![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
438 FXUS63 KFSD 132340 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 640 PM CDT Sat Jul 13 2024 .KEY MESSAGES... - High humidity brings dangerous heat index readings around 100 to 107 degrees through early this evening. - Low (<30%) chance of isolated showers and storms through this evening. Low confidence in exactly where/when storms will develop if they do. However, if a storm is able to develop, it may quickly become strong to severe. The main threats with the strongest storms will be large hail up to golf ball size and wind gusts up to 60 mph. - Very slightly cooler on Sunday, but high humidity will likely bring high heat index readings of 95 to 105 degrees, hottest south of the I-90 corridor. - Unsettled pattern continues into the middle of next week with periodic low shower and storm chances. Starting Tuesday, temperatures will be near to below normal for this time of year. && .DISCUSSION... Issued at 244 PM CDT Sat Jul 13 2024 TONIGHT: Early this afternoon, satellite images show a cluster of mid level clouds and isolated showers in central SD tracking eastward. Sparked by a mid level wave, this is the most likely forcing for ascent for any isolated strong to severe Tstorms through this evening. A hot, very humid atmosphere remains primed for strong to severe multicell storms with plentiful instability, 7-8 C/km mid level lapse rates, and 25-35 kts 0-6km deep layer shear. However, it is important to note that confidence remains very low regarding where, when, and even if storms could form due to strong capping and lack of a more pronounced wave or jet streak aloft necessary to initiate convection. This low confidence is clear in the convective allowing/hi-res models which have been erratic in where/when/if convection develops at all. If storms can develop, there is potential for quick intensification to strong to severe elevated storms with a main focus from 5 PM to 10 PM and main threats of large hail up to golf ball size (or perhaps even larger if updrafts can sustain) and damaging wind gusts up to 60 mph. Weak low to mid level wind profiles and capping make tornado threat low, though substantial moisture content and a STP of 1 east of I-29 suggest that a brief spin up cannot be entirely ruled out. Much of the evening and overnight are expected to remain dry for much of the region. Beyond low evening storm threat, additional rounds of storms may develop upstream in 1) eastern ND/northwest MN and 2) western ND and northwest SD. A few models suggest the first round may clip portions of southwest MN as it grows upscale and treks southeast through MN late tonight, with a low threat of remnants of the second round grazing the Hwy 14 corridor in the early morning hours Sunday. Severe weather threat with this activity is very low, but cannot entirely rule out potential for weaker showers and storms. Aside from marginal severe weather threat, the main impact continues to be dangerous heat and humidity with heat index readings already at 90 to 105 degrees as of 1 PM. Passing mid level clouds may provide some relief from extremely hot air, capping temperatures in the low to mid 90s, but stifling humidity persists with dew points broadly in the mid to upper 70s east of the approaching inverted sfc trough nosing into south central SD. Some locations may see a bit of relief from heat if cloud debris from storms can develop early this evening, but otherwise diurnal cooling brings low only to around 70 degrees overnight. SUNDAY: The same muggy airmass remains in place across the region through Sunday as dew points linger in the low to mid 70s. The previously approaching inverted sfc trough/weak boundary washes out in the region on Sunday, oriented west to east roughly along the SD/NE border eastward to just south of the MN/IA border. Easterly flow and remnant clouds and/or showers near and north of the boundary will help make for a slightly cooler day. Areas north of the boundary are likely to only reach the upper 80s to lower 90s with lower to mid 90s more likely further south. Additionally, wildfire smoke streaming through aloft may continue to inhibit heating slightly. Coupled with high confidence in dew points in the low to mid 70s, heat index readings of 95 to 105 degrees are very likely near and south of the I-90 corridor. Thus have issued a Heat Advisory for 1 PM to 8 PM again Sunday in the area most likely to see 100+ degree heat index readings. Sunday is poised to be mostly dry with sunny skies in quiet northwesterly flow aloft as strong capping lingers with 850mb temperatures at the top 10% of NAEFS climatology. The next ridge riding disturbance treks into the Northern Plains Sunday late evening or overnight with deterministic guidance increasingly favoring a chance of showers and storms, at least for areas near and north of the Hwy 14 corridor in SD/MN. Moderate instability and enough deep layer shear to support a complex of storms with multicells suggest isolated to scattered severe storms are possible overnight into Monday morning if storms can persist that long. MONDAY: Warm, humid conditions linger into Monday with heat index readings in the upper 90s to near 100 degrees continuing south of I- 90 in the afternoon. Big question is how much of a role north winds, cloud cover, and departing showers will play in heating so have lower confidence on temperatures and any heat related headlines. TUESDAY AND BEYOND: The upper wave stalled over the Canadian Prairie starts to push east Monday night, bringing a cooldown to near to below normal temperatures heading into Tuesday and beyond. Northwest flow aloft thanks to the stalled building ridge over the West brings spotty, low confidence rain chances, but no high impact or widespread rains look to be on the horizon for the remain of the week. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 639 PM CDT Sat Jul 13 2024 Latest satellite imagery shows mid to high level clouds across the area. No rain is expected with these clouds. Showers and storms have developed across parts of the Northern High Plains and Upper midwest but most of the storms are not expected to impact the forecast area let alone any TAF site. The exception is storms across east central Montana late this afternoon. These storms will push southeastwards through the evening and into the overnight hours but questions remain on the exact track and if they will weaken before getting to the Missouri River Valley. As such, have left all TAFs dry but trends will be closely monitored. Aside from storms chances, light southerly winds begin the TAF period but will go light and variable overnight. Winds will turn southeasterly by tomorrow afternoon. The light southeasterly winds and dry conditions will finish out the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Heat Advisory until 8 PM CDT this evening for SDZ038>040-050- 052>071. Heat Advisory from 1 PM to 8 PM CDT Sunday for SDZ050-057>071. MN...Heat Advisory until 8 PM CDT this evening for MNZ071-072-080- 081-089-090-097-098. IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003- 012>014-020>022-031-032. Heat Advisory from 1 PM to 8 PM CDT Sunday for IAZ001>003- 012>014-020>022-031-032. NE...Heat Advisory until 8 PM CDT this evening for NEZ013-014. Heat Advisory from 1 PM to 8 PM CDT Sunday for NEZ013-014. && $$ DISCUSSION...BP AVIATION...Meyers