Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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850 FXUS63 KFSD 162355 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 655 PM CDT Sun Jun 16 2024 .KEY MESSAGES... - Potential for a higher end severe weather risk tonight into Monday across the CWA. Elevated supercells supporting large hail to around baseball size will be very possible, with a smaller wind risk. Best chances near and north of I-90. - An increased risk for heavy rain and potentially flash flooding will also be present late tonight into Monday. Increased confidence that the heaviest rain will be near and north of I-90 towards highway 14. - Low confidence on Monday afternoon and evening but another environment may develop which would support elevated supercells and large hail. - Very unsettled pattern through most of next week. Ensemble guidance through the week suggests nearly a 50% probability for as much as 4" of rain through next weekend. Flooding concerns definitely grow during this time given expected pattern. && .DISCUSSION... Issued at 159 PM CDT Sun Jun 16 2024 By late this afternoon and this evening the low level front should be near the Missouri River into parts of northwest IA with the front around 850mb closer to somewhere between the Mo River and I-90. Model soundings still pretty bullish with capping of the lower levels, suggesting that any forcing or parcel ascent below about 850mb will not produce any convection. The models do have a very weak wave in northeast CO this morning that moves towards northwest IA by early evening. A few models try to produce some scattered convection but this seems very unlikely. Some backing of the low level winds does try to occur from about 6-8pm, but appears to be more focused southwest of the area and motion northeast would be slow. The nam seems too aggressive with moisture around 850mb late afternoon and early evening which might be why the cap weakens and some convection develops. Most other models do not have this and given the latest 850mb analysis the better advection of the deeper moisture will come later when the main wave ejects onto the Plains. Once this wave moves onto the Plains this evening forcing across the boundary increases significantly and convection should rapidly develop between about 3z and 6z. The latest HRRR and Rap showing about 2500- 3000 J/kg CAPE and moderate shear which will support scattered supercells with the main threat being large hail, possibly around baseball size. With the deep stable layer in the low levels tornadoes and wind will be much lower threats. Model soundings still very consistent in suggesting that lift from around 800 mb will see the least amount of convective inhibition which makes that amount of instability all the more impressive. The models are in good agreement on the 800 mb front being roughly from Gregory SD to Flandreau SD to Marshall MN from about 3-6z. The location of this boundary will be something to watch through the evening in case it slides a little farther south this afternoon. Once development takes place supercell motion would likely be east northeast with some potential to build southward into the lower level forcing as deeper moisture and increased instability work into the area. The other concern with this set up will be heavy rain. The upper level flow is still expected to be normal to the low and mid level boundary and with the upper level wave slow to move northeast backing of the mid level winds remains in place through at least mid day Monday which will likely support continuous development through Monday into Monday night. Latest models indicating a very good chance for 2-4 inches of rain north of I-90 from around De Smet then into southwest MN. Really tough to say for sure what will happen from later Monday afternoon into Monday night as tonight and Monday mornings activity will dictate the environment a bit, but given the strength of the wave will not be relying on only instability to get storms going again. By Monday afternoon and Monday night an environment capable of strong elevated supercells may exist once again and another round of severe weather and heavy rain will exist. Once again the environment would be most supportive north of I-90 and possibly west of I-29. Some upper level ridging should keep northwest IA, northeast NE and far southeast SD with very small chances for thunderstorms Monday mid afternoon into Monday night. Upper level troughing to the northwest begins to shift east Monday night into Tuesday and will likely bring renewed chances for showers and thunderstorms into Tuesday night with severe weather again possible. The better chances will be east of the James and likely east of I-29. This system passes and cooler and less unstable air settles in, but for now that does not look like the end of rain and thunderstorms. The right entrance region of the upper level jet lifts northeast and once again enhances low to mid level flow, bringing additional lift and moisture into the area and thus more rain and thunderstorms. A lot between now and then but right now this not does not look like as big of a severe threat, but with the rain possible near and east of I-29 again flooding concerns will begin to grow. Thursday into Sunday will see continued chances for showers and thunderstorms with mostly westerly flow aloft which brings in occasional weak waves. Temperatures should be seasonally warm most days. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 646 PM CDT Sun Jun 16 2024 Multiple rounds of showers and storms are expected to impact the area during this TAF period, reducing conditions to MVFR and lower. Confidence in timing and coverage of any round remains low, especially as you go later into the TAF period. For tonight, some guidance has convection developing across northern NE around 17.00-01z, moving into the KSUX and KCKP areas by 03-04z. Given that most guidance which has this development is struggling with antecedent conditions, confidence is quite low in this scenario. Otherwise, expect convection elsewhere tonight to develop by around 17.05z, expanding in coverage through the overnight hours. Again, confidence in timing/coverage is low for every round. Strong to severe storms are possible through the entire period. Outside of convection, winds shift to east southeastern and become breezy toward the end of the period with gusts to 30 knots. Lower stratus is expected during the latter half of the period, especially if convection is more widespread. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...SG