Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 145 PM EST Sat Jan 18 2020 Valid Jan 18/1200 UTC thru Jan 22/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough/low crossing the Great Lakes/Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A deep closed low crossing the Upper Midwest will quickly eject east across the Great Lakes along with a deepening area of low pressure going through this evening. The closed low will open up into a broad trough across the Northeast before exiting through southeast Canada by Sunday. The model spread with this system is very modest now, so a general model blend will be preferred. ...Amplifying shortwave crossing the Midwest Sunday/Monday... ...Closed low evolution over the Southeast by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM 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. By Tuesday, the system will deepen into a closed low over the Southeast. The 12Z NAM becomes a bit of a slower and deeper outlier with the energy as it arrives over the TN Valley and Southeast. The remaining guidance is generally in good agreement at this point, so a non-NAM blend will be preferred. ...Shortwave/front clipping the Pacific Northwest by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The guidance supports a progressive Pacific shortwave trough clipping the Pacific Northwest by early Monday. There is some modest timing spread seen with the details of a very weak surface wave and attendant frontal system, but a general model blend will be preferred at this time to resolve these minor differences. ...Southern stream shortwave crossing California by Monday... ...Energy crossing the Southwest on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above 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. This energy will then eject quickly down across the Southwest on Tuesday. The 12Z UKMET ends up being slower and deeper than the remaining suite by Tuesday. Will prefer a non-UKMET blend with this system for now. ...Deep upper trough offshore the West Coast on Monday... ...Energy arriving across the Pacific Northwest by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average The guidance depicts a progressive and deep upper trough/closed low offshore the West Coast by Monday which will advance inland by Tuesday. The timing details of the system are generally well agreed upon, although toward the end of the period, the 12Z GFS becomes slower and deeper than the remaining solutions as the energy crosses into the Pacific Northwest. The latest GEFS and ECENS means suggest the GFS is an outlier solution. Given reasonably decent agreement seen with the remaining guidance, a non-GFS blend will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison