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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 2018-02-22.

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
36%
15623
17%
48860
9%
15591
45%
15591
22%
32429

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
20%
780
19%
2716
7%
776
35%
776
18%
1738
January16th to endNight
18%
832
18%
2912
5%
832
35%
832
16%
1895
February1st to 15thNight
17%
764
17%
2329
4%
761
32%
761
19%
1590
February16th to endNight
20%
659
23%
1976
7%
659
40%
659
23%
1300
March1st to 15thNight
27%
720
17%
2160
8%
720
39%
720
20%
1467
March16th to endNight
29%
768
22%
2022
8%
768
40%
768
27%
1358
April1st to 15thNight
37%
718
17%
1796
6%
718
42%
718
26%
1269
April16th to endNight
38%
615
16%
1695
6%
615
42%
615
25%
1195
May1st to 15thNight
40%
540
15%
1620
9%
540
45%
540
20%
1158
May16th to endNight
43%
435
10%
1557
9%
434
46%
434
15%
1100
June1st to 15thNight
44%
360
12%
1440
14%
360
49%
360
15%
978
June16th to endNight
60%
360
13%
1440
18%
360
62%
360
22%
863
July1st to 15thNight
58%
340
11%
1360
17%
340
59%
340
18%
859
July16th to endNight
61%
376
14%
1418
17%
354
64%
354
20%
892
August1st to 15thNight
64%
520
17%
1591
15%
518
64%
518
28%
1000
August16th to endNight
65%
759
20%
1905
13%
759
66%
759
35%
1251
September1st to 15thNight
54%
720
19%
1857
12%
720
56%
720
31%
1234
September16th to endNight
50%
717
21%
1980
17%
717
54%
717
27%
1336
October1st to 15thNight
40%
720
22%
2002
13%
720
49%
720
26%
1337
October16th to endNight
32%
768
18%
2484
9%
768
45%
768
22%
1592
November1st to 15thNight
33%
760
18%
2472
12%
760
44%
760
21%
1630
November16th to endNight
30%
780
20%
2535
10%
780
43%
780
20%
1627
December1st to 15thNight
24%
780
15%
2681
5%
780
36%
780
16%
1813
December16th to endNight
16%
832
18%
2912
4%
832
35%
832
17%
1947

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%24424447%41%
49401
Night
18%6%25%424346%40%
49030
Cloud CoverDay
16%6%2442445%7%41%
49411
Night
17%7%24424346%40%
49035
TransparencyDay
41%6%12%22%14%2
49089
Night
44%5%12%20%14%2
48860
SeeingDay
20%5%23%30%16%2
6403
Night
21%7%28%28%12%1
15623

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
16%6%2442335%444%
1552
16th to endDay
17%6%23423337%43%
1664
February1st to 15thDay
17%7%345%3445%7%36%
1859
16th to endDay
17%6%3342445%7%40%
1644
March1st to 15thDay
19%6%25%423347%40%
1790
16th to endDay
16%7%34424345%43%
2198
April1st to 15thDay
21%423325%5%46%41%
2152
16th to endDay
18%5%2442445%7%41%
2265
May1st to 15thDay
25%6%24433345%35%
2332
16th to endDay
18%6%25%324447%39%
2568
June1st to 15thDay
23%5%2332445%8%35%
2520
16th to endDay
13%5%234245%5%10%42%
2520
July1st to 15thDay
14%5%244235%5%8%42%
2520
16th to endDay
14%4245%2447%8%39%
2654
August1st to 15thDay
13%5%14435%45%8%43%
2346
16th to endDay
11%425%42445%8%46%
2297
September1st to 15thDay
14%5%24324445%48%
2103
16th to endDay
14%5%23434336%47%
1980
October1st to 15thDay
17%6%24323346%44%
1956
16th to endDay
16%424423346%46%
1740
November1st to 15thDay
20%5%23424345%42%
1716
16th to endDay
16%324424437%44%
1755
December1st to 15thDay
20%6%25%324346%41%
1606
16th to endDay
22%9%24422346%37%
1664
January1st to 15thNight
18%6%24423345%43%
2716
16th to endNight
18%9%24423346%40%
2912
February1st to 15thNight
16%8%26%423335%41%
2328
16th to endNight
17%7%24334336%42%
1976
March1st to 15thNight
19%6%25%324446%39%
2147
16th to endNight
16%7%2442334445%
2022
April1st to 15thNight
18%8%25%42435%5%39%
1796
16th to endNight
22%6%26%423345%38%
1695
May1st to 15thNight
21%7%44424436%35%
1620
16th to endNight
20%8%25%5%35%45%8%30%
1555
June1st to 15thNight
25%7%24414346%35%
1440
16th to endNight
16%42432445%9%41%
1440
July1st to 15thNight
17%5%25%436%5%47%37%
1440
16th to endNight
13%5%45%6%36%46%8%36%
1514
August1st to 15thNight
9%6%26%43447%8%41%
1601
16th to endNight
12%42442435%7%47%
1905
September1st to 15thNight
16%425%33445%6%42%
1857
16th to endNight
16%6%2442433445%
1980
October1st to 15thNight
16%6%25%433346%43%
2002
16th to endNight
17%5%2442435%6%42%
2484
November1st to 15thNight
17%6%25%433345%43%
2472
16th to endNight
17%5%24323447%42%
2535
December1st to 15thNight
21%5%25%334345%39%
2681
16th to endNight
19%7%35%424445%39%
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
17%6%25%43435%6%40%
1552
16th to endDay
17%7%23323247%43%
1664
February1st to 15thDay
17%7%25%4245%48%36%
1859
16th to endDay
17%6%3341446%7%40%
1644
March1st to 15thDay
19%6%23424447%40%
1800
16th to endDay
16%7%34334336%43%
2198
April1st to 15thDay
20%41432445%6%42%
2152
16th to endDay
16%5%2432445%7%41%
2265
May1st to 15thDay
24%7%24324346%35%
2332
16th to endDay
17%7%24425%447%38%
2568
June1st to 15thDay
21%5%24425%45%7%35%
2520
16th to endDay
11%5%2342446%9%43%
2520
July1st to 15thDay
12%6%2442446%8%42%
2520
16th to endDay
13%5%25%42446%8%40%
2654
August1st to 15thDay
12%41443446%7%45%
2346
16th to endDay
10%5%2442445%8%48%
2297
September1st to 15thDay
13%42442345%6%48%
2103
16th to endDay
14%5%24423446%46%
1980
October1st to 15thDay
17%6%24423435%45%
1956
16th to endDay
16%425%5%23346%46%
1740
November1st to 15thDay
21%5%24423436%42%
1716
16th to endDay
16%335%423447%43%
1755
December1st to 15thDay
21%6%35%322446%39%
1606
16th to endDay
22%9%34313346%35%
1664
January1st to 15thNight
19%7%25%423347%40%
2716
16th to endNight
19%9%24423446%39%
2912
February1st to 15thNight
16%8%35%5%24345%40%
2321
16th to endNight
18%6%24433346%42%
1976
March1st to 15thNight
19%7%2443435%6%39%
2160
16th to endNight
17%7%24423345%44%
2021
April1st to 15thNight
17%8%34434446%39%
1796
16th to endNight
21%7%24424346%38%
1695
May1st to 15thNight
20%9%345%24446%34%
1620
16th to endNight
20%8%25%5%35%448%30%
1555
June1st to 15thNight
24%8%24424346%35%
1440
16th to endNight
15%5%2442445%9%41%
1440
July1st to 15thNight
14%6%245%45%5%6%8%37%
1440
16th to endNight
11%6%35%7%35%6%6%7%36%
1514
August1st to 15thNight
8%5%25%5%35%47%7%42%
1601
16th to endNight
11%5%15%424348%47%
1905
September1st to 15thNight
15%5%25%43345%6%42%
1857
16th to endNight
16%6%35%43333344%
1980
October1st to 15thNight
17%7%34424346%42%
2002
16th to endNight
17%5%2442445%6%42%
2484
November1st to 15thNight
18%6%35%433345%42%
2472
16th to endNight
17%6%25%425%346%41%
2535
December1st to 15thNight
21%7%34434346%36%
2681
16th to endNight
20%7%35%42335%6%36%
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
43%6%12%21%12%3
1553
16th to endDay
41%5%12%24%14%1
1664
February1st to 15thDay
45%5%14%21%11%1
1862
16th to endDay
42%412%24%12%2
1644
March1st to 15thDay
43%5%14%23%9%3
1800
16th to endDay
42%411%20%16%4
2198
April1st to 15thDay
42%411%21%16%3
2152
16th to endDay
41%5%9%23%15%4
2265
May1st to 15thDay
50%49%19%13%2
2332
16th to endDay
44%6%13%20%11%1
2572
June1st to 15thDay
47%7%12%19%11%
2520
16th to endDay
36%8%15%24%14%
2520
July1st to 15thDay
39%7%13%23%14%1
2371
16th to endDay
38%7%16%23%12%2
2487
August1st to 15thDay
36%8%15%23%15%
2332
16th to endDay
34%7%10%27%17%2
2297
September1st to 15thDay
34%7%12%21%21%1
2103
16th to endDay
37%6%7%22%23%1
1980
October1st to 15thDay
41%5%10%23%16%2
1956
16th to endDay
38%5%13%22%16%2
1740
November1st to 15thDay
44%6%13%17%15%2
1716
16th to endDay
40%5%13%23%14%2
1755
December1st to 15thDay
45%5%16%16%14%
1606
16th to endDay
50%5%14%18%11%
1664
January1st to 15thNight
44%413%22%13%1
2716
16th to endNight
46%411%20%14%2
2912
February1st to 15thNight
46%5%13%19%11%2
2329
16th to endNight
44%311%21%16%2
1976
March1st to 15thNight
46%5%12%19%13%3
2160
16th to endNight
42%49%18%19%5%
2022
April1st to 15thNight
46%410%19%15%2
1796
16th to endNight
48%49%18%15%4
1695
May1st to 15thNight
51%5%10%16%13%3
1620
16th to endNight
50%8%15%14%8%2
1557
June1st to 15thNight
50%6%11%16%14%
1440
16th to endNight
39%6%13%23%15%1
1440
July1st to 15thNight
42%8%13%20%13%
1360
16th to endNight
41%8%16%21%9%2
1418
August1st to 15thNight
37%7%14%25%13%2
1591
16th to endNight
35%6%11%26%18%1
1905
September1st to 15thNight
39%6%12%22%18%1
1857
16th to endNight
44%46%18%23%1
1980
October1st to 15thNight
43%49%22%16%3
2002
16th to endNight
42%5%15%21%14%1
2484
November1st to 15thNight
44%5%11%18%15%3
2472
16th to endNight
43%5%13%22%12%2
2535
December1st to 15thNight
48%5%14%17%12%
2681
16th to endNight
48%5%13%20%11%
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
12%21%41%18%6%
90
16th to endDay
27%9%37%22%3
96
February1st to 15thDay
26%9%43%18%1
297
16th to endDay
18%9%43%24%5%
265
March1st to 15thDay
24%12%29%28%4
270
16th to endDay
19%7%37%25%9%1
288
April1st to 15thDay
23%6%25%34%9%
270
16th to endDay
21%326%33%11%2
270
May1st to 15thDay
31%426%24%11%1
288
16th to endDay
24%116%35%19%3
331
June1st to 15thDay
23%319%30%20%2
315
16th to endDay
16%316%41%20%2
315
July1st to 15thDay
19%19%41%25%2
305
16th to endDay
13%111%39%29%3
326
August1st to 15thDay
15%11%35%30%5%
313
16th to endDay
10%110%39%25%12%
332
September1st to 15thDay
14%221%27%26%6%
315
16th to endDay
21%216%28%22%8%
314
October1st to 15thDay
20%319%29%22%4
315
16th to endDay
17%7%32%29%13%
291
November1st to 15thDay
22%9%24%28%12%1
280
16th to endDay
18%12%29%25%12%
285
December1st to 15thDay
23%12%30%23%8%
136
16th to endDay
28%14%38%17%1
96
January1st to 15thNight
22%14%38%20%3
780
16th to endNight
24%12%39%21%1
832
February1st to 15thNight
21%12%43%21%1
764
16th to endNight
22%10%42%20%3
659
March1st to 15thNight
23%10%33%26%5%
720
16th to endNight
21%6%36%26%8%
768
April1st to 15thNight
22%431%33%8%
718
16th to endNight
23%228%33%11%1
615
May1st to 15thNight
22%323%34%13%2
540
16th to endNight
24%218%36%16%2
435
June1st to 15thNight
26%316%31%21%
360
16th to endNight
17%210%42%26%
360
July1st to 15thNight
18%9%42%26%2
340
16th to endNight
14%19%40%32%2
376
August1st to 15thNight
11%10%46%28%1
520
16th to endNight
13%29%33%33%7%
759
September1st to 15thNight
18%118%36%21%4
720
16th to endNight
19%216%29%25%6%
717
October1st to 15thNight
20%6%26%25%16%3
720
16th to endNight
19%9%34%24%11%
768
November1st to 15thNight
20%8%30%25%13%1
760
16th to endNight
21%12%30%25%8%1
780
December1st to 15thNight
24%13%32%21%6%
780
16th to endNight
23%12%42%18%2
832
Page generated at 2018-02-23 11:21:34. Version ac04

Copyright 2018 A. Danko


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