Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 350 AM EST Wed Jan 12 2022 Valid 12Z Wed Jan 12 2022 - 12Z Sat Jan 15 2022 ...North to Central Great Plains/Upper Mississippi Valley... Days 2/3... A low pressure system currently well off the OR coast and a northern stream shortwave trough to the north over the Gulf of Alaska will shift ENE to the BC/WA coast Wednesday night with the northern stream wave becoming the dominant feature Thursday night as it dives south down the Canadian Prairies through eastern MT. An inverted trough, with a weak sfc low center, develops just ahead of this trough axis Thursday night over the western Dakotas/Nebraska before shifting southeast down the Plains through Friday night. Southerly flow develops on the east side of this inverted trough, bringing elevated Pacific moisture up the Plains with Gulf moisture joining in Friday night across the southern Plains. Well-defined low-to-mid level frontogenesis between the inverted trough and a 1040mb high over northern Ontario will support developing bands of moderate and eventually locally heavy snow to shift south into central/eastern ND Thursday night before further developing as they progress over the eastern Dakotas and western/southern Minnesota into eastern Nebraska and across much of Iowa through Friday night. While it is not unusual for banded snow to develop an orientation similar to directional motion (which increases the duration of snow and thus the max potential), the southward motion of these features means the main bands east of the inverted trough/weak sfc low will be fed by southerly/warm air advective flow. In this case, thermal conditions are cold enough for all snow over the eastern Dakotas/Minnesota, though an increasingly longer transition to snow is expected south from there over the east-central Plains. While the 00Z guidance depicted excellent agreement thermally and QPF-wise, it is noted that the parent features are still well out of the North American raob network and further track changes are likely as the features come into better focus. WPC probabilities for snow accumulations of more than 6 inches or more are 30 to 50 percent over southeastern ND on Day 2.5 and 40 to 60 percent over eastern SD and west-central through southwestern MN, the western 3/4 of IA to along the border with Neb on Day 3. Southwest of the axis of heavier snow and in the inverted trough axis, there should be a narrow stripe of mixed precipitation, including freezing rain potential of less than a tenth inch from northwestern ND to east-central SD for Day 2 and southeast SD into eastern Neb for Day 3. ...Columbia Basin... Days 1/2... A quasi-stationary low level frontal boundary stretched across Washington state this morning, along with steady onshore flow ahead of the aforementioned low pressure system off OR, will continue to provide a focus for freezing rain in the Columbia Basin in eastern WA today and the from low itself on Thursday. However, only light additional freezing rain is anticipated at this time. ...Maine... Day 3... Southern stream energy developing into a low east of FL tonight lifts north through Friday night, likely tracking east of Nova Scotia as it rapidly develops well off the New England coast Friday before reaching Newfoundland late Friday night. Some western solutions, such as the GFS/NAM/CMC allow outer bands from this sprawling system into Down East Maine where there are Day 3 snow probabilities of 20 to 30 percent for more than 4 inches. This complex system may yet track farther west, so attention should be paid in Maine. Jackson