Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 141 AM EST Sun Jan 27 2019 Valid Jan 27/0000 UTC thru Jan 30/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CONUS Overview: ~~~~~~~~~~~~~~~~ Similar to the past several model cycles, model agreement on the synoptic pattern remains high. There is limited model spread with the large-scale height pattern, and there is a high degree of confidence in the position and scope of the broad, amplified trough over the central and eastern US. ...Gulf/Florida Sun/Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z UKMET/ECMWF/GEFS blend Confidence: Slightly below average 07z update: The uncertainty continues even at such a short time from actualization, the most significant shift was the 00z ECMWF shifting significantly faster and slightly left of the cluster, similar to the 12z CMC (if just a bit east), and generally on par with the latitude of the 00z GEFS mean which was a slight bit faster. Interestingly, the CMC shifted slower than the 00z NAM but weaker overall, so not a bad compromise to the initial preference. The UKMET slowed a bit, and generally east/flat...a very good position overall in the mass spread. As such the UKMET will be dominant in a blend with the 00z GEFS/ECMWF allowing for a slightly faster solution than the initial thinking. As such uncertainty keeps confidence slightly below average. ---Prior Discussion--- Moderate uncertainty still remains with the timing and depth of the surface wave developing out of the Florida Straits north of the Bahamas. While the mid-level flow continues to show some small timing differences, the main evolution difference may be related to the magnitude of latent heat release of convection near Florida to further deepen the system. The 12z ECMWF continues to be slowest of the deterministic guidance but has shifted faster and now resides on the northeastern side of the ECENS member cluster. The 00z NAM likewise, is very close to the ECMWF and slow, both suggesting a bit more/stronger convective upscale growth likely from latent heat release. The 00z GFS is on the other side of the scale, with least amount of deep/persistent convection and like its known bias is faster ejecting the wave northeastward away from FL, even outpacing the vast majority of GEFS members, making it suspect. The 12z UKMET is closer to the GFS and faster than the GEFS mean, but is also much flatter than the remaining solutions and minus last evening's 00z run, has never really latched onto the trend that the other guidance suggested. This leaves the 12z CMC which is more central in timing to the cluster but is also a westward outlier, and looks a bit off in mass field aloft. Overall, ensemble trends/continuity seem to compromise with a 18z GEFS mean/00z NAM and 12z ECMWF blend, but confidence remains slightly below average given the amount of uncertainty remaining given proximity to valid time. ...Clipper into Dakotas through Great Lakes & subsequent cold surge/deep closed low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: While the timing/placement of the initial shortwave/surface cyclone in the Midwest continues to tighten, the main spread upstream with the cold air also appears to be resolving a bit better. While typical timing differences still remain with the GFS outpacing all the other guidance, the very slow CMC/ECMWF have come in line, and perhaps only about 3-6hrs behind the NAM/UKMET; both also shifting the deep closed low much closer to the other 3. The initial analysis may have been a bit too harsh on the GFS as there were very small adjustments toward the deeper/slower GFS with the initial wave; as such will back off and support a general model blend at slightly above average confidence with both the lead shortwave as well as the trailing cold air. ---Prior Discussion--- Model consensus continues to grow with the depth/placement of the clipper system deepening across the Upper Midwest into Central Great Lakes by early Tuesday. The only real discrepancies with the deterministic agreement appear with the 00z GFS and 18z FV3-GFS... both suggest a slightly slower progression and increased occlusion of the surface low tilting back to the NW. This is likely under influence of the fastest solution drawing the extreme cold air out of central Canada; reducing the spacing with the upstream wave/deep closed low. While the NAM/UKMET are similarly fast, the spacing is reduced enough to not manifest the slower/northwestward relative track like the GFS. Here a general model blend may be suffice though likely to hedge away from the GFS/FV3. As the cold air descends in latitude, the ECMWF/CMC continue to be very slow to drop south; as a result the closed low becomes well separated from the UKMET/NAM. Ensembles/trends and strength/height packing across central Canada, think the slightly faster solutions are a bit more realistic with the cold air/upper low. Further south, the 00z NAM shows a weak inflection aloft across AR into MS producing increased QPF which is not favored by WPC, still it is favorably timed with the frontal zone with other guidance...unlike the faster GFS. All considered will favor a non-GFS/FV3 blend for the wave/QPF. ...Wave breaking down Pacific ridge Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECENS/00z UKMET/CMC blend Confidence: Below average 07z update: There may be some resolution starting to form with how to handle the shortwave coming breaking down the apex of the ridge in the Northeast Pacific by the end of the forecast period. The 00z ECMWF remains fastest (an atypical position in the cluster) and very compact deep...but the CMC is now very close and the UKMET is also compact and deep, but more in line with the timing of the weaker solutions presented by the GFS/NAM. Still, there remains little to no confidence in a particular solution but perhaps hedging toward something between the UKMET/CMC with a compact solution. As such will include the UKMET/CMC with the ECENS mean as preference. ---Prior Discussion--- The persistent and very strong ridge axis that has dominated the West Coast is expected to be affected by some Pacific energy toward the end of Tuesday into Wed. There is a tremendous amount of model spread and uncertainty with respect to the timing, strength and compact nature of the wave to affect this change. The 12z ECMWF is the most compact, deep and uncharacteristically fast solution crushing the ridge and nearing the Pacific coast by 12z on Wed, while there is some continuity with prior runs with the compact nature, the depth and timing were even further out of context to support it. Both the 00z NAM/GFS suggest weak shortwave trof but the ridge remains in place and strong, though the GEFS members and FV3-GFS are opposed to the solution favoring something similar to the ECMWF (compact), but slower. The UKMET is very similar to the FV3 GFS too with a compact wave just slower than it. The 12z CMC is more like the NAM/GFS supporting the ridge. Ensemble suite/trends are just as muddled so will show no preference for a deterministic solution and support a GEFS/ECENS mean blend for this region at well below 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