This page made possible by the sponsorship of: Dan Gray.

Shepherds Lair Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shepherds Lair Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
39%
14633
12%
46806
10%
14605
42%
14605
15%
34478

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
19%
718
10%
2506
5%
716
27%
716
9%
2002
January16th to endNight
23%
768
12%
2600
6%
768
30%
768
11%
1985
February1st to 15thNight
23%
700
6%
2288
3%
699
27%
699
9%
1876
February16th to endNight
23%
632
10%
1993
4%
632
30%
632
9%
1601
March1st to 15thNight
28%
720
6%
2056
5%
720
29%
720
10%
1725
March16th to endNight
25%
768
6%
2070
4%
768
27%
768
9%
1801
April1st to 15thNight
30%
719
5%
1799
3%
719
30%
719
10%
1543
April16th to endNight
38%
621
9%
1701
6%
621
39%
621
14%
1351
May1st to 15thNight
45%
374
13%
1454
15%
374
48%
374
16%
996
May16th to endNight
43%
375
7%
1496
10%
374
44%
374
10%
1151
June1st to 15thNight
45%
360
6%
1440
9%
360
46%
360
11%
1051
June16th to endNight
53%
360
10%
1440
17%
360
55%
360
17%
934
July1st to 15thNight
79%
340
16%
1360
26%
340
80%
340
36%
653
July16th to endNight
80%
376
27%
1416
40%
354
83%
354
44%
599
August1st to 15thNight
80%
505
23%
1579
24%
503
81%
503
44%
790
August16th to endNight
74%
669
29%
1815
22%
669
75%
669
48%
977
September1st to 15thNight
68%
700
25%
1750
14%
700
70%
700
49%
990
September16th to endNight
60%
656
22%
1807
19%
656
61%
656
29%
1192
October1st to 15thNight
46%
660
16%
1980
16%
660
48%
660
21%
1378
October16th to endNight
35%
704
11%
2148
9%
704
39%
704
14%
1665
November1st to 15thNight
24%
700
8%
2380
7%
700
27%
700
8%
1979
November16th to endNight
22%
720
7%
2520
3%
720
27%
720
10%
1981
December1st to 15thNight
22%
720
8%
2520
5%
720
26%
720
10%
1980
December16th to endNight
20%
768
6%
2688
5%
768
22%
768
6%
2278

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
23%8%35%424345%33%
47844
Night
25%9%35%423345%33%
46974
Cloud CoverDay
26%8%35%423335%32%
47844
Night
27%8%24423345%32%
46978
TransparencyDay
55%410%15%10%3
47515
Night
56%5%9%14%10%3
46807
SeeingDay
31%10%23%24%8%1
5587
Night
33%6%15%24%17%2
14640

By Month

Percentage Cloud Cover NW (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
35%9%46%5%3333320%
1432
16th to endDay
31%10%3442434426%
1623
February1st to 15thDay
30%11%46%6%25%35%5%18%
1576
16th to endDay
30%14%47%5%3423419%
1481
March1st to 15thDay
33%12%5%7%6%35%345%14%
1902
16th to endDay
34%12%5%8%6%35%335%12%
2154
April1st to 15thDay
30%13%48%6%2443416%
2149
16th to endDay
28%12%46%5%23345%22%
2258
May1st to 15thDay
24%9%35%423335%33%
2496
16th to endDay
30%8%36%5%33445%24%
2615
June1st to 15thDay
27%10%36%5%33345%25%
2520
16th to endDay
18%7%25%5%24446%37%
2520
July1st to 15thDay
7%313323336%60%
2520
16th to endDay
9%312223335%63%
2657
August1st to 15thDay
5%413434346%58%
2370
16th to endDay
7%423323346%58%
2387
September1st to 15thDay
8%423323246%58%
2097
16th to endDay
18%7%245%23346%41%
1822
October1st to 15thDay
22%8%26%5%2435%5%33%
1650
16th to endDay
29%8%26%433445%27%
1723
November1st to 15thDay
37%7%37%5%23446%16%
1476
16th to endDay
31%9%46%5%35%43420%
1440
December1st to 15thDay
30%12%45%5%2434421%
1440
16th to endDay
36%13%35%5%2433417%
1536
January1st to 15thNight
33%11%46%43424322%
2506
16th to endNight
29%10%35%433245%26%
2600
February1st to 15thNight
31%11%36%5%34345%21%
2276
16th to endNight
30%12%35%5%13345%23%
1993
March1st to 15thNight
32%11%35%5%25%34420%
2056
16th to endNight
31%12%5%7%433445%16%
2066
April1st to 15thNight
29%15%45%435%335%18%
1799
16th to endNight
27%10%25%425%345%27%
1701
May1st to 15thNight
21%8%25%41435%6%35%
1454
16th to endNight
26%7%36%5%2445%8%24%
1496
June1st to 15thNight
22%10%46%325%335%32%
1440
16th to endNight
16%7%35%5%24445%41%
1440
July1st to 15thNight
5%31231335%5%65%
1440
16th to endNight
3213213236%68%
1512
August1st to 15thNight
3212323348%63%
1587
16th to endNight
5%313313225%66%
1815
September1st to 15thNight
7%31221123468%
1750
16th to endNight
16%5%14433246%46%
1807
October1st to 15thNight
22%7%34422335%40%
1980
16th to endNight
27%6%36%5%2445%5%29%
2148
November1st to 15thNight
37%8%26%5%24345%18%
2380
16th to endNight
33%9%35%5%2333325%
2520
December1st to 15thNight
32%10%35%423235%24%
2520
16th to endNight
35%13%36%5%2333317%
2688

