The Short Answer
A roof that leaks only in heavy rain or wind usually has a weak spot that ordinary rain never reaches. Wind pushes water sideways and uphill under shingle laps, into vents and behind short flashing. Heavy downpours overload valleys and low-slope sections until water backs up past the laps. The leak often depends on wind direction, so logging the date, time, wind and where it drips is the fastest way to find it.
Key Points
- Roofs shed water by gravity and overlap; wind and very heavy rain can push water uphill past those overlaps.
- A leak that only appears with wind from one direction usually points to the face of the house that wind hits.
- Low-slope sections, valleys, short flashing, vents and unsealed shingles are the usual suspects.
- NWS Grand Rapids publishes daily rainfall, wind speed and wind direction, so you can match your leak dates to the weather.
- A careful leak log often lets a roofer find the source on the first visit.
Why Ordinary Rain Stays Out and Some Storms Get In
A shingle roof is not a sealed skin. It works by overlap: each course covers the nails and joints of the one below, flashing laps under the shingle above, and gravity carries water down and off. In a calm, steady rain, water never has a reason to travel uphill, so small imperfections in the laps never get tested.
Wind changes that. It drives rain sideways and pushes water up the slope and under the edges of shingles, flashing and vents. Very heavy rain does something similar by volume: a valley or a low pitch that drains fine in a light rain can carry so much water in a cloudburst that it backs up and spreads sideways past the laps.
So the leak is real; it just needs the right storm. That is why the inspection on a dry day finds nothing obvious, and why the details of the storm are the best clue you have.
Where Wind-Driven Rain Gets In
When the leak only shows up with strong wind, look at the parts of the roof that face the wind and at anything that sticks up through the roof or stands beside it.
Roof vents
Box vents, ridge vents, turbines, gable vents
Code requires attic vent openings to be protected against rain and snow, but a hard wind can still drive water through a cracked or poorly flashed vent, or blow it in through a ridge or gable vent.
Roof vent leaksRoof-to-wall joints
Sidewalls, dormers, second stories
Rain driven against a wall runs down it. Short step flashing, a missing kickout or gaps in the siding above the roof let that water in only when the wind hits that wall.
Sidewall and dormer leaksLifted or unsealed shingles
Usually on the windward slopes
Shingles rely on a sealant strip that bonds them together once warmed by the sun. A shingle that never sealed or has lost its bond can flutter in wind and let water past it.
Shingles not sealingChimneys and skylights
Four sides of flashing
The uphill side and the corners take the most water. Counterflashing that has pulled away or a skylight seal that is aging may only leak when rain hits it sideways.
Chimney leak or roof leak?Where a Downpour Gets in When Wind Is Not the Cause
- Low-slope sections. The Michigan Residential Code allows asphalt shingles only on slopes of 2:12 or steeper and requires double underlayment from 2:12 up to 4:12. Porch roofs, additions and shed dormers built near or below those limits shed water slowly, and in a downpour it backs up under the laps.
- Valleys. A valley collects water from two roof planes. Debris, shingles cut too close or a worn valley lining can hold up fine in light rain and overflow in heavy rain.
- Short flashing. The code sets a minimum of 4 inches up a sidewall for base flashing, and GAF's instructions call for 5 inches. In a heavy storm, water sheeting off a wall or a higher roof can rise above flashing that was cut short.
- Roofs draining onto roofs. A downspout from an upper roof that empties onto a lower roof concentrates a whole slope of water onto a few shingles.
- Gutters on houses with no overhang. Where the gutter hangs right on the wall, overflow in a downpour can run down the siding and get behind it. On a normal overhang, overflow usually just falls to the ground.
- Long storms. Some leaks need hours of rain before enough water works through a small gap to drip. A leak that starts late in a long rain is a clue in itself.
Why West Michigan Roofs See This so Often
West Michigan gets strong winds off Lake Michigan, spring and summer thunderstorms that drop a lot of rain fast, and long fall rains when the leaves are clogging valleys. Each of those tests a different weak point. A roof can go a whole summer without leaking and then leak in the first strong fall storm from an unusual direction.
Shingle wind ratings matter here too. The Michigan Residential Code requires asphalt shingles to be tested and labeled for wind resistance (ASTM D7158, or ASTM D3161 for shingles outside that standard's scope) and classified for the design wind speed where they are installed. A rating only holds if the shingles were nailed and sealed the way the manufacturer requires, which is one reason the same storm lifts shingles on one house and not the next.
Winter adds a different set of leaks that are not caused by rain at all. Ice dams and attic condensation can drip on a clear, cold day, and they are easy to confuse with storm leaks if you are not keeping track.
How Often Grand Rapids Gets the Rain That Finds Weak Spots
NOAA's 1991 to 2020 climate normals for the Grand Rapids airport station put average yearly precipitation at 39.40 inches. More useful for a leak hunt is how that rain arrives. In a normal year the station records about 23.5 days with half an inch or more, 8.3 days with an inch or more, and 1.4 days with two inches or more. A weak point that only lets water in on the heaviest days may therefore leak only a handful of times a year, which is exactly what makes these leaks feel random.
Those heavy days are not spread evenly. The monthly normals show April through October each averaging roughly 3.4 to 4.0 inches of precipitation and about 0.8 to 1.2 days a month with an inch or more. December through February average 2.1 to 2.5 inches and only 0.2 to 0.3 inch-plus days a month. So a leak that comes back with spring and fall storms fits the rain pattern, while a winter "rain leak" is more often melting snow, an ice dam or attic condensation.
The long-term trend matters too. NOAA's 2022 State Climate Summary for Michigan reports that the frequency of extreme precipitation events has increased, with the 2010 to 2014 and 2015 to 2020 periods showing the highest multiyear averages of 2-inch days on record statewide, and it projects extreme precipitation to become more frequent and intense. A flashing detail or low-slope section that leaked once every few years in the past may get tested more often now.
For your log, the NWS Grand Rapids monthly climate report (CF6) lists each day's precipitation and peak wind, and the NOWData tool on the same site goes back for years. Matching your drip dates to days over one inch, or to days with strong wind from one direction, usually separates a downpour problem from a wind problem.
Michigan wind storms and roof damage
Thunderstorm wind, derechos and gradient wind events in West Michigan, and what fails first.
Wind stormsHow to Log an Intermittent Leak
The single most useful thing you can do is write down every leak as it happens. A few notes per storm turn a mystery into a pattern.
- Step 1
Record the Date and Time
Note when the storm started and when the drip started. A leak that starts within minutes of heavy rain behaves differently from one that starts after three hours.
- Step 2
Mark Where It Drips
Which room, which wall, how far from the outside wall. Put a piece of tape on the ceiling at the stain edge each time so you can see if it grows.
- Step 3
Note the Wind
Which way was the rain blowing? Which windows did it hit? If you are not sure, look the date up later.
- Step 4
Check the Attic During the Storm
If it is safe to get into the attic, look with a flashlight for where water is running on the deck or framing, and take a photo. Stay on the framing.
- Step 5
Look Up the Weather Afterward
NWS Grand Rapids publishes a Preliminary Monthly Climate Data report (CF6) for Grand Rapids with daily rainfall, average wind speed, the fastest wind and its direction, and the peak gust and its direction. Add those numbers to your log.
- Step 6
Compare Storms That Did Not Leak
Note big storms that stayed dry too. If every leak came with east or south winds and the west-wind storms stayed dry, that points straight at one side of the house.
How a Roofer Uses Your Log to Find the Source
With a good log, a roofer knows which side of the roof to look at, how much water it takes, and roughly where it enters. They will check the roof surface, flashing and vents on that face, then the attic for water tracks on the deck and framing, which often lead uphill from where the drip lands.
When nothing obvious shows, the next step is a water test: running a hose on one small area at a time, starting low and working up, while someone watches inside. It is slow, and it has to be done in the right order, but it reproduces the storm on demand.
Send the log and your attic photos when you book the visit. They help whoever comes out start on the right side of the roof.
How roofers find leaks
Visual tracing, attic checks, water testing and moisture meters: what each one finds.
Leak detection methodsWhat the Weather Pattern Suggests
| When it leaks | Likely suspects |
|---|---|
| Only with strong wind from one direction | Vents, wall and dormer flashing, chimney or skylight flashing, lifted shingles on that face |
| Only in very heavy downpours | Low-slope sections, valleys, short flashing, an upper roof draining onto a lower one |
| Only late in a long, steady rain | A small gap at a flashing, pipe boot or nail that needs hours to pass enough water |
| After snow and a thaw, or on cold clear days | Ice dams or attic condensation, not rain |
| After rain blowing against a wall, with stains in the wall | Water behind siding or around a window above the roofline |
These are starting points for an inspection, not a diagnosis.
Got a Leak That Only Shows Up in Some Storms?
Send us your notes and photos, or book a free inspection. A good log plus an attic check usually finds what a dry-day look misses.
Related Guides
How to Describe a Roof Leak When You Call
What to note and photograph so the first visit counts.
Learn MoreRoof Vent Leaks
Box vents, ridge vents and turbines in wind-driven rain and snow.
Learn MoreWhy Roof Leaks Show Up Far From the Source
Why the drip is rarely under the hole.
Learn MoreWind Damage
How lake winds lift and crease shingles, and what to look for.
Learn MoreQuestions We Hear
Can wind blow rain under shingles?
Yes. Shingles shed water by overlap, and strong wind can push rain up the slope and under the edges of shingles that are lifted, unsealed or creased. It can also drive water into vents and behind flashing that would stay dry in a calm rain. Shingles that sealed properly and were nailed the way the manufacturer requires resist this much better, which is why wind leaks often point to one specific slope.
Why does my roof leak in thunderstorms but not in normal rain?
Thunderstorms bring a lot of rain in a short time and often strong gusts. That combination overloads valleys and low-slope sections, raises water above short flashing, and drives rain sideways into vents and wall joints. Ordinary rain never tests those spots. Note the time, the wind direction and where it drips during the next storm, then check the attic for where water runs.
Is a leak that only happens a few times a year worth fixing?
Yes. Each time it leaks, the deck, insulation and framing get wet, and a few soakings a year are enough to start rot and mold over time. Intermittent leaks also tend to get more frequent as the gap widens. Fixing the source while the wood is still sound is usually a small repair; waiting can turn it into a deck or framing repair.
How do I find out which way the wind was blowing on the day my roof leaked?
The National Weather Service office in Grand Rapids publishes a Preliminary Monthly Climate Data report for Grand Rapids that lists daily precipitation, average wind speed, and the direction of the fastest wind and the peak gust. Look up the dates your roof leaked and the dates big storms stayed dry. If you are closer to the lakeshore, a nearer station may match your weather better.
Can a roofer find an intermittent leak on a dry day?
Often, yes, especially with a good leak log and attic photos. Water leaves tracks, stains and soft spots on the deck and framing, and those lead back toward the entry point. When nothing obvious shows, a controlled water test with a hose can reproduce the storm one small area at a time. It takes longer, but it is how the hardest leaks get found.
What This Page Cites
- 2015 Michigan Residential Code, Chapter 9 Roof Assemblies, Sections R903.2.1, R905.2.2, R905.2.4.1 and R905.2.8.3, UpCodes (https://up.codes/viewer/michigan/mi-residential-code-2015/chapter/9/roof-assemblies), accessed October 2026
- 2015 Michigan Residential Code, Chapter 8 Roof-Ceiling Construction, Section R806.1, UpCodes (https://up.codes/viewer/michigan/mi-residential-code-2015/chapter/8/roof-ceiling-construction), accessed October 2026
- Timberline HDZ, UHDZ, AS II, CS, HDZ RS and RS+ Installation Instructions (RESTL622, 2023), GAF (https://images.thdstatic.com/catalog/pdfImages/ce/ce744b21-6c3d-4c1e-9396-919c6ffa7fe8.pdf), accessed October 2026
- Preliminary Monthly Climate Data (CF6), Grand Rapids, National Weather Service Grand Rapids (https://forecast.weather.gov/product.php?site=GRR&product=CF6&issuedby=GRR), accessed October 2026
- National Weather Service Grand Rapids, MI home page (Past Weather, Local Storm Reports), NOAA (https://www.weather.gov/grr/), accessed October 2026
- U.S. Climate Normals 1991 to 2020, annual/seasonal and monthly precipitation normals, Grand Rapids station USW00094860, NOAA National Centers for Environmental Information (https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-annualseasonal-1991-2020&stations=USW00094860&format=json&units=standard), accessed October 2026
- Michigan State Climate Summary 2022 (NOAA Technical Report NESDIS 150-MI), NOAA NCEI and CISESS (https://statesummaries.ncics.org/chapter/mi/), accessed October 2026