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
142 FXUS63 KFSD 132315 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 615 PM CDT Thu Jun 13 2024 .KEY MESSAGES... - Near to above normal temperatures will continue, with daily highs expected to peak the upper 70s to 80s. - Confidence continues to increase in more widespread rain chances (60-90%) on Saturday, though amounts are less certain. NBM probabilities for an inch of rain are in the 30-50% range for areas east of the James River Valley. - Active weather pattern is expected for next week with potential for severe weather, though details are uncertain. && .DISCUSSION... Issued at 148 PM CDT Thu Jun 13 2024 Rather pleasant this afternoon, with light northerly winds and temperatures largely in the upper 70s and 80s. This is occurring as weak ridging builds off to our west, with a surface high pressure moving down from southern Canada into the overnight hours. While dewpoints have been dropping throughout the day, they peaked in the upper 50s to lower 60s earlier today. With overnight temperatures expected in the mid to upper 50s, cross over temperatures will likely be reached, so similar to last night we will likely see patchy fog in low-lying areas along with the river valleys. While we`ll see the ridging aloft continue into the morning hours, the current closed off upper level low moving ashore onto southern California turns into a shortwave overnight into Friday, and will eject onto the central plains late Friday morning. With the surface high pressure sliding off to our east and a weak developing surface low pressure off to our west, southeasterly surface flow develops and will advect warm and moist air back into the region. As a result, another afternoon with high temperatures in the lower to mid 80s. Given weak isentropic flow on the backside of the surface high in addition to weak shortwaves out ahead of the main wave, may start to see some weak showers and isolated thunderstorms develop in south- central South Dakota by the early afternoon hours. As the surface high is pushed eastwards, chances for light rain expand eastwards into the evening hours. Not impossible to see a strong wind gusts in along and west of the MO River Valley in south-central SD along the leading edge of the warm front, but the location of said front may end up further west keeping severe chances very low across the area. Overnight, a strong low-level jet develops as stronger shortwaves out ahead of the main wave move overhead. While both of those could create some thunderstorms prior to the main wave, the highest chances for showers and thunderstorms arrive late overnight into the morning hours on Saturday. High resolution convection allowing models (CAMs) all show a mesoscale convective system (MCS) to some capacity moving towards the region overnight into the morning hours, slowly dissipating through the morning hours as the storms outrun the instability. Chances for additional thunderstorms return in the afternoon as shortwaves continue to move across the region, with non- zero chances for severe weather returning as well. Chances for severe weather will be dependent on how the MCS changes the environment, specifically the position of the warm front/sector by Saturday afternoon. SPC has areas along and east of the James River Valley in a threat level 1 out of 5, but again details remain uncertain, so if you have outdoor plans on Saturday afternoon make sure to check on the weather before heading out. Given the numerous chances for rain, temperatures on Saturday will be a touch lower in the mid to upper 70s for areas east of I-29, while normal temperatures in the 80s are expected for areas west of I-29 as they get some afternoon heating. Overnight into Sunday the low pressure system will likely have pushed through the area, though some models have this occurring later in the day, which will bring an end to the rain chances from this system. Models that have the rain chances ending earlier show a rapid warm-up is expected, bringing afternoon temperatures up into the mid 80s to lower 90s, while those that are slower with ending the rain keep us in the upper 70s to mid 80s. The pattern remains active into next week as southwesterly flow aloft continues due to a strong upper level ridge expected to develop along the east coast, in addition to a strong either cut-off upper level low or deep trough along the northwestern CONUS. This sets us up to potentially see periodic chances for rain and severe weather as numerous shortwaves move across the region, with the inverted trough from a surface low pressure system also focusing chances for rain across the region. Model solutions have similar ideas, but do vary in their placement of warmest temperatures and highest rainfall chances, so have left the NBM in place given the uncertainties. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 612 PM CDT Thu Jun 13 2024 Winds tonight become light and variable, eventually shifting to the southeast toward Friday morning/early afternoon. Gusts around 20 knots possible Friday afternoon. Light and variable winds could allow for some patchy fog development in low lying areas and river valleys; however, most guidance this afternoon/evening seems to have backed off on this potential (compared to the this morning). Given low confidence, will continue to exclude. Expect VFR conditions to prevail. Isolated to scattered showers/storms are possible west of the James River toward the end of the period, but will omit for now given uncertainty in convection. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...APT AVIATION...SG