Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1148 PM EST Thu Jan 02 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/18Z GEFS/12Z ECENS/12Z CMC 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 and 12Z CMC are clustered just a little north of the 12Z ECMWF, but close to the consensus of the latest GEFS mean and ECENS mean. The 12Z UKMET is close to the consensus, but gradually outruns it as the low center pulls away from the Northeast. Will recommend a blend GFS/CMC and ensemble means as a result. ...Shortwave trough/low impacting the Pacific Northwest... ...Energy ejecting out across the Plains/Midwest by Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC 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 12Z CMC gradually becomes a bit weaker with the low center that crosses southern Canada compared to the remaining guidance, and so a non-CMC 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 and 12Z UKMET solutions are a tad faster than the 12Z CMC/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