Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 152 PM EST Sun Jan 26 2020 Valid Jan 26/1200 UTC thru Jan 30/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwaves crossing the Great Lakes/OH Valley through Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A shortwave currently digging southeast over the Midwest will race across the OH Valley by late Monday. It will then reach the Mid-Atlantic coast Monday night. In its wake, a second shortwave will also be dropping down from the Great Lakes region which will cross the OH Valley through Tuesday. The 12Z NAM occasionally appears to be perhaps a tad too strong, but the overall model spread is quite minimal, so a general model blend will be preferred. ...Split flow trough crossing the West coast today... ...Energy ejecting through the Southwest and Plains by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z ECMWF/GEFS and 00Z ECENS mean Confidence: Below average The models all take a progressive split-flow trough across the West today, with a southern stream portion of the energy then dropping down across the Southwest and amplifying into a closed low as it approaches the southern High Plains by early Tuesday. Meanwhile, the northern stream component of the trough will be over the northern High Plains by early Tuesday. On Wednesday, portions of the northern stream energy will be attempt to dig and interact with the southern stream energy as it crosses the Gulf Coast states. The 12Z NAM for a period of time from 36 to 60 hours is somewhat of a stronger outlier with respect to the southern stream energy. However, thereafter, the 12Z CMC and 12Z GFS become the strongest solutions, but with the CMC slower and the GFS faster. The 12Z UKMET becomes a progressive/flatter outlier. The 12Z ECMWF though actually is very close to the overall model consensus and splits the difference between slower/faster solutions and the respective deeper/flatter camps. Interestingly, the 12Z GEFS mean has come in deeper and slower than its previous cycle, and suggests that virtually all of the global models are too progressive by the end of the period. The differences with the northern stream energy are not as vast, but the NAM may be too amplified and too far north with this energy. Given the deterministic model spread with timing/depth of the energy crossing especially the southern U.S., confidence is limited, but the preference will be to blend the 12Z ECMWF with the 12Z GEFS and 00Z ECENS mean for the time being which at least addresses the idea of the GFS/UKMET solutions being too progressive and the NAM too slow across the South, and in the case of the UKMET, too flat/weak. ...Progressive upper trough over the Pacific Northwest Tuesday... ...Amplifying into the West on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average Yet another in a series of Pacific shortwave troughs will arrive on Tuesday across the Pacific Northwest, and then dig into the West on Wednesday, with the gradual development of a closed low over the Southwest late Wednesday. The 12Z NAM may be a tad too weak and fast as the energy initially comes into the Pacific Northwest, but then by late Wednesday appears to be a little too slow with its height falls pivoting toward the Southwest. The global models are overall in pretty good agreement with the larger scale mass field evolution, but the ECMWF may be possibly dropping its closed low a little too far south at the end of the period given where the GEFS/ECENS suites suggest it would be. Regardless, will keep the prior recommendation of a non-NAM blend for now. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison