Marine Weather and Tide Forecast for Vermillion, SD

DISCUSSION
Issued at 348 PM CDT Sun Oct 13 2024

Breezy winds persist across the area this afternoon within a cold advective northwest flow regime. Winds are slowly weakening as a surface high from North Dakota begins to push into the forecast area, weakening the surface pressure gradient (SPG). However, dew points continue to drop which is resulting in lower relative humidity (RH) values down to about 30%. While not reaching critical fire danger thresholds, the lower RH and breezy winds will still yield high to very high fire danger across the area through the rest of the afternoon hours. Winds are expected to go light and variable tonight as the surface high moves overhead. The light and variable winds will coincide with mainly clear skies which will allow for temperatures to efficiently radiationally cool. Have lowered low temperatures tonight closer to the NBM 25th percentile to account for the cooler temperatures. With the vast majority of the forecast area falling to 32 degrees F or below, have upgraded the Frost Advisory to a Freeze Warning. The Freeze Warning is in effect for the same period of time from 1 am to 9 am Monday.

Monday begins the work week on the cooler side as an upper level closed low spins across southeastern Canada. This upper low will rotate a strong shortwave trough into the forecast area. The cooling from the wave will strengthen a thermal gradient across the Northern and Central Plains. This gradient will span from about +7 degrees C over south central South Dakota to down to about -1 degrees C over southwest Minnesota. Mixing these temperatures to the surface will result in high temperatures up to the 50s to low 60s from northwest to southeast. The previously mentioned thermal gradient will also result in a strong frontogenetically active elevated frontal zone.
This, combined with lift via positive vorticity advection (PVA) from the shortwave trough looks to be able to cool thermal profiles to saturation and result in very light rain reaching the surface during the afternoon hours. Rainfall amounts will only accumulate up to a hundredth of an inch, mainly along and around the Buffalo Ridge in southwest Minnesota. Any chance for very light rain will come to an end during the evening hours, leaving dry and quiet conditions for the overnight hours. Another surface high pressure system will begin to push into the forecast area during the evening and overnight hours. This will keep winds light at the surface and allow for temperatures to fall to the upper 20s to low 30s. This will set the stage for another widespread frost/freeze.

High pressure remains in control on Tuesday which will continue cooler conditions across the region. Tuesday will also be the coldest day of the week with highs only warming to the 50s. Lows will again fall to the upper 20s and 30s but should begin to see lows rebound back to the mid 30s across south central South Dakota as southerly return flow takes over on the backside of the departing high. With lows still near to below freezing, another night of frost/freeze conditions is possible.

Upper level ridging builds over the Northern Plains for Wednesday and Thursday as low level warm air advection (WAA) strengthens. This will push high temperatures back to above average in the 60s and 70s. The low level jet (LLJ) will also strengthen leading to breezy southerly winds across the area. The warm and breezy conditions will lead to another round of elevated fire danger across the region. An upper level trough will allow for southwesterly flow aloft which will bring additional chances for rain to the area Thursday evening.
Medium range guidance is in good agreement that the upper level trough will transition to a cut off low over the desert southwest.
This should still provide enough dynamical lift to keep rain chance going through Friday. Ensembles support this as they show a broad 30- 50% chance for exceeding a tenth of an inch of rain.

Rain chances may continue through Saturday but there is some uncertainty with this potential. The GFS, Canadian, and Euro all show the cut off low sitting across the desert southwest on Saturday before the low gets recaptured by the jet stream and ejected northeastwards on Sunday. How strong this system will be varies amongst the models with the GFS being the strongest. Cluster analysis shows the most favored cluster suggesting a solution closer to the Euro where the upper low is weaker and any chance for rain pushes east of the forecast area by Sunday morning. Given the uncertainty regarding any rain potential, have stuck with model blended PoPs for the weekend. Outside of rain chances, above average high temperatures in the 60s and 70s look to continue.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
Issued at 1038 PM CDT Sun Oct 13 2024

Variable winds at or below 12kt will prevail through 14/00Z, with potential for isolated gusts 15-20kt from the east to northeast developing after sunset in areas along and west of I-29. VFR conditions are expected through the TAF period with a low (10-20%) chance for sprinkles/very light rain moving through the Buffalo Ridge/southwest Minnesota and portions of northwest Iowa Monday afternoon.

FSD WATCHES/WARNINGS/ADVISORIES
SD...Freeze Warning until 9 AM CDT Monday for SDZ038>040-050- 052>071.
MN...Freeze Warning until 9 AM CDT Monday for MNZ071-072-080-081- 089-090-097-098.
IA...Freeze Warning until 9 AM CDT Monday for IAZ001>003-012>014- 020>022-031-032.
NE...Freeze Warning until 9 AM CDT Monday for NEZ013-014.