Marine Weather and Tide Forecast for Sparta, WI

DISCUSSION
Issued at 319 AM CDT Mon Apr 28 2025

This Morning

A warm front will move through the region this morning. Most unstable CAPES will climb into the 1000 to 1750 J/Kg range.
This will result in the development of elevated showers and storms. With dry air aloft and low freezing levels, hail will be a possibility with any stronger storms. The chances of severe weather remains generally less than 5% due the NCAPE continuing to favor skinny CAPES and 1-6 km weak shear. As a result, hail size should be primarily less than 1-inch in diameter.

This Afternoon

In the wake of the morning warm front, surface dew points will climb into the lower to mid-60s. Meanwhile aloft, an elevated- mixed layer will be moving into the region from the Central Plains. The air mass above 850 mb will dry out and the 700 mb temperatures will climb into the 8-10C range. The combination of moisture in the low levels and very dry air aloft will result in a loaded gun sounding. This would favor rapid development of storms in the event that this cap breaks. The models continue to support this potential between 22z and 00z. Questions remain on whether there will be any low level boundaries to help with the low level convergence. Soundings are very favorable for splitting supercells. The latest HRRR does suggest this potential does exist as it develops a discrete supercell near Interstate 35 in south-central Minnesota. If this does occur, these would be capable of producing large hail (possibly in the excess of 2-inches in diameter), strong (EF2+) tornadoes, and damaging winds.

Tonight

There continues to look like there will be widespread severe storms between 6 PM and Midnight. The highest potential for severe weather will be over southeast Minnesota and along and north of Interstate 90 in western Wisconsin. The severe storm potential in northeast Iowa look lower due to weaker convergence along the dry line/cold front. Meanwhile, the right entrance region of the 250 mb may produce enough subsidence to limit the severe weather development in southwest Wisconsin.

While this is the case, there still are some questions on whether there will be one or multiple lines of storms moving through the region. This is due to uncertainty on when the cold front will catch up with the dry line. Some CAMs show 1 line and others have 2 lines. The shear remains favorable for embedded supercells along these lines. In addition, there still might be some discrete supercells ahead of the line in southeast Minnesota between 6 PM and 9 PM. These storms would be capable of producing damaging winds, tornadoes, and maybe some large hail. One uncertainty with the line/lines is whether you will see any bowing segments since the 0-1 km shear vector is parallel with the line. This might limit the potential of QLCS tornadoes.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
Issued at 1227 PM CDT Mon Apr 28 2025

Main taf concerns through the taf period are showers/storms this afternoon/evening and MVFR/IFR conditions this afternoon and into Tuesday morning. Latest metars show MVFR/IFR conditions across southeast Minnesota/western Wisconsin. Have introduced ceiling heights in IFR conditions at RST (900feet) this afternoon. LSE taf site will remain in VFR through this afternoon
Then
a cold front will move across the Upper Mississippi River Valley this afternoon/evening. Showers/storms will develop along the front and impact both RST/LSE taf sites late this afternoon into the evening hours. Some of the storms could be severe with potential gusts of around 50 knots and large hail. At this time time frame for the potential of severe storms is 01z Tuesday to 05z Tuesday. After cold front passes...ceilings will lower back into MVFR at both taf sites.
Ceilings could improve into VFR late in the taf period...timing would be after 16z Tuesday. Have not introduced VFR condition in the tafs.

ARX WATCHES/WARNINGS/ADVISORIES
WI...None.
MN...None.
IA...None.