Percentage Cloud Cover SW (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
38%10%26%5%3333320%
1432
16th to endDay
33%11%2442334426%
1623
February1st to 15thDay
33%11%46%5%2435%418%
1576
16th to endDay
33%14%37%423325%19%
1481
March1st to 15thDay
37%11%46%6%2424414%
1902
16th to endDay
36%13%47%5%3433412%
2154
April1st to 15thDay
32%13%5%7%7%3333415%
2149
16th to endDay
31%11%37%423345%21%
2258
May1st to 15thDay
26%9%35%423235%33%
2496
16th to endDay
33%7%35%334445%23%
2615
June1st to 15thDay
31%8%36%5%33335%25%
2520
16th to endDay
20%6%25%425%446%37%
2520
July1st to 15thDay
8%313313345%60%
2520
16th to endDay
10%312213335%62%
2657
August1st to 15thDay
6%4135%23336%58%
2370
16th to endDay
8%414323345%58%
2387
September1st to 15thDay
9%413313326%58%
2097
16th to endDay
20%7%25%423336%41%
1822
October1st to 15thDay
25%7%246%23446%32%
1650
16th to endDay
32%7%34423345%27%
1723
November1st to 15thDay
40%7%46%432336%15%
1476
16th to endDay
34%9%47%5%235%2420%
1440
December1st to 15thDay
33%12%35%42333421%
1440
16th to endDay
39%13%25%42422318%
1536
January1st to 15thNight
35%12%25%42333422%
2506
16th to endNight
32%10%3442334426%
2600
February1st to 15thNight
32%11%36%5%24336%20%
2276
16th to endNight
32%14%24432335%23%
1993
March1st to 15thNight
33%12%36%425%34319%
2056
16th to endNight
35%12%46%423445%15%
2070
April1st to 15thNight
33%14%35%5%23335%18%
1799
16th to endNight
29%11%24324346%26%
1701
May1st to 15thNight
24%6%25%323346%35%
1454
16th to endNight
29%7%25%5%2346%7%24%
1496
June1st to 15thNight
24%9%36%32434432%
1440
16th to endNight
18%7%35%5%23345%40%
1440
July1st to 15thNight
6%312322345%64%
1440
16th to endNight
3222312246%68%
1512
August1st to 15thNight
4112324448%62%
1587
16th to endNight
6%313321235%67%
1815
September1st to 15thNight
8%2133223367%
1750
16th to endNight
18%5%14323336%46%
1807
October1st to 15thNight
25%7%24312335%40%
1980
16th to endNight
29%6%26%5%335%5%428%
2148
November1st to 15thNight
40%8%35%5%2333418%
2380
16th to endNight
36%9%345%2323325%
2520
December1st to 15thNight
34%9%35%423235%24%
2520
16th to endNight
39%13%45%42333317%
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
70%36%9%8%2
1432
16th to endDay
63%45%10%9%6%
1623
February1st to 15thDay
69%6%8%9%5%
1576
16th to endDay
71%46%10%6%
1481
March1st to 15thDay
75%47%9%3
1902
16th to endDay
78%47%7%2
2154
April1st to 15thDay
74%5%8%7%2
2149
16th to endDay
68%5%9%10%5%1
2258
May1st to 15thDay
56%311%18%8%
2496
16th to endDay
64%6%11%14%2
2619
June1st to 15thDay
63%5%13%12%4
2520
16th to endDay
50%5%15%19%7%2
2520
July1st to 15thDay
27%5%14%25%21%6%
2371
16th to endDay
24%38%26%30%6%
2490
August1st to 15thDay
26%5%15%29%17%6%
2353
16th to endDay
28%5%11%30%18%5%
2387
September1st to 15thDay
28%311%22%20%14%
2097
16th to endDay
45%5%10%18%13%5%
1822
October1st to 15thDay
52%5%9%18%10%4
1650
16th to endDay
59%6%8%12%12%1
1723
November1st to 15thDay
71%49%10%3
1476
16th to endDay
69%47%6%11%
1440
December1st to 15thDay
69%36%10%7%1
1440
16th to endDay
72%37%10%4
1536
January1st to 15thNight
66%47%9%9%2
2506
16th to endNight
63%37%9%9%7%
2600
February1st to 15thNight
68%5%8%9%6%2
2288
16th to endNight
66%48%11%8%1
1993
March1st to 15thNight
69%5%8%11%31
2056
16th to endNight
73%5%7%10%3
2070
April1st to 15thNight
71%410%8%4
1799
16th to endNight
62%5%11%13%5%1
1701
May1st to 15thNight
53%412%19%8%2
1455
16th to endNight
60%8%12%13%31
1496
June1st to 15thNight
58%5%14%14%5%
1440
16th to endNight
49%315%21%6%3
1440
July1st to 15thNight
24%5%11%27%22%7%
1360
16th to endNight
19%47%28%30%10%
1416
August1st to 15thNight
22%5%14%33%16%8%
1579
16th to endNight
22%412%33%18%7%
1815
September1st to 15thNight
24%413%23%17%17%
1750
16th to endNight
41%5%11%18%14%8%
1807
October1st to 15thNight
49%48%16%16%4
1980
16th to endNight
59%7%6%11%12%3
2148
November1st to 15thNight
70%5%6%10%6%
2380
16th to endNight
65%46%7%11%3
2520
December1st to 15thNight
65%48%12%8%
2520
16th to endNight
73%5%6%8%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
40%13%26%13%5%1
60
16th to endDay
47%5%22%19%5%
151
February1st to 15thDay
45%13%20%16%4
236
16th to endDay
42%15%26%14%1
221
March1st to 15thDay
54%14%19%8%2
270
16th to endDay
49%15%20%11%2
288
April1st to 15thDay
40%17%19%14%6%1
269
16th to endDay
44%14%21%14%41
270
May1st to 15thDay
35%15%23%19%5%
288
16th to endDay
38%6%20%21%10%2
330
June1st to 15thDay
31%12%22%21%9%2
315
16th to endDay
20%7%33%26%8%2
315
July1st to 15thDay
8%7%25%40%13%3
305
16th to endDay
8%6%29%38%13%3
327
August1st to 15thDay
10%322%42%14%6%
315
16th to endDay
8%6%25%37%17%5%
332
September1st to 15thDay
14%7%27%32%13%3
294
16th to endDay
24%7%26%29%10%
255
October1st to 15thDay
33%10%23%26%6%
255
16th to endDay
42%9%21%20%6%
235
November1st to 15thDay
34%16%19%22%42
72
16th to endDay
45%16%23%10%5%
60
December1st to 15thDay
61%20%13%5%
60
16th to endDay
45%12%15%18%6%1
64
January1st to 15thNight
43%10%22%16%6%
720
16th to endNight
38%9%22%19%9%1
768
February1st to 15thNight
40%7%23%22%5%1
704
16th to endNight
43%11%17%18%9%
632
March1st to 15thNight
44%9%14%22%9%
720
16th to endNight
46%6%16%19%10%1
768
April1st to 15thNight
44%6%13%22%11%1
719
16th to endNight
37%6%12%24%15%3
621
May1st to 15thNight
30%7%10%28%20%3
375
16th to endNight
33%5%11%21%25%2
375
June1st to 15thNight
31%6%10%25%22%2
360
16th to endNight
21%5%13%33%25%1
360
July1st to 15thNight
9%25%31%48%2
340
16th to endNight
5%18%36%44%3
376
August1st to 15thNight
6%16%27%47%10%
505
16th to endNight
8%29%34%35%9%
669
September1st to 15thNight
10%314%28%38%5%
700
16th to endNight
22%39%30%29%4
656
October1st to 15thNight
31%413%28%18%3
660
16th to endNight
32%6%17%25%15%2
704
November1st to 15thNight
47%7%16%22%6%
700
16th to endNight
44%8%22%19%5%
720
December1st to 15thNight
40%10%21%20%5%
720
16th to endNight
48%9%18%17%6%
768
Page generated at 2017-09-11 16:35:17. Version ac04

Copyright 2017 A. Danko


Shepherds Lair Observatory Clear Sky Chart | Charts Home