Spring Gulch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring Gulch clear sky chart from 2005-11-05 to 2018-03-21.

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
56%
16704
22%
49248
18%
16663
60%
16663
32%
29816

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
50%
894
18%
2638
15%
892
53%
892
27%
1711
January16th to endNight
53%
832
22%
2704
22%
832
55%
832
27%
1685
February1st to 15thNight
46%
760
14%
2483
12%
759
49%
759
22%
1660
February16th to endNight
39%
684
20%
2085
13%
684
48%
684
25%
1349
March1st to 15thNight
52%
780
21%
2181
15%
780
57%
780
34%
1333
March16th to endNight
49%
770
21%
2156
14%
770
54%
770
30%
1383
April1st to 15thNight
45%
539
17%
1798
15%
539
49%
539
24%
1110
April16th to endNight
45%
540
20%
1800
19%
540
51%
540
24%
1137
May1st to 15thNight
49%
539
18%
1620
14%
539
54%
539
27%
1027
May16th to endNight
57%
563
21%
1498
14%
561
61%
561
35%
906
June1st to 15thNight
65%
540
26%
1440
20%
540
68%
540
51%
749
June16th to endNight
74%
540
29%
1440
24%
540
78%
540
60%
707
July1st to 15thNight
77%
510
18%
1360
16%
510
78%
510
39%
815
July16th to endNight
80%
564
17%
1572
16%
531
82%
531
37%
889
August1st to 15thNight
78%
539
18%
1611
17%
536
79%
536
38%
900
August16th to endNight
78%
573
28%
1893
31%
573
80%
573
38%
1007
September1st to 15thNight
75%
540
27%
1800
27%
540
80%
540
37%
979
September16th to endNight
71%
635
34%
1968
29%
635
77%
635
47%
995
October1st to 15thNight
59%
720
27%
2160
19%
720
64%
720
38%
1229
October16th to endNight
62%
768
32%
2304
24%
768
68%
768
42%
1240
November1st to 15thNight
54%
884
26%
2404
18%
884
58%
884
40%
1406
November16th to endNight
53%
975
25%
2691
18%
975
57%
975
37%
1604
December1st to 15thNight
44%
975
12%
2730
9%
975
46%
975
25%
1857
December16th to endNight
40%
1040
16%
2912
12%
1040
43%
1040
19%
2138

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
45%35%5%35%5%5%7%48%
49609
Night
35%25%42445%7%53%
49431
TransparencyDay
38%6%12%20%16%5%
49294
Night
33%6%14%23%16%5%
49248
SeeingDay
9%16%30%28%13%2
6351
Night
6%7%24%36%22%2
16712

By Month

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
6%47%6%46%5%6%8%43%
1640
16th to endDay
19%47%6%2335%6%48%
1872
February1st to 15thDay
210%5%10%7%35%436%39%
1710
16th to endDay
9%6%8%6%36%6%5%6%39%
1675
March1st to 15thDay
27%47%43445%6%50%
2107
16th to endDay
29%27%5%45%6%6%9%41%
2194
April1st to 15thDay
38%46%6%45%6%48%41%
2150
16th to endDay
47%37%7%36%6%7%7%37%
2160
May1st to 15thDay
6%6%36%6%36%5%6%8%39%
2330
16th to endDay
5%425%5%36%6%6%8%45%
2616
June1st to 15thDay
431332445%8%59%
2520
16th to endDay
11232345%6%66%
2520
July1st to 15thDay
5%2245%36%6%6%8%47%
2520
16th to endDay
5%425%6%46%6%6%9%41%
2486
August1st to 15thDay
7%425%6%46%6%6%8%41%
2340
16th to endDay
3315%5%346%7%9%47%
2308
September1st to 15thDay
6%2134345%5%7%53%
2160
16th to endDay
6%2143235%5%5%57%
1989
October1st to 15thDay
7%31432445%5%55%
1800
16th to endDay
5%5%232135%46%58%
1920
November1st to 15thDay
35%2432345%6%58%
1772
16th to endDay
15%37%323345%60%
1596
December1st to 15thDay
29%5%8%7%45%345%44%
1560
16th to endDay
210%410%7%36%5%5%5%37%
1664
January1st to 15thNight
8%37%5%35%346%49%
2638
16th to endNight
28%46%6%33345%50%
2704
February1st to 15thNight
16%46%6%35%5%6%7%44%
2472
16th to endNight
19%5%7%435%45%7%45%
2085
March1st to 15thNight
16%26%32445%6%54%
2181
16th to endNight
37%24435%45%8%49%
2156
April1st to 15thNight
36%35%4345%6%7%48%
1798
16th to endNight
6%8%36%5%34346%47%
1800
May1st to 15thNight
7%5%26%4345%6%7%47%
1619
16th to endNight
4313425%46%8%55%
1497
June1st to 15thNight
311221235%8%66%
1440
16th to endNight
1121245%8%70%
1440
July1st to 15thNight
4212425%5%6%9%54%
1440
16th to endNight
32135%35%5%8%11%49%
1679
August1st to 15thNight
42134236%8%9%52%
1620
16th to endNight
322343347%9%56%
1893
September1st to 15thNight
32144245%5%8%56%
1800
16th to endNight
322323437%66%
1968
October1st to 15thNight
5%31332345%6%58%
2160
16th to endNight
5%5%13322346%62%
2304
November1st to 15thNight
36%1221446%6%58%
2404
16th to endNight
26%24323446%58%
2691
December1st to 15thNight
38%46%8%45%445%45%
2730
16th to endNight
27%5%9%8%46%5%46%39%
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%7%21%18%7%1
1641
16th to endDay
40%6%18%20%12%1
1872
February1st to 15thDay
50%7%16%16%7%2
1710
16th to endDay
50%5%11%21%9%1
1675
March1st to 15thDay
38%5%15%24%14%1
2107
16th to endDay
42%7%13%23%9%2
2194
April1st to 15thDay
45%6%11%17%14%3
2150
16th to endDay
46%6%13%20%11%1
2160
May1st to 15thDay
45%7%9%20%15%
2330
16th to endDay
37%7%11%22%16%3
2620
June1st to 15thDay
26%48%17%28%14%
2520
16th to endDay
19%46%17%31%21%
2520
July1st to 15thDay
35%6%12%13%15%15%
2371
16th to endDay
39%8%15%17%12%6%
2330
August1st to 15thDay
42%8%13%13%13%9%
2325
16th to endDay
35%8%13%17%19%5%
2308
September1st to 15thDay
32%7%10%15%22%11%
2160
16th to endDay
30%5%8%24%27%4
1989
October1st to 15thDay
34%49%26%21%3
1800
16th to endDay
29%6%13%28%19%3
1920
November1st to 15thDay
29%6%14%24%22%4
1772
16th to endDay
30%5%15%32%12%3
1596
December1st to 15thDay
45%6%16%21%8%
1560
16th to endDay
52%7%11%20%6%1
1664
January1st to 15thNight
39%7%18%22%10%1
2638
16th to endNight
40%416%23%11%2
2704
February1st to 15thNight
42%9%16%20%9%1
2483
16th to endNight
41%5%14%25%10%1
2085
March1st to 15thNight
32%6%16%29%13%1
2181
16th to endNight
36%7%12%30%11%2
2156
April1st to 15thNight
37%8%13%20%17%3
1798
16th to endNight
40%6%10%24%16%1
1800
May1st to 15thNight
37%7%13%24%14%1
1620
16th to endNight
28%8%14%24%20%4
1498
June1st to 15thNight
18%5%8%21%30%15%
1440
16th to endNight
14%39%15%29%27%
1440
July1st to 15thNight
26%9%13%14%16%19%
1360
16th to endNight
26%9%24%17%13%9%
1572
August1st to 15thNight
26%7%20%19%13%12%
1611
16th to endNight
24%7%13%19%22%10%
1893
September1st to 15thNight
26%7%14%15%21%14%
1800
16th to endNight
21%49%26%31%6%
1968
October1st to 15thNight
28%6%10%24%23%7%
2160
16th to endNight
25%5%12%30%22%4
2304
November1st to 15thNight
27%6%13%25%22%3
2404
16th to endNight
29%6%13%30%17%3
2691
December1st to 15thNight
43%6%17%18%12%
2730
16th to endNight
50%7%13%18%8%
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
10%14%23%36%15%
135
16th to endDay
5%10%37%30%14%1
144
February1st to 15thDay
12%20%33%26%7%
135
16th to endDay
6%27%33%23%7%1
120
March1st to 15thDay
11%27%32%21%5%
292
16th to endDay
11%35%35%15%2
311
April1st to 15thDay
13%32%29%16%5%1
269
16th to endDay
18%35%30%12%2
270
May1st to 15thDay
13%24%34%21%6%
312
16th to endDay
9%15%27%29%15%2
517
June1st to 15thDay
7%13%30%28%18%1
495
16th to endDay
28%31%31%23%2
495
July1st to 15thDay
6%426%28%28%5%
475
16th to endDay
8%430%38%15%2
345
August1st to 15thDay
13%5%34%31%11%2
315
16th to endDay
5%5%27%42%15%3
332
September1st to 15thDay
7%11%34%33%9%4
315
16th to endDay
11%15%28%28%11%4
246
October1st to 15thDay
8%17%26%28%13%4
135
16th to endDay
10%12%31%31%11%2
144
November1st to 15thDay
7%17%27%27%19%1
135
16th to endDay
8%21%34%25%9%
135
December1st to 15thDay
8%14%38%28%11%
135
16th to endDay
7%19%31%31%9%
144
January1st to 15thNight
5%10%25%38%17%2
897
16th to endNight
7%7%25%40%16%2
832
February1st to 15thNight
37%33%43%10%
764
16th to endNight
6%11%35%37%9%
684
March1st to 15thNight
5%9%28%38%16%1
780
16th to endNight
6%9%29%40%13%
770
April1st to 15thNight
7%12%33%34%11%
539
16th to endNight
11%11%28%30%16%1
540
May1st to 15thNight
10%7%30%36%14%1
540
16th to endNight
8%7%21%33%25%3
563
June1st to 15thNight
5%5%21%42%23%1
540
16th to endNight
2217%43%32%2
540
July1st to 15thNight
5%9%38%44%3
510
16th to endNight
35%33%54%3
564
August1st to 15thNight
6%18%36%45%2
539
16th to endNight
49%31%48%6%
573
September1st to 15thNight
4111%41%38%2
540
16th to endNight
4317%30%37%5%
635
October1st to 15thNight
6%5%25%36%22%3
720
16th to endNight
8%5%20%36%25%4
768
November1st to 15thNight
7%8%26%35%20%1
884
16th to endNight
6%10%26%34%18%2
975
December1st to 15thNight
8%9%32%37%11%
975
16th to endNight
7%13%31%34%12%
1040
Page generated at 2018-03-22 09:34:27. Version ac04

Copyright 2018 A. Danko


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