Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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460 FXUS63 KFSD 251740 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1240 PM CDT Tue Jun 25 2024 .KEY MESSAGES... - River crests have already occurred or will occur within the next 24-36 hours. While no significant amounts of rainfall are expected, areal flooding caused by the prior excessive rainfall continues across portions of the area. - A conditional severe weather risk this afternoon and evening, with the greatest risk along the Missouri River into northwestern Iowa from 4 to 11 PM. Storms could quickly intensify leading to 2 inch hail and wind gusts to 70 mph. Locally heavy rain is also possible. - Unsettled weather pattern continues through the weekend with numerous chances for rain across the area. Next potential for more widespread heavy rainfall is Thursday into Friday. && .DISCUSSION... Issued at 401 AM CDT Tue Jun 25 2024 CURRENTS: With the front still have to our northwest across northern SD, we`re currently "enjoying" 3 AM temperatures in the 70s to lower 80s with dew points in the 70s as well. Convection tied to additional WAA and a mid level vorticity maximum continues to decay as it encounters more stable air. However, a brief shower at Chamberlain did result in a heat burst, with temps rising 10 degrees in 40 minutes with a dew point drop from the mid 70s to the mid 50s! Winds gusted to around 45 mph, with the very dry sounding. With dew points as high as they are, lows this morning won`t drop more than a few degrees from our 3 AM temps. Northwest winds may occasionally gust to around 20 mph. TODAY: Aforementioned cold front slides south with the vort max sliding east. This keeps some isolated pops along the Hwy 14 corridor through the morning hours, although dry sub cloud layer will likely limit most precipitation from reaching the ground. Meanwhile, attention this afternoon and evening will turn to the front draped south of I-90, along the MO River toward Hwy 20, with this morning`s models runs seeming to keep this feature a little further north. Showers and storms are expected to fire along/near the front. There is less of a cap in place than yesterday, so do expect some at least isolated activity in this area. Any storm that develops could quickly become strong to severe, with CAPE values over 3500 J/kg, bulk shear values 40 knots or more, and steep mid level lapse rates again over 7-8 deg C/km. Strong to severe storms could produce hail to 2" diameter and wind gusts to 70 mph. Locally heavy rainfall is possible as well, with PWAT values around 1.5 inches - so any thunderstorm could produce an inch to 1.5" of rain. If a storm can become surface based, there is a very low, but non- zero tornado chance (greatest risk south of Hwy 20). Overall between the front and mid level forcing, greatest severe weather risk stretches from the MO River in south central SD eastward into northwestern IA north of Hwy 20 between 4 and 11 PM. Highs today will be a little cooler, in the 80s (did decrease highs by a couple of degrees due to forecast increase in cloud cover). High humidity especially across northwestern IA will lead to heat indices in the 90s. TONIGHT: Cold front barely gets south of our area before the next short waves dive into our area - a weak wave from the west along the MO River with a much more defined wave diving south from ND. This second wave brings isolated showers and storms to the Hwy 14 corridor into southwestern MN near I-90 through the overnight hours, ending after daybreak Wednesday. Lows tonight in the 60s. WEDNESDAY: A brief reprieve during the day on Wednesday as a weak mid level ridge slides overhead and surface high pressure slides over the eastern portion of the area. A bit cooler with more sun than clouds with highs in the upper 70s to lower 80s. WEDNESDAY NIGHT ONWARD: Active pattern continues through the weekend, with a series of short waves swinging across the synoptic pattern keeping periodic shower and storm chances in place. More defined system and trough axis along with a cold front Thursday into Friday brings the next chance for more widespread, potentially locally heavy rainfall as PWATs climb again to over 2"; however, with some location differences in track, this heaviest rain threat currently lies just outside our areas in IA. This time period could also bring some severe weather threat, but confidence is low due to the aforementioned timing issues. With upper low pressure swinging across the Upper Midwest during the latter part of the weekend, northwesterly flow aloft prevails with surface high sliding overhead at some point this weekend and ridging aloft by the end of the weekend. Another system/wave is poised to move in to start the work week. Temperatures through this period will be in the 70s and 80s for highs and 50s and 60s for lows. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1230 PM CDT Tue Jun 25 2024 VFR conditions with occasional MVFR/IFR conditions will be possible this TAF period mostly due to developing showers and thunderstorms late this evening. Taking a look across the area, any lingering showers from this mornings activity are dissipating as they head eastwards just north of the Hwy-14 corridor. The only other thing of note is the developing cumulus field setting up over the Missouri River and Hwy-20 corridors. By late afternoon to early evening, scattered showers and thunderstorms will like develop along the outlined area and surge southeastwards with a few potentially becoming severe. Otherwise, expect the lighter winds to continue for the duration of the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...Gumbs