Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Tue Mar 27 2018 Valid Mar 27/1200 UTC thru Mar 31/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...including model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream trough over the Four Corners advancing east... ...Surface low tracking from the lower Mississippi valley Thursday morning to the Northeast Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS, 06Z GEFS mean, 00Z UKMET blend...to 60 hours 12Z GFS, 06Z GEFS mean blend...after 60 hours Confidence: Below average The models take the southern stream closed low over the Four Corners region and eject it east out across the southern Plains by Wednesday as a progressive trough axis. The system will then lift quickly northeast up across the Ohio Valley Thursday night and then across the Northeast on Friday. There are some considerable timing differences seen in the latest guidance with the low evolution. The 00Z ECMWF and many of the euro ensemble members are faster than the 12Z GFS, 00Z CMC and 00Z UKMET. Only the 12Z NAM is as fast the ECMWF, but many GEFS members are slower like the GFS. One concern is that the GFS might be tracking its surface low a bit too far to the left of the model consensus and it is also a bit left of the 06Z GEFS mean. The stronger model clustering would suggest support toward a compromise of the GFS, GEFS mean and UKMET solutions through 60 hours which allows the ECMWF/NAM cluster to be fastest and the CMC overall the slowest with the ejecting low center. After 60 hours, the UKMET hangs on to a slower ejecting shortwave trough across the Ohio Valley and becomes the slowest solution by that time. So, will lean toward a GFS/GEFS mean blend after 60 hours. ...Northern stream trough currently over the northern Plains... ...Lifting northeastward across eastern Canada by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with this system so a general model blend will be preferred. ...Shortwave digging across the northern Rockies today... ...Energy ejecting across the northern Plains Wednesday... ...Surface low crossing near the U.S./Canadian border... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with this system so a general model blend will be preferred. ...Shortwave moving over the Northwest by Friday... ...Surface low dropping down across Montana... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 06Z GEFS mean and 00Z ECENS mean Confidence: Average The models bring a shortwave in across the Northwest by Friday and drop a surface low down across Montana. The 00Z ECMWF and 00Z UKMET are slower than the 12Z NAM, 12Z GFS and 00Z CMC. Stronger ensemble support lies with the GFS as the GEFS mean and ECENS mean favor the GFS versus the slower ECMWF/UKMET camp. The NAM despite being more progressive likely has its surface low a bit too far north of the model consensus. Will lean toward a blend of the GFS, GEFS mean and ECENS mean at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison