence in incorporating it within a general model blend at this point. 19z update: Like prior 12z guidance, the 12z ECMWF and UKMET both trended a bit slower, but not appreciably so with limited differences. As such a general model blend preference remains preferred at above average confidence. ...Northern stream shortwaves consolidating over the Upper Midwest by Wednesday, and pushing into the Northeast on Thursday. Surface low moving through the Great Lakes with cold front sweeping across the northern tier of states... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average GOES-WV suite depicts string of shortwave features from Northern Plains toward NM, with the most mature wave over the Dakotas at this time. This wave will continue to amplify across the Great Lakes under influence of digging larger scale trof across north central Canada and the associated undercutting jet streak. Guidance shows fairly similar evolution/interaction between the two waves, with the 12z GFS/00z ECMWF a tad deeper at times, but still well within the ensemble suite that is fairly tight even through New England/Southeast Canada Fri. Concern with earlier runs of the NAM remain with the 12z run, depicting a stronger surface/lower level mass response to convection across MI late Wed into Thursday. While the surface reflection remains on the 12z run, it is much weaker and more in the realm of possibility to keep in the preference. Even though pattern could have potential for upscale feedback spread due to small timing/depth issues, the spread is quite tight and reasonable to support a general model blend at above average confidence for these waves. 19z update: Small timing adjustments were noted between the 00z ECMWF/UKMET runs and the 12z runs, with no significant departure in initial preference. As such a general model blend remains preferred at above average confidence. ...Upper level trough approaching the Pacific Northwest Tuesday and Tuesday Night followed by general evolution to zonal flow over the western U.S. before redevelopment of closed low into Great Basin by late Fri...emerging surface wave into Central Plains Fri ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-*00* CMC blend Confidence: Average More substantial model differences exist in the western U.S. mass fields mainly in the transfer of influential mean flow regime. Currently a closed low exists just off the NW Coast that is expected to break down on approach toward the Northwest, shearing/elongating toward the NW as new height falls approach out of the Gulf of AK by Wed. Deterministic guidance depicts this shortwave to undercut the older wave at different strengths which lead to a general increase in spread entering the weekend. The good news is run to run ensemble spaghetti analysis shows that flow regime differences have significantly reduced as now the vast majority of ensemble members have consolidated on the two shortwave features to interact tightly enough to support a binary interaction that along with a subtle downstream block, builds a closed low over the Northwest into the northern Great Basin by 00z Sat. The spread remains in the magnitude and precise placement of the closed low...which of course leads to spread in the development of a broad surface low pattern across the Central Rockies and emergent surface wave in the Central Plains Fri. The 00z CMC is the most stark outlier, having rapidly weakened the initial closed low in favor of the upstream Gulf of AK wave leading to an earlier digging with greater depth of end closed low in the Great Basin nearly 60dm deeper than the next deterministic member. The 12z NAM shows some typical negative feedback...with the under-cutting Gulf of AK wave early Thursday into NW WA, and while this leads to an offset of the closed low toward the end of the period, it is not tremendously offset and generally in the overall trend toward a westward retrograde. Likewise, the 12z GFS shifted toward westward following initial trend by the ECMWF/ECENS members at the 00z run. The 00z UKMET evolution is in the line of the ECMWF/ensemble suite, but has a bit of an eastward shift, against the overall trend, but also west of the 00z/06z NCEP guidance, so still well within the realm of support in a favored blend. As such a non-CMC blend is preferred though weighted toward the ECMWF being most central to the ensemble suite in placement/intensity. Confidence is average. 19z update: The 12z ECMWF/UKMET both trended a bit stronger with the under-cutting shortwave through the Northwest by Thursday, in the vain of the NAM...just not to the same stronger extent. Still, this stronger more amplified solution lead to greater binary imbalance as it reconstitutes further south and east over the Great Basin, also in the line of the NAM/GFS and more so ECMWF to the UKMET. As such the clustering became a bit tighter and continued the westward shift from cycle to to cycle. The 12z CMC was not received at the time of this product, so it was not evaluated. A non-00z CMC blend still seems appropriate at average confidence. ...Pacific shortwave quickly reaches CA Thurs moves through west into upper Midwest/Western Great Lakes by Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ Preference: 12z NAM/ECMWF/UKMET blend Confidence: Average While not a major player on the larger scale mass fields, there is good signal for a fast moving shortwave to reach the central West Coast by late Wed, early Thurs in the flattest/zonal pattern between closed lows described in section above). The larger scale trough in the west, provides the largest surface low influence, but this quick hitter system will enhance low level wind flow/warm air advection regime enough to strengthen a weak surface inverted trof over the Central Plains Friday. Most of the guidance are agreeable to the timing/strength of the wave with possible exception of the 00z UKMET and 12z NAM which are a bit deeper, though differences in latitude appears the greatest spread as the GFS is a bit north with the UKMET and the CMC is south. The ECMWF is more centralized and seems a good fit overall with the modest spread, but the guidance...so at this point, will favor it as preference for mass. Though please refer to QPFPFD for additional important QPF model preferences for more details. 19z update: The 12z ECMWF trended significantly slower than the 00z run and while it remains fairly well placed compared to the 00z run, the lagging compared to the remaining guidance may be a bit too much. The 12z UKMET on the other had looks remarkably similar to its 00z run, a bit more amplified. Still, at least the track of the UKMET/ECMWF/NAM are more in line than the northern GFS and the southern CMC. To account for some of this variance, will blend the UKMET/ECMWF/NAM at 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