Marine Weather and Tide Forecast for Altoona, WI

DISCUSSION
Issued at 124 PM CDT Sun May 17 2026

Today is setting up to have potential to be a higher end day for portions of the Enhanced Risk area. Latest visible satellite imagery shorting plenty of clearing with the low-level cloud deck through much of MN, but especially across the southern portion of the state. A bubbling cu field is beginning to develop ahead of ongoing convection tied to the surface low near the NE/SD state line. Surface winds are largely out of the SE/ESE for MN and western WI, and dewpoints have been steadily increasing through the day so far. The best environment is across southern MN where dewpoints have climbed into the 60s already and plenty of clearing is allowing for efficient daytime heating, priming the environment for intense convection later today.

Based on satellite and hi-res model data, we expect timing to be maybe slightly earlier than forecast this morning, but generally along the same timeframe. Supercells and storm clusters will develop across Nebraska and South Dakota during the afternoon (around 3-5pm) and progress slightly northeastward into southwest MN and northern IA (around 6-7pm). At this point, storms will be tied to the triple point and situated in a favorable environment for large to very large hail (2-3" in diameter) and damaging wind gusts (60+ mph). Storms will quickly develop into a line along the cold front and turn into a significant wind (70-80+ mph), QLCS setup with line-embedded tornadoes possible within that Enhanced Risk area (stretching from Redwood Falls, MN over to Owatonna, MN and south). Forecast soundings show increasing low-level shear and humped hodographs in the region ahead of the line, which is also reflected in models like the RRFS and HRRR producing a zone of STP values of 5+ across southern MN. Typically QLCS tornadoes are weaker than supercell tornadoes, so we really want to highlight that there is higher- end potential with today's environment compared to your average QLCS setup. Any tornadoes that develop will likely still be brief, like any typical QLCS setup, though the strength of the tornadoes may be capped at an EF2 level rather than EF1.
This is all in general-speak, but the point is that the higher- end environment warrants being prepared for slightly stronger tornadoes than you typically get with linear setups (around here at least). The main time window for this to move through is between 7-10pm. The faster the line develops, the quicker it will move east.

To the north of the main line, we should still see a surge of low-level moisture as the low tracks northeast. The overall environment just is not as impressive north of the Enhanced Risk region, due to the limited northern progression of the warm front today. It will be high shear/low CAPE setup for much of our forecast area today, but especially for areas north of the Redwood Falls to Owatonna line. A Slight Risk (level 2/5)
remains in place to cover this threat for scattered severe storm potential. The primary hazards will be damaging wind (60+ mph)
and large hail (1"+ in diameter). Any high end potential will be limited, including the tornado risk. Storms will move through the western MN to St Cloud, MN region around 6-8pm, the Twin Cities metro and eastern MN around 9-11pm, and eventually progress through western WI around 11pm-1am. The severe threat will begin to decrease as the line progresses into WI given that there will likely be scattered storms ahead the cold front, limiting the environment.

The severe threat for Monday continues to decrease, and although there is still a Slight Risk (level 2/5) extending from south- central MN into west-central WI, we expect that region to shift even further southeast after we realize our round of storms this evening. We will struggle to build in any real instability and deep layer shear will become more limited as well. In reality, tomorrow will likely feel like a typical rainy Spring day with cool showers and storms through much of the second half of the day. Isolated chances for severe weather will exist, mainly for areas along I-35 and east during the evening.

A much drier, and seasonably cool pattern will set up for the rest of the week. Temperatures on Tuesday will be about 10-15 degrees below average, and we could once again have concern for patchy frost overnight (lows in the mid-low 30s) into Wednesday for areas in west- central MN near Stevens, Douglas, and Todd counties. It won't be until Friday that we see our next notable chance for rain as a shortwave develops over the Northern Plains. It looks to be a slow- progressing pattern that would provide us with additional chances for showers and storms throughout the rest of Memorial Day weekend, though confidence is low at this time.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
Issued at 628 PM CDT Sun May 17 2026

Main concern is line of storms over southwest MN. MKT is the only field with much of a severe potential with this line, though several hours of TSRA are expected at MSP and WI terminals. Besides the line of storms, we've seen storms develop ahead of hit within the LLJ and associated WAA that will result in the several hours of TS threat we have. Behind the line, we will dry out, with MVFR/IFR cigs slowly building east across southern MN. Did delay the arrival of MVFR cigs some, but by sunrise Monday, we should see widespread MVFR/IFR cigs over the area that will stay in place this period. By the end of this period, we should see showers developing by the late afternoon as the next wave approaches from the southwest.

KMSP...Scattered shra/tsra currently down by MKT will be in the MSP VCNTY between 1z and 2z. This is out ahead of what will be the northern end of the severe line of storms to our south that will move through roughly between 4z and 6z. By the end of the period, the next round of showers will be rapidly developing, with another round of shra/tsra expected to develop between 0z and 2z (Monday evening) that will last into Monday night.
Doesn't look like we have a big severe risk with this activity, just heavy rain and lightning.

/OUTLOOK FOR KMSP/ TUE.. MVFR cigs becoming VFR. Wind NW 10-15G25kts.
WED...VFR. Wind lgt and vrb.
THU...VFR. Wind SE 10G20kts.

MPX WATCHES/WARNINGS/ADVISORIES
MN...None.
WI...None.