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 2005-11-05 to 2017-09-19.

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
29%
14894
11%
46918
8%
14857
34%
14857
14%
34875

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 15thNight
8%
716
5%
2470
2%
716
11%
716
4%
2179
January16th to endNight
10%
768
4%
2496
1%
768
14%
768
5%
2148
February1st to 15thNight
10%
704
4%
2287
2%
701
14%
701
5%
1954
February16th to endNight
15%
631
7%
2005
2%
631
21%
631
7%
1659
March1st to 15thNight
21%
720
11%
1980
5%
720
25%
720
12%
1586
March16th to endNight
26%
768
16%
2112
8%
768
33%
768
18%
1552
April1st to 15thNight
24%
718
13%
1808
5%
718
28%
718
18%
1377
April16th to endNight
36%
600
19%
1680
8%
600
42%
600
25%
1122
May1st to 15thNight
41%
490
15%
1570
11%
490
47%
490
18%
1095
May16th to endNight
43%
374
17%
1497
15%
374
52%
374
22%
894
June1st to 15thNight
42%
360
13%
1440
12%
360
51%
360
18%
916
June16th to endNight
40%
360
11%
1440
12%
360
48%
360
20%
895
July1st to 15thNight
52%
340
15%
1360
21%
340
56%
340
26%
757
July16th to endNight
52%
492
15%
1525
12%
461
55%
461
28%
906
August1st to 15thNight
57%
539
15%
1609
11%
536
60%
536
30%
984
August16th to endNight
55%
649
19%
1795
11%
649
59%
649
33%
1118
September1st to 15thNight
48%
720
19%
1800
11%
720
52%
720
30%
1212
September16th to endNight
49%
673
20%
1880
14%
673
52%
673
27%
1244
October1st to 15thNight
35%
660
15%
1980
12%
660
40%
660
20%
1390
October16th to endNight
17%
704
8%
2112
4%
704
23%
704
10%
1674
November1st to 15thNight
31%
700
17%
2344
15%
700
36%
700
16%
1631
November16th to endNight
18%
720
8%
2520
6%
720
22%
720
9%
2009
December1st to 15thNight
12%
720
3%
2520
2%
720
14%
720
4%
2184
December16th to endNight
9%
768
2%
2688
0%
768
12%
768
4%
2389

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%10%36%5%3445%6%31%
47893
Night
17%11%47%6%34446%29%
47098
Cloud CoverDay
16%10%36%5%3445%7%31%
47903
Night
17%10%47%5%34446%29%
47102
TransparencyDay
52%7%12%17%9%
47592
Night
56%5%11%16%8%1
46918
SeeingDay
22%13%26%21%11%4
5410
Night
25%13%26%23%10%1
14899

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 15thDay
20%18%6%10%8%4343412%
1467
16th to endDay
14%19%8%12%10%5%6%44310%
1728
February1st to 15thDay
17%17%8%12%8%46%43312%
1575
16th to endDay
17%14%6%10%9%45%335%17%
1467
March1st to 15thDay
17%14%6%9%7%35%345%21%
1969
16th to endDay
17%12%36%5%35%45%5%30%
2112
April1st to 15thDay
21%10%36%424445%31%
2140
16th to endDay
18%8%25%433345%38%
2291
May1st to 15thDay
17%6%35%5%345%5%7%35%
2379
16th to endDay
12%6%344245%6%8%41%
2618
June1st to 15thDay
16%6%35%4235%6%8%37%
2520
16th to endDay
13%41443446%9%42%
2520
July1st to 15thDay
9%424425%5%6%8%45%
2520
16th to endDay
11%425%437%5%7%10%36%
2536
August1st to 15thDay
9%5%245%35%5%7%9%40%
2340
16th to endDay
11%5%2442446%10%43%
2393
September1st to 15thDay
16%5%25%42345%6%41%
2160
16th to endDay
15%5%14445%5%6%7%39%
1821
October1st to 15thDay
21%7%26%6%34445%32%
1650
16th to endDay
25%12%47%6%25%5%35%21%
1760
November1st to 15thDay
13%11%36%6%35%5%47%32%
1511
16th to endDay
22%14%5%8%6%24445%21%
1440
December1st to 15thDay
20%21%6%9%6%245%5%414%
1440
16th to endDay
21%22%8%10%7%344349%
1536
January1st to 15thNight
23%18%7%9%7%3434413%
2470
16th to endNight
17%19%8%11%8%35%445%13%
2496
February1st to 15thNight
18%18%9%11%7%3433416%
2285
16th to endNight
18%14%5%12%9%3434417%
2005
March1st to 15thNight
21%13%47%6%3434424%
1968
16th to endNight
17%11%46%5%34345%33%
2112
April1st to 15thNight
23%10%35%5%2434431%
1808
16th to endNight
15%6%15%425%5%46%41%
1680
May1st to 15thNight
17%6%26%6%25%5%6%7%33%
1570
16th to endNight
12%435%425%46%8%42%
1495
June1st to 15thNight
14%6%245%36%5%5%6%38%
1440
16th to endNight
13%5%246%35%5%6%7%39%
1440
July1st to 15thNight
8%4245%3445%9%47%
1440
16th to endNight
9%4244345%7%7%45%
1630
August1st to 15thNight
9%4145%3446%9%45%
1620
16th to endNight
9%424425%5%5%7%47%
1795
September1st to 15thNight
16%5%2432345%7%43%
1800
16th to endNight
16%5%244235%45%44%
1880
October1st to 15thNight
21%7%25%433436%36%
1980
16th to endNight
27%8%36%5%35%45%6%23%
2112
November1st to 15thNight
18%9%35%423446%36%
2344
16th to endNight
19%12%5%8%7%35%45%6%21%
2520
December1st to 15thNight
21%21%6%8%6%3444414%
2520
16th to endNight
23%18%7%10%7%4424411%
2688

Percentage Cloud Cover SE (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 15thDay
20%19%6%10%8%4433412%
1467
16th to endDay
14%19%7%12%10%46%44410%
1728
February1st to 15thDay
17%18%6%13%8%47%33412%
1575
16th to endDay
17%15%5%11%9%44435%16%
1467
March1st to 15thDay
18%15%5%10%7%35%345%21%
1980
16th to endDay
17%12%46%5%34346%30%
2111
April1st to 15thDay
21%12%35%5%24435%31%
2140
16th to endDay
19%9%24434346%38%
2291
May1st to 15thDay
17%7%26%5%3445%6%34%
2379
16th to endDay
13%6%35%32445%8%40%
2618
June1st to 15thDay
17%6%25%43446%7%36%
2520
16th to endDay
14%5%1442446%10%40%
2520
July1st to 15thDay
9%434425%5%6%9%44%
2520
16th to endDay
11%425%5%36%5%8%9%36%
2536
August1st to 15thDay
10%5%246%45%6%6%10%39%
2340
16th to endDay
11%5%244245%6%9%42%
2393
September1st to 15thDay
16%6%25%42345%6%40%
2160
16th to endDay
14%5%245%445%5%7%38%
1821
October1st to 15thDay
22%7%36%5%34446%32%
1650
16th to endDay
26%12%37%5%35%445%21%
1760
November1st to 15thDay
13%11%36%7%35%437%31%
1511
16th to endDay
22%13%48%6%345%35%21%
1440
December1st to 15thDay
22%20%6%9%5%245%45%13%
1440
16th to endDay
21%22%8%11%7%343349%
1536
January1st to 15thNight
22%18%7%10%8%3423413%
2470
16th to endNight
17%19%8%11%7%34345%13%
2496
February1st to 15thNight
18%17%9%12%7%3432416%
2278
16th to endNight
18%14%5%13%8%35%34417%
2005
March1st to 15thNight
21%12%47%6%34445%24%
1980
16th to endNight
16%11%47%434345%33%
2112
April1st to 15thNight
23%11%35%42444431%
1808
16th to endNight
15%5%25%5%25%5%46%41%
1680
May1st to 15thNight
17%6%36%5%35%46%7%32%
1569
16th to endNight
12%425%425%5%5%8%42%
1495
June1st to 15thNight
14%6%245%35%5%5%6%38%
1440
16th to endNight
13%5%245%35%5%6%7%40%
1440
July1st to 15thNight
7%5%25%42445%8%47%
1440
16th to endNight
9%42443447%7%45%
1630
August1st to 15thNight
9%4145%35%46%9%45%
1620
16th to endNight
9%3144346%5%8%47%
1795
September1st to 15thNight
15%5%2431345%8%43%
1800
16th to endNight
16%5%15%424446%44%
1880
October1st to 15thNight
21%6%26%5%24336%37%
1980
16th to endNight
27%8%36%5%35%45%6%23%
2112
November1st to 15thNight
18%8%35%5%24446%36%
2344
16th to endNight
20%12%5%8%7%25%5%5%6%21%
2520
December1st to 15thNight
22%20%6%9%6%34345%14%
2520
16th to endNight
23%18%7%10%6%35%34411%
2688

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 15thDay
77%48%7%2
1468
16th to endDay
77%7%8%5%1
1728
February1st to 15thDay
77%6%7%7%
1577
16th to endDay
69%5%10%10%2
1467
March1st to 15thDay
65%5%10%13%3
1980
16th to endDay
54%5%9%20%8%
2112
April1st to 15thDay
55%411%18%10%
2140
16th to endDay
47%49%20%15%2
2291
May1st to 15thDay
47%6%11%22%11%
2379
16th to endDay
39%7%15%22%12%1
2622
June1st to 15thDay
44%7%12%22%11%
2520
16th to endDay
37%9%16%23%12%
2520
July1st to 15thDay
35%8%11%25%18%1
2371
16th to endDay
39%10%16%21%11%1
2379
August1st to 15thDay
36%10%15%22%12%1
2327
16th to endDay
35%7%14%27%12%1
2393
September1st to 15thDay
43%6%13%23%11%
2160
16th to endDay
41%8%12%23%13%
1821
October1st to 15thDay
53%5%12%16%11%
1650
16th to endDay
66%5%14%10%3
1760
November1st to 15thDay
53%7%13%15%8%1
1511
16th to endDay
65%6%11%11%4
1440
December1st to 15thDay
74%7%10%6%
1440
16th to endDay
81%5%7%4
1536
January1st to 15thNight
78%48%5%2
2470
16th to endNight
74%5%10%6%2
2496
February1st to 15thNight
74%410%8%1
2287
16th to endNight
69%410%11%3
2005
March1st to 15thNight
62%5%10%15%4
1980
16th to endNight
52%5%8%17%13%1
2112
April1st to 15thNight
55%5%9%17%11%
1808
16th to endNight
42%5%11%21%15%3
1680
May1st to 15thNight
48%6%9%22%11%1
1570
16th to endNight
38%7%13%22%15%2
1497
June1st to 15thNight
43%7%10%22%14%
1440
16th to endNight
41%7%13%21%14%1
1440
July1st to 15thNight
35%5%13%24%19%3
1360
16th to endNight
35%6%16%24%14%3
1525
August1st to 15thNight
34%7%17%26%13%1
1609
16th to endNight
33%7%15%28%13%1
1795
September1st to 15thNight
39%5%14%23%13%1
1800
16th to endNight
40%6%11%24%16%
1880
October1st to 15thNight
49%5%11%18%14%
1980
16th to endNight
62%5%14%12%4
2112
November1st to 15thNight
50%6%12%18%10%2
2344
16th to endNight
65%6%12%12%3
2520
December1st to 15thNight
75%5%11%5%1
2520
16th to endNight
78%5%9%5%
2688

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 15thDay
33%34%16%9%41
66
16th to endDay
33%22%27%14%2
96
February1st to 15thDay
31%41%22%5%
90
16th to endDay
28%25%32%11%1
114
March1st to 15thDay
33%17%25%17%6%
270
16th to endDay
26%17%28%21%42
288
April1st to 15thDay
31%16%27%15%6%2
270
16th to endDay
23%14%26%17%12%4
270
May1st to 15thDay
29%12%23%18%11%4
288
16th to endDay
18%14%29%22%8%5%
331
June1st to 15thDay
25%9%28%22%11%1
315
16th to endDay
19%12%30%26%9%1
315
July1st to 15thDay
14%7%28%29%15%5%
305
16th to endDay
13%8%30%28%12%6%
326
August1st to 15thDay
12%7%25%26%17%10%
313
16th to endDay
14%7%25%22%17%12%
332
September1st to 15thDay
15%7%21%26%20%7%
315
16th to endDay
16%8%20%23%21%9%
266
October1st to 15thDay
23%8%26%20%16%5%
255
16th to endDay
32%19%27%15%4
272
November1st to 15thDay
22%9%32%23%9%3
129
16th to endDay
36%18%21%21%1
60
December1st to 15thDay
41%28%15%11%3
60
16th to endDay
46%35%14%3
64
January1st to 15thNight
34%22%27%14%2
720
16th to endNight
30%21%29%14%3
768
February1st to 15thNight
29%23%28%16%2
704
16th to endNight
28%19%29%19%2
631
March1st to 15thNight
31%15%27%20%4
720
16th to endNight
23%11%32%21%9%1
768
April1st to 15thNight
29%15%27%23%4
718
16th to endNight
20%9%29%29%10%1
600
May1st to 15thNight
21%7%22%33%13%1
490
16th to endNight
14%6%30%31%14%1
375
June1st to 15thNight
17%6%27%31%15%1
360
16th to endNight
16%5%32%33%11%
360
July1st to 15thNight
10%326%42%17%
340
16th to endNight
11%327%34%20%2
492
August1st to 15thNight
11%322%38%21%3
539
16th to endNight
12%422%32%25%2
649
September1st to 15thNight
20%5%20%29%21%2
720
16th to endNight
18%6%20%24%24%4
673
October1st to 15thNight
23%10%24%23%15%1
660
16th to endNight
33%16%27%17%3
704
November1st to 15thNight
24%15%25%24%8%1
700
16th to endNight
29%20%25%16%7%
720
December1st to 15thNight
38%20%23%14%3
720
16th to endNight
37%19%26%14%2
768
Page generated at 2017-09-20 04:49:46. Version ac04

Copyright 2017 A. Danko


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