Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 230 PM EDT Sat Apr 07 2018 Valid Apr 07/1200 UTC thru Apr 11/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low tracking across the Southeast today and offshore the East Coast tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with the details of the surface low crossing the Southeast today and then exiting offshore the East Coast tonight. ...Strong closed low and trough impacting the Northwest through Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A strong closed low and associated surface low center will approach the Pacific Northwest and move gradually inland through Sunday. Model spread is minimal at least through Sunday, and so a general model blend will be preferred. ...Series of shortwaves crossing the Plains Sunday/Monday... ...Advancing across the Mississippi and Ohio Valleys Tuesday... ...Surface low activity from the Plains to the Gulf Coast and Southeast U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Average A lead shortwave is expected to kick east out of the Northwest and across the Plains on Sunday which will drive a wave of low pressure down across the immediate northern High Plains and across South Dakota before then crossing the upper Midwest by Monday. The guidance is well clustered with this surface wave, but the 12Z NAM does get to be a little slower and deeper than the multi-model consensus with this energy as it crosses the Midwest. Meanwhile, a secondary shortwave making up the remnants of the former closed low will eject east from the Northwest and drop down across the Plains Monday and then toward the Ohio Valley by Tuesday. The guidance is in good agreement with this until late in the period when the NAM again is a bit stronger than the remaining guidance. This also allows the NAM to temporarily have a stronger surface low developing off the Southeast coast by late Monday compared to the other models. The NAM is also focusing the low pressure a bit north of the global models. By Tuesday, the model spread increases with the details of this low as it lifts offshore the East Coast. Gradually the 12Z UKMET and 12Z CMC become the strongest solutions with the surface wave, with the NAM then becoming the weakest. The GFS and ECMWF splits the difference and are reasonably well clustered and also close to the model consensus. Will recommend a blend of the GFS and ECMWF at this point with these shortwaves and with the surface wave activity. ...Upper trough and cold front approaching West Coast by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM and 12Z GFS Confidence: Average The models are in good agreement bringing an upper trough toward the West Coast on Tuesday along with a cold front that will be arriving across coastal areas of Washington, Oregon and northern California. The 12Z NAM and 12Z GFS are a bit more progressive than the 12Z CMC and 12Z ECMWF solutions. The 12Z UKMET which had been a bit slower has now trended toward the NAM/GFS camp. However, the UKMET has a notably stronger surface low lifting up along the approaching cold front which is not supported by the remaining guidance. The CMC is overall the slowest solution. The NAM and GFS though have trended a little more progressive with this cycle, and given the relatively fast flow pattern seen offshore the West Coast by the end of the period, the more progressive NAM/GFS camp will be preferred versus the slower UKMET/ECMWF solutions. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison