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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 2017-08-12.

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%
14848
17%
46453
9%
14816
45%
14816
22%
30885

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%
720
18%
2506
7%
716
34%
716
17%
1627
January16th to endNight
18%
768
18%
2688
6%
768
34%
768
16%
1753
February1st to 15thNight
18%
704
17%
2146
4%
701
32%
701
19%
1451
February16th to endNight
20%
631
23%
1893
7%
631
40%
631
24%
1231
March1st to 15thNight
27%
720
17%
2160
8%
720
38%
720
20%
1467
March16th to endNight
29%
768
22%
2022
8%
768
41%
768
27%
1358
April1st to 15thNight
37%
718
17%
1796
6%
718
43%
718
26%
1269
April16th to endNight
37%
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
44%
435
10%
1557
9%
434
47%
434
15%
1100
June1st to 15thNight
44%
360
12%
1440
14%
360
49%
360
15%
978
June16th to endNight
61%
360
13%
1440
18%
360
63%
360
22%
863
July1st to 15thNight
60%
340
11%
1360
17%
340
60%
340
18%
859
July16th to endNight
62%
376
14%
1418
17%
354
65%
354
20%
892
August1st to 15thNight
65%
509
17%
1558
15%
507
66%
507
28%
973
August16th to endNight
64%
695
18%
1745
11%
695
65%
695
34%
1160
September1st to 15thNight
56%
660
20%
1702
12%
660
58%
660
30%
1142
September16th to endNight
52%
657
21%
1815
17%
657
56%
657
29%
1202
October1st to 15thNight
39%
660
23%
1835
13%
660
48%
660
25%
1230
October16th to endNight
32%
704
16%
2277
7%
704
44%
704
22%
1471
November1st to 15thNight
33%
700
19%
2277
12%
700
44%
700
21%
1498
November16th to endNight
30%
720
18%
2340
9%
720
41%
720
20%
1529
December1st to 15thNight
24%
720
16%
2475
6%
720
36%
720
16%
1659
December16th to endNight
16%
768
18%
2688
4%
768
34%
768
16%
1820

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%41%
47529
Night
18%6%25%424346%40%
46623
Cloud CoverDay
16%6%2442445%7%41%
47539
Night
17%7%24424446%40%
46628
TransparencyDay
41%6%13%22%14%2
47217
Night
44%5%12%20%14%2
46453
SeeingDay
20%5%23%30%16%3
5794
Night
20%7%28%28%13%1
14848

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%7%2442345%5%42%
1432
16th to endDay
16%6%24423338%43%
1536
February1st to 15thDay
16%6%344345%5%7%37%
1712
16th to endDay
17%5%2342445%7%40%
1580
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%44%
2294
16th to endDay
11%425%42445%7%46%
2105
September1st to 15thDay
14%5%23324445%47%
1928
16th to endDay
14%5%23424336%48%
1815
October1st to 15thDay
17%6%24323346%44%
1793
16th to endDay
15%425%424446%45%
1595
November1st to 15thDay
21%5%23423335%43%
1581
16th to endDay
16%4245%34447%43%
1620
December1st to 15thDay
20%6%24324346%41%
1483
16th to endDay
23%9%24423345%37%
1536
January1st to 15thNight
19%7%24423345%41%
2506
16th to endNight
18%9%24423346%40%
2688
February1st to 15thNight
15%8%26%423335%42%
2145
16th to endNight
16%6%24334346%43%
1893
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%42%
1568
16th to endNight
12%425%43435%8%45%
1745
September1st to 15thNight
16%425%334446%42%
1702
16th to endNight
16%42442434446%
1815
October1st to 15thNight
16%5%25%5%33346%43%
1835
16th to endNight
16%5%2442435%6%41%
2277
November1st to 15thNight
17%6%25%333345%43%
2277
16th to endNight
18%5%2432345%7%40%
2340
December1st to 15thNight
22%5%25%334345%40%
2475
16th to endNight
20%6%35%424445%38%
2688

