Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 136 AM EST Sat Mar 02 2019 Valid Mar 02/0000 UTC thru Mar 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low offshore New England Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average GOES-16 WV suite depicts nice baroclinic leaf along the Mid-Atlantic indicative a deepening surface wave just off the mouth of the Chesapeake that will track toward the 40N70W benchmark. Only the NAM remains out of phase with this thinking initially SE of the otherwise tightened deterministic packing, then bending back westward under deeper cyclonic development generally outpacing the other guidance. The 00z GFS remains a bit weaker, which has been a weakness throughout this winter, but remains within the overall fold to support an above average confidence non-NAM blend for this cycle. ...Coast to Coast southern stream shortwave with sharpening northern vortex enhance fast moving deepening surface wave from Mid-South through Nova Scotia (Tues) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average 07z update: Some significant 12z to 00z changes in the Non-NCEP solutions actually increase overall agreement. The most significant was a sizable shift in the ECMWF in the northern stream, pressing the inner core, lead shortwave further east. This reduces the divergence in the mid-level height fields pushing more zonal and keeping the southern shortwave further south. As such the surface wave/frontal zone is much further south on par with the 00z GFS and earlier favored solutions. The UKMET/CMC both shifted a bit east too, but more importantly trended faster and flatter, especially by late Monday evening. This leaves the 00z GFS as the only solution that is slower and deeper (even closing off the 7H low east of the Gulf of Maine). Still this is a positive trend in the guidance with only the fast but strong NAM departing from the growing consensus. As such will favor a non-NAM blend, but there remains fairly moderate smaller scale variance to have only an average confidence in this blend. ---Prior Discussion--- Southern stream shortwave currently approaching the Central/Southern CA coast will continue a progressive eastward track through the Southwest into the Southern Plains by Sunday, shearing into the increasing zonal flow with time. Concurrently, the deep global vortex over Ontario will begin to shift eastward and open southeasterly trajectory of deep cold airmass over Southern Canada at this time; pouring into the Central Plains and northern Great Lakes (modifying a bit in the increasing solar insolation of the day). Some guidance is a bit more progressive pressing the inner core of the vortex east (GFS/UKMET), allowing the southern stream system to press eastward and intersect return Gulf moisture further south. ECMWF/ECENS mean both continue to stand out with a stronger/sharper northern stream trof through the Plains (subsequent shortwave ridging downstream in the Northeast), this is fairly high consistency over the last few ensemble cycles. This enhances increased overrunning across the TN Valley into KY, and with increasing dual jet features (given tightening of the low level temp gradient upstream in the Plains). This allows for a very strong surface response in the Mid-Atlantic early Monday. Upper level mass-fields support this evolution, of course, but the sharpness of the 150+ kt jet evolution Monday, leaves some pause for concern this may be a bit too aggressive, particularly in persistent progressive flow (and no significant downstream blocking ridge over the Northwest Atlantic). It is interesting, the 00z NAM, which initially is further south and more in line with the CMC/UKMET, shows typical day 3 over amplification bias. While faster than the ECMWF (which seems more reasonable without the block), there are quite a few similarities to the upper level jet structure/mass fields. Knowing this bias, this does not bode well for the more extreme nature of the ECMWF. The 12z CMC is more middle ground, especially in QPF, and is not as aggressive pressing the closed low over Ontario (and southward extending northern stream shortwave trofs). Mass-wise, the CMC is closer to the UKMET and 00z GFS now that it has a slight northward shift, slowing and strengthening. As such will continue to favor a 12z CMC heavy blend with the 00z GFS and 12z UKMET. ...Closed mid-level low nearing the coast of Washington on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/UKMET blend Confidence: Average 07z update: All 3 non-NCEP guidance members shifted eastward, with the CMC shifting most, even slightly east of the 00z GFS. Interestingly, this leaves the 00z NAM on the broader but also well west-most solution. As such would favor the 00z UKMET/ECMWF which are most central and show greater run to run consistency. Confidence is average given this increased uncertainty. ---Prior Discussion--- At the tail end of the northern stream trof (west of the cold air and terrain), anti-cyclonic wave brake occurs with a closed low along the Pacific Northwest coast by the end of day 3. A typical eastward bias (faster flow east with the jet/trof) seen in the 00z GFS leads the closed low to develop over WA, which is generally out of phase with the otherwise tight clustering of the other deterministic guidance. As such, a non-GFS blend is supported here, though sensible weather is quite limited with this feature. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina