Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 208 PM EST Sun Feb 10 2019 Valid Feb 10/1200 UTC thru Feb 14/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Western U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 12Z GFS/00Z ECMWF blend...after 48 hours Confidence: Average...through 48 hours Below average...after 48 hours Three systems impacting the western U.S. will keep an active weather pattern in place and especially down along the West Coast. The first system, a mid/upper level closed low now moving inland across Oregon will advance east through the Intermountain West as it opens up and becomes absorbed into the large scale troughing over the region. The current model guidance has a fairly good handle on this with respect to the mass fields as it crosses through the West. A second mid/upper trough will drop into Washington State tonight and is then also followed by a stronger Pacific system that comes through Monday. This pair eventually phase into a longwave positively tilted trough that hangs up over the region into mid-week. The 12Z GFS and especially the 12Z NAM are more aggressive with the height falls digging in across the Pacific Northwest by 72 hours in association with the positively-tilted trough. The 12Z UKMET has trended close to the GFS solution, with the 12Z CMC/ECMWF solutions still focusing stronger height falls closer to the coast and a bit offshore. Meanwhile, even farther offshore of the West Coast by 72 hours will be development and elongation of a new closed low as energy becomes trapped underneath a deep layer ridge nosing across the Gulf of Alaska. A model consensus would support this around 34N 142W at 72 hours. The models all also agree in developing surface low pressure offshore California which then advances off to the northeast and toward the coastal areas of either central/northern California or southwest Oregon. Much of this is related to energy associated with the strong deep layer closed low currently approaching Hawaii, with at least a portion of this system shearing off to the east and then northeast underneath the new closed low center at 34N 142W. There remains a fair degree of spread in the guidance with the details of the low track and intensity. The ECMWF is the strongest solution, but is a bit more progressive and also in better agreement with the CMC and UKMET with timing versus the slower NAM and GFS. In any event, there will be a significant surge of moisture and onshore flow that will promote very heavy precipitation totals over central/northern California and possibly into southwest Oregon. A general model blend will be preferred through about 48 hours, but thereafter, given the spread between the NCEP and non-NCEP solutions, a compromise between the 12Z GFS and 12Z ECMWF mass fields will be preferred with limited confidence. ...Central/Eastern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 12Z NAM/GFS/GEFS mean blend...after 48 hours Confidence: Slightly above average...through 48 hours Slightly below average...after 48 hours A weak lead shortwave tracking through the central Plains and Upper Midwest will be dampening/shearing out tonight over the Great Lakes region as the system encounters highly confluent mid/upper level flow downstream. There is above average agreement in the latest model guidance with this feature and a general model blend can be preferred as a result. The deeper closed low currently moving into Oregon will track through the Rockies and move into the Plains by Monday evening, and taking on a negative tilt on Tuesday as it approaches the Great Lakes region. A surface low developing in response is expected to take a southeast Colorado to northern Oklahoma to southern Missouri to southeast lower Michigan track going through Tuesday evening. There is much better agreement today generally with the low track evolution through this period compared to yesterday, as the model consensus has shifted notably farther south for this period. The overall biggest correction appears to be to the 12Z NAM which is hundreds of miles farther south with its low track involving the Midwest compared to yesterday's 12Z run. Today's 12Z NAM though is a somewhat stronger outlier with energy it has ejecting through the base of the trough Monday and into Tuesday which leads to a rather well-defined 500/700 mb deformation zone and closed low feature crossing southern MO through central/southern IL. The global models are a little more modest with this by comparison. Bigger differences arise though as the heights falls shift across the northern Mid-Atlantic and Northeast Tuesday night and Wednesday along with secondary low pressure that forms near or along the northern Mid-Atlantic coast and lifts northeast near coastal New England. The 12Z NAM/GFS and 12Z UKMET all tend to focus the stronger height falls a bit east of the 12Z ECMWF and even more so the 12Z CMC which gradually ends up slower with its upper trough progression. This translates into a surface low track that especially by 48 hours and beyond is farther south and east relative to the track over the lower Great Lakes. The 12Z GEFS mean is close to the NAM/GFS camp, and suggests that the UKMET may be a bit too far south and east, but that the CMC and ECMWF are too far to the north and west. Regarding the secondary low evolution, the 12Z CMC is the biggest outlier as it focuses its low much farther inland over the Northeast whereas the remaining guidance all focuses secondary low development and track much closer to the northern Mid-Atlantic and New England coastline or just inland of the coast through Wednesday. Given the latest model clustering and trends, the preference will be toward a general model blend through 48 hours, and then leaning toward a compromise of the 12Z NAM/GFS and also incorporating the 12Z GEFS mean thereafter. One key point again though is that the NAM is a bit of an outlier with its stronger deformation zone/height falls across southern MO and central/southern IL which is generally in the 48 to 60 hour time period. Confidence, especially after 48 hours remains a bit limited but is rather good now prior to this. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison