Poland’s September 2024 Rainfall: What the National Average Hid
Poland’s nationwide rainfall total described September 2024 as wet. Station observations show why that single number did not describe the month experienced in every part of the country.
IMGW reported an area-averaged total of 67.9 millimetres across Poland, equal to 118% of the 1991–2020 September normal. In the national series beginning in 1951, that placed the month 19th—not first.
At individual stations, the range was much wider. Archived IMGW daily observations sum to 293.0 mm at Jelenia Góra, 296.0 mm at nearby high-elevation Śnieżka, and 15.9 mm at Białystok in northeastern Poland.
One Accurate Average, Several Different Local Months
The national figure and the station totals answer different questions. The 67.9 mm figure summarizes precipitation across Poland. Each station value describes a measurement at one location.
An area average is useful for comparing one month or year with another at the national scale. But it can soften opposing local departures when very wet and very dry areas are combined. In September 2024, the national result was only 10.5 mm above the 1991–2020 average even though IMGW reported station totals ranging from less than 20 mm in parts of the northeast to more than 290 mm in the southwest.
This is the central lesson of the month: “118% of normal” was true for Poland as an area, but it was not a description of a typical station. Jelenia Góra received more than four times its September normal, while Białystok received less than one-third of its normal.
Five Days Supplied Most of the Southwest Totals
The daily observations add another layer that a monthly total cannot show. Copernicus identifies 12–16 September as the core five-day precipitation period associated with Storm Boris across central Europe.
During those five days, Jelenia Góra accumulated 197.4 mm and Śnieżka accumulated 189.1 mm. Those amounts supplied 67.4% and 63.9%, respectively, of the stations’ entire September totals. Białystok recorded 0.0 mm in the same window.
In ordinary terms, roughly two-thirds of the monthly rain at the two southwestern stations arrived during five calendar days. The chart’s sharp rise therefore carries information that the final monthly endpoints alone do not: not only were the totals far apart geographically, much of the southwestern accumulation was compressed into a short period.
These are daily totals. They cannot identify the most intense hour or establish how rapidly rain fell within each day.
Rainfall Observations Are Not a Complete Flood Explanation
The timing connects the station observations to the wider Storm Boris event, but precipitation and flooding are not interchangeable measurements. A rain gauge records water falling at one point. River levels respond across catchments and can be affected by the location and timing of rainfall, terrain, soils, reservoirs, tributaries, exposure and infrastructure.
Copernicus separates the 12–16 September precipitation period from later river-flow peaks. Its European assessment reports that flooding in the lower Oder peaked on 20 September, several days after the main five-day rainfall window.
The station data can therefore establish how much precipitation was recorded and when it accumulated. They cannot, by themselves, assign responsibility for particular flood impacts or show the rainfall received across an entire river basin.
Explore or verify the result: Open the IMGW Climate Explorer, choose Daily resolution, select Jelenia Góra, Śnieżka or Białystok, set the period to 1–30 September 2024, and inspect Daily Precipitation. IMGW-PIB owns and publishes the observations; Climate Explorer is an independent interface and is not affiliated with or endorsed by IMGW-PIB.
Data Sources and Verification
The analysis uses IMGW’s archived 2024 daily synoptic files for stations 500, 510 and 295. In those files, SMDB is the daily precipitation total in millimetres. IMGW’s format documentation defines status 9 as “no phenomenon,” so a blank precipitation field paired with that status was treated as zero. All three station series contain a resolvable value or no-phenomenon status for each of the 30 September dates.
Monthly totals were calculated by summing the 30 daily values. Event totals use the inclusive period from 12 through 16 September; event shares divide that five-day total by the station’s September total. Values are rounded to one decimal place for display.
The live Climate Explorer was checked on 18 August 2026 using Daily resolution and the 1–30 September 2024 window. It returned the same monthly totals and daily peaks: 293.0 mm and 81.3 mm at Jelenia Góra, 296.0 mm and 76.5 mm at Śnieżka, and 15.9 mm and 5.0 mm at Białystok.
Station names and traditional WMO identifiers were cross-checked against NOAA/NCEI’s station-history table. The WIGOS identifiers in the annex use the corresponding 0-20000-0- form described in WMO guidance.
Conclusion
Poland’s September 2024 national rainfall average did not conceal an error; it concealed detail. The 67.9 mm area average accurately summarized the country, while the station records revealed a much sharper local contrast: close to 300 mm at two selected southwestern stations and 15.9 mm at Białystok.
Daily observations make the contrast more useful. They show that roughly two-thirds of the southwestern stations’ monthly rain accumulated during 12–16 September, while Białystok recorded none in that window.
The broader lesson extends beyond this event. National climate summaries and local station observations are both valid, but they describe different spatial scales. Reading them together provides a more faithful account than asking either one to stand for the other.
Editor’s note: This analysis uses historical IMGW files retrieved on 18 August 2026. Upstream files may be revised; the analyzed copies are identified by SHA-256 hashes in the reproducibility package.
Frequently Asked Questions
What Does 118% of Normal Rainfall Mean?
It means Poland’s area-averaged September 2024 precipitation was 18% above the average for September during the 1991–2020 reference period. It does not mean every station received 18% more rain than normal.
Was September 2024 Poland’s Wettest September?
Not according to IMGW’s national area-average series. IMGW placed it 19th among Septembers since 1951. That national ranking can coexist with much more unusual conditions at individual stations.
Did Storm Boris Cause Every Millimetre Shown in the Five-Day Window?
This analysis does not make that attribution. It uses the 12–16 September period identified in Copernicus’s Storm Boris assessment and reports the precipitation recorded at three IMGW stations during those dates.
Data Annex
Station Metadata
| Station | IMGW identifier | WIGOS identifier | Latitude | Longitude | Elevation | Role in comparison |
|---|---|---|---|---|---|---|
| Jelenia Góra | 350150500 |
0-20000-0-12500 |
50.900° N | 15.800° E | 344 m | Southwestern foothill station |
| Śnieżka | 350150510 |
0-20000-0-12510 |
50.733° N | 15.733° E | 1,613 m | Southwestern mountain station |
| Białystok | 353230295 |
0-20000-0-12295 |
53.100° N | 23.167° E | 151 m | Northeastern comparison station |
Key Calculated Values
| Station | September total | 12–16 September | Share of monthly total | Wettest day |
|---|---|---|---|---|
| Jelenia Góra | 293.0 mm | 197.4 mm | 67.4% | 81.3 mm on 13 September |
| Śnieżka | 296.0 mm | 189.1 mm | 63.9% | 76.5 mm on 14 September |
| Białystok | 15.9 mm | 0.0 mm | 0.0% | 5.0 mm on 10 September |
Data Sources
- IMGW-PIB assessment of September 2024 climate conditions
- IMGW-PIB archived daily synoptic observations for 2024
- IMGW-PIB daily synoptic file format
- Copernicus European State of the Climate 2024 flooding assessment
- NOAA/NCEI Integrated Surface Database station history
- WMO guidance on WIGOS Station Identifiers