Sunrise 6:06 AM   Sunset 8:20 PM Moonrise 3:01 AM   Moonset 2:08 PM

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FXUS63 KFSD 031742 AFDFSD

Area Forecast Discussion National Weather Service Sioux Falls SD 1242 PM CDT Fri May 3 2024

KEY MESSAGES

- Rain returns late this afternoon/evening and continues through Saturday morning. Rainfall amounts between a quarter to up to a half an inch are expected. Ponding on roads along with minor stream and river flooding are again possible.

- Dry through the weekend with temperatures at or just below normal for this time of year.

- A strong low pressure system looks to bring renewed storm chances and moderate to heavy rain on Monday but details remain uncertain as of now.

DISCUSSION
Issued at 310 AM CDT Fri May 3 2024

Look for a quiet start to the day before a cold front/inverted surface trough encroaches on the area by late afternoon/evening.
Although skies are clear very early this morning, clouds will increase during the day as the system approaches. Warm air advection overspreading the region will allow 850 temperatures to climb to 8- 10 degrees C over the southeastern CWA, and this will result in highs climbing into the upper 60s to lower 70s over that area. Back to the west where clouds will be increasing and warm air advection is less pronounced on the back side of the inverted trough, highs will only reach the upper 50s to near 60 from east central SD back into south central SD. By late afternoon and early evening, a shortwave lifts into the area in a southwesterly upper level flow, as the inverted trough/frontal boundary begins to push to the east.
Models indicate strong mid/low level frontogenesis developing through central SD during this time frame - with upper level lift increasing as a jet streak streams from west/central SD into MN.
With that, a band of rain will develop in our far west around 22Z, then move eastward across the CWA during the overnight period.
Models indicate any significant instability remaining bottled up over NE, so precipitation should be primarily in the form of rain, with only a low chance of isolated lightning strikes. Latest guidance would suggest rainfall amounts of a quarter to half an inch across the area through early Saturday morning.

The majority of the CAMs have the band of rain to the east of our CWA by 12Z on Saturday morning. With the departure of this system, we look on track for a dry weekend as surface high pressure settles into the Northern Plains. The 850 mb thermal trough drops across the area on Saturday, and with cold air advection highs will fall back to the lower to mid 60s. By Sunday the surface ridge shifts into the Mississippi Valley, and in a returning southerly flow, temperatures will warm into the the mid and upper 60s.

Our next significant chance of rain comes into the forecast for the beginning of next week. Models continue to indicate a strong upper level low ejecting out of the Rockies and into the Northern/Central Plains by Monday. Still seeing model differences with regard to the evolution of this low, with the GFS/Canadian swinging the low into the Central Plains initially, then into the Northern Plains by Tuesday. The ECMWF offers a more northerly solution, taking the low directly into the Northern Plains on Monday - so there does remain some uncertainty in the details. While there will be the potential for thunderstorms with the system, confidence in severe chances is low. Both the GEFS/GEPS ensembles indicate moderate probabilities (40- 50%) of CAPE exceeding 1000 J/KG on Monday afternoon, though the ENS ensembles indicate only a 10-20% - again a reflection of differences in how the system evolves. As mentioned in the previous discussion, CIPS analogs do have low probabilities of severe storms in our area - the higher potential definitely remains to the south of our area - through the Central and Southern Plains. What does look more certain is the potential for at least moderate rain, with ensembles showing a 80-90% probability of at least a quarter inch of rain for the period Monday into Tuesday - and even a 40-50% probability of receiving at least a half an inch during the same time frame.

Models indicate the upper level low remaining stagnant and rotating over the Northern Plains, albeit weakening, through the middle and end of next week. This will keep at least some chance of showers over our area through the period. Temperatures look to be just either side of normal.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
Issued at 1241 PM CDT Fri May 3 2024

VFR conditions to begin the period will deteriorate to MVFR through the afternoon as clouds build in from the west. Winds are currently northwesterly at around 5 kts at KHON, and southwesterly around 10 kts at KFSD and KSUX. A cold front is just entering the area near KHON and will trek southeastward through the afternoon and evening.
Winds behind the front will be northerly 5-10 kts with occasional gusts of 15-20 kts. The front is expected to be through KFSD between 04.00Z and 04.02Z, and KSUX between 04.05Z and 04.07Z.

Rain showers will follow the front. Some have already begun to the west of our area and are expected to move eastward through the afternoon. Severe weather is not expected, but there could be occasional lightning strikes. Rain is expected to be fully clear of the area around mid morning Saturday.

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

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