This page made possible by the sponsorship of: Karen Miller SLC.

Salt Lake City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salt Lake City clear sky chart from 2005-11-05 to 2020-06-03.

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%
19486
21%
58048
18%
19450
59%
19450
30%
36030

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
46%
896
15%
2912
14%
896
49%
896
19%
2040
January16th to endNight
51%
960
15%
3120
15%
960
53%
960
19%
2190
February1st to 15thNight
48%
879
14%
2873
15%
879
50%
879
19%
1995
February16th to endNight
41%
792
19%
2393
15%
792
47%
792
21%
1674
March1st to 15thNight
48%
900
18%
2524
14%
900
52%
900
25%
1745
March16th to endNight
47%
960
16%
2640
12%
960
50%
960
24%
1829
April1st to 15thNight
44%
809
16%
2332
12%
809
48%
809
25%
1547
April16th to endNight
54%
669
23%
2007
17%
669
59%
669
29%
1240
May1st to 15thNight
55%
674
21%
2024
17%
674
58%
674
33%
1203
May16th to endNight
58%
705
18%
2117
15%
705
61%
705
30%
1298
June1st to 15thNight
66%
637
24%
1785
22%
637
70%
637
43%
964
June16th to endNight
70%
630
28%
1805
23%
630
77%
630
61%
818
July1st to 15thNight
71%
600
20%
1800
18%
600
74%
600
40%
976
July16th to endNight
74%
660
23%
1881
21%
627
76%
627
42%
1011
August1st to 15thNight
70%
620
27%
1854
20%
617
74%
617
44%
955
August16th to endNight
74%
669
35%
2017
29%
669
77%
669
47%
1023
September1st to 15thNight
72%
798
30%
2268
24%
798
77%
798
48%
1193
September16th to endNight
69%
836
35%
2310
27%
836
74%
836
51%
1198
October1st to 15thNight
58%
840
28%
2446
20%
840
65%
840
38%
1386
October16th to endNight
63%
896
31%
2694
26%
896
68%
896
38%
1511
November1st to 15thNight
56%
880
25%
2860
23%
880
60%
880
30%
1673
November16th to endNight
51%
986
21%
3011
19%
986
54%
986
27%
1897
December1st to 15thNight
46%
1125
12%
3150
10%
1125
48%
1125
23%
2227
December16th to endNight
38%
1065
13%
3225
11%
1065
41%
1065
15%
2437

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
8%7%2442445%7%48%
58337
Night
8%8%2442345%7%47%
58243
TransparencyDay
35%6%10%18%18%9%
58032
Night
36%6%11%20%17%8%
58049
SeeingDay
12%13%31%29%10%1
9031
Night
13%6%19%34%22%3
19498

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
13%14%5%6%6%2445%6%29%
2016
16th to endDay
12%16%5%6%5%2445%7%28%
2160
February1st to 15thDay
13%14%5%7%6%24346%31%
1980
16th to endDay
8%14%6%8%5%345%6%6%30%
1959
March1st to 15thDay
8%11%36%435%5%5%7%37%
2426
16th to endDay
10%12%35%5%35%5%5%8%33%
2640
April1st to 15thDay
12%10%35%4335%5%6%38%
2602
16th to endDay
9%8%245%245%5%8%45%
2888
May1st to 15thDay
7%5%245%245%6%9%46%
2916
16th to endDay
9%425%5%35%5%6%9%42%
3053
June1st to 15thDay
432432445%7%58%
2876
16th to endDay
31221223475%
2806
July1st to 15thDay
211232346%6%62%
2730
16th to endDay
32233245%6%7%58%
2883
August1st to 15thDay
311342446%7%60%
2680
16th to endDay
22332335%6%65%
2888
September1st to 15thDay
321232345%5%65%
2349
16th to endDay
8%212212245%66%
2310
October1st to 15thDay
9%6%23323345%55%
2174
16th to endDay
7%6%13324346%54%
2230
November1st to 15thDay
10%8%245%2235%5%49%
1989
16th to endDay
11%10%46%5%24345%41%
1920
December1st to 15thDay
12%13%47%434447%32%
1800
16th to endDay
14%17%5%8%5%23346%26%
2062
January1st to 15thNight
13%12%45%5%2345%7%34%
2912
16th to endNight
10%15%36%4236%6%7%33%
3120
February1st to 15thNight
13%11%35%425%45%7%37%
2862
16th to endNight
6%14%6%6%5%2345%6%37%
2393
March1st to 15thNight
9%11%36%424447%41%
2524
16th to endNight
8%12%34425%5%6%7%39%
2640
April1st to 15thNight
12%10%25%423346%44%
2332
16th to endNight
10%7%2442435%7%47%
2007
May1st to 15thNight
6%5%235%3346%7%50%
2024
16th to endNight
9%4245%2445%9%47%
2116
June1st to 15thNight
431332335%7%60%
1785
16th to endNight
211212347%71%
1805
July1st to 15thNight
23234345%7%6%55%
1890
16th to endNight
331342446%9%55%
1989
August1st to 15thNight
32134345%5%7%58%
1863
16th to endNight
21134235%6%6%62%
2017
September1st to 15thNight
3213323345%64%
2268
16th to endNight
7%212212235%68%
2310
October1st to 15thNight
7%5%13323245%58%
2446
16th to endNight
8%6%13223346%57%
2694
November1st to 15thNight
10%7%2332336%6%51%
2860
16th to endNight
12%9%3332345%6%45%
3011
December1st to 15thNight
12%12%36%5%2435%6%37%
3150
16th to endNight
17%13%5%8%5%34346%27%
3225

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
55%8%15%16%3
2017
16th to endDay
54%7%15%13%7%1
2160
February1st to 15thDay
54%8%11%15%8%1
1980
16th to endDay
54%8%12%16%6%1
1959
March1st to 15thDay
46%9%13%20%8%1
2426
16th to endDay
48%9%14%18%6%2
2640
April1st to 15thDay
46%7%12%18%12%2
2602
16th to endDay
37%7%12%22%19%1
2888
May1st to 15thDay
34%7%9%25%18%4
2916
16th to endDay
37%8%11%21%18%2
3056
June1st to 15thDay
24%6%8%20%28%10%
2876
16th to endDay
14%35%13%32%31%
2806
July1st to 15thDay
21%5%7%13%25%27%
2591
16th to endDay
22%6%8%11%23%28%
2728
August1st to 15thDay
21%5%7%15%22%26%
2665
16th to endDay
18%47%16%32%20%
2888
September1st to 15thDay
20%5%6%16%30%21%
2349
16th to endDay
21%47%21%31%13%
2310
October1st to 15thDay
32%5%7%23%23%6%
2174
16th to endDay
30%7%12%28%19%2
2230
November1st to 15thDay
37%6%12%24%16%2
1989
16th to endDay
46%5%11%23%11%
1920
December1st to 15thDay
50%9%17%16%5%
1800
16th to endDay
60%6%13%14%4
2062
January1st to 15thNight
48%7%15%20%6%1
2912
16th to endNight
48%7%16%17%7%2
3120
February1st to 15thNight
48%7%13%18%11%
2873
16th to endNight
47%6%11%22%9%2
2393
March1st to 15thNight
44%6%11%23%12%
2524
16th to endNight
42%9%13%21%10%2
2640
April1st to 15thNight
42%5%13%21%13%3
2332
16th to endNight
37%5%12%21%21%2
2007
May1st to 15thNight
32%6%10%23%21%5%
2025
16th to endNight
33%8%12%25%16%3
2117
June1st to 15thNight
23%5%8%20%30%11%
1785
16th to endNight
13%26%12%28%35%
1805
July1st to 15thNight
25%6%6%15%18%27%
1800
16th to endNight
24%6%7%12%20%28%
1881
August1st to 15thNight
23%49%15%20%26%
1854
16th to endNight
20%6%7%12%31%22%
2017
September1st to 15thNight
21%46%15%25%25%
2268
16th to endNight
20%35%18%32%19%
2310
October1st to 15thNight
29%48%23%24%8%
2446
16th to endNight
29%5%9%25%26%3
2694
November1st to 15thNight
34%5%11%23%19%5%
2860
16th to endNight
38%6%12%25%13%2
3011
December1st to 15thNight
46%7%16%20%7%
3150
16th to endNight
58%412%17%6%
3225

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
28%7%23%24%15%1
225
16th to endDay
23%10%26%27%10%1
240
February1st to 15thDay
22%20%24%20%11%
225
16th to endDay
10%18%40%24%41
378
March1st to 15thDay
17%18%33%21%8%
450
16th to endDay
18%20%34%21%3
480
April1st to 15thDay
21%22%29%20%41
449
16th to endDay
16%22%29%24%6%
438
May1st to 15thDay
8%21%35%23%8%1
468
16th to endDay
11%15%32%27%11%2
522
June1st to 15thDay
5%13%32%32%13%2
562
16th to endDay
211%35%35%13%1
511
July1st to 15thDay
36%31%42%12%2
425
16th to endDay
4340%39%10%1
455
August1st to 15thDay
6%5%39%36%9%2
419
16th to endDay
46%33%40%13%2
460
September1st to 15thDay
5%11%29%36%14%2
435
16th to endDay
10%12%27%34%13%2
435
October1st to 15thDay
12%19%29%26%12%
299
16th to endDay
12%11%32%29%14%
240
November1st to 15thDay
14%13%20%33%13%4
225
16th to endDay
25%14%19%24%13%3
225
December1st to 15thDay
20%9%27%28%11%3
225
16th to endDay
21%10%29%34%4
240
January1st to 15thNight
18%5%21%30%19%4
900
16th to endNight
19%5%17%32%19%5%
960
February1st to 15thNight
19%6%19%36%15%2
884
16th to endNight
14%6%28%31%17%1
792
March1st to 15thNight
14%8%22%33%17%3
900
16th to endNight
15%11%20%35%13%3
960
April1st to 15thNight
18%11%21%31%14%2
809
16th to endNight
14%9%17%36%19%2
669
May1st to 15thNight
10%6%22%37%20%2
675
16th to endNight
10%7%17%33%25%5%
707
June1st to 15thNight
6%8%14%42%25%1
637
16th to endNight
25%19%37%32%3
630
July1st to 15thNight
4314%34%40%3
600
16th to endNight
4112%37%41%2
660
August1st to 15thNight
4216%43%31%1
620
16th to endNight
3314%39%35%3
669
September1st to 15thNight
4314%40%30%6%
798
16th to endNight
8%5%14%27%33%10%
836
October1st to 15thNight
10%5%21%32%23%5%
840
16th to endNight
11%5%16%33%27%5%
896
November1st to 15thNight
13%6%18%32%23%3
880
16th to endNight
18%6%19%31%17%6%
986
December1st to 15thNight
20%423%33%16%2
1125
16th to endNight
23%8%20%32%13%1
1065
Page generated at 2020-06-04 01:18:54. Version ac04

Copyright 2020 A. Danko


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