Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 229 PM EDT Wed Oct 16 2019 Valid Oct 16/1200 UTC thru Oct 20/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Great Lakes closed low transferring to developing Northeast coastal surface Low ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 19z update: The 12z CMC shifted toward better overall agreement in depth, shape and timing. This made smaller variations after the system moves into the St. Lawrence Seaway a bit more obvious with the ECMWF and GFS wobbling north and east a bit faster than the other guidance. Still, it is minor so a general model blend can be employed with above average confidence. ---Prior Discussion--- This morning's suite of guidance appears to have latched on to a common evolution including the placement/intersection of the warm conveyor belt and active convection that feeds back on the already strong baroclinic cyclogenesis. The only differences appear to the be the magnitude of the deepening. Given the orientation/intersection of the warm conveyor to the negative tilt/diffluent upper level pattern, extremely deep (sub 973mb) solutions may be a bit too aggressive. Still, this is becoming more likely to break non-tropical cyclone pressure October records across New England. On the weaker side of the guidance is the 00z CMC; its solution becomes evolutionarily out of place after 42hrs wobbling out of the CONUS into SE Canada a bit too fast and more elongated in shape. As such, a non-CMC blend is supported at slightly above average confidence. Pressure records can be viewed at www.wpc.ncep.noaa.gov/research/roth/SLPrecords.html . Short wave energy affecting Texas through midweek shearing drawing tropical energy, developing surface wave into the Central Gulf states and Southeast Fri/Sat. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/ECMWF/CMC blend Confidence: Below average 19z update: Further uncertainty is cast with the 12z UKMET and ECMWF, both trending much stronger with the UKMET much faster than initially preferred. The ECMWF also trended stronger with the shortwave in the northern stream/TX allowing for a slightly faster progression of the developing tropical/subtropical system eastward as well as stronger than the 00z run. The ECWMF also remains north of the remaining NAM/CMC and 06z GEFS, but at least shows more favorable timing. The 12z GEFS further expanded the potential speed/timing of the developing wave, so with a few members close to the operational GFS and a few lagging near the NAM/ECMWF/CMC, the GEFS is no longer viable as a blending member, but can help with with determining preference. As such will replace the UKMET and GEFS with the 12z CMC/ECMWF in the preference but confidence remains low (below average) given the uncertainty and interactions between two streams. ---Prior Discussion--- Northern portions of the tropical wave that spawned Tropical Depression 17E, are lifting north across the Bay of Campeche into the Western Gulf under the influence of the remaining small but compact shortwave energy near the Big Bend of TX. Guidance has come into better agreement in the placement and evolution of the shortwave as it slides southeast down the Rio Grande, including the general weakening in favor of the portion of the tropical wave. The 12z GFS continues to be the strongest/broadest with the wave and melds it with the tropical energy over the NW Gulf by early Friday, given a slightly faster base to the northern stream longwave trof approaching from the Southwest Fri (see section below), this shortwave amplifies and ejects much faster than any other guidance member, even increasing strength and speed from the 06z run which was already well displaced from the bulk of 06z GEFS members. As such the GFS is not favored in this region. On the other side of the guidance suite, the 00z ECMWF and bulk of ECENS members support a full shearing of the northern stream shortwave into the tropical wave, this allows for a westward adjustment of the lower level wave (including the developing surface reflection) back west toward the Central Gulf coast Fri into Sat feeling the approach of the base of the northern stream trough. While this is more in line with the other remaining guidance (including the 06z GEFS mean), it does appear to have some typical known negative slow bias so suggest either removing the EC/ECENS or weighting much lower in any blend. The 12z NAM, looks the best compromise and meteorologically sound in the interaction of the two streams, supported strongly by a fairly consistent UKMET (though may be a bit too aggressive with the convective coverage and magnitude, as it is apt to do). Again, both are supported by the bulk of GEFS solutions. The CMC is also generally favorable but is on the southeast side of the ensemble suite to have high confidence for inclusion at this point. So overall a 12z NAM, 06z GEFS and 00z UKMET blend is preferred at slightly below average confidence. Western U.S. longwave trough (Wed-Thurs) shifts into Rockies with Northern Plains cyclogenesis Thurs into Fri and southern Plains surface cyclone by early Sat ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 19z update: The 12z CMC trended a bit stronger and therefore a bit north with the northern stream shortwave within the deep latitude long wave trof. While still generally favorable in the southern/base of the larger wave, it become a bit offset north of the CONUS after about 19.00z. Still, a general model blend could be employed across the CONUS as the timing of the front is not too delayed by the northward shift north of the border. --Prior Discussion--- Deep latitudinal long wave trof is entering the West currently, this wave ushers in a welcome change of pattern with broad flat but strong westerly Pacific jet pushing the trough along. Overall, the guidance is in solid agreement in orientation, timing and strength through the wave for the bulk of the forecast period. The northern portion of the wave has trended weaker over the last few cycles but the guidance is also much tighter in timing with only small typical timing biases (NAM/UKMET/GFS fast: ECMWF/CMC slow). As for the base of the trof, there was a trend toward slightly southward trend, sharper base of the trof. There is still very good agreement in the evolution including spurring Southern Plains surface cyclogenesis by early Sat. The only departure/difference is the 12z GFS has trended much faster on Day 3, likely in combination with the stronger shortwave lingering across the Gulf Coast into the Southeast. This is a negative affect for the southeast, and would be negative for portions of the middle to lower Red River Valley on day 3, particularly aloft. This is fairly minor so much like the northern stream a general model blend is supported at above average confidence. Pacific Northwest reinforcing shortwave(s) late Thurs/Fri and early Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 19z update: The 12z UKMET trended a bit south, while potentially a bit slower than normal, the overall evolution of the elongated NW to SE trof/shortwave is agreed upon with modest uncertainty given the fast generally zone flow preceding it and the shear axis breakdown occurring across the Gulf of AK into NW Canada...as such a general model blend is preferred. ---Prior Discussion--- In the wake of the initial longwave trough across the Pacific Northwest, a stronger/compact shortwave piece of energy pushes into the region late Thursday into Friday. In the prior few cycles this wave continues to come into better agreement and while there are some sharper/deeper solutions, the spread is fairly minor to support a general model blend for this wave. By Day 3, the elongated shear axis across the Bering Sea/Gulf of AK into Northwest Canada is breaking down with vortical roll-up in laminar flow. This allows for a couplet along the jet to amplify into a more solid wave. As it approaches the eastern edge of the influence of the multiple smaller closed lows along the shear axis, it deepens slightly with a high negative tilt angle entering the Pacific Northwest. This is fairly well agreed upon in the guidance, though the 12z GFS is a bit flatter than the prior run, but still oriented closely to the consensus. The 00z UKMET however, is further north and east, and favors orientation of onshore flow to the N WA Cascades while the remaining guidance favors further south in the S WA and Oregon Cascades. As such a Non-UKMET blend is favored after 19.00z at slightly above average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina