Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 345 PM EST Thu Nov 23 2023 Valid 00Z Fri Nov 24 2023 - 00Z Mon Nov 27 2023 ...Winter storm brings rounds of heavy snow for the post-holiday travel weekend across portions of the North-Central through Southern Rockies, and extending over the South-Central Plains... ...Eastern End of Michigan's Upper Peninsula... Day 1... The pressure gradient between high 1042mb high hover ND and 994mb low pressure near Newfoundland will maintain NWly flow over Lake Superior into Friday. LES bands on the far eastern margin of the Lake, into Whitefish Bay, will persist over the far eastern U.P. through this time with localized snowfall around 6" possible near Sault Ste Marie. ...Wyoming into Nebraska... Day 1... Upper divergence downstream of an upper low over the ID/NV border will continue to allow bands of heavy snow to spread across much of WY and extend through much of western Neb through tonight before easing Friday. A sprawling 1040mb sfc high shifting south over western ND provides upslope post-frontal flow with the right entrance region of a Wly jet over the northern Plains promotes further lift. Day 1 snow probs for >6" are high over most central WY terrain and moderate for the High Plains east through the Neb Panhandle to as far east as the 100W parallel. This activity sags south of the WY border into northern CO tonight, but heavy snow in northern CO is generally limited to the Front Range. ...Northern Great Basin through the southern Rockies... Days 1-2... Closed upper low developing over the NV/ID border this afternoon is drawing Pacific moisture north over the Four Corners with snow in maintain terrain over northern NV/UT and southern ID. This upper low slowly digs southeast over UT through Friday before shearing open as it ejects east over the south-central Plains Saturday/Saturday night in a developing Wly jet over the southern Plains and ahead of a reinforcing trough dropping south from the Canadian Prairies Saturday night. Prolonged moderate to locally heavy snow over the main UT ranges through Friday and over the southwest CO/northern NM ranges through Friday night. Snow levels generally decrease from 6000ft to 4000ft with the approaching upper low. Day 1 snow probs for >8" are moderately high (40 to 80%) over terrain in south-central ID, through the Wasatch and Uinta mountains of UT and over the San Juans of CO. Day 2 snow probs for >8" are also moderately high (40-80%) for the San Juans again as well as the Sangre de Cristos of NM. ...Southern High Plains through Kansas... Days 2/3... The opening of the mid-level closed low sheds a potent vorticity lobe eastward Saturday which will drive height falls and PVA across NM/KS and the TX/OK Panhandles, while jet streak intensification over the southern Plains causes a few rounds of favorable left exit diffluence over the south-central Plains. Sufficient sharpness to the mid-level troughs drives downstream deformation from NM into KS, overlapping with some mid-level fgen driven by both the diving south cold front and the ageostrophic response of the upper jet position. With moisture increasing on a low level fetch from the western Gulf, expect renewed expansion and intensification of precipitation Saturday morning over northeast NM into southwest KS. Sufficient cold air on the north side combined with dynamic cooling in precip bands should allow heavy snowfall to develop on the cold side of the transition zone. Increased confidence in the placement of these heavier bands over western KS spreading east across much of the state through Saturday evening. Day 2.5 snow probs for >6" are moderate (40-70%) over much of central KS. A tight gradient from snow to rain is expected near the KS/OK border with a stripe of freezing rain possible Saturday morning over northwestern OK where Day 2 ice probs are low (10-30%) for >0.1" accretion. As the wave shifts east Saturday into Sunday, the sharpness of the mid-level trough axes decreases as the wave shears so lowering snow rates are expected with Day 2.5 probabilities for >4" snow limited to areas west of the KC metro. However, a stripe of up to a couple inches is possible from northeast KS through northern MO and into the Midwest. Models are sometimes too quick to weaken waves like these over the Plains, so the eastward extent (as well as southern extent of the transition zone) of heavy snow will continue to be monitored. ***Key Messages for Thanksgiving Weekend Winter Storm*** --Heavy snow at times through Saturday Heavy snow expands from Wyoming into western Nebraska through tonight while northern Great Basin mountain snows shift southeast through the southern Rockies through Friday. There are high (>70%) chances for at least 8 inches of snowfall through Friday night in terrain of the south-central Rockies with local maxima over 12 inches. Also, there is a swath of moderately high (50-80%) chances for snow exceeding 6 inches through Friday from eastern Wyoming through much of western Nebraska. --Heavy snow bands in Kansas Saturday Moderate to locally heavy snow bands will spread across much of western and central Kansas Saturday. Embedded bands of heavier snow with rates exceeding 1"/hr should lead to snowfall above 6 inches, especially in west-central Kansas. --Hazardous travel due to snow, wind, and icy roads Snowfall rates of 1"/hr combined with gusty winds will cause hazardous travel due to snow covered/slippery roads and reduced visibility. Additionally, rapid temperature drops behind an arctic front may cause flash freezes tonight. --Much colder temperatures for the Rockies and Plains An arctic front will push southward through Saturday, bringing much colder temperatures to the Rockies and Plains with large areas of high temperatures remaining below freezing Friday and Saturday. Jackson