Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 121 AM EDT Sat Mar 24 2018 Valid Mar 24/0000 UTC thru Mar 27/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS evaluation...including preliminary model preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low offshore the Northwest early this morning, opening up into a pair of shortwaves moving into the Intermountain West this weekend... ...Shortwave currently near the Aleutians digging down the West Coast Sunday and leading to trough amplification and renewed Plains lee cyclogenesis by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z UKMET blend Confidence: Slightly Below Average The differences out West are minor until Monday morning when energy diving down the western U.S. coastline results in a large southern stream trough/closed low forecast to anchor over the Four Corners region early in the week. The GEFS and GFS has been trending faster with the leading edge of the southern stream trough, but the 00Z GFS did back off a little. The 00Z NAM is faster as well with a weak surface low moving across the central Plains on Monday compared to the remaining available guidance. The amplified nature of the upper pattern over the eastern Pacific into the western U.S. supports an evolution near the consistent ECMWF mean...which lies nearest to the 12Z ECMWF and 12Z UKMET. The 12Z CMC also supports near the ECMWF/UKMET but is even a bit slower. Prefer to stay toward the consistent ECMWF mean. ...Shortwave traversing the Midwest this morning and becoming sheared out as it pushes through the Ohio Valley and Carolinas... ...Accompanying surface low cross the the middle Mississippi valley today, weakening into the southern Appalachians Sunday morning in favor of a surface low developing offshore of the Carolinas... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z NAM blend Confidence: Slightly above average The 00Z NAM remains slightly north of the deterministic/ensemble consensus concerning a surface low moving through the TN valley. The difference is small, but the ensemble scatter low plots continue to support a non 00Z NAM/21Z SREF consensus with the 21Z SREF north like the 00Z NAM. Concerning the secondary surface low, the models have come into better agreement until the surface low moves well offshore into the Atlantic. ...Arctic shortwave digging sharply south through Quebec on Saturday with closed low developing off the Northeast by Sunday... ...Associated strong surface high settling into New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 12Z ECMWF and 12Z UKMET blend Confidence: Average Despite trending slightly slower, the 00Z GFS continues to take the 500 mb low more quickly into the Atlantic compared to the remaining consensus. Ensemble spaghetti plots continue to support a slower solution. The 12Z CMC is also slower, but it is weaker with the upper trough/closed low through 12Z/27 in the western Atlantic. The 00Z NAM, 12Z ECMWF and 12Z UKMET are similar and agree well with the ensemble guidance outside of the GEFS, which matches the GFS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto