Mountain Meadows Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mountain Meadows Observatory clear sky chart from 2005-11-05 to 2017-04-30.

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
40%
14915
19%
45699
11%
14876
48%
14876
22%
29681

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
21%
717
19%
2327
9%
716
34%
716
15%
1548
January16th to endNight
19%
768
17%
2496
6%
768
32%
768
16%
1667
February1st to 15thNight
24%
702
17%
2287
6%
701
37%
701
17%
1465
February16th to endNight
19%
631
18%
1925
6%
631
32%
631
14%
1322
March1st to 15thNight
25%
720
19%
1980
8%
720
35%
720
20%
1344
March16th to endNight
25%
768
17%
2112
9%
768
32%
768
19%
1460
April1st to 15thNight
28%
718
16%
1826
5%
718
35%
718
22%
1269
April16th to endNight
39%
669
18%
1744
8%
669
44%
669
25%
1180
May1st to 15thNight
41%
495
16%
1485
9%
495
47%
495
21%
1030
May16th to endNight
52%
421
17%
1447
14%
420
57%
420
26%
897
June1st to 15thNight
56%
330
19%
1320
19%
330
63%
330
23%
781
June16th to endNight
63%
330
17%
1320
19%
330
68%
330
25%
758
July1st to 15thNight
63%
404
12%
1334
12%
404
65%
404
24%
868
July16th to endNight
72%
522
15%
1469
12%
489
74%
489
37%
857
August1st to 15thNight
70%
494
19%
1474
14%
491
71%
491
33%
921
August16th to endNight
68%
637
20%
1687
14%
637
69%
637
33%
1070
September1st to 15thNight
61%
660
25%
1655
16%
660
64%
660
35%
1071
September16th to endNight
51%
657
22%
1842
17%
657
56%
657
28%
1204
October1st to 15thNight
49%
660
24%
1980
21%
660
56%
660
27%
1244
October16th to endNight
38%
704
25%
2112
15%
704
51%
704
27%
1290
November1st to 15thNight
43%
700
25%
2155
18%
700
52%
700
26%
1322
November16th to endNight
32%
720
18%
2520
12%
720
42%
720
18%
1592
December1st to 15thNight
28%
720
15%
2520
9%
720
38%
720
14%
1709
December16th to endNight
27%
768
18%
2682
9%
768
40%
768
15%
1812

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
13%7%36%5%35%5%5%7%36%
46007
Night
12%6%35%5%3445%7%40%
45891
Cloud CoverDay
14%6%36%5%35%5%5%7%36%
46017
Night
12%6%25%5%35%5%5%7%40%
45895
TransparencyDay
44%7%12%20%13%2
45717
Night
40%6%13%22%14%2
45699
SeeingDay
18%11%21%22%17%8%
5015
Night
17%12%23%30%14%1
14921

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
13%6%47%7%45%5%46%33%
1611
16th to endDay
14%9%46%5%3345%6%36%
1728
February1st to 15thDay
12%11%47%435%45%6%33%
1575
16th to endDay
10%9%48%5%24445%37%
1545
March1st to 15thDay
15%9%35%424345%40%
1969
16th to endDay
16%8%46%5%25%45%5%34%
2112
April1st to 15thDay
13%9%45%42345%6%39%
2122
16th to endDay
16%6%25%5%2445%7%39%
2204
May1st to 15thDay
19%6%35%6%25%5%5%6%32%
2136
16th to endDay
13%5%25%6%36%45%8%37%
2314
June1st to 15thDay
12%4245%35%7%6%10%36%
2310
16th to endDay
10%436%6%46%6%7%9%36%
2310
July1st to 15thDay
11%6%37%6%45%6%7%7%32%
2204
16th to endDay
8%5%26%7%47%6%8%10%33%
2283
August1st to 15thDay
9%5%27%6%5%7%8%6%8%32%
2145
16th to endDay
11%5%26%6%46%6%6%9%34%
2151
September1st to 15thDay
12%5%25%6%35%5%5%7%41%
1972
16th to endDay
15%6%36%5%345%46%37%
1788
October1st to 15thDay
19%7%24323346%42%
1650
16th to endDay
13%8%35%5%235%45%42%
1760
November1st to 15thDay
11%7%25%324345%48%
1699
16th to endDay
16%8%35%425%346%37%
1440
December1st to 15thDay
15%9%345%35%5%5%5%35%
1440
16th to endDay
17%9%37%5%35%45%6%31%
1539
January1st to 15thNight
12%9%37%5%3445%7%36%
2327
16th to endNight
13%11%46%4245%45%36%
2496
February1st to 15thNight
12%7%46%6%2445%6%38%
2285
16th to endNight
10%10%37%7%35%5%5%7%33%
1925
March1st to 15thNight
13%8%27%6%33346%38%
1968
16th to endNight
14%8%36%5%3435%5%39%
2112
April1st to 15thNight
11%8%26%5%245%5%6%40%
1826
16th to endNight
13%6%24435%45%7%41%
1744
May1st to 15thNight
14%6%36%5%36%46%7%36%
1485
16th to endNight
10%6%14225%5%5%9%45%
1445
June1st to 15thNight
9%414435%46%9%44%
1320
16th to endNight
6%425%4345%7%8%46%
1320
July1st to 15thNight
9%5%25%5%35%6%6%8%41%
1423
16th to endNight
5%224435%6%7%14%44%
1577
August1st to 15thNight
6%424425%5%7%9%46%
1485
16th to endNight
8%42443446%9%46%
1687
September1st to 15thNight
11%31442446%8%47%
1655
16th to endNight
14%5%2343445%6%45%
1842
October1st to 15thNight
17%413423446%46%
1980
16th to endNight
14%5%24424445%47%
2112
November1st to 15thNight
12%8%35%313445%46%
2155
16th to endNight
13%6%46%5%35%45%6%38%
2520
December1st to 15thNight
14%7%47%6%36%5%36%33%
2520
16th to endNight
12%9%37%6%35%447%33%
2682

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
13%6%48%6%45%5%46%33%
1611
16th to endDay
15%8%46%434445%37%
1728
February1st to 15thDay
12%10%36%6%35%45%6%34%
1575
16th to endDay
11%9%47%6%2446%5%38%
1545
March1st to 15thDay
16%9%345%34336%40%
1980
16th to endDay
17%7%46%5%25%5%5%5%34%
2111
April1st to 15thDay
13%7%46%5%24447%39%
2122
16th to endDay
17%6%25%43445%6%39%
2204
May1st to 15thDay
21%6%25%6%25%5%5%6%32%
2136
16th to endDay
13%5%36%5%36%45%8%37%
2314
June1st to 15thDay
13%425%5%36%6%6%9%36%
2310
16th to endDay
10%426%6%45%6%7%8%36%
2310
July1st to 15thDay
12%7%27%7%36%6%6%6%32%
2204
16th to endDay
9%436%7%47%6%7%10%32%
2283
August1st to 15thDay
10%437%6%5%7%7%6%8%32%
2145
16th to endDay
13%5%25%6%36%6%6%8%34%
2151
September1st to 15thDay
12%5%25%435%5%47%41%
1972
16th to endDay
17%6%25%5%3445%6%37%
1788
October1st to 15thDay
21%6%24323346%41%
1650
16th to endDay
14%6%26%5%24445%41%
1760
November1st to 15thDay
11%5%35%424445%48%
1699
16th to endDay
17%8%35%5%24446%37%
1440
December1st to 15thDay
15%9%35%5%35%5%5%5%36%
1440
16th to endDay
16%10%36%5%35%5%5%6%31%
1539
January1st to 15thNight
13%8%37%5%3445%7%36%
2327
16th to endNight
14%9%46%5%246%45%36%
2496
February1st to 15thNight
11%7%36%5%35%45%6%39%
2278
16th to endNight
10%9%36%6%46%5%5%6%34%
1925
March1st to 15thNight
14%7%25%6%35%5%5%7%37%
1980
16th to endNight
14%7%26%5%3445%5%39%
2112
April1st to 15thNight
11%7%36%6%45%45%6%39%
1826
16th to endNight
13%5%25%5%3445%8%40%
1744
May1st to 15thNight
16%5%36%5%35%5%6%7%35%
1484
16th to endNight
12%424325%46%8%44%
1445
June1st to 15thNight
10%424435%46%8%44%
1320
16th to endNight
7%325%4346%6%8%46%
1320
July1st to 15thNight
11%4245%35%6%5%9%40%
1423
16th to endNight
5%323435%6%8%12%44%
1577
August1st to 15thNight
7%414435%5%7%9%45%
1485
16th to endNight
8%5%14435%46%10%45%
1687
September1st to 15thNight
12%3144235%6%7%47%
1655
16th to endNight
15%5%23424447%44%
1842
October1st to 15thNight
19%413434345%45%
1980
16th to endNight
13%5%24424445%47%
2112
November1st to 15thNight
11%6%35%424346%46%
2155
16th to endNight
14%6%34435%45%7%39%
2520
December1st to 15thNight
14%7%37%6%35%5%47%34%
2520
16th to endNight
13%8%36%6%36%5%5%7%33%
2682

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
49%6%11%18%12%2
1612
16th to endDay
47%5%12%19%12%2
1728
February1st to 15thDay
47%6%12%18%13%2
1577
16th to endDay
44%5%14%22%10%1
1545
March1st to 15thDay
46%411%23%12%2
1980
16th to endDay
49%6%10%18%13%1
2112
April1st to 15thDay
43%5%10%20%17%3
2122
16th to endDay
43%6%9%19%16%4
2204
May1st to 15thDay
50%7%13%18%10%
2136
16th to endDay
44%8%12%21%10%2
2318
June1st to 15thDay
40%10%15%19%12%1
2310
16th to endDay
42%8%16%18%12%2
2310
July1st to 15thDay
47%9%10%17%11%3
2064
16th to endDay
42%9%14%18%12%1
2128
August1st to 15thDay
45%10%12%18%12%
2132
16th to endDay
43%9%12%22%10%1
2151
September1st to 15thDay
40%6%13%18%18%2
1972
16th to endDay
46%6%7%21%15%1
1788
October1st to 15thDay
43%410%25%12%4
1650
16th to endDay
41%5%9%23%17%2
1760
November1st to 15thDay
35%5%11%20%21%6%
1699
16th to endDay
45%5%11%20%15%1
1440
December1st to 15thDay
47%6%12%18%12%2
1440
16th to endDay
50%7%11%19%10%1
1539
January1st to 15thNight
45%5%12%17%15%3
2327
16th to endNight
45%6%12%20%13%1
2496
February1st to 15thNight
42%5%13%21%14%1
2287
16th to endNight
45%7%13%20%12%1
1925
March1st to 15thNight
43%6%13%24%9%2
1980
16th to endNight
44%6%13%20%13%1
2112
April1st to 15thNight
44%6%10%21%15%2
1826
16th to endNight
40%7%10%20%16%5%
1744
May1st to 15thNight
45%7%13%20%11%1
1485
16th to endNight
36%9%16%24%11%1
1447
June1st to 15thNight
35%9%13%27%13%
1320
16th to endNight
32%9%16%23%15%2
1320
July1st to 15thNight
39%9%16%18%12%3
1334
16th to endNight
26%9%21%25%15%
1469
August1st to 15thNight
32%9%16%24%16%
1474
16th to endNight
33%8%14%29%12%1
1687
September1st to 15thNight
33%8%15%19%20%2
1655
16th to endNight
39%6%9%24%19%1
1842
October1st to 15thNight
40%310%26%17%1
1980
16th to endNight
35%5%10%26%19%1
2112
November1st to 15thNight
38%49%20%19%7%
2155
16th to endNight
42%5%12%20%16%2
2520
December1st to 15thNight
48%6%11%19%12%1
2520
16th to endNight
46%7%14%19%11%1
2682

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%33%26%8%6%3
90
16th to endDay
32%25%30%9%3
96
February1st to 15thDay
30%35%28%41
90
16th to endDay
23%22%29%23%1
150
March1st to 15thDay
25%20%23%23%7%
270
16th to endDay
20%20%28%20%8%2
288
April1st to 15thDay
18%20%24%22%11%2
270
16th to endDay
22%11%25%19%15%6%
266
May1st to 15thDay
24%11%21%20%13%8%
228
16th to endDay
19%7%19%21%19%12%
267
June1st to 15thDay
14%6%25%22%20%10%
255
16th to endDay
12%6%25%27%20%7%
255
July1st to 15thDay
15%224%28%20%8%
245
16th to endDay
8%114%29%28%17%
270
August1st to 15thDay
13%115%22%32%13%
253
16th to endDay
13%19%26%23%25%
268
September1st to 15thDay
10%6%14%19%29%19%
255
16th to endDay
23%118%21%22%11%
254
October1st to 15thDay
23%7%13%25%22%6%
255
16th to endDay
15%16%27%25%13%2
272
November1st to 15thDay
19%8%19%28%19%3
233
16th to endDay
31%11%25%18%10%3
60
December1st to 15thDay
26%25%20%13%10%5%
60
16th to endDay
26%26%32%10%4
65
January1st to 15thNight
23%18%30%23%4
720
16th to endNight
21%19%35%23%1
768
February1st to 15thNight
20%21%28%28%1
704
16th to endNight
21%22%31%22%1
631
March1st to 15thNight
23%17%29%25%4
720
16th to endNight
19%19%29%22%7%1
768
April1st to 15thNight
18%20%29%24%6%
718
16th to endNight
19%11%25%31%12%
669
May1st to 15thNight
17%8%26%30%15%1
495
16th to endNight
15%322%33%22%3
422
June1st to 15thNight
11%323%38%23%1
330
16th to endNight
7%217%50%20%1
330
July1st to 15thNight
14%112%38%30%1
404
16th to endNight
6%113%36%36%6%
522
August1st to 15thNight
8%111%43%32%2
494
16th to endNight
12%11%38%33%4
637
September1st to 15thNight
13%215%29%33%4
660
16th to endNight
17%419%30%26%2
657
October1st to 15thNight
21%8%17%29%20%3
660
16th to endNight
16%14%25%30%11%
704
November1st to 15thNight
15%13%20%35%14%1
700
16th to endNight
20%18%23%26%10%
720
December1st to 15thNight
20%16%28%26%7%
720
16th to endNight
20%15%29%32%1
768
Page generated at 2017-04-30 20:40:01. Version ac04

Copyright 2017 A. Danko


Mountain Meadows Observatory Clear Sky Chart | Charts Home