Watertown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Watertown clear sky chart from 2005-11-06 to 2024-01-27.

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%
22786
12%
74965
7%
22744
30%
22744
13%
55807

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
10%
760
7%
2649
3%
757
15%
757
5%
2245
January11th to 20thNight
12%
760
7%
2660
4%
760
16%
760
6%
2248
January21st to endNight
15%
820
8%
2740
4%
820
20%
820
8%
2183
February1st to 10thNight
9%
720
5%
2340
1%
720
14%
720
5%
2007
February11th to 20thNight
12%
703
10%
2251
3%
700
22%
700
8%
1800
February21st to endNight
15%
592
11%
1776
4%
592
23%
592
10%
1390
March1st to 10thNight
17%
720
12%
2145
7%
720
23%
720
12%
1665
March11th to 20thNight
17%
720
14%
1980
6%
720
25%
720
14%
1506
March21st to endNight
20%
792
17%
2070
6%
792
28%
792
17%
1548
April1st to 10thNight
18%
720
14%
1800
3%
720
23%
720
16%
1364
April11th to 20thNight
23%
711
14%
1775
5%
711
28%
711
18%
1328
April21st to endNight
26%
686
15%
1766
5%
686
31%
686
19%
1298
May1st to 10thNight
32%
360
15%
1440
14%
360
38%
360
14%
971
May11th to 20thNight
28%
354
19%
1416
13%
354
42%
354
18%
873
May21st to endNight
37%
388
14%
1551
12%
388
48%
388
20%
944
June1st to 10thNight
34%
360
12%
1440
10%
360
44%
360
16%
943
June11th to 20thNight
39%
360
14%
1440
17%
360
48%
360
20%
864
June21st to endNight
35%
360
11%
1440
11%
360
44%
360
18%
916
July1st to 10thNight
51%
350
15%
1400
20%
350
58%
350
25%
781
July11th to 20thNight
47%
348
17%
1392
20%
348
56%
348
24%
801
July21st to endNight
44%
394
15%
1486
15%
372
49%
372
23%
872
August1st to 10thNight
48%
451
15%
1515
13%
449
52%
449
25%
932
August11th to 20thNight
49%
565
16%
1629
11%
565
53%
565
26%
1093
August21st to endNight
44%
792
17%
1980
8%
792
47%
792
30%
1330
September1st to 10thNight
43%
720
14%
1800
6%
720
45%
720
30%
1240
September11th to 20thNight
47%
720
23%
1800
13%
720
51%
720
36%
1151
September21st to endNight
41%
720
20%
2033
16%
720
44%
720
25%
1379
October1st to 10thNight
29%
720
13%
2160
10%
720
34%
720
17%
1570
October11th to 20thNight
24%
720
11%
2160
7%
720
30%
720
15%
1623
October21st to endNight
17%
792
9%
2488
4%
792
25%
792
9%
2003
November1st to 10thNight
22%
740
13%
2407
9%
740
27%
740
14%
1747
November11th to 20thNight
19%
760
14%
2604
9%
760
26%
760
11%
1945
November21st to endNight
16%
760
8%
2660
5%
760
21%
760
7%
2174
December1st to 10thNight
11%
760
5%
2660
2%
760
14%
760
5%
2307
December11th to 20thNight
10%
759
7%
3267
3%
759
15%
759
5%
2691
December21st to endNight
8%
829
3%
4845
0%
817
11%
817
2%
4075

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
19%11%47%6%35%45%7%31%
74848
Night
19%12%48%6%34446%29%
75196
TransparencyDay
54%5%12%19%9%1
74553
Night
57%6%11%17%8%1
75025
SeeingDay
26%18%30%17%7%2
13496
Night
26%17%28%22%7%1
22795

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
17%20%9%13%8%3444415%
1517
11th to 20thDay
19%19%7%11%8%3433419%
1520
21st to endDay
14%17%8%13%8%45%45%5%17%
1758
February1st to 10thDay
16%18%8%13%8%4445%5%15%
1620
11th to 20thDay
16%18%5%12%8%35%335%22%
1596
21st to endDay
19%16%8%10%7%25%345%21%
1480
March1st to 10thDay
16%16%7%10%6%35%33426%
1810
11th to 20thDay
18%15%5%8%6%4435%5%27%
1980
21st to endDay
22%11%46%5%24345%35%
2286
April1st to 10thDay
22%13%445%24445%33%
2160
11th to 20thDay
22%9%2443445%6%37%
2134
21st to endDay
23%10%35%5%35%346%32%
2207
May1st to 10thDay
20%8%36%5%45%5%46%34%
2520
11th to 20thDay
17%7%35%435%5%6%8%38%
2478
21st to endDay
16%6%35%5%35%5%6%9%38%
2725
June1st to 10thDay
22%7%35%435%46%7%33%
2520
11th to 20thDay
19%5%25%425%5%6%8%38%
2520
21st to endDay
19%6%25%5%35%5%5%8%35%
2520
July1st to 10thDay
13%4246%245%6%10%44%
2520
11th to 20thDay
14%6%25%5%35%5%6%9%41%
2520
21st to endDay
13%5%26%5%35%6%6%9%39%
2744
August1st to 10thDay
13%6%25%5%35%6%7%9%41%
2410
11th to 20thDay
14%6%25%5%45%5%7%9%38%
2254
21st to endDay
16%5%25%6%25%5%5%9%38%
2376
September1st to 10thDay
16%6%35%5%3445%8%42%
2160
11th to 20thDay
15%6%245%24448%45%
2160
21st to endDay
19%5%36%5%345%5%8%38%
1923
October1st to 10thDay
23%9%37%43445%6%31%
1800
11th to 20thDay
24%10%37%5%35%5%5%6%27%
1800
21st to endDay
30%10%37%5%35%446%23%
1868
November1st to 10thDay
16%12%46%7%3446%8%29%
1671
11th to 20thDay
16%14%5%8%8%44446%26%
1573
21st to endDay
20%19%5%9%7%45%45%5%17%
1520
December1st to 10thDay
23%22%7%9%7%35%345%13%
1520
11th to 20thDay
20%23%7%9%7%44435%15%
1906
21st to endDay
27%18%7%11%7%3342314%
2772
January1st to 10thNight
18%22%8%11%7%3433316%
2649
11th to 20thNight
17%19%7%11%8%345%4417%
2660
21st to endNight
14%17%6%11%7%5%443423%
2740
February1st to 10thNight
18%16%8%14%9%45%43416%
2340
11th to 20thNight
15%15%8%11%6%45%445%23%
2249
21st to endNight
17%14%8%9%6%44446%24%
1776
March1st to 10thNight
16%16%6%9%7%34445%27%
2135
11th to 20thNight
20%14%5%7%6%23345%30%
1979
21st to endNight
21%11%47%6%33345%33%
2070
April1st to 10thNight
23%11%47%5%34445%31%
1800
11th to 20thNight
22%9%36%5%25%45%6%32%
1775
21st to endNight
23%9%35%5%3445%6%33%
1766
May1st to 10thNight
24%7%25%5%245%5%7%33%
1440
11th to 20thNight
14%8%36%5%35%5%6%8%39%
1415
21st to endNight
13%6%25%6%35%5%6%8%41%
1550
June1st to 10thNight
18%8%25%6%25%5%5%6%36%
1440
11th to 20thNight
17%5%25%436%45%10%40%
1440
21st to endNight
15%7%45%6%35%5%6%8%36%
1440
July1st to 10thNight
12%425%5%25%6%5%9%47%
1440
11th to 20thNight
12%6%25%5%35%5%5%9%44%
1440
21st to endNight
13%6%245%246%7%8%43%
1574
August1st to 10thNight
12%6%26%5%345%7%8%42%
1525
11th to 20thNight
14%6%26%5%4446%7%40%
1629
21st to endNight
11%6%26%6%345%6%8%42%
1980
September1st to 10thNight
16%6%25%4246%5%6%42%
1800
11th to 20thNight
15%5%245%14447%50%
1800
21st to endNight
16%7%25%5%35%45%7%40%
2033
October1st to 10thNight
23%8%38%5%34445%32%
2160
11th to 20thNight
22%9%47%6%3445%6%29%
2160
21st to endNight
29%12%37%6%3445%423%
2488
November1st to 10thNight
18%13%46%6%3445%6%31%
2407
11th to 20thNight
18%13%5%7%6%3445%6%29%
2604
21st to endNight
24%17%5%7%6%445%5%5%20%
2660
December1st to 10thNight
22%23%6%9%6%35%43413%
2660
11th to 20thNight
21%20%6%10%6%2443420%
3288
21st to endNight
29%17%7%11%6%34335%14%
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
74%49%10%3
1518
11th to 20thDay
73%46%10%6%1
1520
21st to endDay
71%5%7%11%5%1
1758
February1st to 10thDay
74%48%10%31
1620
11th to 20thDay
69%38%13%7%1
1605
21st to endDay
68%5%8%12%6%
1480
March1st to 10thDay
64%49%15%7%1
1813
11th to 20thDay
61%410%14%9%2
1980
21st to endDay
55%28%19%13%3
2286
April1st to 10thDay
55%48%19%11%2
2160
11th to 20thDay
49%48%23%13%2
2134
21st to endDay
54%411%17%11%3
2207
May1st to 10thDay
53%49%18%13%2
2520
11th to 20thDay
43%7%11%24%13%2
2482
21st to endDay
43%7%16%20%11%2
2725
June1st to 10thDay
50%5%13%19%11%1
2520
11th to 20thDay
45%5%13%25%11%1
2520
21st to endDay
46%7%15%20%11%1
2520
July1st to 10thDay
37%6%14%28%14%1
2450
11th to 20thDay
40%6%18%29%8%
2445
21st to endDay
40%8%17%23%11%
2591
August1st to 10thDay
41%6%18%25%10%
2396
11th to 20thDay
42%8%18%24%8%
2254
21st to endDay
43%7%14%27%8%1
2376
September1st to 10thDay
43%5%14%26%11%1
2160
11th to 20thDay
40%5%11%28%15%1
2160
21st to endDay
46%5%14%25%10%1
1923
October1st to 10thDay
55%5%9%21%9%
1800
11th to 20thDay
58%6%14%17%5%1
1800
21st to endDay
63%6%10%13%7%1
1868
November1st to 10thDay
55%7%15%16%7%1
1671
11th to 20thDay
60%6%11%14%7%3
1573
21st to endDay
71%5%10%9%5%
1520
December1st to 10thDay
76%5%10%7%1
1520
11th to 20thDay
74%6%8%9%3
1906
21st to endDay
76%5%5%12%2
2772
January1st to 10thNight
75%48%10%3
2649
11th to 20thNight
73%6%7%10%41
2660
21st to endNight
66%48%13%7%1
2740
February1st to 10thNight
75%48%9%4
2340
11th to 20thNight
66%5%8%15%6%
2251
21st to endNight
62%5%11%15%6%
1776
March1st to 10thNight
63%410%15%7%1
2145
11th to 20thNight
58%5%9%19%9%1
1980
21st to endNight
55%47%18%13%3
2070
April1st to 10thNight
56%39%21%9%2
1800
11th to 20thNight
54%5%8%19%14%1
1775
21st to endNight
53%5%10%18%13%2
1766
May1st to 10thNight
52%5%9%17%14%4
1440
11th to 20thNight
44%6%11%23%14%3
1416
21st to endNight
41%6%15%21%15%2
1551
June1st to 10thNight
47%7%13%23%9%1
1440
11th to 20thNight
41%5%15%20%17%2
1440
21st to endNight
44%8%14%23%11%1
1440
July1st to 10thNight
33%8%15%25%18%2
1400
11th to 20thNight
37%6%14%31%12%1
1392
21st to endNight
37%8%15%28%11%1
1486
August1st to 10thNight
38%8%17%27%9%1
1515
11th to 20thNight
42%7%14%25%12%
1629
21st to endNight
37%8%15%29%10%
1980
September1st to 10thNight
40%8%14%26%11%2
1800
11th to 20thNight
36%414%30%15%1
1800
21st to endNight
43%6%13%26%11%1
2033
October1st to 10thNight
54%6%11%18%10%1
2160
11th to 20thNight
55%7%13%17%6%1
2160
21st to endNight
66%6%10%11%7%1
2488
November1st to 10thNight
54%7%13%17%8%2
2407
11th to 20thNight
58%6%10%16%6%2
2604
21st to endNight
67%7%10%12%4
2660
December1st to 10thNight
76%5%9%8%2
2660
11th to 20thNight
71%5%9%10%5%
3288
21st to endNight
75%6%9%9%2
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
32%25%25%14%4
180
11th to 20thDay
31%25%28%14%11
180
21st to endDay
30%25%30%13%2
246
February1st to 10thDay
41%29%24%6%
240
11th to 20thDay
34%31%29%5%
263
21st to endDay
35%27%27%10%1
346
March1st to 10thDay
30%22%32%12%4
420
11th to 20thDay
32%23%32%10%3
420
21st to endDay
37%20%26%11%5%1
462
April1st to 10thDay
38%20%26%13%4
420
11th to 20thDay
34%20%22%16%5%3
412
21st to endDay
34%20%27%12%42
420
May1st to 10thDay
29%20%27%15%7%1
423
11th to 20thDay
24%14%34%21%6%1
447
21st to endDay
21%14%34%18%12%1
485
June1st to 10thDay
27%16%32%18%6%1
450
11th to 20thDay
22%13%34%21%7%3
450
21st to endDay
23%13%36%20%6%1
450
July1st to 10thDay
15%11%31%27%13%2
445
11th to 20thDay
18%9%34%26%10%3
444
21st to endDay
16%10%39%28%7%1
488
August1st to 10thDay
13%9%33%29%11%4
446
11th to 20thDay
17%10%27%28%14%5%
439
21st to endDay
16%13%33%22%12%5%
495
September1st to 10thDay
16%15%31%22%12%5%
450
11th to 20thDay
16%12%28%21%17%6%
450
21st to endDay
17%17%28%23%12%3
450
October1st to 10thDay
29%16%25%16%10%4
450
11th to 20thDay
30%21%28%14%5%2
450
21st to endDay
38%19%25%15%3
439
November1st to 10thDay
28%22%28%15%7%
365
11th to 20thDay
30%21%33%10%6%
233
21st to endDay
28%34%27%9%2
180
December1st to 10thDay
45%17%24%13%2
180
11th to 20thDay
35%28%30%6%1
180
21st to endDay
33%24%32%9%1
198
January1st to 10thNight
31%25%25%15%3
760
11th to 20thNight
28%26%27%16%3
760
21st to endNight
23%23%31%18%5%
820
February1st to 10thNight
28%28%28%15%1
720
11th to 20thNight
27%21%33%16%2
703
21st to endNight
26%24%31%16%2
592
March1st to 10thNight
26%20%32%19%3
720
11th to 20thNight
31%22%27%17%4
720
21st to endNight
28%17%31%19%5%1
792
April1st to 10thNight
31%18%29%20%2
720
11th to 20thNight
28%18%28%22%5%
711
21st to endNight
31%14%26%21%7%1
686
May1st to 10thNight
26%11%27%28%8%1
360
11th to 20thNight
18%11%37%28%6%
354
21st to endNight
15%10%32%30%12%1
389
June1st to 10thNight
24%8%28%32%8%
360
11th to 20thNight
19%8%29%31%13%
360
21st to endNight
16%10%32%34%7%
360
July1st to 10thNight
11%6%26%40%16%1
350
11th to 20thNight
14%5%28%34%18%2
348
21st to endNight
13%7%30%37%11%1
394
August1st to 10thNight
15%5%26%38%15%1
451
11th to 20thNight
16%6%21%35%19%3
565
21st to endNight
13%8%28%33%16%1
792
September1st to 10thNight
17%8%27%31%15%2
720
11th to 20thNight
17%7%26%29%18%4
720
21st to endNight
18%15%23%26%17%2
720
October1st to 10thNight
28%15%24%18%14%2
720
11th to 20thNight
28%17%26%21%7%1
720
21st to endNight
36%16%27%20%2
792
November1st to 10thNight
29%16%29%19%8%
740
11th to 20thNight
27%20%31%15%7%1
760
21st to endNight
35%22%23%16%4
760
December1st to 10thNight
37%24%23%14%2
760
11th to 20thNight
30%27%28%12%21
760
21st to endNight
36%23%27%13%1
836
Page generated at 2024-01-24 09:37:27. Version ac07

Copyright 2024 Attilla Danko


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