Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 345 PM EDT Tue Oct 22 2019 Valid Oct 22/1200 UTC thru Oct 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Final Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Central U.S. cyclone; secondary low from Carolinas to New England Today-Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 19Z Update: Models remain in fairly good agreement across the CONUS during the first half of the forecast period. No adjustments needed to this portion of the evaluation. Previous Discussion: A surface low will continue to lift into Ontario through the next couple of days with an associated cold front traversing the east coast. The trough axis will pivot through New England Wednesday into early Thursday. As much of the CONUS will be under troughing, northwest flow across the northern Rockies will allow mid-level impulses to quickly move south and east into the northern Plains. High pressure will quickly build behind the apparent cold front across the east through Wednesday with ridging in the west. The NCEP/non-NCEP models including ensemble means are in good agreement with the timing and intensity during this time. Stronger shortwave dropping through Rockies into the southern Plains Wednesday PM-Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/ECMWF mean/CMC/UKMET Confidence: Below average 1930Z Update: There is no change to the prelim preferences given the model differences continue. The 12Z GFS/NAM is still faster and more amplified while the EC/UK/CMC is slower and deeper with the closed low in the southern Plains - though a noted adjustment to the east with the mid-level closed low and associated QPF. The 12Z NCEP guidance seems a bit too fast and the non-NCEP seems a bit more reasonable as the models have sped up a bit. Previous Discussion: Models continue to be in disagreement with regards to the pattern changes set for late Wednesday into the weekend. There is a clear dichotomy between the NCEP and non-NCEP models that has led to vastly different synoptic features and thus QPF placement and intensity. NCEP model (GFS/NAM) output continues to progress a trough east with mid-level vorticity cleanly rounding the trough axis. Meanwhile, the non-NCEP models (EC/UKMET/CMC) calves off a shortwave from the main trough axis which is generating a mid-level low into the desert southwest. As a result, the NCEP models are producing a more amplified trough pattern that will generate a more progressive cold front through the central US and surface low off the Gulf Coast region by early Friday. Conversely, the non-NCEP members are developing a strong surface low across NM/TX which is slow to progress eastward through the period. This piece of energy breaking off the main trough will lead to a quicker northern jet stream and surface front through the Great Lakes and Northeast during the day Friday. In observing the run-to-run continuity among the models, it appears they are all fairly consistent. This is making it a challenge in determining which model may be the best choice through Day 3. However, when diving into the ensemble means, it appears the 00Z/12Z GEFS illustrates a trend toward the non-NCEP solutions, slowing the progression of the trough with a bit more interaction with the mid-level impulses. Also, the 12Z GFS compared to the 06Z shows some signs of slowing as well, which has been quite subtle over the past couple of runs. The 12Z NAM also slowed. Based on this and the fact the the 00Z ECMWF has deepened the surface/mid-level low over the past couple of cycles, with the EC mean staying very consistent, feel there is no evidence to change the blend at this point. The WPC preference remains for a heavy weight toward the non-NCEP guidance, with most of the weight toward the ECENS mean which is a good compromise until forecast confidence increases and model spread lowers. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Pagano