Watch Observatory 2
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Watch Observatory 2 clear sky chart from 2005-11-05 to 2017-12-01.

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
25%
14952
14%
47785
7%
14920
33%
14920
15%
33846

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
13%
720
7%
2506
2%
716
19%
716
7%
2016
January16th to endNight
15%
768
11%
2682
4%
768
24%
768
9%
2006
February1st to 15thNight
13%
704
10%
2287
4%
701
21%
701
9%
1767
February16th to endNight
18%
631
14%
1910
5%
631
29%
631
11%
1417
March1st to 15thNight
16%
720
13%
2147
6%
720
25%
720
12%
1604
March16th to endNight
25%
768
21%
2001
8%
768
34%
768
19%
1393
April1st to 15thNight
21%
718
17%
1796
5%
718
27%
718
18%
1324
April16th to endNight
21%
648
17%
1728
3%
648
31%
648
17%
1220
May1st to 15thNight
25%
369
17%
1449
12%
369
38%
369
13%
966
May16th to endNight
26%
375
14%
1497
7%
374
42%
374
15%
957
June1st to 15thNight
27%
360
10%
1440
7%
360
37%
360
12%
985
June16th to endNight
33%
360
10%
1440
9%
360
43%
360
16%
899
July1st to 15thNight
44%
340
15%
1360
19%
340
51%
340
23%
764
July16th to endNight
41%
376
13%
1418
14%
354
52%
354
23%
816
August1st to 15thNight
48%
389
15%
1460
14%
387
54%
387
22%
871
August16th to endNight
44%
749
19%
1895
8%
749
50%
749
32%
1218
September1st to 15thNight
43%
720
15%
1800
7%
720
46%
720
28%
1231
September16th to endNight
45%
717
23%
1952
15%
717
51%
717
31%
1231
October1st to 15thNight
30%
720
18%
2148
10%
720
40%
720
20%
1457
October16th to endNight
22%
768
11%
2439
6%
768
29%
768
13%
1816
November1st to 15thNight
24%
760
16%
2480
10%
760
34%
760
14%
1745
November16th to endNight
17%
780
11%
2730
5%
780
26%
780
10%
2013
December1st to 15thNight
13%
724
8%
2532
3%
724
19%
724
7%
1985
December16th to endNight
8%
768
10%
2688
2%
768
17%
768
6%
2145

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
17%8%36%5%35%45%6%32%
48648
Night
18%9%46%5%34446%32%
47954
Cloud CoverDay
17%8%36%5%3445%6%33%
48657
Night
18%9%36%5%34446%31%
47960
TransparencyDay
51%411%20%10%1
48335
Night
52%411%20%9%1
47785
SeeingDay
20%20%26%19%9%2
5790
Night
20%24%24%21%8%
14952

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
22%14%5%8%7%35%34420%
1432
16th to endDay
14%16%5%6%5%45%5%5%6%23%
1539
February1st to 15thDay
15%13%5%10%7%45%5%46%22%
1575
16th to endDay
18%12%6%7%7%35%335%26%
1563
March1st to 15thDay
17%12%410%8%3433427%
1802
16th to endDay
18%8%345%24445%38%
2223
April1st to 15thDay
22%8%37%5%33335%33%
2152
16th to endDay
20%7%36%5%34345%35%
2232
May1st to 15thDay
20%6%36%5%35%446%33%
2511
16th to endDay
19%6%25%5%2445%7%34%
2618
June1st to 15thDay
23%6%35%6%25%45%8%30%
2520
16th to endDay
18%5%35%5%36%6%6%8%31%
2520
July1st to 15thDay
12%5%36%436%46%7%39%
2520
16th to endDay
12%5%25%5%46%5%8%9%35%
2654
August1st to 15thDay
12%5%26%6%45%5%5%9%35%
2487
16th to endDay
10%4145%35%6%5%8%43%
2294
September1st to 15thDay
15%5%344245%46%43%
2160
16th to endDay
13%5%24423347%47%
2007
October1st to 15thDay
19%7%36%5%3445%5%35%
1810
16th to endDay
22%10%37%5%345%4426%
1785
November1st to 15thDay
16%8%35%5%46%5%47%31%
1706
16th to endDay
21%9%47%6%4435%6%26%
1560
December1st to 15thDay
24%12%47%6%45%45%5%18%
1442
16th to endDay
25%15%48%5%3433321%
1536
January1st to 15thNight
19%14%6%10%6%345%4419%
2506
16th to endNight
13%15%6%8%6%45%445%25%
2682
February1st to 15thNight
14%12%5%10%8%46%446%21%
2285
16th to endNight
16%11%6%8%5%35%5%4427%
1910
March1st to 15thNight
19%11%46%7%24345%28%
2134
16th to endNight
16%9%35%5%23335%40%
2001
April1st to 15thNight
25%6%36%5%24335%33%
1796
16th to endNight
21%6%35%5%34345%36%
1728
May1st to 15thNight
21%8%35%5%23345%36%
1449
16th to endNight
17%6%35%5%245%5%7%37%
1495
June1st to 15thNight
23%6%346%2445%6%31%
1440
16th to endNight
15%5%25%5%25%6%5%9%35%
1440
July1st to 15thNight
9%315%435%6%6%10%41%
1440
16th to endNight
11%4245%25%5%6%8%43%
1514
August1st to 15thNight
10%435%6%25%46%10%40%
1470
16th to endNight
11%5%234336%5%7%47%
1895
September1st to 15thNight
15%5%26%5%3435%6%40%
1800
16th to endNight
15%5%13334346%47%
1952
October1st to 15thNight
18%7%25%43435%6%38%
2148
16th to endNight
23%8%47%5%35%445%28%
2439
November1st to 15thNight
20%8%26%5%35%345%33%
2480
16th to endNight
20%10%48%6%34445%26%
2730
December1st to 15thNight
22%15%5%7%6%3443421%
2532
16th to endNight
24%16%47%6%2434321%
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
22%13%5%8%7%3434420%
1432
16th to endDay
14%15%5%6%6%45%5%47%23%
1539
February1st to 15thDay
15%12%5%10%6%36%5%5%6%22%
1575
16th to endDay
18%11%6%7%5%35%435%26%
1563
March1st to 15thDay
17%11%5%9%7%4443328%
1812
16th to endDay
19%7%35%5%24336%38%
2222
April1st to 15thDay
22%8%37%5%33445%32%
2152
16th to endDay
19%7%35%6%24346%35%
2232
May1st to 15thDay
19%7%35%5%245%46%33%
2511
16th to endDay
18%6%26%43445%8%35%
2618
June1st to 15thDay
22%5%35%5%3445%8%30%
2520
16th to endDay
17%5%25%5%36%5%6%9%31%
2520
July1st to 15thDay
11%6%25%5%35%5%6%8%39%
2520
16th to endDay
12%5%245%45%5%7%9%37%
2654
August1st to 15thDay
11%5%26%6%46%5%6%8%36%
2487
16th to endDay
10%3245%35%5%5%8%45%
2294
September1st to 15thDay
15%5%25%5%24447%43%
2160
16th to endDay
13%424324446%48%
2007
October1st to 15thDay
19%7%25%434445%35%
1810
16th to endDay
22%10%37%5%345%45%26%
1785
November1st to 15thDay
16%9%36%5%35%45%7%31%
1706
16th to endDay
21%9%37%6%3445%7%25%
1560
December1st to 15thDay
24%13%47%6%35%5%5%6%17%
1442
16th to endDay
26%14%5%7%5%2435%319%
1536
January1st to 15thNight
19%14%5%10%7%3445%418%
2506
16th to endNight
14%16%5%8%7%35%34425%
2682
February1st to 15thNight
14%13%5%11%7%46%445%20%
2278
16th to endNight
16%11%5%8%7%245%45%27%
1910
March1st to 15thNight
20%11%47%6%3434428%
2147
16th to endNight
17%10%4442334439%
2001
April1st to 15thNight
25%7%35%5%2335%5%32%
1796
16th to endNight
21%7%25%5%24445%36%
1728
May1st to 15thNight
21%8%35%5%33335%36%
1449
16th to endNight
18%5%35%5%3445%6%36%
1495
June1st to 15thNight
24%6%35%435%45%8%29%
1440
16th to endNight
15%5%26%425%6%5%8%36%
1440
July1st to 15thNight
9%424436%5%7%9%42%
1440
16th to endNight
11%425%425%5%6%8%43%
1514
August1st to 15thNight
10%5%25%5%345%6%10%40%
1470
16th to endNight
12%41443346%8%46%
1895
September1st to 15thNight
16%5%27%433446%41%
1800
16th to endNight
16%423334447%47%
1952
October1st to 15thNight
19%7%25%42435%6%37%
2148
16th to endNight
23%8%37%6%3445%428%
2439
November1st to 15thNight
21%8%36%5%34446%32%
2480
16th to endNight
21%10%48%5%24445%26%
2730
December1st to 15thNight
23%14%5%7%6%3444420%
2532
16th to endNight
25%16%5%6%6%2443420%
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
67%37%15%5%
1433
16th to endDay
60%411%14%8%
1539
February1st to 15thDay
63%210%19%3
1577
16th to endDay
60%310%15%9%1
1563
March1st to 15thDay
61%211%15%7%1
1812
16th to endDay
48%38%18%16%4
2223
April1st to 15thDay
54%26%20%12%2
2152
16th to endDay
50%37%19%14%4
2232
May1st to 15thDay
51%48%19%13%1
2511
16th to endDay
48%411%20%12%1
2622
June1st to 15thDay
53%411%20%10%
2520
16th to endDay
48%5%14%20%10%
2520
July1st to 15thDay
39%6%13%27%12%
2371
16th to endDay
42%6%17%24%8%
2487
August1st to 15thDay
43%6%16%23%8%
2473
16th to endDay
35%5%16%28%12%
2294
September1st to 15thDay
40%5%12%28%12%
2160
16th to endDay
37%312%34%11%
2007
October1st to 15thDay
49%410%24%10%
1810
16th to endDay
59%413%15%7%
1785
November1st to 15thDay
51%5%14%18%9%
1706
16th to endDay
58%5%12%16%6%
1560
December1st to 15thDay
66%5%12%12%2
1442
16th to endDay
68%410%11%5%
1536
January1st to 15thNight
67%5%9%12%4
2506
16th to endNight
60%310%17%7%
2682
February1st to 15thNight
64%311%16%4
2287
16th to endNight
57%39%18%9%
1910
March1st to 15thNight
58%39%18%8%1
2147
16th to endNight
47%28%21%15%4
2001
April1st to 15thNight
53%26%20%14%1
1796
16th to endNight
49%37%18%16%3
1728
May1st to 15thNight
50%47%18%15%4
1449
16th to endNight
45%5%10%21%13%2
1497
June1st to 15thNight
53%411%20%9%
1440
16th to endNight
43%5%13%20%15%
1440
July1st to 15thNight
33%7%13%29%16%
1360
16th to endNight
36%6%17%24%14%
1418
August1st to 15thNight
38%5%20%23%11%
1460
16th to endNight
34%5%15%31%11%
1895
September1st to 15thNight
43%311%27%13%
1800
16th to endNight
37%410%33%13%
1952
October1st to 15thNight
46%410%27%10%
2148
16th to endNight
58%313%17%6%
2439
November1st to 15thNight
52%414%18%8%1
2480
16th to endNight
59%312%17%5%
2730
December1st to 15thNight
65%411%15%2
2532
16th to endNight
68%310%13%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
25%25%18%25%6%
60
16th to endDay
32%23%24%15%4
65
February1st to 15thDay
34%28%30%5%1
90
16th to endDay
29%24%27%16%2
222
March1st to 15thDay
22%30%27%17%2
270
16th to endDay
22%26%25%16%5%2
288
April1st to 15thDay
25%28%27%11%5%1
270
16th to endDay
18%27%25%17%9%1
270
May1st to 15thDay
22%27%24%15%6%2
288
16th to endDay
19%25%30%14%8%1
331
June1st to 15thDay
24%20%31%18%41
315
16th to endDay
19%17%31%21%8%1
315
July1st to 15thDay
14%15%29%23%14%1
305
16th to endDay
14%13%25%29%13%3
326
August1st to 15thDay
12%11%26%32%12%5%
313
16th to endDay
10%10%29%25%16%8%
332
September1st to 15thDay
15%12%23%21%18%8%
315
16th to endDay
12%15%22%19%19%9%
314
October1st to 15thDay
21%18%22%20%15%1
315
16th to endDay
24%25%24%19%5%
302
November1st to 15thDay
20%24%24%20%9%1
270
16th to endDay
30%23%26%17%2
90
December1st to 15thDay
28%15%38%16%1
60
16th to endDay
42%18%35%3
64
January1st to 15thNight
19%32%29%15%3
720
16th to endNight
19%30%27%17%4
768
February1st to 15thNight
18%31%28%18%3
704
16th to endNight
20%30%25%19%4
631
March1st to 15thNight
24%29%25%17%3
720
16th to endNight
19%27%23%24%4
768
April1st to 15thNight
23%28%23%21%3
718
16th to endNight
22%27%24%17%7%
648
May1st to 15thNight
21%24%22%21%7%2
369
16th to endNight
16%22%31%21%8%
375
June1st to 15thNight
21%23%22%27%5%
360
16th to endNight
15%21%24%24%13%1
360
July1st to 15thNight
11%16%24%29%16%
340
16th to endNight
11%18%24%31%13%1
376
August1st to 15thNight
12%11%19%34%20%1
389
16th to endNight
12%14%23%27%19%2
749
September1st to 15thNight
16%13%22%31%14%1
720
16th to endNight
17%14%19%23%22%2
717
October1st to 15thNight
20%18%25%23%11%
720
16th to endNight
25%20%25%21%5%
768
November1st to 15thNight
20%24%25%21%8%
760
16th to endNight
21%31%24%14%8%
780
December1st to 15thNight
28%30%21%16%3
724
16th to endNight
29%31%22%10%4
768
Page generated at 2017-12-02 09:14:20. Version ac04

Copyright 2017 A. Danko


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