Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1250 AM EDT Sun Sep 22 2019 Valid Sep 22/0000 UTC thru Sep 25/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Synoptic Overview... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The synoptic pattern will feature a deep layer ridge over the Southeast through Sunday, as a pair of robust northern stream troughs traverse the western and central U.S. The first trough will advance east across the upper Midwest through Sunday along with an attendant cold front and a wave of low pressure riding up along it. This energy will break down the ridge over the Southeast and allow a cold front to arrive across the OH Valley and lower Great Lakes region by Monday. The height falls are expected to sharpen over the Northeast by Tuesday as an upper low deepens and fosters cyclogenesis over northern New England. This will advance the upstream cold front across the East Coast. Meanwhile, a second upstream trough will cross the West Coast and move into the Great Basin by Monday before then cutting off from the westerlies and dropping down into the Southwest on Tuesday. This upper trough will tap some of the remaining moisture and energy associated with weakening Tropical Storm Lorena which will be crossing northwest Mexico. By Tuesday and Wednesday, a new northern stream trough will dig across the northern Plains and upper Midwest along with a cold front. ...Deep trough crossing the Plains/Midwest through Sunday... ...Energy closing off over the Northeast early next week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-GFS blend...after 60 hours Confidence: Above average Model differences with the first trough are rather small through most of the weekend as the energy crosses the Intermountain West and advances across the Plains and Midwest, but by later Monday and Tuesday as the energy crosses the Great Lakes and moves into the Northeast, the 00Z GFS becomes a bit more progressive than the remaining well clustered guidance. Will recommend a general model blend through about 60 hours, and then a non-GFS blend thereafter. ...Upper trough digging into the West by Monday... ...Closed low evolution over the Southwest by Tuesday... ...Moisture/energy associated with T.S. Lorena... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/GFS and 12Z ECMWF Confidence: Average...becoming below average by Tuesday Regarding the second trough moving into the West, the model guidance is well clustered and in good agreement with respect to timing and depth through most of Monday. However, by Monday night and Tuesday as the energy cuts off and drops south into the Southwest, the 12Z CMC suggests a faster and somewhat weaker evolution which allows the height falls to advance more bodily across the Four Corners versus being more concentrated across southeast CA and AZ. The 00Z NAM/GFS and 12Z ECMWF are very well clustered on a more compact closed low evolution that ultimate allows the closed low to cross the Desert Southwest and then drop into the far northern Gulf of CA and the immediate adjacent areas of northwest Mexico. The 12Z UKMET is a tad east of this consensus. The ensemble means foster some increased uncertainty in the forecast as the 12Z ECENS mean basically mimics the UKMET and the 18Z GEFS mean favors a solution in between the UKMET and CMC, and ultimately east of the NAM/GFS/ECMWF cluster. All of the models do indicate some interaction with the remnant moisture and energy associated with weakening Tropical Storm Lorena which is expected to lift across northwest Mexico Sunday before then dissipating Sunday night. For now, a blend of the 00Z NAM/GFS and 12Z ECMWF will be preferred, but confidence becomes a tad limited by the end of the period given some of the model mass field spread by that time. ...Upper trough over the northern Plains by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-GFS blend...after 60 hours Confidence: Above average The models have good agreement overall with the details of a northern stream trough and associated cold front crossing the northern High Plains by Tuesday and upper Midwest by Wednesday. The 00Z GFS is just a tad sharper and more progressive than the remaining guidance toward the end of the period. The 18Z GEFS mean suggests a modestly slower solution that is closer to the remaining well-clustered multi-model consensus. So, will prefer a general model blend through about 60 hours, and a non-GFS blend thereafter. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison