Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1132 AM EST Sun Feb 23 2020 Valid Feb 23/1200 UTC thru Feb 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid level shortwave and attendant front clipping the Great Lakes/northern ME Sun/Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The differences with this wave still remain mainly north of the boarder related to precise depth of the shortwave, but the timing, placement of the clipping frontal zone through the Great Lakes into the northern Northeast. The 12z NAM/GFS are a tad stronger, but this does not seem to affect the CONUS substantially, so a general model blend can be supported at above average confidence. ...Southwest closed low interaction with amplifying northern stream wave across Plains/Great Lakes Mon/Tuesday...Associated surface low crossing NM to Ohio Valley/Great Lakes Tues/Wed, developing coastal low Wed night.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Through 26.00z - 12z GFS/NAM/06z GEFS and 00z ECWMF/ECENS blend After 26.00z - 06z GEFS/00z ECENS mean blend with some 12z NAM/00z ECMWF Confidence: Average to slightly above average through 26.00z Average to slightly below average after A complex evolution will occur from three main features across the Central Plains into the Great Lakes early in the week. Currently, a southern stream shortwave/closed low is tracking along the CO/NM border supporting surface cyclogenesis in the High Southern Plains of the OK/TX panhandles, this surface cyclone will track progressively through the Ozarks to the Lower Ohio Valley by early Tuesday with very little model difference as the mid-level wave weakens. Similarly, a strong/compact stacked closed low and surface cyclone in Vancouver Island will progress through the Northern Rockies with increased model agreement through about 25.00z. As the jet streak rounds the bend of this northern stream and supports diffluent flow aloft of the weakening southern stream wave, the timing/orientation differences that are relatively small lead to large model evolution variation thereafter in the binary interaction between the systems. The 12z NAM/GFS continue to be more aggressive and stronger initially which leads to leading edge of the northern stream shortwave to snap through the lower MO Valley and draw moisture/energy back across the Ohio Valley/Great Lakes and support surface cyclogenesis near Chicagoland/southern Lake Michigan by late Tuesday. The 12z NAM and lesser so the 12z GFS both trended a bit slower and weaker toward the 06z GEFS/00z ECENS mean solutions that have been and continue to be very middle ground and fairly consistent over the last 3-4 cycles, building a preference and confidence. This while the 00z ECMWF is a tad slow but also much weaker with the inner core of the developing closed low. The UKMET continues to be well south of this solution with nearly zero binary interaction, and stands out as a clear outlier at this time. The 00z CMC is better overall, but remains slow and west overall...also sticking out, even prior to 60hrs (26.00z). So through 26.00z a NAM/GFS/ECMWF blend anchored by the 06z GEFS/00z ECENS is preferred at average to slightly above average confidence. ---Day 3 Great Lakes-- Complexity/increased uncertainty will once again be injected to the developing system, as it matures on Wed, based on timing/placement of drawing Arctic stream shortwave energy through the Western Great Lakes on Day 3. As usual, the 12z GFS followed by the NAM, are faster, both in typical speed bias but also because they are a bit stronger overall relative to the GEFS/ECENS and ECMWF solutions pulling the energy south. This leads to the GFS shifting the deformation zone much further north and away from greater consensus and continuity but also in line with typical negative bias. The NAM seems a better compromise but may be a tad too fast lifting the initial combined wave through the Great Lakes too fast given it is also much stronger within the mean flow, which is counter intuitive. Once again, the 06z GEFS anchors a more central/consistent solution added by the ECENS mean. So will be favoring the GEFS over the GFS on Day 3 in the preference but confidence reduced to average to slightly below average in a GEFS/NAM/ECMWF/ECENS mean blend. ---Day 3 Mid-Atlantic--- Through the Southeast/Mid-Atlantic, the moisture stream/timing of the initial cold front is quite agreeable, but the CMC/UKMET fall out of preference by 26.00z here as well. As the upstream energy of the northern stream wave swings through the base of the expanding eastern trof Wed, a surface coastal low will develop in/near the Delmarva. Here, the NAM shows some typical day 3 stronger solution, but is not too bad. The GFS is much too fast and north due to interaction described above on Day 3...but the GEFS is a great replacement...so by Day 3 in the Mid-Atlantic a similar 06z GEFS/00z ECENS blend with inclusion of the 12z NAM and 00z ECWMF is preferred. ...Mid-level shortwave trough/surface cold front clipping the Pacific Northwest on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average In the wake of the dominant/compact closed low entering Southern BC today, enhanced ridging will build over the Pacific Coast. However, the Pacific train continues to shift shortwave through the Southern Gulf of AK, with a strong lead wave late Tuesday. While the wave will be further north, the trailing frontal zone and moisture transport will clip the Pacific Northwest late Tuesday into Wed. While the spread is moderate further north, the trailing edge is quite agreeable with perhaps the 00z UKMET a tad further south, but that is fairly minor before the surface high pressure builds in late Wed into Thursday. So a general model blend can be preferred at slightly above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina