Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 AM EDT Mon Apr 01 2019 Valid Apr 01/0000 UTC thru Apr 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough exiting the Northeast on Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in excellent agreement with the details of the upper trough exiting the Northeast on Monday. A general model blend will be preferred. ...Four Corners to Southern Plains trough/closed low... ...Reaching the Gulf Coast/Southeast by Mon/Tues... ...Cyclogenesis near the Southeast Coast by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ARW/NMMB/GEM and 12Z non-NCEP model blend...through 48 hours Non-NCEP model blend (UKMET/CMC/ECMWF)...after 48 hours Confidence: Average A trough and weak associated closed low over the Four Corners region will eject southeast across the southern Plains through Monday. On Tuesday, the energy will be traversing the Gulf Coast states and moving toward the Southeast. This will drive cyclogenesis along a frontal zone draped from the eastern Gulf of Mexico northeast across the FL Peninsula and up offshore the Carolinas. The dominant area of low pressure is expected to emerge just offshore of the Southeast near coastal areas of northeast FL with low pressure then lifting northeast offshore of the Carolinas by late Tuesday and then well east of New England on Wednesday. The 00Z NAM is the strongest solution with the closed low/trough that ultimately swings through the southern Plains and it once again tends to hang onto stronger height falls as it crosses the Gulf Coast states and Southeast U.S. which helps to drive cyclogenesis that tucks in closer to the East Coast on Tuesday. The NAM takes the low center notably west of the global models as it has a low track that crosses the NC Outer Banks by 00Z/Wednesday. Of the global models, which are all a tad weaker with the height falls, the 00Z GFS is the farthest east solution although it has trended a bit north and west with its low track. The 12Z CMC/12Z UKMET and 12Z ECMWF are all rather well clustered in between the NAM and GFS tracks. The 00Z hires model guidance led by the ARW/NMMB solutions and also the GEM regional are all well clustered on a low track through 48 hours that is very close to the non-NCEP model guidance with perhaps a slight westward adjustment. The 18Z GEFS members are highly supportive of the farther east GFS solution, with the 12Z ECENS member suite clustered farther to the north and west toward the ECMWF, but with some members rather close to that of the NAM. The 12Z CMC ensemble spread is a bit larger with some members supporting both the farther west NAM and farther east GFS. Based on the latest model clustering, ensemble spread and hires model grouping, the preference will be to blend the 00Z ARW/NMMB/GEM regional solutions with the non-NCEP models through 48 hours, and then just a non-NCEP model blend thereafter given that the NAM and GFS each appear to be outlier solutions. ...Trough/Low approaching the West Coast on Mon... ...Surface low approaching the Pacific Northwest... ...Energy reaching the Four Corners by Wed... ...Cyclogenesis over the Southern Plains by Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours 00Z GFS/12Z ECMWF...after 60 hours Confidence: Slightly above average The guidance depicts a fairly compact closed low approaching northern CA by late Monday which will be gradually opening up into a trough axis Monday night through early Tuesday while advancing inland. By Wednesday, this open trough will reach the Four Corners region. There will also be a wave of low pressure focused a bit farther north that will be approaching coastal areas of the Pacific Northwest and also under the influence of a northern stream trough/closed low west of Vancouver Island. The guidance overall is well clustered with the surface low evolution, and generally speaking with the height falls at least through about 60 hours. After 60 hours, the 12Z CMC becomes a bit slower with the height fall evolution. More substantial model differences though begin to show up over the southern Plains at the surface as cyclogenesis takes shape and a frontal system begins to advance off to the east. The 12Z CMC/UKMET solutions are a bit slower with the surface wave evolution near the Red River Valley. The 00Z NAM appears perhaps a bit too weak with its low center and perhaps a little too progressive with its frontal progression. The 00Z GFS and 12Z ECMWF represent a reasonable cluster that better approximates the model consensus. Will prefer a general model blend through 60 hours, followed by a blend of the GFS and ECMWF thereafter which also is well supported by the 18Z GEFS mean 12Z ECENS mean. ...Upper trough over the Northern Plains/Midwest Tues... ...Surface cold front crossing the Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...led by the 12Z UKMET/ECMWF Confidence: Slightly above average The guidance support the intrusion of a new northern stream trough digging down over the northern Plains and Midwest by Tuesday along with a cold front. A weak wave of low pressure is also expected to traverse the front across portions of the Midwest. There is reasonably good model agreement through about 48 hours, but after this time frame, the NAM becomes more out of tolerance with the global models. Among the global models, there tends to be a bit better support for the 12Z UKMET/ECMWF solutions. This applies in particular to details of surface low pressure over Canada near and to the south of Hudson Bay. Will prefer a non-NAM blend led by the 12Z UKMET/ECMWF solutions which tend to have reasonably good ensemble support. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison