Fort Erie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Erie Observatory clear sky chart from 2005-11-06 to 2024-01-31.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
27%
22993
7%
75090
5%
22946
31%
22946
8%
62755

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
8%
757
2%
2649
0%
757
11%
757
2%
2462
January11th to 20thNight
11%
760
1%
2508
0%
760
12%
760
2%
2358
January21st to endNight
11%
835
3%
2711
1%
835
12%
835
3%
2470
February1st to 10thNight
8%
720
4%
2340
1%
720
11%
720
3%
2107
February11th to 20thNight
13%
703
4%
2275
1%
700
17%
700
4%
2020
February21st to endNight
12%
592
5%
1853
1%
592
17%
592
4%
1651
March1st to 10thNight
21%
720
8%
1980
3%
720
25%
720
7%
1708
March11th to 20thNight
20%
720
10%
1980
5%
720
25%
720
8%
1669
March21st to endNight
26%
792
11%
2178
5%
792
30%
792
10%
1814
April1st to 10thNight
21%
720
9%
1818
3%
720
24%
720
12%
1522
April11th to 20thNight
27%
711
11%
1775
4%
711
30%
711
12%
1463
April21st to endNight
32%
540
10%
1620
5%
540
36%
540
11%
1319
May1st to 10thNight
38%
540
11%
1620
7%
540
41%
540
12%
1293
May11th to 20thNight
37%
371
15%
1433
12%
371
45%
371
11%
1055
May21st to endNight
46%
388
12%
1551
12%
388
51%
388
12%
1121
June1st to 10thNight
39%
360
10%
1440
9%
360
47%
360
9%
1107
June11th to 20thNight
42%
360
11%
1440
12%
360
49%
360
11%
1051
June21st to endNight
39%
360
9%
1440
9%
360
45%
360
10%
1094
July1st to 10thNight
52%
350
11%
1400
14%
350
56%
350
13%
993
July11th to 20thNight
45%
348
11%
1392
11%
348
52%
348
13%
1006
July21st to endNight
51%
570
11%
1653
7%
539
52%
539
16%
1234
August1st to 10thNight
58%
537
10%
1600
7%
534
60%
534
14%
1227
August11th to 20thNight
54%
534
12%
1598
7%
534
57%
534
16%
1187
August21st to endNight
48%
707
11%
1895
6%
707
50%
707
16%
1461
September1st to 10thNight
47%
720
11%
1800
5%
720
49%
720
15%
1433
September11th to 20thNight
52%
720
17%
1872
10%
720
56%
720
19%
1411
September21st to endNight
41%
720
10%
2035
7%
720
43%
720
12%
1651
October1st to 10thNight
35%
720
10%
2160
7%
720
39%
720
11%
1723
October11th to 20thNight
25%
720
6%
2160
5%
720
27%
720
7%
1845
October21st to endNight
20%
792
7%
2376
5%
792
23%
792
6%
2052
November1st to 10thNight
29%
740
11%
2415
9%
740
32%
740
10%
1913
November11th to 20thNight
19%
760
10%
2660
6%
760
25%
760
6%
2222
November21st to endNight
16%
760
5%
2660
3%
760
18%
760
4%
2308
December1st to 10thNight
12%
760
1%
2660
0%
760
13%
760
2%
2460
December11th to 20thNight
11%
759
2%
3281
0%
759
13%
759
2%
2897
December21st to endNight
8%
827
0%
4862
0%
817
9%
817
1%
4448

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
16%11%47%6%35%5%5%7%31%
74825
Night
18%12%48%6%35%45%6%29%
75300
TransparencyDay
35%38%8%12%6%1
74541
Night
38%38%8%10%6%1
75119
SeeingDay
23%17%28%20%9%3
13449
Night
23%15%27%24%10%1
23007

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
18%18%7%13%10%5%5%44411%
1517
11th to 20thDay
19%19%7%13%8%5%5%34413%
1671
21st to endDay
15%19%7%13%11%6%7%5%449%
1872
February1st to 10thDay
19%17%7%13%9%47%5%4412%
1620
11th to 20thDay
15%17%8%12%9%5%5%5%3416%
1573
21st to endDay
21%13%6%11%8%45%446%17%
1401
March1st to 10thDay
16%14%6%10%8%35%45%5%25%
1977
11th to 20thDay
15%15%5%8%7%3445%6%29%
1980
21st to endDay
20%12%48%6%35%45%5%28%
2178
April1st to 10thDay
19%13%47%434446%31%
2142
11th to 20thDay
20%8%36%435%45%7%35%
2150
21st to endDay
21%10%37%6%3445%5%34%
2340
May1st to 10thDay
18%9%36%6%45%5%6%6%33%
2340
11th to 20thDay
16%7%36%6%35%5%6%7%37%
2460
21st to endDay
12%6%35%4345%6%8%43%
2725
June1st to 10thDay
15%7%36%6%345%6%7%39%
2520
11th to 20thDay
13%5%35%5%45%5%7%10%40%
2520
21st to endDay
15%6%25%43445%8%44%
2520
July1st to 10thDay
9%424435%5%6%9%49%
2520
11th to 20thDay
12%5%25%5%35%5%7%10%39%
2520
21st to endDay
10%5%36%5%37%6%8%10%38%
2565
August1st to 10thDay
9%5%25%5%35%6%7%9%44%
2327
11th to 20thDay
11%5%35%5%46%6%7%10%39%
2303
21st to endDay
12%5%25%5%3446%10%44%
2441
September1st to 10thDay
15%6%25%5%346%5%7%41%
2160
11th to 20thDay
13%425%4345%6%8%45%
2084
21st to endDay
15%8%35%6%5%5%6%6%8%33%
1924
October1st to 10thDay
20%8%36%7%345%5%6%34%
1800
11th to 20thDay
22%10%47%6%35%5%5%6%27%
1800
21st to endDay
27%14%48%6%3443421%
1980
November1st to 10thDay
16%11%37%6%35%5%5%5%33%
1657
11th to 20thDay
16%13%49%6%345%5%6%28%
1520
21st to endDay
22%18%5%7%6%35%447%19%
1520
December1st to 10thDay
21%18%7%10%8%45%5%5%413%
1520
11th to 20thDay
21%21%6%10%7%345%45%14%
1906
21st to endDay
27%25%7%9%6%3433311%
2772
January1st to 10thNight
21%19%7%10%8%45%34414%
2649
11th to 20thNight
21%20%7%11%8%45%445%12%
2508
21st to endNight
16%19%8%12%9%45%45%5%14%
2711
February1st to 10thNight
20%18%9%12%6%35%44415%
2340
11th to 20thNight
18%14%6%11%8%46%446%18%
2273
21st to endNight
21%14%6%12%8%34445%19%
1853
March1st to 10thNight
16%14%5%8%8%45%445%28%
1970
11th to 20thNight
19%12%47%5%34445%31%
1979
21st to endNight
18%11%48%6%3445%5%31%
2178
April1st to 10thNight
22%11%47%6%25%35%431%
1818
11th to 20thNight
19%9%37%5%345%5%6%35%
1775
21st to endNight
19%9%35%5%35%5%5%6%35%
1620
May1st to 10thNight
18%9%37%6%35%5%5%7%33%
1620
11th to 20thNight
14%437%7%45%46%8%37%
1432
21st to endNight
13%6%34435%5%6%8%44%
1550
June1st to 10thNight
12%8%35%7%47%6%6%7%36%
1440
11th to 20thNight
12%5%25%5%46%5%6%7%42%
1440
21st to endNight
14%6%346%346%5%8%41%
1440
July1st to 10thNight
8%425%6%345%5%8%51%
1440
11th to 20thNight
12%5%345%345%6%9%44%
1440
21st to endNight
11%426%5%35%5%7%8%44%
1750
August1st to 10thNight
10%5%246%345%7%9%45%
1611
11th to 20thNight
11%6%25%5%35%5%6%8%44%
1598
21st to endNight
10%5%35%6%45%6%5%8%45%
1895
September1st to 10thNight
15%7%345%3445%8%43%
1800
11th to 20thNight
13%5%2432345%7%51%
1872
21st to endNight
17%6%35%5%346%6%7%37%
2035
October1st to 10thNight
19%6%36%6%44447%38%
2160
11th to 20thNight
22%10%46%5%445%5%6%28%
2160
21st to endNight
28%9%36%5%45%5%5%5%24%
2376
November1st to 10thNight
19%9%36%5%3445%6%36%
2415
11th to 20thNight
17%12%48%7%45%45%6%28%
2660
21st to endNight
20%14%5%8%7%45%46%6%20%
2660
December1st to 10thNight
22%19%6%10%8%3445%5%14%
2660
11th to 20thNight
19%20%7%10%7%4444416%
3288
21st to endNight
30%19%6%9%6%35%44411%
4884

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
51%40%5%31
1518
11th to 20thDay
50%41%5%3
1671
21st to endDay
54%37%5%31
1872
February1st to 10thDay
50%38%6%6%1
1620
11th to 20thDay
48%38%6%6%2
1582
21st to endDay
49%37%6%5%2
1401
March1st to 10thDay
41%37%9%11%3
1980
11th to 20thDay
37%38%8%10%6%1
1980
21st to endDay
37%38%6%13%5%1
2178
April1st to 10thDay
34%37%8%13%8%1
2142
11th to 20thDay
32%37%8%13%10%1
2150
21st to endDay
34%37%6%13%9%1
2340
May1st to 10thDay
33%37%7%12%9%2
2340
11th to 20thDay
28%40%6%14%10%2
2464
21st to endDay
24%39%10%16%9%2
2725
June1st to 10thDay
27%38%11%13%10%1
2520
11th to 20thDay
26%39%10%17%8%1
2520
21st to endDay
26%39%10%17%8%
2520
July1st to 10thDay
22%40%8%18%10%1
2450
11th to 20thDay
26%40%11%14%9%
2445
21st to endDay
25%41%12%15%7%
2422
August1st to 10thDay
24%41%10%17%7%
2314
11th to 20thDay
23%39%12%16%9%1
2303
21st to endDay
25%38%10%17%9%1
2441
September1st to 10thDay
29%38%8%16%8%1
2160
11th to 20thDay
25%39%10%19%7%
2084
21st to endDay
34%38%9%13%5%1
1924
October1st to 10thDay
34%38%9%10%8%
1800
11th to 20thDay
40%38%10%10%2
1800
21st to endDay
43%37%8%7%31
1980
November1st to 10thDay
30%42%7%13%7%1
1657
11th to 20thDay
35%42%10%8%42
1520
21st to endDay
43%41%6%7%2
1520
December1st to 10thDay
47%43%5%5%
1520
11th to 20thDay
51%35%8%42
1906
21st to endDay
63%27%5%4
2772
January1st to 10thNight
50%40%5%41
2649
11th to 20thNight
51%41%5%21
2508
21st to endNight
51%36%7%5%1
2711
February1st to 10thNight
49%36%7%6%1
2340
11th to 20thNight
45%38%8%6%3
2275
21st to endNight
47%37%6%7%3
1853
March1st to 10thNight
40%38%8%10%21
1980
11th to 20thNight
38%37%7%11%6%1
1980
21st to endNight
37%37%5%12%7%2
2178
April1st to 10thNight
36%37%6%12%8%1
1818
11th to 20thNight
34%36%7%12%10%1
1775
21st to endNight
35%38%6%11%9%2
1620
May1st to 10thNight
32%37%5%14%10%2
1620
11th to 20thNight
27%37%7%15%11%2
1433
21st to endNight
24%39%9%13%13%2
1551
June1st to 10thNight
30%39%7%14%9%1
1440
11th to 20thNight
25%38%10%14%12%1
1440
21st to endNight
29%39%9%15%8%
1440
July1st to 10thNight
22%39%8%17%12%2
1400
11th to 20thNight
24%39%10%16%9%1
1392
21st to endNight
23%40%11%16%10%1
1653
August1st to 10thNight
26%39%10%17%7%1
1600
11th to 20thNight
24%38%11%17%10%
1598
21st to endNight
26%38%8%17%9%2
1895
September1st to 10thNight
28%38%8%16%9%1
1800
11th to 20thNight
23%37%10%19%10%1
1872
21st to endNight
32%39%9%12%8%1
2035
October1st to 10thNight
33%37%8%14%8%1
2160
11th to 20thNight
39%38%8%10%4
2160
21st to endNight
42%38%7%8%5%1
2376
November1st to 10thNight
29%42%6%16%6%2
2415
11th to 20thNight
36%41%9%8%5%1
2660
21st to endNight
40%42%9%7%2
2660
December1st to 10thNight
48%42%6%41
2660
11th to 20thNight
49%36%9%5%1
3288
21st to endNight
62%28%6%4
4884

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
28%30%23%12%5%2
180
11th to 20thDay
27%30%26%12%41
252
21st to endDay
27%24%26%19%4
294
February1st to 10thDay
32%29%31%7%1
240
11th to 20thDay
29%33%28%8%1
240
21st to endDay
40%20%29%10%1
249
March1st to 10thDay
26%22%31%16%5%
420
11th to 20thDay
30%16%34%16%41
420
21st to endDay
32%19%27%16%5%2
462
April1st to 10thDay
25%23%28%17%6%1
420
11th to 20thDay
30%21%23%16%8%3
412
21st to endDay
29%17%30%15%7%2
420
May1st to 10thDay
27%16%29%16%7%4
423
11th to 20thDay
21%14%30%21%9%3
447
21st to endDay
18%12%31%24%11%5%
485
June1st to 10thDay
21%15%34%21%8%1
450
11th to 20thDay
17%15%30%25%10%3
450
21st to endDay
20%14%31%24%9%2
450
July1st to 10thDay
10%10%25%31%19%4
445
11th to 20thDay
16%12%28%25%13%5%
444
21st to endDay
13%10%34%28%11%4
488
August1st to 10thDay
13%9%24%30%16%8%
446
11th to 20thDay
12%8%28%26%17%8%
439
21st to endDay
14%8%31%24%15%8%
495
September1st to 10thDay
16%12%24%26%15%7%
450
11th to 20thDay
13%8%22%26%22%10%
450
21st to endDay
19%16%26%21%12%6%
450
October1st to 10thDay
26%12%24%18%14%6%
450
11th to 20thDay
27%22%27%18%5%1
450
21st to endDay
37%19%24%14%6%
495
November1st to 10thDay
26%19%30%16%7%1
315
11th to 20thDay
33%26%26%10%23
180
21st to endDay
33%28%24%11%3
180
December1st to 10thDay
32%26%30%8%41
180
11th to 20thDay
33%28%23%14%2
180
21st to endDay
35%30%23%10%21
198
January1st to 10thNight
32%24%26%13%4
760
11th to 20thNight
32%24%26%15%3
760
21st to endNight
25%21%31%17%6%
835
February1st to 10thNight
28%27%29%13%2
720
11th to 20thNight
26%23%30%17%3
703
21st to endNight
30%23%28%17%2
592
March1st to 10thNight
23%18%31%22%6%
720
11th to 20thNight
27%17%30%21%5%1
720
21st to endNight
24%13%30%23%8%1
792
April1st to 10thNight
25%17%32%23%3
720
11th to 20thNight
23%17%29%23%8%1
711
21st to endNight
24%8%31%29%9%
540
May1st to 10thNight
21%11%23%32%12%2
540
11th to 20thNight
16%8%31%37%8%
371
21st to endNight
14%10%25%33%16%1
389
June1st to 10thNight
14%8%32%33%13%1
360
11th to 20thNight
15%10%28%35%12%
360
21st to endNight
16%8%33%32%11%
360
July1st to 10thNight
10%5%25%41%18%1
350
11th to 20thNight
12%7%28%33%18%1
348
21st to endNight
14%425%38%16%2
570
August1st to 10thNight
11%420%39%23%2
537
11th to 20thNight
10%6%21%34%26%3
534
21st to endNight
13%5%25%32%22%2
707
September1st to 10thNight
18%8%21%33%18%3
720
11th to 20thNight
15%5%23%28%24%5%
720
21st to endNight
19%11%24%27%16%4
720
October1st to 10thNight
20%11%27%24%16%2
720
11th to 20thNight
28%16%25%22%8%1
720
21st to endNight
34%14%26%22%4
792
November1st to 10thNight
24%16%27%24%9%1
740
11th to 20thNight
24%22%29%16%8%1
760
21st to endNight
28%22%28%17%5%
760
December1st to 10thNight
35%23%22%15%4
760
11th to 20thNight
29%27%25%16%3
760
21st to endNight
35%20%28%16%2
836
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