Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 204 PM EST Fri Jan 17 2020 Valid Jan 17/1200 UTC thru Jan 21/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Progressive central to eastern U.S. storm system... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/ECMWF Confidence: Slightly above average A progressive upper trough crossing the Intermountain West along with a lead mid-level trough/closed low feature over the central Plains will generally consolidate later today and tonight over the Upper Midwest with a deepening area of surface low pressure. By Saturday, the guidance agrees in depicting a deep closed low crossing the Great Lakes that then opens up into a broad trough across the Northeast before exiting through southeast Canada by Sunday. The 12Z NAM and 12Z UKMET are a tad north of the multi-model suite of guidance with the low center as it crosses the Great Lakes, and the UKMET is more distinct northerly outlier relative to the track across the Northeast. The 12Z NAM and 12Z CMC both gradually end up a tad more progressive than the model consensus as the system crosses and exits the Northeast. Overall, the 12Z GFS and 12Z ECMWF both have good agreement with their mass fields and more closely represent the model consensus, and given good ensemble support, a blend of the GFS and ECMWF will be preferred. ...Amplifying shortwave crossing the Midwest Sunday/Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average A progressive, but vigorous, northern stream shortwave will dig southeast from Canada and cross the Upper Midwest Sunday night before then swinging down through the OH/TN Valleys on Monday. The 12Z global models have overall trended slower, and toward the already slower NAM solution. The outlier solution at this point is now the GFS which appears to be too progressive. Thus, a non-GFS blend will be preferred given the strong non-NCEP model trend toward the NAM. ...Shortwave/front clipping the Pacific Northwest by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above average The guidance supports a progressive Pacific shortwave trough clipping the Pacific Northwest by early Monday. The 12Z UKMET is a tad deeper with the system compared to the remaining suite of guidance, and is also a tad slower with its surface reflection which is a somewhat stronger surface low/wave along an a frontal boundary nearing Vancouver Island and trailing near the coastal ranges of western WA. A non-UKMET blend will be preferred with this system. ...Southern stream shortwave crossing California by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Southern stream shortwave energy will be crossing especially central/southern areas of California on Monday ahead of a deep upper trough/closed low farther offshore of the West Coast. The 12Z GFS/CMC solutions edge toward the more progressive side of the guidance, with the 12Z UKMET/ECMWF slower. The 12Z NAM tends to split the difference. The latest GEFS ensemble cluster favors the more progressive camp, with the ECENS ensemble cluster siding with the slower camp. Overall, the differences are relatively modest, so a general model blend will be preferred to resolve this. ...Deep upper trough offshore the West Coast on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GEFS/00Z ECENS means Confidence: Below average The guidance depicts a progressive and deep upper trough/closed low offshore the West Coast by Monday. The timing details of the system are generally well agreed upon, but the latest NAM/GFS and UKMET all take the closed low a tad south of the CMC and especially the ECMWF. The ensembles means are split as well, with the GEFS mean supporting the southerly camp, and the ECENS mean in favor of the ECMWF albeit perhaps a tad slower. A check of the latest CMCE mean suggests the northerly CMC/ECMWF camp having some support. Based on the latest spread/split in camps, a blend of the GEFS/ECENS means will be preferred at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison