Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 142 PM EST Sun Dec 09 2018 Valid Dec 09/1200 UTC thru Dec 13/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southeast storm/Lingering frontal zone... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average 19z update: No change in preference. Models have come into solid agreement with the system in the Southeast, with exception of the 12z NAM which continues to be a bit stronger and further north with the surface wave, and then again being a bit too slow with the secondary shortwave dropping out of the Missouri River Valley currently. Even with that stated, the spread between the NAM and the remaining guidance is fairly good, and provides above average confidence in supporting a non-NAM blend. ...North, Great Lakes and Northeast Tues/Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/ECMWF/UKMET blend Confidence: Slightly above average 19z update: The 12z CMC trended a bit slower at least initially through the Great Lakes and matches the ECMWF, though does accelerate through New England like the 12z GFS by Wed. The UKMET shifted a bit deeper to match the ECMWF, and given the slight timing difference seen in New England with the GFS and CMC, will support a slight adjustment to support a 12z ECMWF/NAM/UKMET blend at slightly above average confidence. Along the southwest periphery of the larger scale global trof in northeast Canada, the ECMWF continues to resolve a very strong compact vort center with the digging wave across the Great Lakes Tuesday, though the overall shape of the cold air and mid-level trof look more on par with the remaining guidance, with exception of the 00z CMC. The CMC is uncharacteristically fast with the wave favoring a stronger core to the global trof and enhanced jet speeds rounding the base and therefore would remove it from the preference. This system is dry, but small details of timing/amplification affect the upstream ridge (and therefore the approaching elongated trof out of the Rockies by the end of the forecast period (Wed)...here is where the stronger internal wave with the ECMWF may have negative consequences upstream, but specific for this feature a non-CMC blend is supported at slightly above average confidence. ...Pair of troughs through the West shifting into the Plains by late Tues/Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z FV3-GFS/UKMET/CMC blend Confidence: Below average 19z update: The northern portion of the trof continues to trend toward a deepening closed low by the end of the forecast period across the Midwest, supported by the 12z UKMET/FV3-GFS and CMC. The 12z ECMWF likewise is very bullish on the closed low but continues a southward shift into the Ohio River Valley more so than toward Lake Michigan. The ECMWF, also favorably trended weaker in the southern stream (no closed low) and digs well south into Mexico lagging the majority of ECENS members and other deterministic guidance. The 12z UKMET and FV3-GFS continue to be most sensible with the southern feature as well. The 12z CMC may have utility as well given the timing of the southern wave, in line with the currently favored solutions. A FV3-GFS/UKMET/CMC blend is preferred and while there seems to be an overall consolidation of solutions, the spread being high and the cycle variability remaining high keeps confidence below average for this pattern. ---Prior Discussion--- While there continues to be solid agreement with the lead height-falls/elongated trof entering the Pacific coast Sunday in Monday, the very strong fairly flat Pacific Jet screams in and further narrows the width of the trof and stretches it further south and enters a more progressive pattern overall. The strength of the downstream ridge and precise placement of strongest vort centers and jet speed maxima have lead to tremendous model spread and run to run variability as the trof cross the Intermountain West and emerges into the Plains by early Wed, as well as the strength/timing with the base of the trof in the Southwest. For a QPF perspective, the system is quite dry, which should help with some WPC decision processes, but the mass difference provides very low confidence in any particular solution. The good news is the more meteorological impact wave with prolonged orthogonal moisture flux into the Pacific Northwest midday Tues into Wed, shows fairly strong agreement in placement/strength and orientation into E ID/UT and by 13/00z Thursday, starting the process of developing the closed low (see WPC PMDEPD for medium-range uncertainty) through the South. As the trof crosses the Rockies, certain models such as the 12z NAM/00z ECMWF strengthen and close off the northern portion of the elongated trof across the Midwest by Wed. This was also hinted at by a significant shift from the 00z run to the 06z run of the FV3-GFS, but also seems to be the most center solution both here in the northern stream as well as the base of the trof. The 12z GFS and 00z UKMET remain a bit more elongated and given the shape/orientation of the slowly progressing downstream ridge in the Great Lakes, seems a bit more reasonable. However, the 12z GFS and 12z NAM remain very fast with the base of the trof, which given the weaker flow further south (relative to the orientation of the jet) seems much less plausible. The 00z ECMWF continues to be very amplified/strong and therefore slow with this portion of the wave in northern Mexico. Here, the medium speed, UKMET and FV3-GFS seem much more sensible in placement/timing and fit more into the middle of the ensemble spaghetti analysis. As such, will favor the FV3-GFS and UKMET as preference for this lead wave(s), though more inclusion of the NAM/ECMWF is likely helpful with the Atmospheric River and translation of the second wave into the Intermountain West late Wed. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina