Driftway Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Driftway Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
27%
15579
17%
48753
8%
15546
38%
15546
17%
32568

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
15%
780
17%
2716
5%
776
30%
776
13%
1770
January16th to endNight
12%
832
17%
2912
3%
832
30%
832
12%
1908
February1st to 15thNight
13%
760
16%
2320
3%
757
28%
757
13%
1599
February16th to endNight
16%
631
23%
1893
5%
631
37%
631
19%
1241
March1st to 15thNight
20%
720
16%
2147
6%
720
31%
720
14%
1472
March16th to endNight
22%
768
21%
2046
7%
768
35%
768
20%
1399
April1st to 15thNight
22%
718
17%
1796
5%
718
29%
718
20%
1286
April16th to endNight
25%
593
16%
1673
4%
593
33%
593
19%
1180
May1st to 15thNight
25%
540
14%
1620
6%
540
33%
540
15%
1173
May16th to endNight
28%
457
10%
1580
6%
457
34%
457
12%
1137
June1st to 15thNight
35%
360
12%
1440
13%
360
41%
360
14%
976
June16th to endNight
46%
360
11%
1440
12%
360
52%
360
18%
892
July1st to 15thNight
42%
340
11%
1360
14%
340
45%
340
17%
863
July16th to endNight
46%
378
14%
1420
16%
356
54%
356
17%
913
August1st to 15thNight
51%
539
15%
1608
11%
535
54%
535
25%
1025
August16th to endNight
58%
726
21%
1872
12%
726
61%
726
32%
1218
September1st to 15thNight
44%
720
19%
1873
10%
720
48%
720
30%
1230
September16th to endNight
43%
717
21%
1980
13%
717
50%
717
24%
1309
October1st to 15thNight
34%
720
21%
1986
11%
720
43%
720
23%
1342
October16th to endNight
24%
768
18%
2496
8%
768
38%
768
19%
1606
November1st to 15thNight
26%
760
17%
2472
9%
760
37%
760
16%
1641
November16th to endNight
22%
780
21%
2535
8%
780
37%
780
16%
1625
December1st to 15thNight
19%
780
16%
2656
5%
780
32%
780
11%
1795
December16th to endNight
12%
832
18%
2912
4%
832
30%
832
11%
1968

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%6%24424447%40%
49326
Night
18%6%25%424446%39%
48925
Cloud CoverDay
17%6%2442445%7%40%
49336
Night
17%7%25%42445%6%38%
48930
TransparencyDay
42%6%12%21%14%2
49016
Night
45%5%12%20%14%2
48753
SeeingDay
19%16%26%24%11%1
6409
Night
19%23%24%22%8%
15580

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%7%15%423346%42%
1552
16th to endDay
17%6%25%423346%43%
1664
February1st to 15thDay
19%6%25%4345%46%38%
1841
16th to endDay
17%7%24434445%41%
1580
March1st to 15thDay
20%6%24433347%38%
1802
16th to endDay
16%8%24423346%42%
2176
April1st to 15thDay
20%5%24424447%38%
2152
16th to endDay
18%5%14424446%40%
2286
May1st to 15thDay
26%7%345%24446%33%
2332
16th to endDay
17%5%34435%448%37%
2545
June1st to 15thDay
23%6%25%42445%7%33%
2520
16th to endDay
13%6%2442446%9%41%
2520
July1st to 15thDay
14%6%25%5%2445%8%39%
2520
16th to endDay
14%5%244345%7%8%39%
2639
August1st to 15thDay
13%4244345%6%8%42%
2340
16th to endDay
11%424434448%46%
2327
September1st to 15thDay
14%42442435%5%47%
2085
16th to endDay
16%5%24423346%46%
1980
October1st to 15thDay
20%5%24423335%44%
1971
16th to endDay
16%424423336%46%
1728
November1st to 15thDay
22%6%24423245%41%
1716
16th to endDay
17%5%25%33335%7%42%
1755
December1st to 15thDay
20%7%25%423236%41%
1631
16th to endDay
22%9%24325%345%36%
1664
January1st to 15thNight
18%7%24424446%40%
2716
16th to endNight
18%10%24323335%39%
2912
February1st to 15thNight
17%8%36%5%34346%38%
2319
16th to endNight
15%8%25%5%25%345%42%
1893
March1st to 15thNight
18%6%35%4245%47%37%
2134
16th to endNight
16%7%35%434345%42%
2046
April1st to 15thNight
17%8%25%4345%46%37%
1796
16th to endNight
22%5%35%6%2334439%
1673
May1st to 15thNight
22%8%45%424435%33%
1620
16th to endNight
19%8%36%5%345%5%7%30%
1578
June1st to 15thNight
23%7%35%414437%34%
1440
16th to endNight
18%5%243245%5%7%39%
1440
July1st to 15thNight
17%7%35%3245%48%37%
1440
16th to endNight
14%6%26%6%36%5%6%8%34%
1516
August1st to 15thNight
9%5%25%5%35%6%7%7%41%
1620
16th to endNight
13%5%1433445%8%45%
1872
September1st to 15thNight
15%425%42335%7%44%
1873
16th to endNight
17%6%2442344445%
1980
October1st to 15thNight
17%6%25%434336%42%
1986
16th to endNight
17%5%25%433446%42%
2496
November1st to 15thNight
18%6%25%424345%41%
2472
16th to endNight
17%6%25%42235%7%41%
2535
December1st to 15thNight
21%5%25%5%24445%38%
2656
16th to endNight
20%7%35%423447%36%
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%7%24334447%40%
1552
16th to endDay
16%6%24423346%42%
1664
February1st to 15thDay
19%6%2442445%8%36%
1841
16th to endDay
17%7%2442445%6%40%
1580
March1st to 15thDay
20%5%345%2435%7%38%
1812
16th to endDay
16%7%24423445%42%
2176
April1st to 15thDay
19%6%2332445%6%40%
2152
16th to endDay
17%5%24435%447%40%
2286
May1st to 15thDay
25%7%35%423346%33%
2332
16th to endDay
16%7%345%3445%8%35%
2545
June1st to 15thDay
21%7%344145%5%8%33%
2520
16th to endDay
13%6%243245%6%9%41%
2520
July1st to 15thDay
13%6%35%435%45%8%40%
2520
16th to endDay
13%5%35%435%46%9%38%
2639
August1st to 15thDay
12%5%1443446%8%44%
2340
16th to endDay
10%5%25%423448%47%
2327
September1st to 15thDay
13%5%2332445%7%47%
2085
16th to endDay
15%7%13423445%46%
1980
October1st to 15thDay
19%6%24423445%44%
1971
16th to endDay
15%5%15%5%22447%46%
1728
November1st to 15thDay
21%6%25%314245%41%
1716
16th to endDay
16%5%24424448%40%
1755
December1st to 15thDay
20%7%25%413336%39%
1631
16th to endDay
22%9%24424346%35%
1664
January1st to 15thNight
18%7%25%424448%37%
2716
16th to endNight
19%10%34323346%37%
2912
February1st to 15thNight
17%8%35%5%2335%6%36%
2312
16th to endNight
16%7%15%5%24347%40%
1893
March1st to 15thNight
19%6%35%42435%8%36%
2147
16th to endNight
16%7%25%424436%42%
2045
April1st to 15thNight
17%9%25%42445%6%37%
1796
16th to endNight
21%6%26%433435%37%
1673
May1st to 15thNight
20%9%46%5%33346%32%
1620
16th to endNight
19%10%35%5%245%47%30%
1578
June1st to 15thNight
24%9%25%22335%7%33%
1440
16th to endNight
17%6%243245%5%8%38%
1440
July1st to 15thNight
16%6%35%426%36%8%37%
1440
16th to endNight
12%6%45%5%46%5%6%9%33%
1516
August1st to 15thNight
9%5%345%35%6%6%8%41%
1620
16th to endNight
13%4245%2435%7%46%
1872
September1st to 15thNight
14%5%1442446%7%43%
1873
16th to endNight
17%7%2443334443%
1980
October1st to 15thNight
18%6%25%424445%41%
1986
16th to endNight
17%5%24434347%41%
2496
November1st to 15thNight
18%6%34434445%40%
2472
16th to endNight
17%6%3442345%7%40%
2535
December1st to 15thNight
20%6%345%24445%37%
2656
16th to endNight
20%8%35%42345%6%35%
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%22%11%3
1553
16th to endDay
42%412%25%14%1
1664
February1st to 15thDay
46%5%14%19%11%1
1844
16th to endDay
42%5%12%23%13%2
1580
March1st to 15thDay
45%6%13%22%9%3
1812
16th to endDay
43%412%20%15%4
2176
April1st to 15thDay
43%5%10%19%17%2
2152
16th to endDay
42%5%10%21%15%3
2286
May1st to 15thDay
52%5%9%17%13%2
2332
16th to endDay
45%6%13%21%10%1
2549
June1st to 15thDay
49%7%11%19%11%
2520
16th to endDay
38%7%14%23%15%
2520
July1st to 15thDay
40%8%12%21%15%1
2371
16th to endDay
39%8%14%22%13%2
2473
August1st to 15thDay
37%7%15%22%15%1
2327
16th to endDay
34%8%10%26%18%1
2327
September1st to 15thDay
35%7%12%21%21%1
2085
16th to endDay
38%6%7%23%21%2
1980
October1st to 15thDay
42%411%23%15%2
1971
16th to endDay
38%5%13%24%15%2
1728
November1st to 15thDay
46%5%12%18%14%2
1716
16th to endDay
42%5%12%24%12%2
1755
December1st to 15thDay
46%415%17%13%1
1631
16th to endDay
50%5%13%18%11%
1664
January1st to 15thNight
45%5%13%21%12%1
2716
16th to endNight
47%411%20%13%1
2912
February1st to 15thNight
48%5%12%20%10%1
2320
16th to endNight
43%312%22%15%2
1893
March1st to 15thNight
46%6%12%19%12%3
2147
16th to endNight
43%5%9%17%19%4
2046
April1st to 15thNight
47%410%18%15%2
1796
16th to endNight
49%48%18%14%4
1673
May1st to 15thNight
52%5%9%16%13%2
1620
16th to endNight
52%7%13%16%8%2
1580
June1st to 15thNight
50%6%11%17%13%
1440
16th to endNight
41%6%13%21%14%1
1440
July1st to 15thNight
44%6%12%22%13%
1360
16th to endNight
44%8%14%22%8%2
1420
August1st to 15thNight
37%8%14%24%14%1
1608
16th to endNight
36%5%11%27%17%
1872
September1st to 15thNight
38%5%13%23%17%1
1873
16th to endNight
42%47%20%22%1
1980
October1st to 15thNight
43%5%9%22%15%2
1986
16th to endNight
42%5%14%22%13%1
2496
November1st to 15thNight
45%5%13%18%14%2
2472
16th to endNight
42%5%12%23%12%2
2535
December1st to 15thNight
48%5%15%18%12%
2656
16th to endNight
49%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
16%26%37%16%2
90
16th to endDay
23%16%38%19%1
96
February1st to 15thDay
25%23%35%13%1
309
16th to endDay
13%25%37%20%3
239
March1st to 15thDay
24%26%26%18%3
270
16th to endDay
17%25%32%18%5%
288
April1st to 15thDay
20%19%30%23%5%
270
16th to endDay
20%18%29%22%8%1
270
May1st to 15thDay
30%18%25%15%7%1
288
16th to endDay
20%12%27%28%10%
331
June1st to 15thDay
22%13%24%24%14%
315
16th to endDay
15%14%26%31%10%1
315
July1st to 15thDay
18%8%18%35%17%1
305
16th to endDay
12%12%18%37%16%2
326
August1st to 15thDay
15%7%18%37%19%2
313
16th to endDay
12%6%15%36%21%7%
332
September1st to 15thDay
16%7%23%30%17%4
315
16th to endDay
24%7%22%21%13%10%
314
October1st to 15thDay
20%12%21%23%18%2
313
16th to endDay
15%19%27%28%9%1
288
November1st to 15thDay
21%19%30%16%10%1
280
16th to endDay
18%28%25%17%9%
285
December1st to 15thDay
19%19%32%20%6%
161
16th to endDay
29%27%35%6%2
96
January1st to 15thNight
17%33%31%15%2
780
16th to endNight
23%31%28%14%2
832
February1st to 15thNight
19%30%32%16%1
760
16th to endNight
18%28%32%17%2
631
March1st to 15thNight
21%28%26%20%3
720
16th to endNight
16%26%29%20%5%
768
April1st to 15thNight
20%22%30%22%3
718
16th to endNight
18%21%27%24%7%
593
May1st to 15thNight
20%20%26%22%8%1
540
16th to endNight
24%20%19%25%10%
458
June1st to 15thNight
22%20%15%28%12%
360
16th to endNight
18%17%13%38%12%
360
July1st to 15thNight
18%12%16%34%17%
340
16th to endNight
14%16%14%35%17%
378
August1st to 15thNight
12%10%17%41%18%
539
16th to endNight
14%9%12%35%24%3
726
September1st to 15thNight
14%11%23%32%16%2
720
16th to endNight
21%11%16%25%20%4
717
October1st to 15thNight
21%15%23%25%12%1
720
16th to endNight
18%21%29%19%9%
768
November1st to 15thNight
19%25%23%19%9%1
760
16th to endNight
16%32%24%19%6%
780
December1st to 15thNight
23%30%23%16%5%
780
16th to endNight
24%33%27%12%
832
Page generated at 2018-02-15 10:58:40. Version ac04

Copyright 2018 A. Danko


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