Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 131 PM EST Thu Feb 06 2020 Valid Feb 06/1200 UTC thru Feb 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Latest Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Full latitude trough impacting the Central/Eastern U.S... ...Embedded vigorous shortwave trough lifting northeast... ...Consolidating lows from the TN Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Above average 19z update: The small adjustments noted in the new GEFS/ECWMF/UKMET and CMC are minimal to break from initial general model blend. ---Prior Discussions--- Northern stream shortwave is starting to interact with the base of the positive-tilt full latitude trof across the MS Valley, allowing for the kick/amplification as it lifts north through the Southeast and East Coast by Friday. This will allow for a consolidation of the surface low through the Mid-Atlantic tomorrow morning with a weak wave that continues to rapidly deepen through Downeast Maine Friday evening. Guidance has come into very strong agreement with the mass fields, including the surface trof/weak wave along the coast precursory to the main system. TROWAL/Commahead snow areas also continue to climb in QPF but with solid agreement in orientation and small variation in QPF to have above average confidence in going with a general model blend for the duration of the system. ...Shortwave crossing the Plains and OH Valley by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average 19z update: No change in thinking/preference given new GEFS/ECMWF/CMC or UKMET. Strong flow will continue to over-top a broad but dominant eastern Pacific/West Coast ridge axis through the remainder of the week. This will allow subtle shortwave energy cresting the ridge to dive southeast across the central/northern Plains on Friday and then toward the OH Valley on Saturday. A weak area of surface low pressure and a front will be associated with this energy. The 00z UKMET continues to be a bit fast, but not terribly out of position in amplification/depth, so just a tad faster than the GFS which of course is faster than the ECMWF/CMC. The 12z NAM while much better still seems to have a bit greater amplification across the TN Valley on Sat, but this may be getting too picky, but for highest confidence a non-NAM blend is supported. ...Deep trough/cyclone crossing the Pacific Northwest Saturday... ...Digging energy over the Great Basin/Southern California by Sunday... ...Downstream troughing over the northern Plains by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend, remove 12z NAM after 78hrs Confidence: Slightly above average 19z update: The ECMWF trended a bit weaker overall allowing for a tad faster solution but remains a bit west of the GFS through CA/NV on Day 3. The CMC looks remarkably similar to the ECMWF. The 12z UKMET continues to start further south with the system still and keeps being a fast solution through OR/NV/CA. So thinking staying with initial preference of Non-UKMET blend and removing the 12z NAM after 09.18z (Sun). ---Prior Discussion--- A well advertised compact shortwave/closed low evolves in the Gulf of AK out of the larger scale Bering Sea low. Even early in the forecast period, the 00z UKMET is generally south and slightly faster with this system in an otherwise tight clustering. As the low enters the Pacific Northwest, the flow begins to split...this draws the surface low into the Northern High Plains (please see section below), though the majority of mid to upper level energy begins to open with the upstream energy digging a deep trof through OR into the Great Basin, and eventually into S CA by 00z Monday as an "Inside Slider". The ECMWF is a bit slower and allows for greater energy west of the spine of the Sierra Nevada (so not a 'slider' per se), but it may just be a tad too slow (typical of any potential negative bias) as the GFS/GFS/CMC are more east. The 12z NAM, about mid-way through the evolution process remains strong (as it typically does) but also become quite fast, even out pacing the GFS, and nears the UKMET. This is less favored overall and so the non-UKMET blend will transition to a 12z GFS and 00z ECMWF/CMC blend at 78-84hrs. Confidence is slightly above average ...Separating shortwave energy;surface low tracking out of Northern High Plains into upper Midwest Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/ECMWF/CMC blend Confidence: Slightly above average 19z update: The UKMET continued to be south and fast initially, though being a bit stronger/slower after crossing the Rockies brings it much closer to the initial preference/clustering for some potential inclusion across the Plains, but not to the level of other more consistent guidance. The ECMWF trended a bit faster and so matches the GFS well, and with the CMC similarly timed though weaker, will exclude the NAM from the final preference. ---Prior Discussion--- As described above, as the strong shortwave enters the Pacific NW, broadening global trough across Canada, allows for the leading edge/inner core of the closed low to split eastward along the spine of the Northern US Rockies. The UKMET is already too fast and south, but also sheds the least amount of energy eastward and therefore the surface low weakens and slows as the upper level core shears through to the far NW Great Lakes by 00z Mon. The other guidance is fairly solidly agreeing through much of the early weekend; however, the typical late day 3 biases manifest. The 12z NAM while centrally located is a bit deeper/amplified...the GFS is a tad weaker and faster, the ECMWF is a bit slower but slightly stronger than the equally slow CMC. So overall, a non-UKMET blend is supported but will hedge toward a more traditional ECMWF/GFS blend with lower weighting of the NAM/CMC. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina