Marine Weather and Tide Forecast for Vermillion, SD

DISCUSSION
Issued at 155 PM CDT Fri May 16 2025

Low pressure will shift east of the area tonight into Saturday, slackening the pressure gradient and taking the lift with it. So winds will diminish tonight, although they remain breezy into Saturday, and showers should mainly be out of the area by mid evening.

Saturday night into Sunday morning a surface ridge of high pressure noses into the area which will allow winds to drop further, likely less than 5 mph in many locations. This will then allow temperatures to drop with lows likely sneaking into the mid 30s in some locations. This may lead to some frost across the area and will need to be watched as the chance for lows below 35 are running about 30- 50% north of I-90.

Sunday will see increasing easterly flow and increasing cloud cover as low pressure deepens over the Northern and Central Rockies. A fairly weak mid level wave will swing north into central SD with some moisture return in the mid levels as well. This should result in some spotty showers during the day, mainly west of I-29.
Otherwise highs will likely top out in the 60s.

Sunday night will see a much better surge of elevated warm and moist advection. Models are indicating about 500-1500 J/kg CAPE with 20-30 knots of elevated speed shear which could result in some isolated, elevated hailers. Currently timing for this would be in the evening to overnight hours. Fairly deep easterly flow in the lower levels should help preclude any wind threat.

As this wave of lift moves through Sunday night into Monday morning some question marks arise for Monday and just how much and how widespread rain and thunderstorm chances will be. If enough warm air aloft moves in, the dendritic layer is well elevated and fairly dry, so instability will be needed to get showers and thunderstorms going. Most models do indicate decent instability (1000 J/kg CAPE)
through the day, but are less agreeable on this warm layer aloft potentially cutting off development.

On thing that continues to work in favor of additional development is a persistent inflow from the southeast of moisture and a bit more unstable air which should help produce enough lift for further development. One big thing to watch will be the upper level low and how this wobbles eastward with the potential for another low to develop in roughly IA Monday evening as a jet races into the Central Plains. This could bring a more distinct northern edge to the heavier rain and thunderstorms Monday afternoon into Tuesday morning and keep the bulk of this activity across NE and IA.

Tuesday will likely see rain diminish from northwest to southeast as the low pressure wraps up and moves southeast. Still a lot of question marks regarding just where and when this low will end up, but for the most part unless some major changes occur, rainfall will be much diminished by Tuesday night.

Flow becomes more westerly aloft Wednesday into Friday which should allow for milder temperatures and more sporadic chances for showers and thunderstorms.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/
Issued at 655 PM CDT Fri May 16 2025

Scattered showers will continue to fade through the evening as its parent low pressure system slides east of the area. MVFR clouds will linger; however, through the rest of the night and into Saturday morning. Biggest forecast challenge of the period was ceiling heights from KHON to KFSD in regards to the 2 kft level.
Guidance indicates constant fluctuation on either side of 2 kft through much of the night into tomorrow morning in those locations. Based on downstream observations and which guidance has the best handle on the situation, opted to stay at 2 kft for KHON and mostly just below 2 kft for KFSD.

All the clouds associated with this low pressure system will move away from southwest to northeast through the day Saturday, starting along the Missouri River Valley by mid-morning Saturday. These clouds will clear the entire area by Saturday afternoon, leaving mainly clear skies in place to end the period.

Gusty 30-35 kt northwest winds will continue through this evening.
Winds will gradually diminish through tonight and into Saturday morning. Gusts will be in the 15-20 kt range to end the period.

FSD WATCHES/WARNINGS/ADVISORIES
SD...Wind Advisory until 7 PM CDT this evening for SDZ038>040-050- 052>071.
MN...Wind Advisory until 7 PM CDT this evening for MNZ071-072-080- 081-089-090-097-098.
IA...Wind Advisory until 7 PM CDT this evening for IAZ001>003- 012>014-020>022-031-032.
NE...Wind Advisory until 7 PM CDT this evening for NEZ013-014.