Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 145 AM EST Fri Jan 03 2020 Valid Jan 03/0000 UTC thru Jan 06/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Amplifying longwave trough across the central U.S.... ...Surface low from the Lower MS Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/ECMWF/CMC/GEFS AND 12Z ECENS mean blend Confidence: Average A split flow upper trough will eject out across the Plains going through the end of the week, with initially the dominant amplification occurring down over the southern High Plains. However, by late Friday, multiple pieces of energy in the northern stream will dig down across the Midwest and lead to a more dominant northern stream trough and closed low evolution which will interact with the southern stream energy. This will lead to surface low development over the lower MS Valley which will lift northeast toward the OH Valley by Saturday. This system will cross the northern Mid-Atlantic by Saturday evening with low pressure redeveloping south of Long Island by early Sunday. The models have overall trended weaker compared to last night, and do not suggest as phased of a system impacting New England. The 00Z NAM overall becomes a bit more progressive with the system compared to the global models. The 00Z GFS, 00Z CMC and 00Z ECWMF are rather well clustered now and close to the 00Z GEFS/12Z ECENS means, although the 00Z ECMWF did tend to shift its low track a little farther north as it crosses southern New England on Saturday. The 00Z UKMET is also very close to the model consensus now, although as the low pulls away from New England, the UKMET starts to edge toward the faster side of the guidance. Will recommend a multi-model blend of the GFS/ECMWF/CMC and the latest GEFS/ECENS means. ...Shortwave trough/low impacting the Pacific Northwest... ...Energy ejecting out across the Plains/Midwest by Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with the details of fast upstream Pacific flow aiming toward the Pacific Northwest which will drive another shortwave and strong surface low eastward to near the northern end of Vancouver Island by Friday night. A cold front associated with this will then cross the Pacific Northwest by early Saturday. This system will advance very quickly downstream across the Intermountain West and across the northern Plains and Midwest Saturday and Sunday before impacting the Great Lakes on Monday. The 00Z CMC has come in much closer to the otherwise well clustered model suite, and so a general model blend will be preferred. ...Split flow trough near the Pacific Northwest by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show a new split flow upper trough and attendant front approaching the Pacific Northwest by Sunday. The 00Z NAM/GFS solutions are a tad faster than the 00Z CMC/UKMET/ECMWF solutions with the system. However, collectively all of the solutions are quite progressive with the large scale flow. Some the energy with this will spill out across the northern High Plains by early Monday with a weak leeside low developing east of the Rockies. Given the modest mass field spread with this system, a general model blend will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison