Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 241 AM EDT Sat Oct 26 2019 Valid Oct 26/0000 UTC thru Oct 29/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough crossing the Northeast on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A shortwave trough currently clipping the Great Lakes will advance east across the Northeast early Saturday morning and then exit through the Canadian maritimes late in the day. Any model differences with this system are minor and therefore a general model blend will be preferred. ...Amplified trough/closed low lifting toward the OH Valley... ...Post T.C. Olga... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Effective at 03Z, T.S. Olga has merged with the strong cold front advancing east across the lower MS Valley and is now an extratropical cyclone positioned 170 miles south-southeast of Lake Charles, LA. The latest model guidance shows the low center lifting northeast and inland by early Saturday morning over south-central LA with the system then rapidly lifting north-northeast toward the OH Valley later in the afternoon and across the lower Great Lakes region by early Sunday. The supporting upper trough will be encountering increasingly confluent downstream flow aloft with time and the system will weaken substantially late Sunday as it reaches the Northeast. As the attendant cold front reaches the East Coast late Sunday, the original low center will dampen out in favor of a new area of cyclogenesis near southern New England. This low center will move east and offshore Monday as the remnant energy aloft shifts east toward the western Atlantic and continues to weaken. All of the models are in good agreement now with the details of the mass field evolution, and so a general model blend will be preferred. ...Deep trough digging across the Intermountain West/Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GEFS/12Z ECENS mean Confidence: Slightly above average A strong deep layer ridge is forecast to evolve over the Gulf of AK this weekend and toward northwest Canada early next week which will allow shortwave energy to dig south across southwest Canada and then into Intermountain West and High Plains through the period, leading to the development of a deep longwave trough over the Intermountain West and Plains by Tuesday. The 00Z non-NCEP models are all a little slower than the 00Z NAM and 00Z GFS with the initial surge of energy that pivots across the Four Corners region Sunday through Monday. The latest GEFS mean and ECENS mean support a solution toward the modestly more progressive camp, but it should be noted that the ECMWF did trend slower and away from the NAM/GFS camp compared to its previous run and is now aligned with the latest UKMET/CMC solutions. Toward the end of the period with the details of the longwave trough, the NAM appears to be perhaps slightly too deep over the Rockies and immediate High Plains with the energy. Also, the 00Z non-NCEP model suite via the UKMET, CMC and ECMWF are all a tad slower than the NAM and GFS with the core of height falls/jet energy digging south across the northern Rockies. A blend of the latest GEFS mean and ECENS mean will be preferred to account for the relatively modest model spread. ...Shortwave/clipper low over MT/ND by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average As the highly amplified deep layer flow pattern evolves across North America early next week, the guidance favors a vigorous shortwave/jet-streak diving southeast toward the northern High Plains on Monday which will drive a clipper low and reinforcing cold front southeast across MT/ND. The latest non-NCEP model suite did trend a tad slower and is again a little slower than the NAM and GFS, but for now, a general model blend will continue to be preferred. ...Surface cold front over the lower/mid MS Valley by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GEFS/12Z ECENS mean Confidence: Average As the deep longwave trough ejects out over the Plains Sunday and Monday, a cold front will settle well south and east, and will be approaching the lower/middle MS Valley region late Monday and Tuesday. Spread increases with the timing of the front as the 00Z GFS becomes more progressive than the remaining guidance. Meanwhile, the 00Z UKMET becomes the slowest. There is also some support for a weak wave of low pressure to develop along the front and lift up across the Great Lakes region by the end of the period. The better model clustering with the surface front and the surface wave is with the latest GEFS mean and ECENS mean, so a blend of these solutions will be preferred. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison