Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1157 PM EST Fri Feb 07 2020 Valid Feb 08/0000 UTC thru Feb 11/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave crossing the OH Valley/Appalachians on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Weak shortwave energy will be quickly crossing the OH Valley and central Appalachians on Saturday. A weak area of surface low pressure and a front will be associated with this energy. Model spread is minimal, and so a general model blend will be preferred. ...Deep trough/cyclone crossing the Pacific Northwest Saturday... ...Digging energy over the Great Basin/Southwest by Sunday... ...Downstream troughing over the northern Plains by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...Pacific Northwest to the Upper Midwest 12Z CMC/ECMWF and 18Z GEFS/12Z ECENS blend...Southwest Confidence: Slightly above average A strong compact closed low and associated upper trough will be crossing the Pacific Northwest through early Saturday. By Sunday, a portion of this energy will quickly eject downstream across the northern Rockies, northern Plains and toward the Upper Midwest. On Monday, the energy should be shearing across the Great Lakes and Northeast. The 00Z NAM is a bit of a deeper outlier with its mid-level reflection once the system exits the northern Rockies. As a result, its surface low evolution over the northern Plains and upper Midwest, along with its corresponding QPF axis, is just a shade north of the otherwise well-clustered global model guidance. Thus, a non-NAM blend is preferred with this northern stream energy evolution. Meanwhile, a split in the upper flow will allow for a substantial amount of energy associated with the original trough to then dig southward over the Great Basin and into the Southwest around the eastern side of a strong deep layer ridge developing offshore the West Coast this weekend. In fact, all of the guidance shows a well-defined and fairly robust upper low developing and dropping south through California going through Sunday. On Monday, the energy is expected to begin ejecting east. The 00Z GFS with this system is a much more progressive outlier by the end of the period with its closed low advancing into the Four Corners region. The 00Z NAM for its part gradually becomes a slower and deeper outlier, with the 12Z non-NCEP models all splitting the difference between faster and slower camps. The UKMET though does lean notably toward the faster side of the guidance, but not quite to the extent as the GFS. The CMC/ECMWF solutions are actually in much better alignment with the ensemble means, and especially the 12Z ECENS mean. Thus a 12Z CMC/ECMWF blend along with the 18Z GEFS mean and 12Z ECENS mean will be preferred for now with the evolving southern stream energy. ...Northern stream trough/front over the Midwest by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The guidance indicates a northern stream trough and attendant cold front dropping southeast from Canada and crossing the northern Plains late Monday and arriving across the Midwest on Tuesday. The 00Z NAM is a more progressive outlier solution by the end of the period with its height falls. Although spread with the cold front is actually quite modest. Given good global model agreement with the height falls, a non-NAM blend will be preferred. ...Quasi-stationary front over the Gulf Coast states by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average The models all agree in placing a quasi-stationary front across the Gulf Coast states by Tuesday, which is expected to play a key role in what is likely to be the start of a multi-day excessive rainfall event (see latest QPFERD) for the region. The model spread with the placement of the front is modest, but the 00Z GFS is a tad farther north with its frontal placement from central MS/northern AL northeast into the southern Mid-Atlantic region. Perhaps more concerning with the GFS though is its mass field solution aloft, which at least for the late Monday/early Tuesday time frame is much more diffluent compared to the remaining guidance. This is a result of the GFS being more progressive with the energy upstream over the Southwest which helps to back the mid/upper-level flow more downstream over the lower MS Valley. Consequently, the GFS has a broader and heavier axis of rain impacting an area from the lower MS Valley to the TN Valley through Tuesday morning. At least for this period, a solution away from the GFS is preferred, and thus a non-GFS blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison