Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1216 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 much more aggressive with the height falls digging in across the Pacific Northwest by 72 hours in association with the positively-tilted trough, but the 00Z UKMET/CMC/ECMWF solutions are all farther offshore. However, all of the models generally support a new closed low evolution. 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. The models all 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. However, the guidance is quite divergent with the timing and depth of this surface wave approaching the West Coast as it depends on the evolution of the original northern stream height falls and potential for stronger phasing with the energy shearing away from Hawaii. 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 00Z ECMWF will be preferred with limited confidence. ...Central/Eastern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS and 00Z UKMET Confidence: Average...through 60 hours Below average...after 60 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 00Z UKMET all tend to focus the stronger height falls a bit east of the 00Z ECMWF which has a much stronger upper low evolving over southeast Ontario and southeast Quebec by midday Wednesday. The 00Z CMC tends to agree with the non-ECMWF consensus. However, the 06Z GEFS mean and especially the 00Z ECENS mean tend to give more support for the ECMWF. Regarding the secondary low evolution, the 00Z 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 through Wednesday. Given the latest model clustering and trends, the preference will be toward a blend of the 12Z NAM/GFS and 00Z UKMET, although with low confidence after 60 hours. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison