Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 205 PM EST Sun Mar 01 2020 Valid Mar 01/1200 UTC thru Mar 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave crossing the Upper Midwest/Great Lakes by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A shortwave and associated cold front will cross the Upper Midwest and Great Lakes region tonight through Monday. The guidance is in very good agreement with this energy, so a general model blend will be preferred. ...Shortwave over the northern Plains/Midwest by Tuesday... ...Weak surface wave/energy lifting over crossing the OH Valley... ...Deepening low center over northern New England by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/UKMET/ECMWF Confidence: Average...becoming below average after 60 hours A new northern stream shortwave trough and associated cold front will drop across southern Canada and dig across the northern Plains and Midwest by Tuesday. A surface low center with this system will cross southern Canada through the period. The 12Z GFS again is perhaps a tad more amplified with the upper trough. After about 60 hours, the GFS tends to become a bit more progressive with this energy, along with energy/wave activity advancing northeast across the OH Valley. However, the 12Z CMC/UKMET solutions have trended in this direction. The 12Z ECMWF is now slower than the multi-model consensus, and becomes the slowest solution on Wednesday as shortwave energy consolidates and deepens while going negative tilt over portions of southeast Canada and New England, although there is some support for the ECMWF from the 12Z GEFS mean and 00Z ECENS mean. The guidance all favors deepening of the OH Valley low center as it crosses interior New England. The GFS is still a bit on the strong side of the guidance with the low center, but there again has been a multi-model trend toward a more vigorous trough amplification over southeast Canada and northern New England over the last few model cycles. Based on the latest trends and clustering, a blend of the GFS/UKMET and ECMWF will be preferred to attempt to resolve timing and depth spread. Confidence is average, but becomes below average after about 60 hours given run to run, and model to model spread with timing and depth of the trough/low center over northern New England/southeast Canada. ...Shortwave approaching British Columbia on Tuesday... ...Amplifying down across the northern Rockies/High Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z CMC/UKMET/ECMWF Confidence: Average The guidance suggests a shortwave embedded within fast upstream Pacific flow will approaching British Columbia on Tuesday, and will then tend to amplify southeast across the northern Rockies and far northern High Plains on Wednesday. The guidance is in very good agreement with the energy through about 60 hours. Thereafter, the 12Z GFS edges toward the slower and deeper side of the guidance. The 12Z non-NCEP models per the UKMET, CMC and ECMWF solutions are all clustered a bit weaker and more progressive. The 12Z NAM splits the difference between camps. There is a trend to amplify this energy a bit more, and it would appear that the ensemble means are a tad too flat given the multi-cycle trends, although the 12Z GEFS mean did trend more amplified. A non-NCEP blend will again be preferred. ...Deep trough amplifying across California today... ...Energy ejecting east across the southern Plains Tuesday... ...Arriving toward the lower MS Valley on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 12Z CMC/ECMWF blend...after 48 hours Confidence: Above average...becoming average after 48 hours A digging trough along the West Coast will yield a robust closed mid-level low center down across coastal areas of California by late today. The energy is expected to advance east across northern Mexico and then eject out across the Rio Grande Valley and adjacent areas of the southern High Plains on Tuesday. On Wednesday, this energy will arrive across eastern Texas and adjacent areas of the lower MS Valley which will drive deepening surface low pressure along the western Gulf Coast and toward southern Louisiana. The 12Z NAM is still overall somewhat of a stronger outlier with this system, and especially as it approaches and crosses the Rio Grande Valley. The 12Z GFS has continued its slower trend over the last day or so, but still ends up a tad faster than the non-NCEP model guidance by Tuesday and Wednesday. The 12Z GEFS mean is just a tad slower than the GFS by comparison. Of the 12Z non-NCEP models, the UKMET ends up being the slowest solution. The 12Z CMC trended a tad faster and is now close to the 12Z GEFS mean and is just a tad faster than the 12Z ECMWF. Model agreement is such that a general model blend can be preferred through 48 hours, but a solution more strongly toward the ECMWF and CMC is recommended thereafter as they very closely approximate the model consensus toward the end of the period. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison