Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1133 PM EST Sat Jan 11 2020 Valid Jan 12/0000 UTC thru Jan 15/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large scale pattern/very cold closed low in S Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average With the shearing/stretching of the lead shortwave currently over Ohio Valley lifting into confluent flow in the Northeast by early morning today, a very broad large scale trof develops across the entire continent as a smaller lobe of the larger polar vortex settles into Western Canada by Sunday. Strong but a low wavy amplitude flow along the periphery of this center will allow for numerous shortwaves to progress quickly across the CONUS (please see sections below). As for the central hub and associated Arctic air mass, the GFS has been too far east throughout the last week's cycles and while the ECMWF/CMC both have anchored the western solutions, there is greater consistency there as well as, given the overall pattern with the active WNW flow across the Bering Sea into the Gulf of Alaska and the other 'half' of the vortex locked on Baffin Island. The 18z GEFS is much further west than the operational 00z GFS and while not as far west as the ECWMF/CMC and ECENS ensemble solutions it is closer to the UKMET and CMC particularly at the end of the short-range. The good news is there are limited influences along the active shortwave axis, so even though the GFS is not preferred with the cold air, it may very well be preferred in the shortwave features across the CONUS. The 00z NAM has trended north, but still has been further south than the consistent pattern, however, this is the best it has been relative to the solutions for the last few days, that incorporating it (along with the GEFS) may help to stabilize the uncertainty remaining in the overall pattern. So a non-GFS pattern is preferred north of the CONUS and any thermals that bleed over the US/Canadian border that could be better handled with other guidance solutions. ...Shortwave #1 - Upper Ohio Valley into Northeast today (Sunday)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average This system has matured and is sliding into increasingly confluent flow as it tracks into the Northeast later today and through the Canadian Maritimes. Overall the spread is quite low to support a general model blend for this system at above average confidence. ...Shortwave #2 - Central Rockies Today Thur Great Lakes Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average Next shortwave currently exiting UT into CO, per GOES-WV suite, vertically stretches across the High Plains this morning, and the 12z CMC is the greatest amplification within the suite and remains so lifting through the Upper Midwest into the Northern Great Lakes in an otherwise solid agreement. As such, above average confidence can be given to a non-CMC blend for this wave even into S Canada and clipping Interior New England by early next week. ...Shortwave #3 - Amplifying along Vancouver Island Sunday Through WY/Central Plains Mon & Great Lakes by Tues/early Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 18z GEFS/12z ECENS mean Confidence: Slightly below average The next system is a bit stronger and longer in wavelength as it enters the Pacific NW late today into Monday. It also has the greatest connectivity to the central hub/cold air in W Canada given the timing of it, so it also stretches more into a weakly negative tilt as it slides out of the Rockies into the Central Plains by early Tuesday. The ECMWF, here the ECMWF and CMC are further south loading the trof likely due to less connectivity to the closed low in SW Canada while the GFS/NAM and lesser so UKMET slide through, further north and as it curls into a more mature deeper cyclone it is over Lake Superior relative to the LP/lower Lakes presented by the CMC/ECMWF. Given the CMC is already out of place due to the prior system, this leaves the ECMWF solutions as the only southward solutions; though the operational ECMWF is southwest of the majority of ECENS members. With the issues the 00z GFS has with the polar vortex, the 18z GEFS and ECENS are fairly congruent and will prefer a blend of the GEFS and ECENS mean solution over the GFS or ECMWF. The NAM and UKMET show some typical late Day 2/3 over amplification which seems less likely given a greater stretched/elongated trof in fast flow is more likely. So will prefer a 18z GEFS/12z ECENS mean blend at slightly below average confidence for this shortwave. ...Shortwave #4 - Reaching OR/N CA Late Monday/Early Tues into S portions of Northern Plains Wed ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12Z ECMWF blend Confidence: Average The next shortwave slides under the Omega Block in Alaska and quickly through the Gulf of AK toward the OR/N CA by late Monday. Here, the distance to the closed upper low in Canada is not influencing its track. The 00z NAM is flatter and fast, while the 00z CMC shows greatest amplification. The UKMET is fast, typical of bias with the NAM while the ECMWF/GFS are timed and shaped very well in the middle of the suite including a bulk of the ensembles to have average confidence in a GFS/ECMWF blend. But this system is well out in the data void of the Pacific/Eastern Asia to have tremendous confidence. ...Shortwave #5 - Sharpening Shortwave near Pacific NW Coast Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/12z ECMWF blend with lower weighted inclusion of the 00z GFS Confidence: Average Similar to the prior shortwave, a stronger but also more amplified wave crosses the Alaskan Peninsula and upper Aleutians late Monday into Tuesday, a relatively flat downstream 'ridge' or lack thereof, allows for greater buckling of the flow that the lead portion of the wave support strong cyclogenesis by late Tuesday into Wed nearing 130W. This is presented by nearly all the guidance with exception of the CMC, which is uncharacteristically fast (due to narrowed spacing between the prior wave). The UKMET shows some typical negative feedback in the inner core, which allows for a southward drift relative to the remaining guidance and ensemble suite. The GFS is a bit faster while the NAM/ECMWF are slower (NAM a bit slower, but stronger). A blend of the NAM/ECMWF and GFS seems appropriate but hedging toward the ECMWF/NAM given the GFS may be showing fast bias. Uncertainty, is obviously high given the progressive flow, but the agreement even at 84hrs is high enough to have average confidence in a NAM/ECMWF weighted blend with the GFS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina