Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 201 AM EST Thu Jan 23 2020 Valid Jan 23/0000 UTC thru Jan 26/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough moving onshore the Pacific Northwest Thu night-Fri, then into the Plains Sat-Sat night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model consensus through day 2, then ECMWF with GEFS/ECENS Mean by day 3. Confidence: Average...then below average by day 3. A piece of energy shedding from a closed low near the Gulf of Alaska will eject eastward into the Pacific Northwest on Friday, accompanied by an intensifying, although still modest, Pacific Jet streak bringing heavy rainfall to the Northwest. Fairly stark model differences emerge by the end of day 2 into day 3 -- both with the timing and phasing (or lack thereof) of both northern/southern shortwaves. The GFS, NAM, CMC and to a lesser extent the UKMet, are too amplified and slow with the northern stream shortwave trough and downstream shortwave ridge when compared to the ECMWF and global ensemble means. While any of these solutions may certainly pan out, given the timing/amplitude disparity of the operational guidance as a whole, at this point (day 3 forecast) the recommendation would be to opt for the flatter operational ECMWF along with the ECENS and GEFS means. ...Next shortwave trough moving onshore the West Coast by early Sun (day 3)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF with GEFS/ECENS Mean Confidence: Average The 00Z GFS is on the faster edge of the model spread (including GEFS/ECENS) with the shortwave coming ashore by 12Z Sun, while the NAM, UKMet, and CMC were a bit more amplified/slower compared to the ECMWF and the ECENS and GEFS means. ...Phasing northern and southern stream troughs and eventual closed upper Low Thu through Sat night from the Plains into the OH Valley and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model consensus through day 2...ECMWF and UKMet blend on day 3 Confidence: Slightly below average Many details still need to be ironed out with two mid-level impulses moving through the Plains today into Thursday, and how they will interact through the rest of the week. Multiple features interacting create lower than usual confidence, but the leading shortwave moving through the northern Rockies should eventually become dominant and intense, especially late on Friday night from the Missouri Valley and into the Ohio Valley. This should lead to strong cyclogenesis along a triple point across the Mid-Atlantic by Saturday, with this triple point extending from a primary surface low beneath the trailing upper trough over the Upper Midwest. Given the minimal spread, a general model consensus would appear viable through day 2. By Saturday, the GFS, NAM, and to a lesser extent the CMC begin to outpace the other guidance with the progression of the mid-level low across the OH Valley and into the eastern Great Lakes region. As a result, the GFS and NAM are faster with the surface FROPA off the mid Atlantic coast Saturday morning, and thus quicker with the low-mid layer cold advection. These solutions are also faster with the absorption of the Great Lakes surface low. A blend of the ECMWF and UKMet is therefore favored, especially when compared to the GEFS and ECENS, which both maintain a surface low over the Great Lakes (eastern lower MI) through 00Z Sun. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hurley