Sunrise 6:17 AM   Sunset 8:27 PM Moonrise 2:07 AM   Moonset 11:35 AM

  Print   HELP   Reset   Save   Recall

FXUS63 KFSD 011134 AFDFSD

Area Forecast Discussion National Weather Service Sioux Falls SD 634 AM CDT Wed May 1 2024

KEY MESSAGES

- Near normal temperatures are favored for today, with chances for light scattered showers increasing throughout the day.

- Wednesday night into Thursday will see a round of scattered showers and thunderstorms, with highest rainfall amounts across portions of northwestern IA where up to an inch is possible. While severe weather is not expected, minor flooding issues are possible.

- Continue to have a couple periods where overnight lows dip into the upper 30s through Saturday night, but widespread frost/freeze conditions not expected.

- Additional chances for scattered showers and thunderstorms Friday night into Saturday, and again Monday night into Tuesday.

DISCUSSION
Issued at 400 AM CDT Wed May 1 2024

On the northern edge of a weak surface high pressure, early morning satellite imagery shows cloud coverage increasing up into the I-90 corridor, with some light returns seen on radar across portions of northeastern Nebraska. These showers/storms are occurring as isentropic lift from the northwest quadrant of the surface high pressure moves across the region, aided by some very scattered shortwave moving through the mid-levels. Soundings and surface observations show cloud bases are currently at 7.5-12.5 kft, so as this activity continues into the mornings hours as the surface high drifts northwards, expect low chances for showers/storms into the morning hours for areas south of I-90.

Warmer air is brought into the region by the surface high during the morning hours, which looks to bring the region into the mid to upper 60s by the afternoon hours. Winds will remain on the lighter side, but will be varying in direction throughout the day. Attention turns to a developing surface low pressure forming down in the southern plains, with the inverted trough working on extending itself up into the region during the afternoon and evening hours. Further aided by shortwaves from an upper level low over the International Border, chances for rainfall will be increasing into the overnight period.
Confidence in exact timing is medium, as some of the higher resolution guidance suggests we won't see much rainfall activity until shortly before midnight, so have kept pops on the lower end before increasing them during the late evening hours.

Rainfall amounts will be highest for areas southeast of a line from Jackson, MN to Canton, SD to Vermillion, SD, where over an inch of rainfall is possible. NBM and HRRR both show roughly a 30 to 50% chance for an inch of rain for that area, with probabilities for half an inch in the 70 to 90% range. Areas northwest of the aforementioned line will see chances for half an inch dwindle fairly quickly the further away from the line one travels, with areas from Huron to Burke looking to see between a tenth to a quarter inch of rain. Given the recent rainfall across northwestern Iowa and adjacent area, there are some minor flooding concerns as the soil moisture content remains high. Thankfully rainfall rates are not looking to impressive in the 0.25-0.5 inch per hour range, so mostly expecting ponding of water in low-lying areas and additional rises on local streams/rivers.

The main mid-level wave pushes the inverted trough axis off to the east, which brings an end to that round of rainfall throughout the daytime hours. With clouds clearing throughout they day, slightly below normal temperatures are expected, in the mid to upper 50s north of I-90, and upper 50s to mid 60s south of I-90.

After a mostly dry day on Friday with highs in the lower to upper 60s, a weak cold front moves through the area. The trough axis moves in quickly behind it, and will lead to additional chances for scattered showers and thunderstorms overnight into Saturday.
Ensemble clustering analysis shows there remains good agreement amongst the various ensemble members, so have left NBM pops as is, which increase rainfall chances during the evening hours on Friday and continuing into Saturday. Upper level ridging on Sunday leads to warming temperatures across the region, though some models are hinting that some shortwaves may move across the region giving us more rainfall. Most hold off on the rain chances until the main wave from the cut-off upper level low moves onto the central plains on Monday, leading to rain chances Monday night into Tuesday. Some model solutions show the cut-off upper level low stalling out somewhere over the northern plains, but we'll have to see if that solution continues over the coming days.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
Issued at 1042 PM CDT Tue Apr 30 2024

VFR conditions overnight and into much of Wednesday. Winds tonight out of the northwest around 10 knots and gusts to 20 knots at times. As gusts weaken tonight, LLWS (around 300 degrees and 50 knots) may develop across southwestern MN and adjacent areas of SD and IA as the LLJ increases. This should stay to the east of KFSD. Direction shifts and winds will briefly become light as weak high pressure slides over the forecast area. Easterly winds prevail and increase during the late afternoon/early evening Wednesday, with gusts approaching 25 knots Wednesday night.

Rain and storm chances increase from south to north through the evening hours and into Wednesday night. Have omitted thunder mention as confidence is too low in occurrence, but did increase coverage of -SHRA based on latest hi-res guidance. Expect lower end VFR conditions later in the period.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/
Issued at 634 AM CDT Wed May 1 2024

Weak showers are possible this morning south of I-90, with additional showers and thunderstorms building into the region throughout the afternoon hours, though are most likely during the late evening and overnight hours. Going back to this morning, winds will start out from the west-southwest, but will be varying in direction throughout the day as a surface high pressure drifts across the area, which will keep winds on the lighter side.

Have kept thunder mention out of this set of TAFs as that is not expected until after 5/2 00Z. MVFR to LIFR cigs will moving into the area overnight with the scattered showers and thunderstorms, with MVFR/IFR visbys expected as well.

FSD WATCHES/WARNINGS/ADVISORIES
SD...None.
MN...None.
IA...None.
NE...None.

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Des Moines, IA,