Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 346 AM EST Tue Feb 11 2020 Valid 12Z Tue Feb 11 2020 - 12Z Fri Feb 14 2020 ...Southern Rockies and the southern High Plains... Day 1... Low pressure just south of AZ will shear apart as a northern stream trough dips down through AZ early this morning. The resultant positively tilted trough will shift east across the southern Rockies tonight. The complex combination of this trough, surface high pressure pressing south from CO and surface low pressure south of the Rio Grande will create a tight baroclinic zone over southeastern NM and the southern TX Panhandle over which ample moisture from the Gulf of Mexico as well as tropical eastern Pacific will flow. Convergent moist flow ahead of the trough will result in heavy mountain snow across southern NM today with snow probabilities for 8 or more inches moderate to high east from the White Mtns of AZ to the Sacramento Mtns. Later tonight, convergent low level flow with upslope enhancements between the high and low will promote banded snow to spill east/northeast from southeastern NM across the TX Panhandle into western OK. Localized heavy snow is likely with the risk of a narrow stripe to receive a quick 4 to 6 inches of snow, but placement is still variable by 50 or more miles among the 00Z guidance suite. Snow probabilities for 4 or more inches are 10 to 20 percent in this swath. ...Montana... Day 1... A cold front will dive south from the Canadian Prairies today to the northern Plains tonight. Mid-level shortwave energy will ride along this front and aide lift as the front banks up against northeastern facing slopes of the MT Rockies tonight. Lift in the dendritic snow growth zone maximize snow to liquid ratio which is why there are moderate probabilities for 8 or more inches for west-central MT mountains such as the Little Belt and Big Snowy. ...Midwest and Northeast... Days 2-3... Remnant southern stream energy lifts northeast and into the next northern stream trough over the Midwest Wednesday. A powerful southwesterly jet forms ahead of the northern stream trough with precip spreading across the Upper Midwest/Northeast through Wednesday night. At the same time, a polar cold front pushing southeast from the norther Plains will sweep into the Upper Midwest and northern Great Lakes, allowing enhancement of the low as it tracks over the Northeast states. The north side of the precip shield is cold enough for snow and the abundant moisture available to the rapidly developing low warrants an increase in snow risk from the previous forecast. A stripe of 20 percent probabilities for 6 or more inches are on Day 2.5 from northern IL across Lake Erie to western NY and again for the Adirondacks, and the Green/White Mtns. Probabilities for 4 or more inches are 20 to 40 percent from northeast MO across southern Lake Erie. A warm nose along and just east of the low track from the northern Mid-Atlantic will allow for some freezing rain and sleet, particularly east across the PA/NY border, the Catskills, and the Berkshires of western MA Wednesday night and early Thursday where Day 2 ice probabilities for a tenth inch stretch from central OH to MA. There are 20 percent probabilities for a quarter inch or more of freezing rain in the Catskills. Jackson