Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 239 AM EDT Fri Oct 25 2019 Valid Oct 25/0000 UTC thru Oct 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough over the Upper Midwest/Great Lakes on Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A shortwave trough clipping the northern Plains and upper Midwest will cross through the Great Lakes on Friday, before then advancing east over the Northeast by Saturday. There is some modest timing differences associated with the energy as it crosses the Northeast, but a general model blend will be preferred to resolve these minor differences. ...Amplifying trough/closed low over the southern Plains... ...Energy lifting northeast toward the OH Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z CMC/ECMWF and 12Z ECENS mean Confidence: Average The models show very good agreement in taking amplifying trough/closed low over the southern High Plains off to the east across the broader southern Plains on Friday, and then northeastward across the lower/middle MS Valley on Saturday, and finally across the OH Valley and lower Great Lakes region on Sunday. There continues to be a bit of model spread with timing of the height falls as they eject out of the lower MS Valley. Gradually the 00Z NAM and especially the 00Z GFS become the more progressive solutions which results in a more progressive surface low evolution up across the OH Valley and lower Great Lakes through the weekend. The 00Z non-NCEP models are all slower, with the 00Z UKMET again the slowest solution. The CMC/ECMWF solutions better approximate the model consensus and have better ensemble support via the 00Z GEFS mean and 12Z ECENS mean. A preference toward the CMC/ECMWF and ECENS mean solutions will be preferred, and this will apply as well to the baroclinic low formation over the northwest Gulf of Mexico that ultimately lifts northeast through the lower MS Valley and toward the lower Great Lakes through the weekend. ...Low pressure lifting north out of the Bay of Campeche... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z CMC/ECMWF and 12Z ECENS mean Confidence: Average An area of low pressure lifting north out of the Bay of Campeche is forecast to advance north-northeast toward areas of south-central to southeast LA by late Friday night or early Saturday morning as the system gets picked up by the lower MS Valley trough/closed low system. This low should merge with the attendant cold front digging southeast across the northwest Gulf of Mexico. The 00Z NAM suggests the low center gets left behind over the central Gulf of Mexico on Sunday, before then advancing northeast toward the FL Panhandle by early Monday. The 00Z GFS suggests the system weakens and dissipates over the central Gulf of Mexico. However, the 12Z non-NCEP guidance, along with the 12Z ECENS mean and 00Z GEFS mean all strongly support a low center that maintains sufficient definition to come north and advance inland across south-central or southeast LA before then elongating and dissipating along the aforementioned front as it moves up across southern MS and portions of AL. The NAM and GFS solutions will be dismissed for the time being considering the current level of organization seen with the system in the latest satellite imagery along with its current northward heading. The CMC/ECMWF and ECENS mean overall reflect good model clustering and a blend of these solutions will be preferred. ...Upper trough digging across the Intermountain West by Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z ECMWF/GEFS mean and 12Z ECENS mean Confidence: Above 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. Some stream separation is expected as energy pivots down toward the Four Corners region. The 00Z non-NCEP models overall are a tad slower than the 00Z NAM and 00Z GFS with the height falls, although the 00Z UKMET looks too slow by the end of the period. The 00Z ECMWF is strongly supported by the 00Z GEFS mean and 12Z ECENS mean, and a blend of these solutions will be preferred as this best approximates the multi-model consensus. ...Shortwave/clipper low over MT/ND by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The guidance supports a sharply amplified large scale flow pattern across North America by Monday with a strong deep layer ridge over western North America and a deep trough/vortex evolving down across south-central Canada and portions of the central U.S. There will be a vigorous shortwave/jet-streak diving southeast toward the northern High Plains on Monday which will drive a clipper low and reinforcing cold front south across MT/ND. The 00Z NAM is a tad faster with the energy/forcing by early Monday compared to the global model consensus. A non-NAM blend will be preferred at this point with this next system. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison