Sunrise 6:13 AM   Sunset 8:30 PM Moonrise 3:33 AM   Moonset 3:35 PM

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FXUS63 KFSD 041722 AFDFSD

Area Forecast Discussion National Weather Service Sioux Falls SD 1222 PM CDT Sat May 4 2024

KEY MESSAGES

- Rain will exit the CWA by mid morning, with total rainfall amounts of up to 0.50-0.75" over northwestern IA, and lesser amounts back to the north and west. Dry weather expected for the remainder of the day.

- Cooler temperatures today (low 60s), with middle and upper 60s on Sunday. Dry conditions also expected on Sunday.

- Winds approaching advisory criteria may arrive Monday, prior to the arrival of late afternoon and overnight thunderstorms.

- The greatest severe weather risks continue to remain focused south of the Missouri River and Highway 20 corridor, however continue monitoring of the forecast is recommended.

DISCUSSION
Issued at 330 AM CDT Sat May 4 2024

A frontal boundary/inverted surface trough resides east of Interstate 29 very early this morning. Current radar and observations indicate showers - with a few isolated lightning strikes - pushing eastward across the CWA This in conjunction with midlevel frontogenesis and theta e advection pushing through the region. This area of showers will continue to push eastward through the morning hours, exiting the CWA sometime around 14Z. Additional rainfall amounts during the late night/early morning hours will range from a few hundredths in the western CWA, to a half to three quarters of an inch over northwestern IA. For the remainder of the day, surface high pressure begins to build into the region, with skies clearing from west to east through the day. With cold air advection on the backside of the system, afternoon temperatures will remain in the upper 50s to lower 60s. With the surface ridge axis sliding over the area tonight, light winds and clear skies will allow temperatures to fall into the upper 30s to lower 40s.

The high pressure slides into the Mississippi Valley on Sunday. With that, winds will become southerly, increasing to 15 to 25 mph west of Interstate 29 in the afternoon as the surface pressure gradient tightens up - this the result of a deepening surface trough over eastern MT and WY. With weak warm air advection during the day, temperatures will bump up just a bit - into the mid and upper 60s.

A well advertised upper level low over the Rockies lifts into the Northern Plains on Monday, as a surface low deepens over the western Dakotas on Monday into Monday night - pulling a warm front northward across the region during the day. Models still vary in the amount of instability over our area - generally ranging around 500-1000 J/KG in our southern CWA on Monday afternoon - depending on model of choice. Latest ensembles indicate only a 30-40% probability of CAPE greater than 1000 J/KG through the lower MO River Valley into northwest IA on Monday afternoon, while CIPS analogs and machine learning probs do give us at least some potential for severe storms on that day. So in summary, uncertainty still does exist, though cannot rule out a few strong to severe storms on Monday afternoon and evening - as supported by the SPC Day 3 outlook. Even so, the much better chance looks to be to the south of our CWA In addition to the storm potential on Monday, it will also be quite windy - and there will be at least some potential for a Wind Advisory at some point. Any storms that develop will move eastward on Monday night, exiting the area sometime on Tuesday morning. We could receive another round of moderate to heavy rain with the system, and ensembles indicate around a 70% probability of portions of our area receiving a half an inch or greater of rainfall during this time frame.

The upper level low meanders over the Northern Plains through at least midweek, before shifting to the east by the end of the week.
This will keep at least small chances (20-30%) of showers for much of the week as various shortwaves rotate around the upper level trough. Highs through the period will mostly be in the 60s to lower 70s.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 1214 PM CDT Sat May 4 2024

Mostly VFR conditions with occasional MVFR ceilings are expected for this TAF period. Taking a look at satellite imagery, a cumulus field has developed across most of the area in response to some elevated instability with parts of northwestern IA dealing with lingering stratus from this morning's cold front. As the surface high continues to move into the area this evening, expect conditions to begin to clear from west to east. Otherwise, breezy northwesterly winds will continue through the late afternoon before diminishing as the surface high moves overhead tonight. Lastly, some high resolution guidance has started to hint at some patchy fog developing across northwestern IA overnight. However, confidence is still low in occurrence so far.

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

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