Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 17 2025 21:04:39 FOUS11 KWBC 172104 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 504 PM EDT Mon Mar 17 2025 Valid 00Z Tue Mar 18 2025 - 00Z Fri Mar 21 2025 ....California, Great Basin, and Pacific Northwest...=20 Days 1 and 3... Amplified trough along the northern CA coast this afternoon will dig across the Desert Southwest through Tuesday before swinging across the Great Plains. Moderate to heavy snow will shift down the rest of the Sierra Nevada through this evening with probabilities=20 for an additional >6" after 00Z are 50-80% on the southern Sierra with snow levels dropping from 6000ft to 3000ft. A reinforcing shortwave shifts over the WA coast this evening providing lift and enhancement to the onshore flow and moderate snow to the WA/OR Cascades into Tuesday. Day 1 PWPF for >6" are 30-70% on the central/southern WA and northern/central OR Cascades. The cold front shifting inland ahead of this trough will cross from eastern NV into UT this evening. Increasing frontal forcing, low=20 level moisture, and some instability (12Z HREF mean MUCAPE of 100-200 J/kg) will allow a snow squall potential along the frontal zone. Expect brief bursts of accumulating snow and rapidly reduced visibility, causing dangerous overland travel in snow squalls. Otherwise, terrain enhancements to the flow from the large trough will allow heavy snow to continue behind the front in eastern NV and the ranges of UT where Day 1 PWPF for >8" are 40-80% above the post-frontal snow levels of 3000-4000ft. The next trough rotates around a Gulf of Alaska low, crossing the PacNW coast late Wednesday which is then followed by prolonged onshore flow/continual precip through this weekend. Snow levels Wednesday night/Thursday fluctuate between 2500ft and 4000ft along the length of the Cascades and the Klamath Mtns where Day 3 PWPF for >8" is 40-80%. ....Central Rockies, HIgh Plains...=20 Days 1-2... ....Heavy snow tonight/Tuesday over the north-central High Plains and WY/CO Rockies... A wave ahead of the parent trough/low tracks over WY early Tuesday with strong lee-side cyclogenesis on the south-central Plains (aka KS) through Tuesday. 1025mb high pressure over the Canadian Prairies allows a frontal focus for snow over the Bighorn Mtns east to and north of the Black Hills late tonight, sagging south=20 through Tuesday. This leading swath of snow has increased in=20 intensity and coverage given strong dynamics to overcome marginal=20 thermal conditions (it is currently around 50F in the lower=20 elevations of this swath). Day 1 PWPF for >6" are 50-80% east of=20 the Bighorns into SD and 50-90% for >18" in the Bighorns themselves with ideal backing flow from east to north encountering upslope on the Bighorns with ample Pacific and Gulf moisture. The trough to=20 the south will allow heavy snow on the western slopes of the CO=20 Rockies Tuesday where Day 1.5 PWPF for >8" are 50-90%. ....Central Plains through Upper Midwest... Days 2/3... ....Blizzard conditions for portions of the Central Plains into the Upper Midwest Tuesday night into Wednesday night... The trough takes on a negative tilt as it pushes over the south- central Plains Tuesday night, closing into a mid-level low Wednesday morning over Iowa before tracking northeast over MI Wednesday night. Peak intensity of the surface low looks to be around 985mb along the IA/MO border Wednesday morning which will generate a powerful wind field. As has been the case with the past few of these March systems, the antecedent airmass is warm, and the moist/warm advection funneling in the higher PW air will cause the precipitation to begin as rain=20 in many areas of the Plains. However, this should have minimal=20 affect on snowfall accumulations, as extreme dynamic cooling=20 combined with ageostrophic flow into low and cold advection as the=20 low moves east will cause a rapid p-type transition from rain to=20 snow, with snow likely becoming quite heavy within the deformation=20 axis NW of the low Wednesday. Snowfall rates of 1-2"/hr, possibly higher in thundersnow, will overcome the warm ground/low level thermals quickly. Thus, the limiting factor to snowfall amounts=20 appears to be more the speed of this system as it remains=20 progressive. Confidence continues to increase in a swath of >6" snow from eastern Neb to Lake Superior with enhancements from the lake on the Huron Mtns of U.P. where >12" is likely in Day 2, 2.5=20 PWPF. More modest snow totals of 2-4" are likely from northern KS through central Neb, though intense winds driven by 850mb northerly flow=20 of 60 kts will produce strong/damaging gusts and blizzard=20 conditions. Blizzard looks to be met well into the Upper Midwest until the northern forests limit the blowing snow potential which is highlighted well in the probabilistic WSSI. Wrap around snow shifts over southern WI/northern IL/MI/IN Wednesday night into Thursday, though the parent low shifting well into Quebec by Thursday morning should limit snow potential. Jackson ....Winter Storm Key Messages are in effect as linked below... https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!76sopEbkEJd7dK1iYt_iVkTxW7d-9d5eQfjzBet-YWnbe= kADyvht8GHZALYuKoVdJS3K7qctsKY8604HWIv7ASbfgZw$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .