Watches, Warnings, Advisories
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Forecast Discussion
000 FXUS63 KFSD 301129 AFDFSD AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 629 AM CDT Thu Mar 30 2023 .SHORT TERM...(Today through Friday Night) Issued at 357 AM CDT Thu Mar 30 2023 Key Messages: 1. Multi-faceted, multi hazard system impacts the region today through Friday night. Isolated severe weather, locally heavy rain, moderate to heavy snow, are possible. Strong winds are expected. 2. Reprieve for the weekend, with a warmer temps Sunday. 3. Another system may impact the region early to mid next week. Confidence remains low in details. _______________________________________________________________ Short Term Discussion: Through Daybreak: Clouds continue tracking northeast along the first WAA push as mid level ridge builds. Winds are strengthening with tightening surface pressure gradient as surface high moves east. With southerly flow and WAA, have started to see temperatures begin to rise, with most of the area solidly in the 20s at 08z/3AM CDT. Although we`re seeing some returns on radar, dry sub cloud layer has been precluding precip from reaching the ground thus far. Today into This Evening: Mid level trough continues to deepen across the southwestern US, moving northeast through the day. By this afternoon, surface low begins to eject out of the Rockies into western KS and NE. In response, warm front treks north with ample WAA, leading to a warm day for most of the area. Folks near the Hwy 14 corridor likely stay in the upper 30s, increasing to the lower/mid 60s along Hwy 20. Temperatures will likely also be dependent on cloud cover, with models varying on coverage across our southern CWA. LLJ also cranks up in the east (northwestern IA and southwestern MN) through the early afternoon. Cloud cover and subsequent warming plays a role in the possible convective threat as well. With the LLJ, WAA, and increasing dew points, expect some shower activity east of I-29 today and into the afternoon. Rumbles of thunder are possible. Attention will turn to the possible severe weather threat - mainly this evening and into tonight - with elevated convection likely forming in NE and marching northeastward. Most models continue to show a high shear/low CAPE environment through most of the afternoon, with instability tracking northward during the evening. If convection to our south can form and if instability gradient shifts north/storms can break the cap, can`t rule out isolated strong to severe storms from northeastern NE stretching northeast into southeastern SD/southwestern MN/northwestern IA (outlined by the 06z SPC Day 1 Marginal Risk). Hail would be the main threat given lapse rates over 7 deg C per km. Additionally, could see some locally heavy rainfall, especially with convection. Tonight: Temperatures begin to fall along the Hwy 14 corridor to below freezing, leading to a transition to freezing rain. Soundings support a fairly long period of freezing rain, with little to no sleet and/or snow mixing in. One uncertainty tonight with respect to precip will be the potential dry slotting and periodic loss of saturation. This could lead to drizzle/freezing drizzle. One other uncertainty remains the temperatures, and just how quickly they fall both aloft and at the surface. Lows in the upper 20s to lower 30s in the north and west, with northwestern IA staying mild in the mid/upper 40s. Instability aloft, albeit weak, could be enough to lead to some convective precip, which could create some moderate to heavy precip in addition to thunder. Friday: Highs on Friday will range from near 30 east of the James and along Hwy 14, to the upper 50s and lower 60s in northwestern IA (who stays in the warm sector the longest). Increasing CAA could lead to falling temperatures through the day as surface low travels east. Winds strengthen and turn northwesterly during the afternoon, which will lead to blowing/drifting snow. Transition from either rain or freezing rain to snow occurs through the day, with most of the area switching to snow by the evening. The exact timing is uncertain due to timing issues with CAA. Snow will be heavy at times, and northwesterly winds ramping up in the afternoon will likely lead to blowing/drifting snow and reduced visibility. Although could see some thunderstorms along and east of Hwy 75 in northwestern IA/southwestern MN, severe threat has shifted just to the east of our area. Can`t rule out a stronger storm with initial development, if convection can get going mid morning, although this scenario seems unlikely. Friday Night: With wrapping low and LLJ paired with increasing CAA on the backside of the system as it moves to the east, expect winds to ramp up quickly. NBM continues to