Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 137 AM EST Sat Jan 18 2020 Valid Jan 18/0000 UTC thru Jan 21/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Progressive central to eastern U.S. storm system... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 07z update: While the 00z CMC is not perfectly aligned with the remaining guidance, it has trended very close to the ECMWF evolution and mass field solutions are tight enough that a general model blend is preferred at above average confidence for the remainder of time in the CONUS/CONUS waters. ---Prior Discussion--- GOES-WV suite depicts pivot hub/closed low over W MN at this time with sharpening Pacific stream shortwave progressing through the Lower MO Valley into the Central MS/Lower Ohio Valley currently with a stream of deeper confluent/strong low level jet streaking across S MO into S IL/IND. This Pacific shortwave will continue to press eastward quickly and through the Northeast by early Sunday, elongating the binary interaction with the current hub in MN across the Great Lakes...with solid model agreement. As the hub wave tracks eastward under stronger westerly flow aloft the CMC is the only lagging/compact wave which leads to sufficient mass field differences as well as surface low development difference. The 00z NAM continues to be stronger than than the other guidance, and as the two waves tighten the binary interaction across Southeast Canada the NAM is strongest/most compact, but this has little impact for the remaining CONUS as the trailing mid-level trof and frontal zone are offshore. So a non-CMC is preferred at above average confidence. ...Amplifying shortwave dropping south across the Midwest into South Sunday-Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: The 00z ECMWF did shift a bit further east with the track of the amplified shortwave crossing the Mid-MS and TN valleys late Mon to Tuesday, pairing with the CMC. This while the UKMET trended slower toward the GFS/NAM. Again, this has low impacts and small timing differences mainly in thermal fields that employing a general model blend results in slightly above average confidence. ---Prior Discussion--- A cut-off warm ridge over the Yukon/N NW Territories will be breaking down wit a very strong cross-polar 250mb jet drops south on Sunday. This phases with sharper ridging across Alberta/Saskatchewan to press mid-level shortwave energy due south across the Upper Midwest into the Lower MS valley combining with lingering trailing trof energy across the Great Lakes by late Monday. This is a dry trof but does affect the mid-level flow and jet orientation for upstream ridge/pattern evolution, as well as drawing colder than normal air south across the Ohio/Tennessee Valley. Here the 00z GFS has trended toward consensus but still remains inconsistently slower than the ECMWF which matches better with the NAM/UKMET and CMC. Given the impacts and increasingly solid model agreement a general model blend is preferred. ...Pacific Northwest to Northern California... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average 07z update: The UKMET trended a bit weaker/faster with the initial smaller/narrower trof entering the Olympics Monday, but this served to shift the next wave a bit further north, toward the ECMWF/ECENS mean and CMC. This while the 00z GEFS also trended a bit weaker, with increased spread toward the north relative to the 00z GFS. This, along with some fast timing issues toward OR Coast by Tuesday suggests the northern/stretched solutions show better results, which seems logical given the time of year and tendency for dissipating closed lows/large scale gyre to spin down too fast in the GFS. As such will favor a non-GFS blend or replace it with the 00z GEFS in the blend but only at average confidence. ---Prior Discussion--- A prolonged atmospheric river will be directed across Vancouver Island today through Monday with the approach of the next shortwave. This wave is a bit smaller and elongated northwest-southeast relative to a stronger/broader compact wave upstream across the Southern Gulf of AK. This lead wave will continue to sharpen and clip the Pacific Northwest, mainly affecting the Olympic peninsula and extreme northern WA Cascades through Monday afternoon. This is a hard system to lock down both in timing and sharpness however, there is strong agreement with the exception of the UKMET which is a bit stronger and further southeast in the trof. The next wave has solid agreement but the precise intensity will determine the angle of rotation around the rapidly weakening/devolving gyre in the Gulf of AK into S AK itself. The faster to weaken are the GFS/NAM which therefore allow for less northward shearing of the vorticity energy into the dying closed low...compared to the ECMWF/CMC, making them a bit further north with the track of the surface low. The affects with timing of QPF seem to be more traditional with the GFS leading faster while the ECMWF/CMC lag and the UKMET/NAM are between. Given the UKMET is less favored with the leading wave and it shows similar uncertainty here through the vertical depth of the cyclonic system, will continue a non-UKMET blend here with only slightly below average confidence, given spread and difficulty to lock down on the larger scale pattern devolution. ...Subtropical shortwave entering Central/Southern California Monday-Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/UKMET/CMC blend Confidence: Slightly below average 07z update: The ECMWF/CMC and UKMET all trended a bit less deep in amplitude in the northern stream, this delays the effective trailing shortwave emerging across the Subtropical EPAC (south of 30N) and reducing the spacing from the initial warm advective shortwave that slows across S CA. This allows the GFS/NAM to significantly outpace and have different affects across the southwest. Given the reduction in preference in the GFS in the northern stream, feel similarly here and prefer a 00z ECMWF/UKMET/CMC blend at slightly below average confidence. ---Prior Discussion--- As larger scale gyre over the Gulf of AK directs the pair of shortwaves toward the Pacific northwest Sunday into Monday, it taps the subtropical flow northeast toward Central/S CA. The upstream ridge over the Rockies will block progression allow for the first shortwave (more associated with warm advective processes) to stall/delay across S CA before the a secondary shortwave to reach Tuesday evening. The NAM is much too strong and fast particularly with the secondary shortwave...while the ECMWF/CMC are tapping greater moisture. This is always a difficult region for the global models to assimilate data to have higher confidence, but the ECMWF tends to be a bit better given reliance on satellite observations; yet the GFS is timed well with it the the GEFS/ECENS means support it as well. As such will favor a non-NAM blend overall but maybe hedge a bit more ECMWF with the moisture advection. Confidence is slightly below average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina