Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1210 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: Non-UKMET 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 generally show good agreement at this point with the mass field details, although the 12Z UKMET is seen as being still a tad too slow with its height falls and surface low evolution, so a non-UKMET blend will be preferred. ...Deep trough digging across the Intermountain West/Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 18Z GEFS/00Z 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 12Z CMC and 12Z UKMET are both a little slower than the 00Z NAM/GFS and 12Z ECMWF 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. 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. The global models do not differ substantially, but at this point, a simple blend of the latest GEFS mean and ECENS mean will be preferred. ...Shortwave/clipper low over MT/ND by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: 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 guidance is in good agreement with the details of this system and so a general model blend will be preferred. ...Surface cold front over the lower/mid MS Valley by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 18Z GEFS/00Z 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 12Z 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 12Z ECMWF is the strongest solution with this feature and overall is an outlier. 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