Fort Falstaff Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Falstaff Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
33%
15039
13%
47782
9%
15008
39%
15008
16%
34462

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
24%
720
10%
2506
6%
716
29%
716
9%
1948
January16th to endNight
21%
768
10%
2688
4%
768
28%
768
10%
2013
February1st to 15thNight
19%
704
10%
2269
3%
701
28%
701
9%
1796
February16th to endNight
24%
631
13%
1893
6%
631
33%
631
13%
1436
March1st to 15thNight
24%
720
13%
2160
8%
720
31%
720
14%
1632
March16th to endNight
27%
768
18%
2008
7%
768
36%
768
18%
1458
April1st to 15thNight
26%
718
16%
1796
5%
718
31%
718
18%
1360
April16th to endNight
29%
606
16%
1686
7%
606
35%
606
19%
1172
May1st to 15thNight
28%
472
16%
1552
11%
472
36%
472
18%
1064
May16th to endNight
40%
374
12%
1497
13%
374
47%
374
16%
980
June1st to 15thNight
36%
360
9%
1440
7%
360
44%
360
12%
1011
June16th to endNight
49%
360
9%
1440
11%
360
55%
360
20%
915
July1st to 15thNight
57%
340
11%
1360
19%
340
59%
340
21%
836
July16th to endNight
56%
376
13%
1418
17%
354
59%
354
23%
853
August1st to 15thNight
56%
422
14%
1493
14%
420
59%
420
22%
929
August16th to endNight
56%
739
20%
1885
12%
739
58%
739
35%
1199
September1st to 15thNight
50%
720
14%
1823
8%
720
52%
720
29%
1233
September16th to endNight
52%
717
23%
1980
18%
717
56%
717
33%
1237
October1st to 15thNight
39%
720
16%
2067
11%
720
45%
720
19%
1462
October16th to endNight
27%
768
11%
2482
7%
768
34%
768
13%
1852
November1st to 15thNight
32%
760
15%
2472
11%
760
38%
760
15%
1800
November16th to endNight
27%
780
14%
2633
10%
780
34%
780
12%
1955
December1st to 15thNight
19%
728
5%
2546
3%
728
22%
728
6%
2106
December16th to endNight
18%
768
8%
2688
5%
768
22%
768
6%
2215

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
15%9%47%6%35%5%5%7%29%
48675
Night
14%8%47%6%35%5%5%6%30%
47952
Cloud CoverDay
16%9%47%6%35%45%6%29%
48685
Night
15%9%47%6%35%45%6%30%
47957
TransparencyDay
54%5%11%18%9%
48363
Night
52%6%11%19%9%
47782
SeeingDay
22%13%26%21%12%4
5954
Night
20%12%25%28%10%1
15040

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
12%9%5%13%9%46%6%6%6%18%
1432
16th to endDay
10%10%5%9%10%36%5%6%6%24%
1536
February1st to 15thDay
10%10%6%11%9%5%7%5%5%5%20%
1591
16th to endDay
10%14%5%12%8%5%6%45%422%
1580
March1st to 15thDay
13%12%6%10%7%36%445%23%
1790
16th to endDay
16%10%5%9%6%33445%31%
2212
April1st to 15thDay
17%11%5%8%5%23345%31%
2152
16th to endDay
18%10%25%435%446%33%
2274
May1st to 15thDay
19%10%47%6%24445%29%
2409
16th to endDay
18%7%25%6%4445%8%31%
2618
June1st to 15thDay
26%6%26%6%35%447%26%
2520
16th to endDay
18%6%37%6%25%5%5%8%28%
2520
July1st to 15thDay
12%7%25%6%37%6%6%8%33%
2520
16th to endDay
15%5%26%6%46%6%6%8%31%
2654
August1st to 15thDay
13%6%37%7%45%5%5%9%29%
2445
16th to endDay
12%426%5%345%7%9%36%
2315
September1st to 15thDay
16%8%25%424446%40%
2136
16th to endDay
12%5%243245%48%46%
1980
October1st to 15thDay
19%9%35%6%33446%32%
1890
16th to endDay
17%16%36%6%35%45%5%26%
1741
November1st to 15thDay
13%12%46%6%35%45%7%29%
1716
16th to endDay
14%10%6%9%6%35%5%46%27%
1657
December1st to 15thDay
17%13%5%9%7%45%5%5%6%18%
1451
16th to endDay
16%14%8%10%8%36%46%415%
1536
January1st to 15thNight
11%10%410%9%48%7%7%7%18%
2506
16th to endNight
10%10%5%9%9%37%5%7%7%22%
2688
February1st to 15thNight
9%10%5%12%10%6%7%5%6%6%18%
2268
16th to endNight
10%10%5%11%8%45%446%26%
1893
March1st to 15thNight
13%9%47%8%47%5%5%428%
2147
16th to endNight
13%9%48%6%34446%34%
2008
April1st to 15thNight
17%9%5%7%5%34446%30%
1796
16th to endNight
19%7%2443345%6%37%
1686
May1st to 15thNight
17%8%36%5%3445%6%34%
1552
16th to endNight
17%6%35%5%2446%8%34%
1495
June1st to 15thNight
23%6%25%5%35%5%5%6%30%
1440
16th to endNight
15%435%4335%5%9%38%
1440
July1st to 15thNight
13%415%5%345%6%8%39%
1440
16th to endNight
10%5%24435%5%6%10%40%
1514
August1st to 15thNight
11%5%344345%6%8%40%
1503
16th to endNight
12%42341346%7%47%
1885
September1st to 15thNight
13%6%345%2445%6%43%
1823
16th to endNight
13%5%133245%5%6%47%
1980
October1st to 15thNight
17%9%35%5%23446%34%
2067
16th to endNight
18%12%37%5%34446%26%
2482
November1st to 15thNight
14%11%47%6%45%45%6%30%
2472
16th to endNight
14%9%5%10%7%45%5%45%28%
2633
December1st to 15thNight
18%12%6%11%8%45%5%45%16%
2546
16th to endNight
16%13%8%10%8%46%5%46%15%
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
12%11%5%13%8%36%6%6%7%18%
1432
16th to endDay
10%10%5%8%10%47%6%5%5%25%
1536
February1st to 15thDay
10%11%6%10%9%6%8%45%5%20%
1591
16th to endDay
10%13%7%12%8%46%45%422%
1580
March1st to 15thDay
14%13%6%11%6%36%44423%
1800
16th to endDay
16%10%410%6%23345%31%
2212
April1st to 15thDay
16%12%5%7%5%34335%30%
2152
16th to endDay
19%9%35%434446%33%
2274
May1st to 15thDay
20%10%46%5%34445%29%
2409
16th to endDay
19%6%36%6%3445%7%31%
2618
June1st to 15thDay
27%6%35%5%35%447%26%
2520
16th to endDay
19%7%36%6%35%5%5%8%28%
2520
July1st to 15thDay
14%6%35%7%45%6%6%8%32%
2520
16th to endDay
16%5%25%6%36%5%7%8%31%
2654
August1st to 15thDay
15%7%26%6%47%5%5%7%29%
2445
16th to endDay
13%5%26%5%35%46%9%36%
2315
September1st to 15thDay
17%7%35%424445%40%
2136
16th to endDay
13%5%24424348%46%
1980
October1st to 15thDay
19%9%36%5%23447%32%
1890
16th to endDay
18%16%36%5%35%345%26%
1741
November1st to 15thDay
15%11%37%6%35%36%7%29%
1716
16th to endDay
14%11%6%9%6%35%5%46%27%
1657
December1st to 15thDay
17%15%5%8%7%45%45%6%20%
1451
16th to endDay
18%13%8%11%7%45%44416%
1536
January1st to 15thNight
10%11%5%11%9%47%7%7%6%19%
2506
16th to endNight
10%10%5%10%9%46%6%5%6%21%
2688
February1st to 15thNight
9%10%5%11%10%5%8%5%7%5%19%
2261
16th to endNight
11%12%6%10%8%45%446%25%
1893
March1st to 15thNight
13%10%48%8%47%5%4428%
2160
16th to endNight
13%10%5%8%6%23445%34%
2007
April1st to 15thNight
17%11%48%43445%5%31%
1796
16th to endNight
19%9%2442335%6%37%
1686
May1st to 15thNight
19%9%35%5%2335%7%34%
1552
16th to endNight
17%7%345%245%7%8%33%
1495
June1st to 15thNight
24%6%25%435%45%6%30%
1440
16th to endNight
16%425%5%2446%9%37%
1440
July1st to 15thNight
14%423436%46%9%39%
1440
16th to endNight
11%5%25%435%5%7%8%40%
1514
August1st to 15thNight
13%435%435%46%8%39%
1503
16th to endNight
12%42342436%9%46%
1885
September1st to 15thNight
15%6%24434445%44%
1823
16th to endNight
14%4143235%5%7%47%
1980
October1st to 15thNight
18%8%36%434346%35%
2067
16th to endNight
19%12%47%6%35%445%26%
2482
November1st to 15thNight
15%13%47%5%3445%5%30%
2472
16th to endNight
14%10%6%9%7%44435%28%
2633
December1st to 15thNight
18%13%6%10%9%35%5%45%17%
2546
16th to endNight
16%14%7%10%9%36%445%15%
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
61%8%9%14%5%
1433
16th to endDay
57%5%11%16%8%
1536
February1st to 15thDay
63%6%8%15%4
1594
16th to endDay
63%49%11%10%1
1580
March1st to 15thDay
63%5%9%13%7%1
1800
16th to endDay
54%48%16%13%2
2212
April1st to 15thDay
55%39%17%11%2
2152
16th to endDay
51%49%19%12%2
2274
May1st to 15thDay
57%46%19%10%1
2409
16th to endDay
50%6%12%18%9%1
2622
June1st to 15thDay
57%6%11%16%7%
2520
16th to endDay
52%7%11%18%9%
2520
July1st to 15thDay
45%7%15%22%9%
2371
16th to endDay
46%8%15%20%8%
2487
August1st to 15thDay
51%7%15%19%7%
2431
16th to endDay
41%5%15%24%11%
2315
September1st to 15thDay
45%5%10%26%11%
2136
16th to endDay
37%413%27%15%1
1980
October1st to 15thDay
52%5%9%20%10%
1890
16th to endDay
59%5%11%17%5%
1741
November1st to 15thDay
53%6%12%17%9%1
1716
16th to endDay
57%6%12%14%8%1
1657
December1st to 15thDay
64%6%11%13%4
1451
16th to endDay
70%5%7%8%7%
1536
January1st to 15thNight
60%8%11%12%6%
2506
16th to endNight
59%5%10%15%7%
2688
February1st to 15thNight
63%6%9%13%7%
2269
16th to endNight
59%49%16%9%1
1893
March1st to 15thNight
58%49%18%7%1
2160
16th to endNight
50%410%16%14%2
2008
April1st to 15thNight
54%47%19%12%1
1796
16th to endNight
47%5%9%20%14%2
1686
May1st to 15thNight
49%5%8%18%17%1
1552
16th to endNight
46%7%14%21%9%1
1497
June1st to 15thNight
54%6%12%18%8%
1440
16th to endNight
42%7%14%25%9%
1440
July1st to 15thNight
38%10%15%25%10%
1360
16th to endNight
38%7%16%24%11%
1418
August1st to 15thNight
39%8%16%26%9%
1493
16th to endNight
34%6%16%29%11%
1885
September1st to 15thNight
40%5%13%28%10%
1823
16th to endNight
35%5%13%30%14%1
1980
October1st to 15thNight
49%5%10%21%11%
2067
16th to endNight
58%5%10%18%6%
2482
November1st to 15thNight
55%5%11%17%8%1
2472
16th to endNight
57%5%10%18%6%1
2633
December1st to 15thNight
69%6%9%11%2
2546
16th to endNight
70%49%11%4
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
15%33%16%21%11%1
60
16th to endDay
23%28%21%17%9%
64
February1st to 15thDay
26%15%33%18%6%
139
16th to endDay
22%19%29%20%7%
239
March1st to 15thDay
28%14%25%26%5%
270
16th to endDay
24%18%25%17%10%3
288
April1st to 15thDay
28%14%27%20%7%1
270
16th to endDay
28%17%23%15%10%4
270
May1st to 15thDay
33%13%26%12%8%5%
288
16th to endDay
20%16%33%21%7%1
331
June1st to 15thDay
31%11%26%20%8%
315
16th to endDay
18%11%34%21%11%2
315
July1st to 15thDay
16%9%29%25%14%3
305
16th to endDay
15%5%30%31%13%2
326
August1st to 15thDay
17%7%28%23%16%5%
313
16th to endDay
14%9%21%21%22%10%
332
September1st to 15thDay
17%8%20%19%21%11%
315
16th to endDay
13%9%22%19%18%15%
314
October1st to 15thDay
18%14%22%23%15%5%
315
16th to endDay
28%14%21%26%7%
291
November1st to 15thDay
21%12%22%30%10%2
280
16th to endDay
24%17%23%21%10%2
187
December1st to 15thDay
19%19%30%19%11%1
63
16th to endDay
35%17%31%15%
64
January1st to 15thNight
19%17%29%27%5%
720
16th to endNight
19%17%30%28%3
768
February1st to 15thNight
15%17%34%26%4
704
16th to endNight
19%17%31%24%6%
631
March1st to 15thNight
22%15%31%27%3
720
16th to endNight
22%15%27%24%8%
768
April1st to 15thNight
24%16%27%24%6%
718
16th to endNight
25%16%25%22%8%
606
May1st to 15thNight
22%13%29%26%7%
472
16th to endNight
19%11%24%30%13%
375
June1st to 15thNight
25%7%24%30%11%
360
16th to endNight
15%325%42%12%
360
July1st to 15thNight
15%216%42%20%1
340
16th to endNight
13%118%44%20%
376
August1st to 15thNight
14%417%39%22%
422
16th to endNight
14%5%16%34%24%3
739
September1st to 15thNight
18%6%18%35%18%2
720
16th to endNight
16%7%19%27%24%4
717
October1st to 15thNight
22%10%19%29%15%1
720
16th to endNight
25%13%25%24%10%
768
November1st to 15thNight
21%13%25%27%10%1
760
16th to endNight
22%16%25%24%10%
780
December1st to 15thNight
27%16%28%22%3
728
16th to endNight
27%17%28%23%3
768
Page generated at 2017-12-03 11:16:40. Version ac04

Copyright 2017 A. Danko


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