Weston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weston clear sky chart from 2005-11-05 to 2017-09-18.

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
65%
16254
19%
46952
16%
16214
68%
16214
30%
29640

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
57%
716
18%
2327
16%
716
62%
716
27%
1427
January16th to endNight
55%
768
25%
2469
21%
768
62%
768
32%
1406
February1st to 15thNight
53%
703
27%
2098
21%
699
60%
699
35%
1230
February16th to endNight
59%
631
31%
1735
21%
631
67%
631
42%
981
March1st to 15thNight
60%
720
26%
1980
18%
720
68%
720
42%
1114
March16th to endNight
62%
768
27%
2112
22%
768
65%
768
41%
1208
April1st to 15thNight
70%
718
25%
1976
22%
718
73%
718
49%
1050
April16th to endNight
67%
720
25%
1806
16%
720
70%
720
43%
1077
May1st to 15thNight
74%
719
25%
1799
17%
719
76%
719
49%
1021
May16th to endNight
72%
604
16%
1726
14%
604
73%
604
29%
1129
June1st to 15thNight
65%
540
8%
1620
7%
540
65%
540
17%
1203
June16th to endNight
76%
540
8%
1620
8%
540
76%
540
24%
1112
July1st to 15thNight
72%
510
6%
1530
6%
510
72%
510
20%
1105
July16th to endNight
82%
564
9%
1595
9%
531
83%
531
30%
1038
August1st to 15thNight
77%
608
7%
1678
6%
605
77%
605
28%
1124
August16th to endNight
70%
764
6%
2021
5%
764
70%
764
21%
1472
September1st to 15thNight
67%
720
4%
1980
4%
720
67%
720
18%
1481
September16th to endNight
60%
669
6%
1848
6%
669
60%
669
15%
1432
October1st to 15thNight
68%
660
18%
1919
20%
660
69%
660
25%
1274
October16th to endNight
58%
704
19%
2112
19%
704
61%
704
26%
1389
November1st to 15thNight
67%
700
28%
2101
27%
700
72%
700
37%
1221
November16th to endNight
59%
720
26%
2160
24%
720
65%
720
30%
1357
December1st to 15thNight
62%
720
24%
2244
22%
720
67%
720
29%
1377
December16th to endNight
66%
768
24%
2496
24%
768
70%
768
33%
1412

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
9%6%38%8%5%7%7%7%8%27%
47824
Night
6%425%5%35%6%7%10%41%
47158
TransparencyDay
49%8%13%15%10%2
47525
Night
35%8%18%22%12%3
46961
SeeingDay
9%311%21%26%27%
6063
Night
7%212%31%32%13%
16262

By Month

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
8%6%37%6%37%6%8%8%32%
1611
16th to endDay
7%6%36%6%46%6%6%8%37%
1752
February1st to 15thDay
11%6%25%6%35%46%8%39%
1756
16th to endDay
7%425%5%45%5%5%9%42%
1738
March1st to 15thDay
6%425%6%46%7%6%9%39%
1980
16th to endDay
6%5%27%7%36%7%7%9%36%
2111
April1st to 15thDay
5%336%6%5%6%7%6%11%36%
1972
16th to endDay
7%426%7%47%6%5%11%35%
2154
May1st to 15thDay
4325%7%48%6%7%8%40%
2152
16th to endDay
9%7%48%8%6%7%8%7%9%21%
2395
June1st to 15thDay
12%9%5%10%11%6%8%7%6%7%15%
2340
16th to endDay
9%7%410%10%7%9%8%8%9%15%
2340
July1st to 15thDay
9%8%49%11%6%8%8%8%7%16%
2340
16th to endDay
8%6%410%10%5%9%8%8%10%18%
2465
August1st to 15thDay
9%7%38%10%6%8%8%8%10%18%
2256
16th to endDay
9%6%310%9%6%8%9%9%9%16%
2176
September1st to 15thDay
9%6%5%12%12%7%9%8%7%8%14%
1980
16th to endDay
13%10%5%12%10%5%7%8%6%414%
1837
October1st to 15thDay
9%5%39%10%5%8%7%9%8%20%
1711
16th to endDay
14%7%37%7%46%6%6%7%28%
1760
November1st to 15thDay
6%5%36%7%5%6%6%6%8%37%
1757
16th to endDay
10%6%36%6%46%6%6%8%35%
1800
December1st to 15thDay
10%6%47%7%37%5%6%6%34%
1713
16th to endDay
7%5%35%5%37%6%7%9%37%
1728
January1st to 15thNight
8%435%5%35%6%7%10%40%
2327
16th to endNight
4424435%5%7%9%47%
2469
February1st to 15thNight
9%4244345%5%8%48%
2096
16th to endNight
43135%25%5%6%8%54%
1735
March1st to 15thNight
43143346%6%10%51%
1980
16th to endNight
5%31442446%10%50%
2112
April1st to 15thNight
311332446%10%57%
1976
16th to endNight
5%3243245%7%9%50%
1806
May1st to 15thNight
2213425%5%411%56%
1799
16th to endNight
7%5%345%36%6%8%13%35%
1725
June1st to 15thNight
11%6%36%7%47%7%8%11%24%
1620
16th to endNight
4425%7%38%8%10%13%31%
1620
July1st to 15thNight
5%5%37%7%5%6%6%8%11%32%
1620
16th to endNight
3425%5%46%6%9%13%39%
1703
August1st to 15thNight
4325%6%46%6%8%14%37%
1689
16th to endNight
7%426%6%46%9%8%12%30%
2021
September1st to 15thNight
6%446%8%5%7%8%11%12%25%
1980
16th to endNight
7%6%38%8%6%7%8%8%10%24%
1848
October1st to 15thNight
6%5%25%7%36%7%8%11%35%
1919
16th to endNight
11%7%26%5%35%5%6%8%37%
2112
November1st to 15thNight
6%3246%35%5%5%9%48%
2101
16th to endNight
8%5%26%5%36%45%8%44%
2160
December1st to 15thNight
7%425%5%35%6%6%10%43%
2244
16th to endNight
5%324425%7%6%10%47%
2496

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
46%6%13%16%13%5%
1612
16th to endDay
41%410%21%15%5%
1752
February1st to 15thDay
42%38%20%18%6%
1758
16th to endDay
36%410%24%17%6%
1738
March1st to 15thDay
38%411%23%17%3
1980
16th to endDay
41%5%10%21%15%6%
2112
April1st to 15thDay
38%5%14%23%15%2
1972
16th to endDay
41%6%10%20%17%3
2154
May1st to 15thDay
36%5%13%24%13%6%
2152
16th to endDay
54%7%13%17%6%
2399
June1st to 15thDay
64%9%12%9%3
2340
16th to endDay
57%13%18%9%1
2340
July1st to 15thDay
58%12%21%6%
2201
16th to endDay
55%11%24%8%
2310
August1st to 15thDay
53%11%21%11%
2243
16th to endDay
55%14%20%8%
2176
September1st to 15thDay
61%13%16%7%
1980
16th to endDay
68%9%11%6%2
1837
October1st to 15thDay
54%9%11%14%7%1
1711
16th to endDay
52%5%8%14%14%4
1760
November1st to 15thDay
42%49%18%18%5%
1757
16th to endDay
45%5%8%13%18%7%
1800
December1st to 15thDay
48%5%9%17%15%3
1713
16th to endDay
41%5%10%23%16%3
1728
January1st to 15thNight
38%5%16%23%13%2
2327
16th to endNight
31%6%13%27%16%4
2469
February1st to 15thNight
32%49%27%18%7%
2105
16th to endNight
26%5%14%27%19%5%
1735
March1st to 15thNight
26%5%13%28%20%5%
1980
16th to endNight
28%5%16%27%17%4
2112
April1st to 15thNight
21%5%19%32%18%3
1976
16th to endNight
28%5%14%27%20%4
1806
May1st to 15thNight
22%6%16%33%16%4
1800
16th to endNight
37%8%19%27%7%
1727
June1st to 15thNight
49%12%21%13%3
1620
16th to endNight
36%15%33%13%1
1620
July1st to 15thNight
43%14%30%11%
1530
16th to endNight
31%13%37%15%1
1595
August1st to 15thNight
33%14%33%17%1
1678
16th to endNight
39%17%29%12%
2021
September1st to 15thNight
43%16%27%10%1
1980
16th to endNight
50%14%20%11%3
1848
October1st to 15thNight
39%9%17%20%11%1
1919
16th to endNight
43%5%12%21%13%4
2112
November1st to 15thNight
32%312%23%21%5%
2101
16th to endNight
38%410%19%17%8%
2160
December1st to 15thNight
36%6%14%23%16%2
2244
16th to endNight
32%5%13%26%19%3
2496

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%8%33%27%13%1
90
16th to endDay
17%10%27%33%7%4
96
February1st to 15thDay
10%6%25%39%12%6%
97
16th to endDay
8%225%34%25%2
239
March1st to 15thDay
5%427%34%24%4
270
16th to endDay
7%320%36%25%6%
288
April1st to 15thDay
4420%29%28%12%
270
16th to endDay
7%117%26%31%15%
270
May1st to 15thDay
3115%21%34%22%
288
16th to endDay
6%25%24%33%28%
331
June1st to 15thDay
14%36%15%26%33%
315
16th to endDay
5%1112%26%52%
315
July1st to 15thDay
6%19%25%56%
305
16th to endDay
7%317%23%56%
326
August1st to 15thDay
10%38%22%55%
313
16th to endDay
15%319%24%45%
332
September1st to 15thDay
7%329%21%55%
315
16th to endDay
17%117%22%49%
262
October1st to 15thDay
9%25%25%36%19%
255
16th to endDay
14%219%24%25%14%
272
November1st to 15thDay
8%311%30%33%12%
265
16th to endDay
8%222%30%33%2
270
December1st to 15thDay
20%211%34%22%7%
183
16th to endDay
7%415%42%26%4
96
January1st to 15thNight
9%418%37%26%2
720
16th to endNight
6%425%42%19%1
768
February1st to 15thNight
9%324%41%19%1
704
16th to endNight
6%423%47%17%
631
March1st to 15thNight
6%323%42%22%1
720
16th to endNight
6%320%45%23%1
768
April1st to 15thNight
3216%47%26%2
718
16th to endNight
8%215%44%27%1
720
May1st to 15thNight
4111%45%35%2
720
16th to endNight
7%3433%40%10%
606
June1st to 15thNight
11%3317%41%23%
540
16th to endNight
4118%47%36%
540
July1st to 15thNight
6%18%43%39%
510
16th to endNight
315%42%48%
564
August1st to 15thNight
6%16%44%40%
608
16th to endNight
9%2212%39%34%
764
September1st to 15thNight
8%1210%39%37%
720
16th to endNight
10%114%43%29%
669
October1st to 15thNight
9%5%31%41%11%
660
16th to endNight
15%210%30%30%10%
704
November1st to 15thNight
6%216%37%31%6%
700
16th to endNight
8%316%39%27%3
720
December1st to 15thNight
9%314%39%30%3
720
16th to endNight
6%215%37%34%3
768
Page generated at 2017-09-19 07:32:28. Version ac04

Copyright 2017 A. Danko


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