Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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322 FXUS63 KFSD 151138 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 638 AM CDT Wed May 15 2024 .KEY MESSAGES... - Broken bands of showers and thunderstorms will swing through the forecast area this morning & again in the later afternoon and evening. Severe weather threat is low, but could see a stronger storm or two during the late afternoon/early evening. - Well above normal temperatures will end the week. Moderate to high confidence (70-80%) in widespread highs in the 80s on Friday. Lower confidence (30-40%) in highs for Saturday, depending on timing of cold front. - More active southern stream jet is expected next week which may bring a better chance for increased shower/ thunderstorm coverage. && .DISCUSSION... Issued at 235 AM CDT Wed May 15 2024 TODAY-TONIGHT: Today begins with a surface low in south central SD, with showers most prevalent in an area of weak warm advection across an inverted trough north of the low. As associated mid-upper level wave slides a bit farther east this morning, surface low will slide to the northeast and anticipate a broken line of showers and perhaps a few thunderstorms to expand southward through daybreak before lifting northeast by midday. This should lead to a relative lull in activity for a few hours late morning-early afternoon before we see additional development along an advancing cold front. Main question for the afternoon revolves around timing of said cold front, though broad consensus brings the front to near I-29 around 20-21Z, with the northern end pushing east of Hwy 71 in Minneota by sunset while the southern end lags back across northwest Iowa later into the evening. May see a narrow ribbon of moderate instability (1000 J/kg) ahead of the front, though most solutions are on the weaker side with MUCAPE at or below 500 J/kg. Forecast soundings show any instability to be rather tall/narrow due to weak mid-level lapse rates, while deep layer shear is also meager at <30kt. Thus not expecting severe storms with this activity, though cannot rule out some small hail or gusty winds with stronger cells. A trailing wave rotating around the backside of the upper wave may support some spotty showers behind the cold front this afternoon or early evening, but thunder with this activity should be more sparse. Drying behind the cold front should bring an end to most showers by midnight tonight. THURSDAY-FRIDAY: High pressure slides east across the forecast area Thursday, allowing for mostly sunny skies, relatively light winds, and seasonable highs in the 70s. Increasing southerly flow later Thursday night into Friday will draw a brief shot of warmer air northward into the region. Deterministic models showing 850mb temps +15 to +20C build northward into the forecast area, which should mix out to widespread 80s for highs Friday. This is also supported by various ensembles with better than a 60% probability of temperatures topping 80F over most of the CWA. FRIDAY NIGHT-SATURDAY: Broad warm advection over the area may lead to elevated showers/storms Friday night, though better chance for this activity looks to be north of Highway 14 in line with better convergence at the nose of the low level jet. Approaching mid-upper level wave and associated cold front appear to be trending a little faster on Saturday than previous runs, which would limit additional highs in the 80s to perhaps the far southeast portions of the CWA. However, this is still a lower confidence forecast as timing of the front is still uncertain. Given this trend toward a faster frontal passage, precip chances for Saturday look limited, perhaps a stray shower or storm in our far east in the afternoon. EARLY NEXT WEEK: The first part of the upcoming week is trending a little more unsettled as a stronger southern stream jet develops from the southwest CONUS into the southern/central Plains. This will bring periodic chances for a broader coverage of showers/storms, though still plenty of uncertainty in specifics to pin down timing and/or severe potential. Temperatures remain on the warm side of normal to start the week, though look to trend a little cooler by Tuesday, again depending on timing of various waves and precip chances. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 631 AM CDT Wed May 15 2024 Ongoing band of mainly showers across portions of the I-29 corridor as we start this TAF period will lift northeast through the morning. Could see isolated TSRA within this band, but chance at any one location is too low to include in the TAF. This morning band should rotate northeast and largely exit the forecast area by late morning-midday, but additional development is likely along a cold front pushing east after 19Z-20Z. This afternoon development will be focused near and east of I-29, and could impact both KFSD & KSUX into this evening. Greater chance for thunder with this activity, and did include a few hours at both locations, though timing is still somewhat uncertain. MVFR ceilings and/or visibility may accompany showers/storms, with VFR conditions becoming more prevalent again after sunset tonight. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...JH