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Frosty Drew Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Frosty Drew Observatory clear sky chart from 2005-11-05 to 2020-10-02.

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
29%
18845
19%
58872
9%
18814
41%
18814
19%
38599

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
16%
900
21%
3136
7%
896
34%
896
16%
1978
January16th to endNight
17%
960
20%
3360
6%
960
36%
960
14%
2143
February1st to 15thNight
14%
884
18%
2695
5%
881
31%
881
16%
1825
February16th to endNight
17%
791
24%
2373
8%
791
37%
791
17%
1576
March1st to 15thNight
20%
900
18%
2700
7%
900
33%
900
16%
1828
March16th to endNight
22%
960
23%
2528
7%
960
35%
960
22%
1710
April1st to 15thNight
22%
898
18%
2246
4%
898
31%
898
21%
1584
April16th to endNight
26%
759
18%
2095
5%
759
34%
759
21%
1465
May1st to 15thNight
26%
675
14%
2025
6%
675
33%
675
16%
1447
May16th to endNight
29%
546
9%
1957
7%
546
34%
546
13%
1375
June1st to 15thNight
38%
450
15%
1800
14%
450
46%
450
16%
1168
June16th to endNight
46%
450
13%
1800
13%
450
52%
450
19%
1069
July1st to 15thNight
50%
430
13%
1720
17%
430
53%
430
18%
1070
July16th to endNight
51%
472
16%
1802
19%
450
58%
450
20%
1119
August1st to 15thNight
52%
640
16%
1961
12%
638
55%
638
25%
1247
August16th to endNight
57%
949
21%
2383
11%
949
59%
949
34%
1547
September1st to 15thNight
45%
900
18%
2321
10%
900
49%
900
28%
1570
September16th to endNight
44%
897
23%
2475
15%
897
52%
897
28%
1610
October1st to 15thNight
34%
848
22%
2357
12%
848
43%
848
23%
1595
October16th to endNight
28%
896
19%
2898
9%
896
42%
896
21%
1810
November1st to 15thNight
26%
880
20%
2862
10%
880
40%
880
19%
1842
November16th to endNight
22%
900
22%
2925
8%
900
39%
900
19%
1822
December1st to 15thNight
20%
900
19%
3093
7%
900
35%
900
14%
2012
December16th to endNight
14%
960
21%
3360
5%
960
34%
960
14%
2187

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
17%5%2442445%7%40%
60216
Night
17%6%25%424446%40%
59042
Cloud CoverDay
16%6%2442445%7%40%
60226
Night
17%7%25%424446%40%
59047
TransparencyDay
43%5%11%21%15%2
59904
Night
44%411%21%15%2
58872
SeeingDay
19%13%28%25%10%1
9852
Night
19%19%26%24%9%
18846

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
17%6%245%2435%6%42%
1792
16th to endDay
15%6%24423347%45%
1920
February1st to 15thDay
18%6%3443445%6%36%
2153
16th to endDay
17%7%3442445%6%40%
1980
March1st to 15thDay
19%5%25%5%2335%7%38%
2240
16th to endDay
16%8%25%423345%41%
2747
April1st to 15thDay
21%5%24424346%38%
2692
16th to endDay
19%5%25%434446%39%
2799
May1st to 15thDay
24%7%245%24346%34%
2917
16th to endDay
17%5%2443445%7%39%
3226
June1st to 15thDay
21%6%244245%6%8%33%
3150
16th to endDay
13%5%24425%5%5%10%39%
3150
July1st to 15thDay
14%4245%3446%10%40%
3150
16th to endDay
14%5%24435%5%6%9%38%
3326
August1st to 15thDay
13%5%145%25%5%6%9%40%
2886
16th to endDay
10%5%25%5%35%5%6%7%43%
2874
September1st to 15thDay
15%5%25%324446%44%
2628
16th to endDay
13%6%23423446%47%
2475
October1st to 15thDay
20%7%24423345%41%
2296
16th to endDay
17%415%423345%45%
2030
November1st to 15thDay
20%5%15%423345%43%
1986
16th to endDay
16%434424445%44%
2025
December1st to 15thDay
21%6%23323345%41%
1854
16th to endDay
21%8%34424345%39%
1920
January1st to 15thNight
19%6%24424345%42%
3136
16th to endNight
16%9%34423345%42%
3360
February1st to 15thNight
16%9%26%5%23335%40%
2694
16th to endNight
18%6%24434445%41%
2373
March1st to 15thNight
18%7%25%42445%6%38%
2687
16th to endNight
16%8%25%424335%43%
2528
April1st to 15thNight
18%8%34424446%38%
2246
16th to endNight
22%6%35%5%23345%37%
2095
May1st to 15thNight
20%8%45%433445%34%
2025
16th to endNight
20%7%36%6%345%5%7%30%
1955
June1st to 15thNight
22%7%24424447%36%
1800
16th to endNight
16%6%2443345%9%39%
1800
July1st to 15thNight
16%5%25%435%5%5%7%38%
1800
16th to endNight
13%6%35%5%35%5%6%8%35%
1898
August1st to 15thNight
9%6%246%35%5%8%8%39%
1971
16th to endNight
12%5%2442446%8%45%
2383
September1st to 15thNight
16%5%25%424446%41%
2321
16th to endNight
15%6%2442434446%
2475
October1st to 15thNight
17%7%35%423346%41%
2357
16th to endNight
17%5%24423347%43%
2898
November1st to 15thNight
17%6%25%423335%43%
2862
16th to endNight
17%6%24423446%44%
2925
December1st to 15thNight
21%5%24434335%39%
3093
16th to endNight
19%6%25%424445%39%
3360

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
16%7%2443345%5%41%
1792
16th to endDay
16%6%24323447%44%
1920
February1st to 15thDay
18%7%35%42446%8%35%
2153
16th to endDay
17%7%2442445%7%40%
1980
March1st to 15thDay
18%5%25%42345%7%39%
2250
16th to endDay
16%7%35%5%23346%41%
2747
April1st to 15thDay
20%5%24424447%39%
2692
16th to endDay
19%5%24434447%39%
2799
May1st to 15thDay
23%7%245%23446%34%
2917
16th to endDay
18%6%25%43445%7%38%
3226
June1st to 15thDay
20%6%24335%46%7%35%
3150
16th to endDay
13%5%234345%7%10%39%
3150
July1st to 15thDay
12%5%245%3445%9%41%
3150
16th to endDay
13%5%25%42447%8%40%
3326
August1st to 15thDay
12%5%15%4245%5%9%41%
2886
16th to endDay
10%5%25%5%245%5%7%45%
2874
September1st to 15thDay
14%6%2432445%5%46%
2628
16th to endDay
13%6%24434348%46%
2475
October1st to 15thDay
18%7%25%423345%41%
2296
16th to endDay
16%5%1442335%6%45%
2030
November1st to 15thDay
19%6%24423345%43%
1986
16th to endDay
15%5%245%33437%43%
2025
December1st to 15thDay
21%7%24223346%40%
1854
16th to endDay
21%9%24323346%37%
1920
January1st to 15thNight
18%7%24433346%41%
3136
16th to endNight
16%10%24423346%40%
3360
February1st to 15thNight
17%8%26%423335%40%
2687
16th to endNight
18%7%24434345%41%
2373
March1st to 15thNight
19%7%25%42445%6%37%
2700
16th to endNight
15%8%35%424345%43%
2527
April1st to 15thNight
18%8%2442435%6%38%
2246
16th to endNight
22%7%26%5%23335%38%
2095
May1st to 15thNight
21%9%35%434435%33%
2025
16th to endNight
21%8%25%5%35%45%8%29%
1955
June1st to 15thNight
22%7%34324446%36%
1800
16th to endNight
15%6%34334449%39%
1800
July1st to 15thNight
14%6%25%436%5%5%8%38%
1800
16th to endNight
13%6%35%6%36%5%6%8%36%
1898
August1st to 15thNight
8%6%36%4345%7%8%40%
1971
16th to endNight
11%5%25%32445%8%46%
2383
September1st to 15thNight
16%5%3443445%6%42%
2321
16th to endNight
15%6%24424435%45%
2475
October1st to 15thNight
18%7%35%433246%40%
2357
16th to endNight
17%5%2442445%6%42%
2898
November1st to 15thNight
17%6%25%433345%42%
2862
16th to endNight
17%6%2432435%6%42%
2925
December1st to 15thNight
21%6%25%434336%38%
3093
16th to endNight
19%7%25%42435%5%39%
3360

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
43%412%22%14%3
1793
16th to endDay
40%411%24%16%2
1920
February1st to 15thDay
46%412%20%12%2
2156
16th to endDay
45%310%21%15%3
1980
March1st to 15thDay
46%312%23%11%2
2250
16th to endDay
44%38%20%17%4
2747
April1st to 15thDay
46%49%20%15%3
2692
16th to endDay
45%48%20%16%3
2799
May1st to 15thDay
50%5%9%17%13%3
2917
16th to endDay
43%6%13%22%12%2
3230
June1st to 15thDay
48%6%11%19%12%1
3150
16th to endDay
39%7%15%22%13%
3150
July1st to 15thDay
40%7%12%23%14%1
3001
16th to endDay
39%6%14%23%12%2
3159
August1st to 15thDay
40%6%14%22%14%
2872
16th to endDay
38%6%9%25%17%2
2874
September1st to 15thDay
40%5%10%22%18%2
2628
16th to endDay
37%48%22%24%2
2475
October1st to 15thDay
45%49%22%14%3
2296
16th to endDay
40%411%23%17%2
2030
November1st to 15thDay
44%413%17%16%2
1986
16th to endDay
42%410%25%15%3
2025
December1st to 15thDay
44%313%18%18%1
1854
16th to endDay
48%312%20%13%1
1920
January1st to 15thNight
44%411%22%14%2
3136
16th to endNight
45%410%20%16%2
3360
February1st to 15thNight
47%311%20%13%2
2695
16th to endNight
45%38%20%17%3
2373
March1st to 15thNight
47%411%20%13%3
2700
16th to endNight
44%37%18%21%4
2528
April1st to 15thNight
47%310%19%15%2
2246
16th to endNight
49%37%18%16%4
2095
May1st to 15thNight
51%410%16%14%2
2025
16th to endNight
51%7%15%15%8%1
1957
June1st to 15thNight
47%6%10%19%14%1
1800
16th to endNight
41%415%25%12%
1800
July1st to 15thNight
42%6%12%22%14%
1720
16th to endNight
41%6%14%25%9%2
1802
August1st to 15thNight
38%7%14%24%13%1
1961
16th to endNight
35%6%12%26%18%1
2383
September1st to 15thNight
42%412%22%16%
2321
16th to endNight
40%47%20%24%2
2475
October1st to 15thNight
44%5%8%23%14%3
2357
16th to endNight
41%412%24%15%1
2898
November1st to 15thNight
44%411%20%16%3
2862
16th to endNight
41%312%25%14%2
2925
December1st to 15thNight
47%313%20%14%
3093
16th to endNight
46%410%23%13%1
3360

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
16%31%34%14%4
150
16th to endDay
20%18%36%19%5%
160
February1st to 15thDay
25%22%36%13%1
411
16th to endDay
18%22%37%16%4
399
March1st to 15thDay
21%21%33%21%2
450
16th to endDay
21%17%40%15%4
480
April1st to 15thDay
23%19%30%20%5%
450
16th to endDay
26%14%30%22%5%1
439
May1st to 15thDay
27%15%30%19%5%
468
16th to endDay
20%11%29%27%8%1
523
June1st to 15thDay
20%12%27%27%10%1
495
16th to endDay
17%8%27%30%13%1
495
July1st to 15thDay
17%5%18%36%19%2
485
16th to endDay
13%7%18%38%18%2
518
August1st to 15thDay
15%6%20%38%17%2
478
16th to endDay
12%423%36%17%6%
524
September1st to 15thDay
17%7%23%29%15%5%
495
16th to endDay
18%7%25%27%15%6%
494
October1st to 15thDay
26%10%20%25%15%2
440
16th to endDay
18%16%28%28%7%
389
November1st to 15thDay
19%21%28%20%8%1
370
16th to endDay
17%26%28%19%7%1
375
December1st to 15thDay
24%13%34%21%5%
204
16th to endDay
23%16%40%17%2
160
January1st to 15thNight
19%26%34%16%3
900
16th to endNight
20%27%30%18%2
960
February1st to 15thNight
20%26%33%17%1
884
16th to endNight
21%25%32%16%2
791
March1st to 15thNight
22%25%28%20%3
900
16th to endNight
20%22%31%21%4
960
April1st to 15thNight
22%20%30%21%4
898
16th to endNight
21%18%28%24%7%
759
May1st to 15thNight
22%19%25%24%7%1
675
16th to endNight
23%16%23%27%8%1
547
June1st to 15thNight
20%15%19%29%13%
450
16th to endNight
18%13%14%39%14%
450
July1st to 15thNight
19%10%12%37%19%
430
16th to endNight
14%13%13%37%18%1
472
August1st to 15thNight
12%8%18%40%19%1
640
16th to endNight
14%8%13%35%24%4
949
September1st to 15thNight
18%8%21%31%17%2
900
16th to endNight
18%10%20%27%19%4
897
October1st to 15thNight
22%12%25%24%12%1
848
16th to endNight
19%17%31%22%8%
896
November1st to 15thNight
18%21%27%21%9%
880
16th to endNight
17%27%28%18%7%
900
December1st to 15thNight
23%24%25%19%6%
900
16th to endNight
21%28%30%16%2
960
Page generated at 2020-10-03 13:49:20. Version ac04

Copyright 2020 A. Danko


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