Sourland Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sourland Mountain Observatory clear sky chart from 2005-11-05 to 2018-10-08.

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
34%
16408
20%
51024
10%
16377
45%
16377
23%
32533

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
22%
780
20%
2716
9%
776
38%
776
18%
1677
January16th to endNight
20%
832
22%
2769
8%
832
38%
832
20%
1732
February1st to 15thNight
18%
764
17%
2437
4%
761
34%
761
18%
1586
February16th to endNight
18%
683
26%
2049
7%
683
39%
683
20%
1316
March1st to 15thNight
21%
780
21%
2298
8%
780
36%
780
21%
1489
March16th to endNight
24%
832
23%
2181
8%
832
36%
832
25%
1458
April1st to 15thNight
22%
778
18%
1946
4%
778
30%
778
25%
1324
April16th to endNight
30%
771
19%
1927
5%
771
37%
771
28%
1307
May1st to 15thNight
30%
543
17%
1713
9%
543
38%
543
21%
1146
May16th to endNight
43%
406
15%
1625
13%
406
50%
406
18%
1032
June1st to 15thNight
41%
390
15%
1560
13%
390
51%
390
18%
987
June16th to endNight
55%
390
16%
1560
19%
390
61%
390
27%
873
July1st to 15thNight
54%
370
14%
1480
16%
370
58%
370
22%
901
July16th to endNight
58%
408
16%
1546
16%
386
64%
386
24%
898
August1st to 15thNight
60%
624
17%
1765
13%
622
61%
622
31%
1137
August16th to endNight
58%
828
17%
2070
10%
828
60%
828
31%
1382
September1st to 15thNight
48%
780
22%
1950
12%
780
52%
780
30%
1310
September16th to endNight
52%
777
26%
2115
20%
777
56%
777
32%
1350
October1st to 15thNight
43%
752
21%
2229
16%
752
51%
752
27%
1403
October16th to endNight
34%
768
26%
2367
15%
768
49%
768
28%
1424
November1st to 15thNight
34%
760
22%
2472
13%
760
48%
760
25%
1506
November16th to endNight
30%
780
22%
2607
12%
780
43%
780
20%
1623
December1st to 15thNight
24%
780
16%
2730
6%
780
37%
780
16%
1807
December16th to endNight
20%
832
20%
2912
6%
832
38%
832
17%
1865

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
16%5%245%3445%7%40%
52120
Night
16%5%24424446%43%
51194
Cloud CoverDay
15%6%25%43445%7%40%
52129
Night
15%6%25%42445%6%42%
51200
TransparencyDay
42%5%11%21%16%2
51808
Night
40%5%11%22%16%2
51024
SeeingDay
20%10%26%23%13%5%
7114
Night
18%10%30%28%10%
16409

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
15%5%35%5%3445%5%41%
1552
16th to endDay
15%7%245%24447%40%
1805
February1st to 15thDay
17%7%35%5%23445%39%
1754
16th to endDay
17%6%35%6%3445%5%38%
1710
March1st to 15thDay
17%6%25%6%34346%38%
1980
16th to endDay
18%6%24424345%42%
2395
April1st to 15thDay
18%5%25%424348%39%
2332
16th to endDay
15%5%25%43445%6%43%
2308
May1st to 15thDay
20%6%245%33447%36%
2579
16th to endDay
19%6%245%2445%8%36%
2842
June1st to 15thDay
16%6%25%5%245%6%8%35%
2730
16th to endDay
12%5%25%5%345%6%8%39%
2730
July1st to 15thDay
11%4246%36%6%6%9%37%
2730
16th to endDay
10%5%25%6%36%6%6%8%38%
2878
August1st to 15thDay
12%5%25%5%45%5%6%8%37%
2422
16th to endDay
13%5%245%35%46%7%41%
2484
September1st to 15thDay
16%5%2433345%7%43%
2340
16th to endDay
15%5%25%6%34346%42%
2174
October1st to 15thDay
18%5%245%2335%5%42%
1898
16th to endDay
17%5%1331335%6%46%
1855
November1st to 15thDay
18%6%24414236%45%
1716
16th to endDay
16%42432325%6%47%
1682
December1st to 15thDay
16%8%24335%347%40%
1560
16th to endDay
19%6%24324447%37%
1664
January1st to 15thNight
17%5%24424346%43%
2716
16th to endNight
15%8%24423346%44%
2769
February1st to 15thNight
16%7%35%5%23445%40%
2436
16th to endNight
17%6%24324345%44%
2049
March1st to 15thNight
18%5%24324447%42%
2285
16th to endNight
17%6%24423335%46%
2181
April1st to 15thNight
16%5%25%4335%6%6%40%
1946
16th to endNight
18%5%24423446%42%
1927
May1st to 15thNight
19%7%35%423447%38%
1713
16th to endNight
18%6%25%5%2345%7%39%
1623
June1st to 15thNight
18%434434445%41%
1560
16th to endNight
10%3244345%5%9%46%
1560
July1st to 15thNight
10%4146%35%5%8%10%39%
1560
16th to endNight
10%3245%35%7%6%9%42%
1642
August1st to 15thNight
11%425%435%5%5%8%43%
1775
16th to endNight
13%5%25%5%2436%8%41%
2070
September1st to 15thNight
16%5%14424447%44%
1950
16th to endNight
14%5%24423446%47%
2115
October1st to 15thNight
17%5%25%313446%45%
2229
16th to endNight
17%423323245%49%
2367
November1st to 15thNight
15%5%25%323245%48%
2472
16th to endNight
17%5%3442445%6%41%
2607
December1st to 15thNight
19%6%25%5%3445%5%36%
2730
16th to endNight
17%7%34424446%40%
2912

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
15%5%25%5%3445%5%41%
1552
16th to endDay
15%7%245%25%337%41%
1805
February1st to 15thDay
17%6%26%5%24445%39%
1754
16th to endDay
17%7%35%42445%5%38%
1710
March1st to 15thDay
17%7%26%6%34337%38%
1990
16th to endDay
18%6%24433245%43%
2394
April1st to 15thDay
18%6%25%423348%39%
2332
16th to endDay
15%5%25%43445%6%42%
2308
May1st to 15thDay
19%6%245%34447%36%
2579
16th to endDay
18%6%25%43445%7%36%
2842
June1st to 15thDay
15%6%35%4345%6%8%35%
2730
16th to endDay
12%5%25%5%35%5%6%9%38%
2730
July1st to 15thDay
11%425%6%46%5%7%9%37%
2730
16th to endDay
10%5%36%6%35%5%7%8%38%
2878
August1st to 15thDay
12%5%15%5%45%6%6%8%38%
2422
16th to endDay
12%5%244345%6%8%40%
2484
September1st to 15thDay
15%6%2442445%6%43%
2340
16th to endDay
15%6%25%6%34346%41%
2174
October1st to 15thDay
17%6%24424346%43%
1898
16th to endDay
17%5%23313347%46%
1855
November1st to 15thDay
18%5%24423336%44%
1716
16th to endDay
16%424322347%46%
1682
December1st to 15thDay
17%7%24325%347%40%
1560
16th to endDay
19%6%24424447%38%
1664
January1st to 15thNight
16%5%24424346%43%
2716
16th to endNight
15%7%25%324345%44%
2769
February1st to 15thNight
15%8%35%4245%45%41%
2429
16th to endNight
17%6%24324345%44%
2049
March1st to 15thNight
18%5%25%324346%42%
2298
16th to endNight
18%6%24423335%45%
2181
April1st to 15thNight
17%5%25%3246%47%40%
1946
16th to endNight
17%5%25%42335%6%41%
1927
May1st to 15thNight
18%8%26%423437%37%
1713
16th to endNight
17%5%3442345%7%39%
1623
June1st to 15thNight
17%5%25%334446%41%
1560
16th to endNight
9%42443446%9%45%
1560
July1st to 15thNight
9%5%15%5%36%6%7%9%39%
1560
16th to endNight
9%415%5%35%6%7%8%42%
1642
August1st to 15thNight
10%5%15%5%25%6%5%8%43%
1775
16th to endNight
12%425%5%345%6%8%41%
2070
September1st to 15thNight
15%5%14424446%44%
1950
16th to endNight
13%6%245%23446%46%
2115
October1st to 15thNight
16%6%25%32335%6%45%
2229
16th to endNight
16%5%13322345%49%
2367
November1st to 15thNight
15%5%25%313345%48%
2472
16th to endNight
17%6%2442445%6%40%
2607
December1st to 15thNight
19%6%25%5%2445%6%36%
2730
16th to endNight
17%7%24324446%40%
2912

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
42%5%12%23%11%4
1553
16th to endDay
42%5%11%24%14%2
1805
February1st to 15thDay
45%411%21%13%2
1757
16th to endDay
45%5%9%25%12%1
1710
March1st to 15thDay
46%412%20%12%2
1990
16th to endDay
44%49%20%17%3
2395
April1st to 15thDay
43%49%22%14%4
2332
16th to endDay
39%5%9%17%23%3
2308
May1st to 15thDay
46%5%9%18%16%2
2579
16th to endDay
45%6%12%19%13%1
2846
June1st to 15thDay
44%8%12%22%12%
2730
16th to endDay
39%8%13%21%14%1
2730
July1st to 15thDay
40%7%11%20%17%2
2581
16th to endDay
40%7%12%23%13%2
2711
August1st to 15thDay
41%7%12%20%16%1
2408
16th to endDay
38%8%10%20%19%3
2484
September1st to 15thDay
39%5%10%20%22%1
2340
16th to endDay
43%48%19%22%2
2174
October1st to 15thDay
41%5%12%19%18%1
1898
16th to endDay
37%49%26%18%2
1855
November1st to 15thDay
41%412%21%17%2
1716
16th to endDay
37%311%26%18%2
1682
December1st to 15thDay
43%415%21%13%1
1560
16th to endDay
46%5%13%20%13%
1664
January1st to 15thNight
41%5%12%22%15%3
2716
16th to endNight
41%5%11%25%14%1
2769
February1st to 15thNight
43%5%13%21%13%2
2437
16th to endNight
41%47%23%19%3
2049
March1st to 15thNight
42%411%22%15%3
2298
16th to endNight
42%49%20%18%4
2181
April1st to 15thNight
40%5%11%20%17%3
1946
16th to endNight
40%5%8%18%22%3
1927
May1st to 15thNight
46%5%10%16%19%2
1713
16th to endNight
44%7%13%16%15%2
1625
June1st to 15thNight
43%7%11%20%16%
1560
16th to endNight
33%6%13%29%14%1
1560
July1st to 15thNight
38%9%14%19%15%2
1480
16th to endNight
34%9%15%24%13%2
1546
August1st to 15thNight
35%8%13%23%16%2
1765
16th to endNight
38%6%12%19%20%2
2070
September1st to 15thNight
39%6%10%20%20%1
1950
16th to endNight
37%5%6%23%25%2
2115
October1st to 15thNight
39%412%24%16%2
2229
16th to endNight
36%49%28%18%2
2367
November1st to 15thNight
39%410%21%18%5%
2472
16th to endNight
42%311%24%15%2
2607
December1st to 15thNight
47%5%13%20%11%1
2730
16th to endNight
44%412%22%13%1
2912

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
21%32%28%11%42
90
16th to endDay
25%17%36%17%2
129
February1st to 15thDay
28%25%30%14%1
180
16th to endDay
22%17%39%16%3
291
March1st to 15thDay
23%19%30%21%4
330
16th to endDay
22%17%34%17%5%2
352
April1st to 15thDay
23%16%33%14%8%2
330
16th to endDay
21%15%30%18%9%4
319
May1st to 15thDay
29%13%28%17%9%2
348
16th to endDay
27%6%18%28%17%2
395
June1st to 15thDay
19%9%28%21%16%4
375
16th to endDay
18%7%26%30%12%4
375
July1st to 15thDay
13%321%31%23%7%
365
16th to endDay
13%323%30%22%7%
390
August1st to 15thDay
15%218%34%20%9%
358
16th to endDay
12%20%31%19%16%
396
September1st to 15thDay
20%6%21%23%18%10%
375
16th to endDay
20%6%20%24%13%14%
374
October1st to 15thDay
23%420%26%17%8%
345
16th to endDay
17%12%30%22%15%1
319
November1st to 15thDay
22%8%28%25%12%1
280
16th to endDay
16%18%34%17%10%
212
December1st to 15thDay
28%24%22%8%15%
90
16th to endDay
35%20%30%12%1
96
January1st to 15thNight
20%16%36%22%4
780
16th to endNight
20%15%39%23%1
832
February1st to 15thNight
20%16%39%23%1
764
16th to endNight
21%19%37%20%2
683
March1st to 15thNight
23%17%34%21%2
780
16th to endNight
20%12%37%22%6%
832
April1st to 15thNight
19%15%39%21%4
778
16th to endNight
19%10%35%27%7%
771
May1st to 15thNight
21%11%31%28%7%
543
16th to endNight
19%425%36%12%1
407
June1st to 15thNight
19%425%36%13%
390
16th to endNight
8%224%51%12%
390
July1st to 15thNight
10%224%43%16%2
370
16th to endNight
9%222%44%20%
408
August1st to 15thNight
13%16%42%24%1
624
16th to endNight
14%115%38%26%3
828
September1st to 15thNight
17%323%33%18%2
780
16th to endNight
17%320%30%24%4
777
October1st to 15thNight
19%6%24%28%18%2
752
16th to endNight
19%10%32%27%10%
768
November1st to 15thNight
17%10%30%27%11%1
760
16th to endNight
18%14%30%26%8%
780
December1st to 15thNight
24%13%31%22%7%1
780
16th to endNight
22%14%36%24%2
832
Page generated at 2018-10-09 10:39:11. Version ac04

Copyright 2018 A. Danko


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