have values near and above Wind Headline criteria; however, not convinced via soundings that we`ll be able to consistently mix to 850mb (where the strongest winds lie) to keep these values in. Have reduced with the NBM 10th percentile (although this is still possibly too high), previous forecast, and CONSShort. Trends will need to be monitored for possible headlines. Regardless of headline potential, winds will be strong through the night, leading to blowing and drifting snow. QPF through the event has come in lower this forecast period than previous forecast, and thus have seen a decrease in snow totals tonight through Friday night. Models have shifted the axis of heavier snow to the north and west as well with the low track a touch further to the north. For our area, amounts look highest west of the James and along the Buffalo Ridge (where over 4 inches possible). Probabilities of 6+ inches have dropped a touch, to just over 50% in our far northwest. Also, with saturation issues and temperatures a touch warmer aloft, have seen an increase in ice amounts. Could see a tenth of an inch of ice from south central SD to the Buffalo Ridge, with about a 30% chance of over a tenth along Hwy 14. Did not make any changes to headlines at this point, maintaining the Winter Storm Watch for possible Blizzard Conditions. Did ponder an expansion of the headline to the I-90 corridor with NWS Twin Cities; however, given downward trend in snow amounts and lower confidence in ice accumulations, held off for this package. Folks should prepare today for all possible hazards, and keep an eye on the forecast through the day for updates. Be prepared to alter local and regional travel plans tonight into the weekend. .LONG TERM...(Saturday through Wednesday) Issued at 357 AM CDT Thu Mar 30 2023 Saturday: Low continues to move off to the east Saturday, bringing the return of zonal flow. CAA on the backside of the low will keep us on the cooler side, especially early in the day and into the afternoon across the eastern portion of the forecast area. Any lingering snowfall should come to an end as the low moves to the east as well. Highs Saturday in the 30s and 40s, with lows falling into the 20s and 30s. Increasing clouds and breezy conditions return, with blowing snow possible Saturday night (depending on how much new snow falls across the region Friday/night). Sunday: WAA returns as a mid level short wave is progged to swing across the International Border into ND. Clouds increase ahead of this, but other than breezy conditions, no impacts expected. Warmer day on tap with the WAA and southerly/westerly flow. Highs in the 40s and 50s (close to normal!), with lows in the 20s and 30s. Early/Mid Next Week: Temps generally below/near normal. Slightly cooler Monday with CAA behind the wave and cold surface high sliding south. Highs in the upper 30s to upper 50s, warmest in northwestern IA. By Monday night, trough builds into the western US, deepening through Monday night into early Tuesday. Models are in somewhat agreement with the overall evolutionary trends of the system, but timing and track still have enough variance for low confidence. This system, depending on timing and track, could be another multi- faceted event. Regardless of precip, it will be windy. Folks should keep an eye on the forecast for early/mid next week, especially if you have regional travel plans. && .AVIATION...(For the 12Z TAFS through 12Z Friday Morning) Issued at 621 AM CDT Thu Mar 30 2023 VFR conditions begin the TAF period, with a mix of stratus and cirrus. MVFR and lower stratus develops east of I-29 this afternoon, filling in to the west through the evening. MVFR and lower conditions expected through Friday. Winds increase through the morning, with a lull (relatively) through the latter half of the period as low pressure slides across the area. Expect the strongest winds in northwestern IA. LLWS is possible for northwestern IA and southwestern MN this evening as the LLJ strengthens, but have left out of KFSD and KSUX, as these sites look to be on the far eastern edge. Precip (rain) develops across southwestern MN and northwestern IA later today. Although added with this package, low confidence remains in convection potential this evening for KFSD and KSUX. Any thunderstorm could further reduce visibility/ceilings, as well as create brief erratic winds. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Winter Storm Watch from Friday morning through late Friday night for SDZ040-055-056. Winter Storm Watch from Friday morning through late Friday night for SDZ038-039-050-052>054-057>060-063-064. MN...Winter Storm Watch from Friday morning through late Friday night for MNZ071-072-080-081-097. IA...None. NE...None. && $$ SHORT TERM...SG LONG TERM...SG AVIATION...SG