Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Thu Oct 24 2019 Valid Oct 24/1200 UTC thru Oct 28/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern stream shortwave trough pivoting across the Upper Midwest-Great Lakes-Northeast Thu night-Fri night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Another fast-moving shortwave trough clipping the northern Plains this afternoon will cross the the upper Midwest Thursday night and cross through the Great Lakes on Friday, before then advancing east over the Northeast by Saturday. The latest guidance is collectively in sufficiently good enough agreement that a general model blend can be preferred. ...Amplifying southern stream trough over the southern Plains to lower-mid Mississippi Valley through Sat... ...Initially closed mid/upper low evolving to an open trough across the Ohio Valley-Great Lakes-Northern New England Sat night and Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z ECMWF/12Z Canadian/00Z ECENS mean Confidence: Slightly below average The models continue to show very good agreement in taking an amplifying shortwave currently over the southern Rockies farther south across the southern Plains by Friday morning. Significant model disagreements though take shape thereafter as the system closes off and pivots northeast toward the mid MS Valley Fri night and Sat, with the model differences continuing Sat night and Sun as the system encounters more confluence and becomes an open trough across the OH Valley-Great Lakes-northern New England. Although the 12Z operational GFS has trended slower compared to its previous few runs with the mid/upper trough progression over the weekend (toward the 00Z GEFS mean), both the 12Z GFS and 00Z GEFS mean remain on the faster edges of the guidance spread. Meanwhile, the 12Z NAM has also trended slower with the trough (closer to the EC/ECENS mean), however like the UKMET, maintain a bit more amplification by 12Z Sun as the trough reaches the upper Great Lakes region. The 12Z UKMET meanwhile again appears to exhibit more more interaction with the area of disturbed weather over the Gulf of Mexico. The 00Z CMC meanwhile remains a bit slower than this consensus, and based on the model clustering and ensemble agreement, a blend of the 12Z ECMWF and 00Z ECENS mean will be preferred, though confidence remains below average considering the guidance spread. ...Low pressure development over the Gulf of Mexico... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GEFS/00Z ECENS means Confidence: Slightly below average The latest satellite imagery confirms an area of disturbed weather over the Bay of Campeche which the models unanimously depict lifting north across the western and then north-central Gulf of Mexico over the next few days. There is substantial support among the deterministic global and hires model suites for a low pressure center to develop Thursday night over the Bay of Campeche before the system likely merges with a strong front entering the western Gulf of Mexico. The question will be how quickly this feature will become absorbed into the aforementioned trough over the southern Plains and lower-mid MS Valley on Saturday -- and whether or not another surface low will be left behind south of the main upper height falls and along the tail end of the surface front/low-level baroclinic zone. Both the 12Z GFS and 12Z ECMWF have a separate weak surface low (sub 1008 mb) nearing the central Gulf Coast by 12Z Sat. However, with the 12Z guidance suite, the GFS is now the only operational model that lingers low pressure at the surface beyond 48 hrs (after 12Z Sat). However, the 12Z GEFS, along with the 00Z ECENS, continue to hint at the possibility of a weak surface low traversing the Gulf Coast between Mobile and the western FL Panhandle. Given the support from some of the individual GFS/EC ensembles, for now will continue to favor a blend of the GEFS/ECENS mean. ...Positively tilted upper trough digging across the Western CONUS Sat-Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z ECMWF/Canadian/UKMET Confidence: Average A strong deep layer ridge is forecast to evolve over the Gulf of AK this weekend which will allow shortwave energy to dig south across southwest Canada and then into Intermountain West and northern Plains by Sunday. There is support for some stream separation over the Intermountain West by Sunday which is more strongly supported by the 00Z non-NCEP models. The 12Z NAM and GFS, along with the 12Z GEFS mean, remain a tad progressive compared to the non-NCEP model consensus by late Sun (00Z Mon) -- though it should be noted that both the 12Z NAM and GFS have trended slower toward the non-NCEP consensus. As such, a non-NCEP model consensus is preferred with this system, especially by Sunday. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Hurley