Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 148 AM EST Sat Jan 04 2020 Valid Jan 04/0000 UTC thru Jan 07/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough crossing from the Midwest to the East Coast... ...Surface low crossing the OH Valley to New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Model spread concerning the interaction between two pieces of energy within a longwave split-flow trough shifting eastward has diminished considerably compared to previous days. The models show good agreement now in having the more dominant northern stream component of the trough gradually absorbing the southern stream energy as it advances toward the East Coast over the next day or so. The guidance supports low pressure crossing from the OH Valley through the northern Mid-Atlantic and offshore southern New England by late Saturday, with low pressure gradually deepening as it pulls away from the Northeast by Sunday. Model spread overall has become rather minimal with this system, so a general model blend will be preferred. ...Shortwave trough/low impacting the Pacific Northwest... ...Energy ejecting out across the Plains/Midwest by Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with the shortwave tracking from the Pacific Northwest toward the Great Lakes region by Sunday night. The 00Z GFS becomes a tad faster than the remaining model guidance as the energy arrives across the Great Lakes region, but given the fast/progressive flow across the CONUS it will not be dismissed. Thus, a general model blend will be preferred with this system. ...Split-flow trough near the Pacific Northwest by Sun... ...Clipper type low approaching the Great Lakes by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Similar to the above system, model spread is small with the mid-level trough axis reaching the Pacific Northwest on Sunday. This energy will rapidly advance downstream with a weak low center clipping the northern Plains and reaching the Great Lakes by Tuesday. Like its predecessor, the 00Z GFS is seen as being a tad more progressive than the remaining model suite, but for now a general model blend will be preferred. ...Southern stream trough/low near the TN Valley by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/UKMET/ECMWF Confidence: Average The models take a shortwave trough in the southern stream and advance it across the lower MS and TN Valleys through Monday and Tuesday along with a wave of low pressure. The 00Z GFS becomes a bit of a progressive outlier whereas the 00Z CMC appears to be too slow. The GEFS mean and ECENS mean do not support the faster GFS with this system, and cluster well with the 00Z NAM/UKMET/ECMWF solutions. So, will prefer a blend of the latter camp of solutions as a result. ...Shortwave/fronts approaching the Pacific Northwest Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/00Z CMC blend...with shortwave trough 00Z NAM/ECMWF blend...with lead warm front Confidence: Average Moderate spread exists with an upstream shortwave trough axis that arrives across the Pacific Northwest late Monday into Tuesday. Initially a warm front will cross the region ahead of this energy, and the guidance handles that relatively well, but the 00Z GFS/UKMET is a tad more progressive with this, and the 00Z CMC now a bit slower. Then as the main shortwave and associated cold front arrives on Tuesday, the 00Z NAM/GFS solutions both end up slower than the non-NCEP models. The ensemble means are split with the GEFS mean slower and the ECENS mean faster. The previous 12Z ECMWF was closest to the model consensus, but the 00Z ECMWF has become a bit more progressive. However, the 00Z CMC has slowed a bit and is now rather close to the overall model consensus, and in between the ensemble means. Based on the latest trends, the previous 12Z ECMWF will still be preferred, but now in conjunction with the 00Z CMC with respect to the shortwave trough. With respect to the warm front, the 00Z NAM and 00Z ECMWF tend to have the best clustering, and so a blend of these will be preferred with the leading warm front. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison