Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 147 PM EST Wed Nov 13 2019 Valid Nov 13/1200 UTC thru Nov 17/0000 UTC ..See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave crossing the Plains/Midwest... ...Closed low development over the Southeast... ...Cyclogenesis off the Southeast Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours 12Z GFS...after 36 hours Confidence: Above average...becoming below average after 36 hours A shortwave which is currently crossing portions of the Plains and Midwest will begin to separate out from the westerlies and dig down across the lower MS and TN Valleys on Thursday. As this energy drops southeast across the Gulf Coast states, it should interact with and capture energy associated with an ejecting southern stream closed low crossing from Mexico through south Texas and the western Gulf of Mexico. The result of this interaction will ultimately be a closed low over the Southeast by Friday, with coastal cyclogenesis taking place just southeast of the Carolinas. The 12Z NAM again becomes stronger than the global models with the closed low evolution across the Southeast and then offshore going through Friday and Saturday. The NAM is an outlier solution with a lead surface low that develops near the NC Outer Banks by early Friday which then lifts northeast up along a frontal zone. The entire global model suite focuses the main area of cyclogenesis farther south and offshore of SC by late Friday, although eventually the NAM does develop a new area of low pressure in the area Friday night through Saturday, with all of the models at least agreeing on there being a rather strong area of low pressure southeast of the Carolinas on Saturday. Regarding the global models, the 12Z ECMWF again appears to be too slow with its height fall progression, with the 12Z CMC also on the slower side of the model suite. The 12Z GFS is very close to the multi-model consensus, with the 12Z UKMET just a little east of the GFS with the surface low evolution. The ensemble means are split with timing as the ECENS mean is on the slow side of the guidance and the GEFS mean faster, although the latest GFS is not as progressive as the GEFS mean. Based on the latest model clustering and ensemble spread, a general model blend will be preferred through 36 hours, followed by a solution toward the GFS thereafter, although confidence is limited in time given the rather broad spread seen with the surface low evolution late in the period. ...Strong northern stream trough brushing the Northeast by Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-NAM blend...after 60 hours Confidence: Above average The models place a strong northern stream closed low down over portions of Quebec by Friday, with height falls brushing portions of the Northeast. The models show good overall agreement with this system through 60 hours, with the 12Z NAM then becoming a little slower/deeper than the global models as the energy begins to pull away on Saturday through the Canadian maritimes. Will prefer a general model blend through 60 hours, and a non-NAM blend thereafter. ...Mid-level shortwaves approaching the West Coast on Thurs... ...Energy digging across the Intermountain West Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/CMC/ECMWF Confidence: Average A relatively weak mid-level shortwave is expected to approach the West Coast early on Thursday while a second shortwave farther north aims toward Vancouver Island and southern British Columbia by early Friday. The initial shortwave should dampen out, but the second shortwave farther north is expected to drop southeast down across the Intermountain West and begin to amplify through Saturday. The 12Z UKMET becomes the fastest solution with the amplifying trough, with the 12Z GFS the slowest. The 12Z NAM, 12Z ECMWF and 12Z CMC split the difference between camps and actually cluster together rather well, so a blend of these solutions will be preferred. ...Closed low development offshore southern California on Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/CMC/UKMET Confidence: Above average Additional shortwave energy approaching California late Thursday will break away and dig southeast to offshore southern California on Friday, with the guidance supporting a weak closed low evolution that drops down to west of the Baja Peninsula by Saturday. The 12Z NAM ends up on the southwest side of the model suite by the end of the period, with the 12Z ECMWF now on the northeast side. The better model clustering includes the 12Z GFS, 12Z CMC and 12Z UKMET which as a consensus are well supported by the latest ensemble means. So, will prefer a GFS/CMC/ECMWF blend with this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison