Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 206 AM EST Tue Jan 21 2020 Valid Jan 21/0000 UTC thru Jan 24/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ ...Closed low off the Southeast Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non NAM/UKMET consensus Confidence: Slightly above average Upper low dropping across the Southeast will close off as it exits into the Atlantic. The guidance is in decent agreement with this feature closing off very close to the coast but remaining progressive as it has some interaction with a shortwave leaving New England. The UKMET is a clear outlier in terms of speed and intensity of this feature, while the NAM maintains a surface feature much closer to the coast. While an inverted trough lingering near the coast is likely before the low pulls away, which may spread some moisture through low-level confluent flow into Florida, impacts are expected to be primarily off the coast. ...Impulses moving onto the Pacific Northwest Coast through Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non GFS/UKMET Tuesday, GEFS/ECMWF means D2-D3 Confidence: Slightly below average Closed upper low moving onto the British Columbia coast will weaken today as it lifts northeast. The GFS is deeper and lingers the closed low further east than the global consensus, while the UKMET continues its CONUS-wide behavior of being generally too progressive. After a short period of shortwave ridging during Wednesday, a complex trough feature two distinct shortwaves will approach the PacNW coast Thursday. The stronger feature will remain in the Gulf of Alaska, but a secondary shortwave spinning cyclonically through the base of the trough will advect towards OR/WA by the end of the forecast period. The NAM/CMC are much flatter/faster with this feature, likely due to stronger downstream ridging across the inter-mountain West, while the UKMET is fast with both its jet energy and shortwaves moving into the coast. The GFS is a bit faster than its mean, while the ECMWF may be a bit deeper than the blend of the means. Fortunately, the GEFS and ECMWF means are very similar in timing and intensity of the energy approaching the coast, and a blend of these two is preferred, with some weight on the operational ECMWF as well to maintain some of the finer QPF details in the terrain. ...Interaction of closed shortwaves in the Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: 00Z ECMWF, 12Z ECMWF mean, 00Z NAM, 00Z GEFS Confidence: Below average Guidance continues to suggest binary interaction of closed lows across the Plains D2-D3, but the level to which this occurs and at what temporal evolution remains in question. Two shortwaves will likely dig from Western Canada into the Plains, with a sheared vort lobe racing southeast to close off in the Missouri Valley ahead of a secondary feature which is progged to close off near the Dakotas on D3. The UKMET is again too weak and merges these features together into a broad closed low across the middle of the country. This is the not the global consensus, and in fact the trend in the guidance has been for slower interaction due to a faster primary shortwave and a slower secondary lagging feature. The ECMWF has been quite consistent with its evolution the past three runs, and at this time is close to the NAM evolution, although the NAM is likely too far southeast with the leading closed low based off the ensemble means position. The GFS has shown very little run to run consistency with its placement of these features, but the GEFS mean has reasonable placement when compared to the preferred consensus. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss