Fort Erie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Erie clear sky chart from 2005-11-06 to 2025-01-07.

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%
24040
10%
104212
8%
23731
34%
23731
10%
77713

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
9%
779
4%
4508
3%
762
12%
762
2%
4005
January11th to 20thNight
12%
759
2%
4178
2%
740
14%
740
2%
3837
January21st to endNight
11%
832
3%
4532
2%
814
15%
814
3%
4140
February1st to 10thNight
10%
760
5%
2470
2%
760
15%
760
5%
2109
February11th to 20thNight
14%
743
7%
2405
2%
740
20%
740
7%
1987
February21st to endNight
14%
628
7%
1965
2%
628
20%
628
8%
1619
March1st to 10thNight
21%
756
17%
3392
7%
743
27%
743
9%
2416
March11th to 20thNight
21%
758
11%
3471
6%
740
28%
740
9%
2589
March21st to endNight
24%
835
11%
3705
8%
814
31%
814
12%
2309
April1st to 10thNight
23%
760
13%
1920
5%
760
28%
760
18%
1484
April11th to 20thNight
28%
746
14%
1870
6%
746
32%
746
21%
1374
April21st to endNight
35%
570
15%
1710
8%
570
40%
570
20%
1207
May1st to 10thNight
40%
565
14%
2788
10%
559
43%
559
12%
1971
May11th to 20thNight
43%
388
11%
2509
16%
382
49%
382
11%
1570
May21st to endNight
48%
404
13%
2713
16%
399
55%
399
15%
1397
June1st to 10thNight
42%
380
14%
1520
14%
380
52%
380
17%
989
June11th to 20thNight
49%
380
14%
1520
18%
380
56%
380
21%
920
June21st to endNight
46%
380
12%
1520
14%
380
53%
380
19%
945
July1st to 10thNight
57%
364
15%
2337
22%
360
63%
360
15%
1328
July11th to 20thNight
51%
362
13%
2195
22%
358
58%
358
16%
1280
July21st to endNight
54%
591
10%
2685
11%
552
57%
552
19%
1577
August1st to 10thNight
60%
558
16%
2622
14%
545
64%
545
19%
1642
August11th to 20thNight
57%
549
12%
2664
12%
543
61%
543
16%
1778
August21st to endNight
54%
725
14%
2969
10%
724
57%
724
21%
1768
September1st to 10thNight
51%
760
19%
1900
11%
760
53%
760
30%
1281
September11th to 20thNight
56%
760
24%
1981
16%
760
60%
760
36%
1233
September21st to endNight
43%
760
17%
2147
13%
760
46%
760
21%
1524
October1st to 10thNight
38%
760
11%
2934
13%
740
42%
740
14%
2205
October11th to 20thNight
27%
760
7%
3077
7%
740
30%
740
10%
2367
October21st to endNight
21%
836
9%
3264
7%
814
26%
814
9%
2397
November1st to 10thNight
28%
780
17%
2548
13%
780
35%
780
17%
1801
November11th to 20thNight
19%
800
11%
2800
7%
800
26%
800
11%
2143
November21st to endNight
15%
800
7%
2800
4%
800
19%
800
7%
2279
December1st to 10thNight
11%
795
2%
4564
2%
780
13%
780
2%
3951
December11th to 20thNight
11%
795
2%
5163
1%
779
14%
779
2%
4456
December21st to endNight
10%
862
5%
6866
2%
839
13%
839
2%
5835

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%38%5%5%445%7%31%
105028
Night
18%13%49%5%4435%6%28%
104007
TransparencyDay
52%6%12%19%9%1
108633
Night
57%6%11%17%8%1
108490
SeeingDay
20%15%27%22%11%4
14661
Night
23%14%27%24%11%1
24175

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
19%25%8%12%7%5%434411%
2565
11th to 20thDay
14%23%7%21%11%6%42338%
2776
21st to endDay
22%21%7%13%7%6%5%33310%
3124
February1st to 10thDay
17%19%5%15%8%5%7%44413%
1710
11th to 20thDay
14%18%7%14%8%6%5%435%17%
1663
21st to endDay
21%13%5%12%8%5%445%5%18%
1486
March1st to 10thDay
19%14%48%5%44346%29%
3432
11th to 20thDay
10%19%5%8%5%5%445%6%29%
3480
21st to endDay
18%11%310%6%4435%6%29%
3815
April1st to 10thDay
19%14%38%45%3346%31%
2258
11th to 20thDay
20%10%27%44435%6%34%
2274
21st to endDay
21%10%37%5%4435%5%34%
2470
May1st to 10thDay
21%10%36%5%5%446%6%31%
4108
11th to 20thDay
14%10%39%5%5%5%47%8%30%
4362
21st to endDay
12%7%26%34446%7%45%
4837
June1st to 10thDay
15%8%27%5%4447%7%38%
2660
11th to 20thDay
13%5%26%45%447%9%40%
2660
21st to endDay
15%6%25%435%36%8%43%
2660
July1st to 10thDay
10%5%26%445%46%9%45%
4440
11th to 20thDay
13%5%26%45%447%8%42%
4440
21st to endDay
7%5%37%446%5%8%9%43%
4480
August1st to 10thDay
17%6%26%445%36%7%39%
4104
11th to 20thDay
13%6%37%5%5%6%47%11%34%
4044
21st to endDay
12%5%25%44436%9%46%
4290
September1st to 10thDay
14%7%26%44445%7%42%
2280
11th to 20thDay
12%426%44446%8%46%
2196
21st to endDay
15%8%37%5%6%5%5%6%8%32%
2033
October1st to 10thDay
20%8%37%6%4446%6%34%
1900
11th to 20thDay
21%10%38%45%5%45%6%28%
1900
21st to endDay
26%14%310%5%5%4345%22%
2090
November1st to 10thDay
15%12%39%5%5%5%45%6%32%
1745
11th to 20thDay
15%15%411%5%5%5%45%5%28%
1600
21st to endDay
21%19%5%9%5%5%5%347%18%
1600
December1st to 10thDay
22%18%7%13%7%5%5%45%411%
2600
11th to 20thDay
23%21%5%10%5%44345%16%
2986
21st to endDay
23%23%5%12%7%6%433412%
3960
January1st to 10thNight
20%25%7%11%6%5%433313%
4514
11th to 20thNight
15%22%8%20%10%6%33337%
4180
21st to endNight
25%22%6%14%6%4323410%
4532
February1st to 10thNight
19%20%7%13%6%4435%416%
2470
11th to 20thNight
16%16%6%12%7%6%5%446%18%
2403
21st to endNight
20%15%5%13%7%44345%19%
1965
March1st to 10thNight
20%14%38%5%4333431%
3408
11th to 20thNight
20%18%47%443346%26%
3479
21st to endNight
17%9%38%44435%6%39%
3817
April1st to 10thNight
21%14%37%5%3435%430%
1920
11th to 20thNight
19%9%38%5%4445%6%34%
1870
21st to endNight
18%10%36%445%45%7%35%
1710
May1st to 10thNight
24%10%38%43435%6%31%
2833
11th to 20thNight
14%7%38%6%5%5%47%9%33%
2527
21st to endNight
13%6%35%34446%8%44%
2738
June1st to 10thNight
12%9%36%6%5%6%5%7%7%36%
1520
11th to 20thNight
12%5%26%5%5%5%46%8%41%
1520
21st to endNight
15%7%25%5%445%6%8%39%
1520
July1st to 10thNight
10%6%27%5%5%5%46%9%43%
2520
11th to 20thNight
13%6%26%44436%8%44%
2520
21st to endNight
10%5%26%5%45%47%7%45%
3069
August1st to 10thNight
11%8%37%5%4446%8%40%
2825
11th to 20thNight
14%8%37%5%5%446%7%36%
2785
21st to endNight
9%5%26%5%46%47%9%45%
3334
September1st to 10thNight
15%6%25%43435%7%44%
1900
11th to 20thNight
13%5%25%333348%51%
1981
21st to endNight
17%7%37%5%45%5%6%7%35%
2147
October1st to 10thNight
18%6%37%5%5%435%7%38%
2280
11th to 20thNight
22%10%38%45%445%6%29%
2280
21st to endNight
27%9%37%45%5%45%6%26%
2508
November1st to 10thNight
18%10%37%5%4335%6%36%
2548
11th to 20thNight
16%13%310%6%5%435%6%28%
2800
21st to endNight
20%15%5%10%6%5%445%6%20%
2800
December1st to 10thNight
19%22%7%14%6%4445%5%11%
4580
11th to 20thNight
21%23%5%11%7%5%433414%
5208
21st to endNight
25%20%5%11%6%5%434413%
6996

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
78%8%6%5%3
2566
11th to 20thDay
81%8%6%41
2776
21st to endDay
80%7%9%31
3124
February1st to 10thDay
76%6%10%7%1
1710
11th to 20thDay
71%6%9%11%3
1672
21st to endDay
67%6%11%11%4
1486
March1st to 10thDay
56%6%11%20%6%
3435
11th to 20thDay
54%8%18%14%6%1
3480
21st to endDay
54%9%9%20%7%1
3815
April1st to 10thDay
56%5%11%18%10%1
2258
11th to 20thDay
50%6%11%20%12%2
2274
21st to endDay
53%5%10%17%13%2
2470
May1st to 10thDay
51%6%13%18%10%2
4120
11th to 20thDay
49%11%13%20%7%1
4366
21st to endDay
36%7%14%25%14%3
4837
June1st to 10thDay
43%8%13%20%15%1
2660
11th to 20thDay
40%8%15%23%12%1
2660
21st to endDay
39%8%14%25%13%1
2660
July1st to 10thDay
36%5%13%29%16%2
4370
11th to 20thDay
38%5%14%25%16%
4365
21st to endDay
37%7%18%22%16%1
4337
August1st to 10thDay
44%7%13%23%12%1
4091
11th to 20thDay
45%6%17%24%7%
4083
21st to endDay
37%412%34%11%1
4290
September1st to 10thDay
42%8%14%24%12%1
2280
11th to 20thDay
36%7%14%29%13%1
2196
21st to endDay
49%7%14%20%9%1
2033
October1st to 10thDay
43%5%13%26%13%1
3160
11th to 20thDay
47%416%20%12%1
3140
21st to endDay
53%314%23%7%
3428
November1st to 10thDay
55%6%11%17%8%2
1745
11th to 20thDay
58%8%14%13%5%2
1600
21st to endDay
69%6%11%10%3
1600
December1st to 10thDay
78%5%10%6%1
2600
11th to 20thDay
74%5%10%9%2
2986
21st to endDay
78%5%8%8%2
3960
January1st to 10thNight
76%10%7%6%1
4514
11th to 20thNight
80%9%6%31
4180
21st to endNight
81%7%6%41
4532
February1st to 10thNight
73%6%10%9%2
2470
11th to 20thNight
69%6%10%12%3
2405
21st to endNight
68%6%10%11%5%
1965
March1st to 10thNight
58%5%10%20%6%
3418
11th to 20thNight
59%7%13%14%6%1
3480
21st to endNight
47%5%11%22%13%1
3817
April1st to 10thNight
57%5%9%19%10%1
1920
11th to 20thNight
51%6%10%18%14%2
1870
21st to endNight
49%6%11%18%14%2
1710
May1st to 10thNight
53%7%9%17%10%3
2840
11th to 20thNight
45%10%17%20%8%1
2528
21st to endNight
36%7%12%24%19%2
2739
June1st to 10thNight
44%9%10%22%14%1
1520
11th to 20thNight
40%7%13%21%18%1
1520
21st to endNight
42%7%14%22%13%2
1520
July1st to 10thNight
41%411%24%17%3
2480
11th to 20thNight
40%414%27%14%1
2472
21st to endNight
37%6%17%22%15%2
2971
August1st to 10thNight
41%6%14%26%11%1
2814
11th to 20thNight
47%6%15%24%8%
2812
21st to endNight
37%5%13%32%13%1
3334
September1st to 10thNight
38%8%13%25%14%2
1900
11th to 20thNight
34%5%13%28%18%1
1981
21st to endNight
47%8%12%20%11%1
2147
October1st to 10thNight
45%49%25%17%1
3800
11th to 20thNight
51%413%19%13%
3779
21st to endNight
48%415%24%8%1
4120
November1st to 10thNight
51%6%10%20%10%2
2548
11th to 20thNight
59%7%12%13%6%2
2800
21st to endNight
66%8%13%11%3
2800
December1st to 10thNight
78%5%11%5%1
4580
11th to 20thNight
77%5%7%9%2
5208
21st to endNight
76%5%7%9%2
6996

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
27%26%30%10%6%2
192
11th to 20thDay
27%29%29%12%31
252
21st to endDay
24%26%29%16%4
297
February1st to 10thDay
29%26%31%11%2
270
11th to 20thDay
26%29%35%10%
270
21st to endDay
29%25%35%10%1
277
March1st to 10thDay
23%20%35%17%32
460
11th to 20thDay
24%20%34%17%5%1
460
21st to endDay
28%14%32%19%6%1
506
April1st to 10thDay
23%22%31%18%6%1
460
11th to 20thDay
26%21%25%17%9%3
452
21st to endDay
25%15%31%21%7%2
460
May1st to 10thDay
26%13%27%21%10%3
463
11th to 20thDay
16%11%28%27%14%3
487
21st to endDay
14%8%30%28%15%5%
529
June1st to 10thDay
17%16%27%29%11%1
490
11th to 20thDay
12%13%23%31%17%3
490
21st to endDay
16%10%31%29%11%3
490
July1st to 10thDay
9%8%21%34%23%5%
485
11th to 20thDay
13%9%25%29%19%5%
484
21st to endDay
9%8%28%32%17%6%
532
August1st to 10thDay
12%6%22%31%21%8%
486
11th to 20thDay
14%6%23%29%21%8%
479
21st to endDay
11%7%25%30%18%8%
539
September1st to 10thDay
14%8%24%28%18%8%
490
11th to 20thDay
10%6%19%26%24%15%
490
21st to endDay
16%15%26%21%16%6%
490
October1st to 10thDay
20%12%26%19%17%6%
490
11th to 20thDay
24%18%30%19%7%2
490
21st to endDay
32%20%24%17%6%
539
November1st to 10thDay
23%18%32%18%8%1
342
11th to 20thDay
29%27%25%15%42
200
21st to endDay
34%26%29%11%1
200
December1st to 10thDay
31%26%27%12%6%
200
11th to 20thDay
33%23%25%17%3
200
21st to endDay
30%30%24%12%31
220
January1st to 10thNight
31%24%28%12%5%
785
11th to 20thNight
32%23%27%14%3
760
21st to endNight
24%17%36%18%5%
836
February1st to 10thNight
28%24%29%16%3
760
11th to 20thNight
26%21%32%18%3
743
21st to endNight
28%20%32%18%2
628
March1st to 10thNight
23%17%33%22%5%
760
11th to 20thNight
26%17%30%20%6%1
760
21st to endNight
24%12%34%20%9%1
836
April1st to 10thNight
26%15%30%24%4
760
11th to 20thNight
24%14%29%22%9%1
746
21st to endNight
23%9%27%30%9%1
570
May1st to 10thNight
21%9%23%32%13%2
570
11th to 20thNight
13%9%26%42%10%1
393
21st to endNight
13%6%27%31%21%2
411
June1st to 10thNight
14%6%30%35%15%1
380
11th to 20thNight
14%7%24%37%17%1
380
21st to endNight
14%8%25%38%14%
380
July1st to 10thNight
8%422%42%21%2
370
11th to 20thNight
12%426%36%20%2
368
21st to endNight
11%324%36%23%2
606
August1st to 10thNight
11%417%39%25%3
567
11th to 20thNight
10%6%18%33%30%3
564
21st to endNight
12%5%21%34%25%3
746
September1st to 10thNight
16%7%19%33%21%4
760
11th to 20thNight
14%5%19%27%28%7%
760
21st to endNight
20%10%21%28%17%4
760
October1st to 10thNight
21%8%27%23%18%2
760
11th to 20thNight
26%18%24%23%8%2
760
21st to endNight
31%16%29%20%5%
836
November1st to 10thNight
23%15%30%23%8%1
780
11th to 20thNight
24%22%29%16%7%1
800
21st to endNight
28%23%30%16%5%
800
December1st to 10thNight
35%24%24%13%4
800
11th to 20thNight
32%25%26%15%3
800
21st to endNight
35%18%28%16%2
880
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