Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 329 AM EDT Tue Oct 14 2025 Valid 12Z Tue Oct 14 2025 - 12Z Fri Oct 17 2025 ...California & Central Great Basin... Days 1-2... ...First significant snowfall event of the season continues across the Sierra Nevada today... A deep, vertically stacked mid-upper low churning off the coast of central CA by the start of the forecast period (12Z Tues) is forecast to swing inland today before crossing into the central Great Basin on Wednesday. This mid-upper low pressure system is very anomalous for the time of year, reaching below the 0.5th climatological percentiles and nearing October records for the first part of day 1 just of the CA coast. The depth of the system will allow for ample upper ascent and orographic lift throughout the Sierra Nevada, while decreasing snow levels from around 7000ft this morning to as low as 5500ft this evening under the upper low. Snow levels also drop to around 6000ft over the central NV ranges by Wednesday. The strong inland moisture surge ahead of the low and associated with an occluded/cold front will have IVT values around 500 kg/m/s at the start of the forecast period and allow for moderate to heavy snow rates above the snow level. 00Z HREF mean snow rates are 1-2"/hr over the central/southern Sierra Nevada from 12Z to 18Z today, with lingering bursts of 1"/hr snow possible over the central Sierra underneath the upper low through Tuesday night. WPC probabilities show moderate-to-high chances (40-80%) for at least 12" of additional snowfall after 12Z Tuesday above about 8000ft and greatest across the southern Sierra and White/Inyo Mts just to the east. Probabilities through that time for >8" are also 40-80% around 7000ft (including Donner Pass on I-80). The WSSI highlights Major Impacts for the High Sierra and remote central NV ranges with moderate impacts for most cross Sierra road passes. ...North-Central Rockies... Days 2-3... The low fills as it crosses the Great Basin, but remains closed as it crosses over WY on Thursday. Lee-side cyclogenesis forms over southeast WY Wednesday night with an increasing easterly component to the low level flow to aid moisture transport over the western WY ranges through Thursday morning with snow levels falling to around 7000ft after starting above 9000ft on Wednesday. Overall, snowfall rates are not expected to be that great outside of an isolated convective shower in the highest terrain with mainly longer duration light-to-moderate snow through the forecast period. WPC probs for >8" snow in 72hr ending 12Z Friday are 60-90% for the Absarokas, Teton and Wind River Range, as well as the Uinta Mts in Utah mainly above 10,000ft. The probability of significant freezing rain across CONUS is less than 10 percent. Snell