NZUS93 KABR 261842 LLLABR MNZ039-046-SDZ003>011-015>023-033>037-045-048-051-270642- Public Information Statement National Weather Service Aberdeen SD 142 PM CDT Wed Mar 26 2025 An upper-level shortwave works its way towards SD Friday and Saturday. This shortwave helps to support a surface low moving over SD Friday and another surface low developing over CO and moving east Saturday and Sunday. The first surface low has precipitation staying to the north in ND, though some rain showers could occur along the border of SD and ND during the day Friday. The second low looks to move precipitation into SD late Friday evening into Saturday that could last until Sunday morning. One of the big factors limiting confidence in timing is a pocket of mid-level dry air over central and eastern SD. On different model soundings, this dry air is deep enough to cause precipitation to sublimate/evaporate before reaching lower levels and the surface. The models vary when this dry air becomes saturated enough to allow precipitation into lower level, which causes different start times for the precipitation as well as what type of precipitation will reach the surface. A shallow cold air intrusion starts occurring Friday afternoon and continues into Saturday. This cold air intrusion cools the surface and atmosphere below 925mb, while a warm nose stays aloft for a while. This is a great set-up for freezing rain. However, with the dry air aloft, any hydrometeors that fall into it will likely sublimate/evaporate before reaching the cool layer and surface. Over time, this will help to saturate the dry layer till it allows precipitation to get through it, but models vary how long it will take. The NAM saturates faster than the GFS by a few hours, with both models having the precipitation starting to reach the surface at some point Saturday morning. The highest potential for freezing rain occurs in eastern SD because areas in southcentral SD look to have a weaker cold air intrusion and by the time the surface cools below freezing, the warm nose has also cooled below freezing. The ECMWF p-type chart shows members with freezing rain occurring Saturday morning east of the Missouri River, with Watertown having over 20-30% of members with freezing rain happening Saturday. This is impressive as only 50% of members show precipitation occurring and freezing rain is the dominate precipitation type for a bit. This will need to be watched to see if future model runs start to agree more on the timing for freezing rain. The past couple of model runs have started to increase precipitation amounts. The NBM shows central and eastern SD getting 1-2in of snow, with southcentral SD and northeastern SD seeing the highest totals. The clusters show a 30-50% chance of 1in of snow Saturday and 20-40% for 2in. One of the factors in snow amounts is how long the transition from rain to snow will take and how much freezing rain will come from it. The clusters show mean amounts of freezing rain ice accumulation of 0.01 to 0.1in over areas south of US HWY 12 and east of the Missouri River, with the highest amounts over the Prairie Coteau. The NBM shows less accumulation occurring, with only 0.03in as the maximum over the Prairie Coteau. The freezing rain potential Saturday morning as well as the potential for wind gusts Saturday afternoon to increase over 25kts in the same area could cause some problems. After the upper-level shortwave moves through SD Sunday, the models vary what happens. Some models move upper-level zonal flow over SD while others have northwest flow over the state as an upper-level ridge tries to move in. This variability then causes difference in the lower levels and lowers confidence in the forecast as another precipitation event looks to happens Tuesday into Wednesday. There is currently widespread 45-50% chance for precipitation over central and eastern SD during that time, but this will likely change as the models start to come into more agreement on what will happen. $$