Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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668 FXUS63 KFSD 141703 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1203 PM CDT Fri Jun 14 2024 .KEY MESSAGES... - After mostly quiet conditions through the morning, a few scattered showers and isolated thunderstorms will develop west of I-29 and spread eastward by the late evening. Accumulations are expected to be light. - More widespread shower and thunderstorm chances (60%-90%) will develop to start the day on Saturday. Additional isolated shower and storm development will be possible by Saturday afternoon with a few storms potentially becoming severe. Accumulations of up to half an inch are expected. - An active pattern aloft will continue into next week with the potential for severe weather although details remain uncertain. && .DISCUSSION... Issued at 402 AM CDT Fri Jun 14 2024 The Short Term (Today/Tonight & Saturday): Another warm and mostly quiet day is ahead. Taking a look across the area, the clear conditions are set to continue as the surface high continues to drift southeastwards. Similar to yesterday, some patchy fog development will be possible mostly along our river valleys by daybreak as light and variable winds and lingering cold air advection (CAA) help our temperatures decrease towards our dew points (upper 40s to low 50s). However, as mixing restarts after daybreak and southeasterly winds increase expect any developing fog to quickly dissipate. From there, quieter conditions temporarily return for the rest of the morning as southeasterly flow helps pull in more warm and moist air to our area. With this in mind, expect similar conditions to yesterday as highs approach the low to mid 80s for the day. Shifting gears to our precipitation chances, little bits of isentropic lift ahead of a subtle shortwave will likely trigger a few scattered showers with isolated thunderstorms west of the James River and along the Missouri River Valley by the early afternoon. Expect this developing activity to gradually spread eastwards as the previously mentioned wave moves in to replace the departing surface high. As mentioned in the previous discussion, an occasionally strong wind gust wouldn`t be completely out of the question with developing cells around south-central South Dakota along the leading edge of the warm front/instability gradient. However, with the location of the warm front still in question; confidence still remains low in any severe weather chances. By tonight, the LLJ will strengthen as the main wave ejects out the Colorado Rockies leading to widespread shower and thunderstorms developing across South Dakota and Nebraska into Saturday morning. More specifically, most high resolution guidance continue to show high confidence in an Mesoscale Convective System (MCS) developing across western Nebraska and spreading eastwards overnight. However, as the developing convection outruns/eats up the better instability expect gradually weakening to occur as it heads towards the Nebraska/Iowa border. From here, most of the developing shower activity should exit our area by early parts of Saturday afternoon. Continuous southeasterly surface flow and effective mixing will allow for the atmosphere to slightly recover heading into the evening hours as highs vary between the mid 70s to mid 80s with the warmest conditions situated along the Missouri River Valley with the warm front. Looking at soundings across the area, while the set up will be conducive for scattered shower development, its going to be a bit more difficult to get much true convection during the time period mostly due to borderline convective temperatures and a strong cap in certain areas. However, there is a chance that once the cap begins to weaken near sunset that a few isolated strong storms could get going along the warm front/sector near the Missouri River and portions of northwestern IA. If this does occur, developing parcels would have between 1500-2000 J/kg of MLCAPE and 20-30 kts of shear to work with. With mid-level lapse rates expected to reach between 6.5-7 degrees C/km at this time, could see some large hail develop with stronger cells up to quarter size. With all this in mind, SPC has outlined portion of far southeastern SD and northwestern IA in a Day 2 Slight Risk (Level 2 out of 5) with the primary focus being areas south of Hwy-18 corridor. Lastly, Expect most of this developing activity to exit our region by Saturday night as quieter conditions temporarily return to the area into Sunday. The Long Term (Sunday-Thursday): Heading into Sunday, mostly quiet conditions temporarily return to our area as a mostly dry cold front slides through the region throughout the day. Increased southerly surface winds will become more northerly with the passing of the near-surface boundary with gusts between 20-30 mph possible especially east of I-29. While some weak cold air advection (CAA) likely moves in aloft, +20 to +25 850 mb temps along with efficient mixing will likely help our daily high warm into mid to upper 80s and low 90s with the warmest conditions expected along in northwestern IA. From there, our attention will likely pivot to the Colorado Rockies by Sunday night as a closed low ejects into the northern plains likely bringing our next precipitation chances (40%-70%). While exact rainfall amounts remain uncertain, PWATs up to 1.50" and an lingering stationary boundary ahead of inverted trough gives some decent signals for some heavy precipitation heading into Monday morning. The one remaining question is where the stationary boundary and subtle shortwaves tracks and thats still a bit too early to tell. Looking at ensemble guidance though, there`s continues to be low to medium confidence (20%-40%) in up to an inch of QPF across the area which is always beneficial. Nonetheless, we`ll have to continue to monitor the trends to get a better idea of how this will pan out. Looking into the new week, an active pattern continues aloft as an Upper-level ridging strengthens over the eastern CONUS shifting our area to southwesterly flow aloft. Some deterministic guidance does show some decent potential for periodic rain chances on Wednesday and Thursday. However, with long-range deterministic guidance starting to diverge with the placement of features its too early to tell how things will pan out. As a result, left the default NBM in for the extended. Lastly, temperatures will trend downwards towards our seasonal normal through Thursday with highs expected to be largely in 70s to 80s with a few low 90s possible across northwestern IA on Tuesday. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1200 PM CDT Fri Jun 14 2024 Showers and isolated thunderstorms will move into central SD early this afternoon, but struggle to progress east as dry air below about 12 kft does not support much in the way of showery activity. Later tonight, after about 3-6z, moisture in the mid levels as well as a little bit of instability should support the expansion of showers and thunderstorms which will gradually shift into southwest MN and northwest IA on Saturday morning. LIngering showery activity will remain possible in eastern SD and northeast NE through Saturday morning. Some MVFR ceilings will be possible late tonight into Saturday morning. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Gumbs AVIATION...08