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%7%25%42435%6%40%
1432
16th to endDay
16%7%23424347%42%
1536
February1st to 15thDay
17%6%25%4245%48%37%
1712
16th to endDay
16%6%3341446%7%40%
1580
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
11%4145%3446%7%45%
2294
16th to endDay
10%5%2442445%8%47%
2105
September1st to 15thDay
13%42342445%6%48%
1928
16th to endDay
14%5%23423447%48%
1815
October1st to 15thDay
16%6%34422335%45%
1793
16th to endDay
15%425%5%23446%46%
1595
November1st to 15thDay
21%5%13423336%43%
1581
16th to endDay
16%435%433448%41%
1620
December1st to 15thDay
20%6%24322446%39%
1483
16th to endDay
23%9%34313345%35%
1536
January1st to 15thNight
19%7%25%423346%39%
2506
16th to endNight
19%9%24423446%38%
2688
February1st to 15thNight
15%8%35%5%24345%41%
2138
16th to endNight
16%6%24434346%42%
1893
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%426%5%35%47%7%43%
1568
16th to endNight
11%5%26%434448%46%
1745
September1st to 15thNight
14%5%25%43345%6%42%
1702
16th to endNight
15%5%25%43433446%
1815
October1st to 15thNight
17%7%34424346%42%
1835
16th to endNight
16%6%2443435%6%41%
2277
November1st to 15thNight
18%6%35%333345%42%
2277
16th to endNight
18%6%25%425%35%6%39%
2340
December1st to 15thNight
22%6%23434346%37%
2475
16th to endNight
20%7%35%42335%6%36%
2688

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
44%6%13%20%12%2
1433
16th to endDay
41%5%11%25%14%1
1536
February1st to 15thDay
44%5%15%21%11%
1715
16th to endDay
42%413%24%12%2
1580
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
35%8%15%23%15%1
2280
16th to endDay
35%7%11%26%17%2
2105
September1st to 15thDay
35%7%13%21%21%1
1928
16th to endDay
36%6%8%23%23%2
1815
October1st to 15thDay
41%5%10%23%16%3
1793
16th to endDay
38%5%14%22%16%2
1595
November1st to 15thDay
43%5%14%17%16%2
1581
16th to endDay
41%5%13%23%13%2
1620
December1st to 15thDay
44%5%17%18%13%1
1483
16th to endDay
50%5%14%17%11%
1536
January1st to 15thNight
46%413%21%12%1
2506
16th to endNight
46%410%21%14%2
2688
February1st to 15thNight
45%5%14%20%11%1
2146
16th to endNight
42%411%22%16%2
1893
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
1558
16th to endNight
36%6%11%26%16%1
1745
September1st to 15thNight
40%6%13%22%17%
1702
16th to endNight
41%5%7%19%24%2
1815
October1st to 15thNight
44%49%22%15%3
1835
16th to endNight
42%5%15%20%13%1
2277
November1st to 15thNight
44%5%11%19%15%3
2277
16th to endNight
44%5%13%21%12%2
2340
December1st to 15thNight
47%6%15%18%12%
2475
16th to endNight
49%5%13%20%10%
2688

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
13%21%35%25%5%
60
16th to endDay
23%12%39%21%3
64
February1st to 15thDay
25%9%44%18%2
240
16th to endDay
15%9%43%25%5%
239
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
14%11%35%31%6%
297
16th to endDay
10%19%34%27%15%
268
September1st to 15thDay
14%220%25%28%8%
255
16th to endDay
20%115%30%23%8%
254
October1st to 15thDay
20%321%28%21%4
255
16th to endDay
14%7%36%30%10%
242
November1st to 15thDay
23%9%25%25%14%2
235
16th to endDay
19%11%29%26%12%
240
December1st to 15thDay
22%15%32%22%6%
103
16th to endDay
34%439%20%1
64
January1st to 15thNight
23%14%37%20%3
720
16th to endNight
24%13%38%21%1
768
February1st to 15thNight
20%13%42%21%1
704
16th to endNight
21%10%44%20%3
631
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%47%27%1
509
16th to endNight
13%29%32%33%8%
695
September1st to 15thNight
17%116%36%22%5%
660
16th to endNight
17%216%30%26%6%
657
October1st to 15thNight
20%6%28%25%15%3
660
16th to endNight
19%9%35%25%9%
704
November1st to 15thNight
20%9%29%24%13%1
700
16th to endNight
22%12%29%25%9%1
720
December1st to 15thNight
24%12%33%21%6%
720
16th to endNight
23%11%42%19%2
768
Page generated at 2017-08-13 14:16:27. Version ac04

Copyright 2017 A. Danko


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