Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1243 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: Non-CMC blend Confidence: Above average The models are generally in good agreement with the details of the surface low crossing the Southeast today and then exiting offshore the East Coast tonight. However, the 00Z CMC is seen as being somewhat of a slower outlier. The remaining guidance is pretty well clustered, so will prefer a non-CMC blend at this time. ...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: Non-NAM blend Confidence: Slightly above 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 have a stronger surface low developing off the Southeast coast compared to the other models. The NAM is also focusing the low pressure a bit north of the global models. Will prefer a non-NAM blend with all of this energy ejecting east through the period. ...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 faster than the non-NCEP guidance as per the 00Z UKMET/CMC/ECMWF solutions. The 00Z CMC overall is the slowest. The NAM and GFS though have trended a little more progressive with this cycle, and so the preference will be to lean toward the more progressive NAM/GFS camp for the time being, and especially given the relatively fast flow pattern seen offshore the West Coast by 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