Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1129 AM EST Thu Feb 14 2019 Valid Feb 14/1200 UTC thru Feb 18/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central to Eastern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF/CMC blend; heavily weighted to ECMWF Confidence: Average Northern stream amplified flow digs south across the northern Great Lakes Friday and through northern New England into the weekend, this system is fairly well handled by the guidance with only the 00z UKMET showing a bit of lagging/slowness across southeast Canada which seems minor. Greater uncertainty remains with the strong/compact low currently nearing the CA Coast, that along with the very strong zonal 150+kt 250mb jet, allows for it to shear and accelerate across the central US with increased warm air advection precipitation breaking out across the Ozarks and central MS River Valley into the TN valley by Fri into early Sat. Timing differences as well as latitudinal differences manifest mainly driven by the differences in shearing through the mean ridge on Fri or some amplification through the Mid-Atlantic/N Carolinas as there is some increased phasing with the lingering trof across the Northeast; ensembles continue to favor slightly slower but also a bit further north preference; which has been favoring something closer to the 00z ECMWF/CMC. The 12z GFS has trended a bit more amplified into the Carolinas which allows for slightly northward shift which is favorable; however, there appears to be some enhanced convection across N Carolina that may be negatively feeding back in an upscale manner, making it a bit less favorable than the ECMWF/CMC yet still included in the preference. The 00z UKMET was clearly too far south and very slow, while the 12z NAM remains well south and slow too. As such will favor a 12z GFS and 00z ECMWF/CMC blend weighted heavy to the 00z ECMWF. Confidence is average for this system but above average with the closed low in the northern stream (non-UKMET blend). ...Western CONUS into Plains/Midwest by late Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/CMC and ECENS mean Confidence: Slightly below average (higher further west by Day 3). The West starts off today with compact shortwave west of San Francisco Bay, that rapidly shears eastward through the ridge along 150+kt 250mb jet. This break down/acceleration is driven mainly by strong digging height-falls and closed low out of the eastern Gulf of Alaska. On the western side of the closed low, strong northerly jet will swing around the base later today into early Friday supporting strong DPVA into N CA that will translate into the Great basin by 00z Sat. The inner core will continue to weaken with a vortex breakdown pattern shedding energy to the outer periphery of the broadening upscale development of a western trof that expands from WA to CO, CA to MT by midday Sat. This breakdown is a difficult pattern to fully forecast given the outer edge shortwaves will be of different magnitudes/compact nature as well as timed differently. Broadly, the lead shortwave is a bit more intense swinging into the Central high Plains into the Midwest (NEB/IA) by 12z Sunday; while strong jet continues to have strong energy on the western side of the upper low that will dig south into CA by 00z Mon. The 12z GFS continues to aggressive and fast with the lead height-falls supporting a closed 534dm low across the Midwest. The 12z NAM supports this but this seems to be in line with a typical Day 3 negative bias with over-amplification. The 00z CMC/ECMWF both suggest this wave is there but is a bit slower, and weaker allowing for increased flatter SW to NE height packing, more in line with the expected flow given the strong subtropical jet/stream...making it a bit more favorable. The 00z UKMET is a clear outlier especially further upstream with faster/southward dug trof, and was not considered in the preference. As alluded to, the confidence in a preference toward the 00z CMC/ECMWF (00z ECENS mean) is fairly low with the impactful shortwave/sensible weather features even though the larger scale trof is well placed/timed and even shaped even in the GFS/GEFS suite. There is more confidence in the western side of the trof and digging shortwave through OR/CA by Sun than the lead wave as well. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina