Driftway Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Driftway Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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
31%
23303
12%
80670
6%
23214
37%
23214
10%
61575

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 10thNight
17%
751
19%
4323
3%
737
29%
737
6%
2651
January11th to 20thNight
14%
759
18%
4346
3%
740
23%
740
4%
2957
January21st to endNight
16%
829
8%
4862
4%
814
28%
814
5%
3814
February1st to 10thNight
18%
760
11%
2340
3%
760
28%
760
9%
1794
February11th to 20thNight
14%
743
12%
2220
3%
740
25%
740
10%
1723
February21st to endNight
17%
628
15%
1884
5%
628
30%
628
11%
1457
March1st to 10thNight
23%
760
15%
2280
6%
760
34%
760
11%
1733
March11th to 20thNight
23%
752
11%
2142
5%
752
30%
752
10%
1733
March21st to endNight
25%
792
15%
2080
5%
792
32%
792
14%
1652
April1st to 10thNight
26%
720
13%
1800
5%
720
30%
720
14%
1448
April11th to 20thNight
28%
701
12%
1765
3%
701
33%
701
13%
1431
April21st to endNight
27%
540
13%
1620
5%
540
33%
540
11%
1276
May1st to 10thNight
28%
540
8%
1620
4%
540
31%
540
10%
1339
May11th to 20thNight
26%
532
12%
1594
6%
532
32%
532
11%
1272
May21st to endNight
43%
430
8%
1593
8%
430
45%
430
9%
1271
June1st to 10thNight
41%
360
8%
1440
9%
360
45%
360
8%
1148
June11th to 20thNight
47%
360
9%
1440
12%
360
50%
360
9%
1095
June21st to endNight
50%
360
7%
1440
11%
360
51%
360
8%
1134
July1st to 10thNight
48%
350
6%
1400
9%
350
50%
350
9%
1109
July11th to 20thNight
53%
348
7%
1392
8%
348
55%
348
10%
1070
July21st to endNight
53%
395
10%
1487
13%
373
55%
373
10%
1136
August1st to 10thNight
56%
538
8%
1600
6%
534
57%
534
13%
1265
August11th to 20thNight
58%
563
10%
1627
6%
563
59%
563
14%
1283
August21st to endNight
58%
792
11%
1980
6%
792
59%
792
16%
1576
September1st to 10thNight
49%
720
13%
1819
7%
720
51%
720
17%
1432
September11th to 20thNight
48%
720
16%
1980
9%
720
53%
720
18%
1479
September21st to endNight
43%
720
13%
1980
8%
720
48%
720
14%
1556
October1st to 10thNight
35%
720
10%
1980
6%
720
40%
720
13%
1565
October11th to 20thNight
35%
720
14%
2168
6%
720
43%
720
12%
1676
October21st to endNight
24%
792
10%
2574
5%
792
31%
792
10%
2016
November1st to 10thNight
33%
740
12%
2407
7%
740
40%
740
13%
1822
November11th to 20thNight
22%
760
14%
2470
7%
760
32%
760
10%
1909
November21st to endNight
25%
760
12%
2470
5%
760
34%
760
10%
1903
December1st to 10thNight
20%
760
10%
2552
3%
760
28%
760
7%
2005
December11th to 20thNight
17%
760
12%
3196
2%
759
28%
759
7%
2324
December21st to endNight
17%
828
8%
4799
3%
817
26%
817
4%
3521

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
18%7%35%5%3445%7%40%
78534
Night
18%8%35%5%3445%6%40%
81242
TransparencyDay
29%37%9%15%9%1
78241
Night
32%35%8%15%9%1
81069
SeeingDay
20%11%29%27%11%2
14273
Night
22%12%29%26%10%1
23329

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 10thDay
16%8%35%433445%45%
2517
11th to 20thDay
20%9%345%34445%40%
2520
21st to endDay
22%11%37%5%33335%34%
2772
February1st to 10thDay
20%8%25%5%35%45%6%36%
1837
11th to 20thDay
15%7%25%5%4445%6%43%
1848
21st to endDay
20%9%35%5%35%446%37%
1570
March1st to 10thDay
17%9%3443435%7%41%
1897
11th to 20thDay
16%6%24425%5%5%8%42%
1983
21st to endDay
18%9%36%5%23446%39%
2273
April1st to 10thDay
20%7%25%3345%5%7%38%
2160
11th to 20thDay
18%6%25%5%245%46%42%
2142
21st to endDay
21%7%25%5%35%45%6%37%
2340
May1st to 10thDay
25%8%45%5%24447%33%
2340
11th to 20thDay
19%6%35%5%25%447%39%
2301
21st to endDay
17%6%35%5%345%49%40%
2697
June1st to 10thDay
19%7%35%5%35%6%6%8%33%
2520
11th to 20thDay
17%7%35%5%25%5%5%9%37%
2520
21st to endDay
16%7%245%3446%8%40%
2520
July1st to 10thDay
14%6%35%5%345%6%8%42%
2520
11th to 20thDay
14%6%25%5%345%6%9%40%
2520
21st to endDay
13%6%35%5%35%5%7%8%40%
2722
August1st to 10thDay
11%5%25%5%45%6%6%9%41%
2327
11th to 20thDay
13%6%25%5%45%5%6%8%41%
2269
21st to endDay
13%5%25%5%35%6%5%8%44%
2376
September1st to 10thDay
15%6%345%2445%6%45%
2139
11th to 20thDay
13%6%2432445%6%51%
1980
21st to endDay
20%5%25%42435%5%43%
1980
October1st to 10thDay
23%5%35%5%23335%43%
1980
11th to 20thDay
15%7%3442345%7%47%
1788
21st to endDay
19%5%25%5%33447%43%
1782
November1st to 10thDay
18%6%35%424345%47%
1671
11th to 20thDay
17%5%25%33345%7%44%
1710
21st to endDay
17%7%35%5%3435%6%43%
1710
December1st to 10thDay
21%8%35%434346%39%
1625
11th to 20thDay
21%7%25%323336%44%
1906
21st to endDay
22%11%46%5%3435%5%34%
2772
January1st to 10thNight
18%6%24323346%48%
4429
11th to 20thNight
17%10%47%423345%41%
4440
21st to endNight
22%12%5%7%5%3444430%
4884
February1st to 10thNight
17%8%46%6%34346%40%
2340
11th to 20thNight
18%8%35%5%24445%41%
2218
21st to endNight
18%8%26%5%3445%5%40%
1884
March1st to 10thNight
18%7%35%4345%47%41%
2270
11th to 20thNight
16%8%36%5%445%47%38%
2141
21st to endNight
18%9%36%5%2445%5%40%
2080
April1st to 10thNight
19%9%35%5%34446%38%
1800
11th to 20thNight
19%7%35%5%2445%6%39%
1765
21st to endNight
22%7%36%6%3344438%
1620
May1st to 10thNight
24%9%46%5%345%5%6%30%
1620
11th to 20thNight
19%8%36%5%35%45%7%35%
1593
21st to endNight
19%9%36%6%26%6%6%6%32%
1592
June1st to 10thNight
19%9%46%5%35%45%8%34%
1440
11th to 20thNight
20%6%35%43445%8%39%
1440
21st to endNight
19%7%35%42446%8%37%
1440
July1st to 10thNight
16%8%35%445%6%5%6%37%
1440
11th to 20thNight
16%6%35%6%35%5%7%8%34%
1440
21st to endNight
15%6%26%6%35%5%6%8%38%
1575
August1st to 10thNight
9%7%35%5%36%7%7%8%40%
1612
11th to 20thNight
11%7%36%5%46%7%5%9%38%
1627
21st to endNight
15%6%2442446%8%45%
1980
September1st to 10thNight
15%5%36%5%3446%7%42%
1819
11th to 20thNight
15%6%24423446%50%
1980
21st to endNight
21%6%24435%5%45%42%
1980
October1st to 10thNight
20%8%35%434335%39%
1980
11th to 20thNight
16%5%2443345%7%46%
2168
21st to endNight
20%8%36%434446%39%
2574
November1st to 10thNight
16%6%25%43445%6%45%
2407
11th to 20thNight
17%8%35%424445%44%
2470
21st to endNight
15%5%35%42346%8%45%
2470
December1st to 10thNight
21%6%25%5%34445%39%
2552
11th to 20thNight
20%7%24424446%42%
3288
21st to endNight
20%11%46%5%23345%37%
4884

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 10thDay
32%26%8%24%10%
2518
11th to 20thDay
37%28%8%18%8%1
2520
21st to endDay
45%24%6%18%7%1
2772
February1st to 10thDay
31%36%9%12%10%1
1837
11th to 20thDay
26%37%9%17%9%2
1857
21st to endDay
33%35%8%13%9%2
1570
March1st to 10thDay
27%37%9%15%10%2
1900
11th to 20thDay
29%37%10%15%8%1
1983
21st to endDay
29%37%7%12%12%3
2273
April1st to 10thDay
26%38%9%14%11%2
2160
11th to 20thDay
29%38%7%13%11%2
2142
21st to endDay
30%37%7%13%10%3
2340
May1st to 10thDay
34%37%6%13%8%2
2340
11th to 20thDay
29%38%8%12%11%2
2305
21st to endDay
29%38%9%15%8%2
2697
June1st to 10thDay
32%39%9%13%6%
2520
11th to 20thDay
29%39%11%14%7%
2520
21st to endDay
29%40%11%13%6%
2520
July1st to 10thDay
28%41%8%15%7%
2450
11th to 20thDay
26%40%11%17%7%1
2445
21st to endDay
25%41%9%13%10%1
2570
August1st to 10thDay
26%39%12%15%7%
2314
11th to 20thDay
27%39%9%15%8%1
2269
21st to endDay
26%40%8%13%11%1
2376
September1st to 10thDay
25%38%8%14%14%1
2139
11th to 20thDay
21%37%9%17%14%2
1980
21st to endDay
28%38%5%14%14%2
1980
October1st to 10thDay
27%36%8%15%12%1
1980
11th to 20thDay
25%38%10%18%8%1
1788
21st to endDay
26%38%9%16%10%2
1782
November1st to 10thDay
26%41%8%13%11%1
1671
11th to 20thDay
24%41%9%15%10%1
1710
21st to endDay
29%40%8%16%6%1
1710
December1st to 10thDay
29%41%9%12%7%2
1625
11th to 20thDay
32%32%10%10%11%4
1906
21st to endDay
40%29%9%16%7%
2772
January1st to 10thNight
29%26%10%27%6%2
4429
11th to 20thNight
37%26%9%18%10%1
4440
21st to endNight
48%24%7%14%6%1
4884
February1st to 10thNight
31%35%10%15%9%1
2340
11th to 20thNight
31%35%8%15%8%2
2220
21st to endNight
32%33%7%17%9%2
1884
March1st to 10thNight
29%36%7%17%10%2
2280
11th to 20thNight
33%38%7%13%7%2
2142
21st to endNight
30%37%6%12%12%4
2080
April1st to 10thNight
30%38%6%14%11%2
1800
11th to 20thNight
33%36%5%13%12%2
1765
21st to endNight
32%36%6%13%10%3
1620
May1st to 10thNight
36%37%7%10%9%1
1620
11th to 20thNight
31%39%7%12%9%3
1594
21st to endNight
33%40%8%11%9%
1593
June1st to 10thNight
34%39%10%11%6%
1440
11th to 20thNight
31%37%9%14%8%
1440
21st to endNight
33%39%10%12%6%
1440
July1st to 10thNight
32%40%9%14%5%
1400
11th to 20thNight
30%40%11%15%5%
1392
21st to endNight
29%40%9%14%6%2
1487
August1st to 10thNight
28%40%11%14%6%
1600
11th to 20thNight
27%40%10%14%8%
1627
21st to endNight
28%38%8%15%9%1
1980
September1st to 10thNight
27%38%8%14%12%1
1819
11th to 20thNight
24%37%8%16%14%1
1980
21st to endNight
29%37%5%13%13%2
1980
October1st to 10thNight
30%37%7%13%11%2
1980
11th to 20thNight
28%38%9%18%7%
2168
21st to endNight
31%37%9%13%8%1
2574
November1st to 10thNight
23%41%8%14%11%2
2407
11th to 20thNight
27%41%8%15%9%1
2470
21st to endNight
26%41%9%16%8%1
2470
December1st to 10thNight
29%40%11%12%7%1
2552
11th to 20thNight
30%34%11%11%12%2
3288
21st to endNight
40%27%8%17%7%
4884

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 10thDay
24%21%30%21%41
180
11th to 20thDay
20%23%35%17%5%
180
21st to endDay
19%18%38%19%6%1
198
February1st to 10thDay
24%21%32%19%2
429
11th to 20thDay
23%21%40%15%1
456
21st to endDay
23%20%34%19%4
382
March1st to 10thDay
23%17%35%20%5%
460
11th to 20thDay
18%20%37%21%3
449
21st to endDay
21%15%36%19%6%2
462
April1st to 10thDay
25%16%31%20%7%
420
11th to 20thDay
21%13%37%25%4
412
21st to endDay
26%10%34%22%7%1
420
May1st to 10thDay
29%14%31%20%6%
423
11th to 20thDay
21%8%39%23%9%1
447
21st to endDay
22%426%30%14%2
485
June1st to 10thDay
20%5%28%31%15%1
450
11th to 20thDay
19%5%31%34%11%1
450
21st to endDay
18%427%36%13%2
450
July1st to 10thDay
18%420%36%20%2
445
11th to 20thDay
12%420%37%23%3
444
21st to endDay
13%6%23%42%14%2
488
August1st to 10thDay
13%422%40%19%2
446
11th to 20thDay
17%6%17%38%19%4
439
21st to endDay
14%422%36%19%5%
495
September1st to 10thDay
19%422%31%17%6%
450
11th to 20thDay
17%6%22%33%16%6%
450
21st to endDay
23%6%28%26%13%4
450
October1st to 10thDay
24%11%22%26%14%4
450
11th to 20thDay
18%10%28%28%15%2
399
21st to endDay
24%14%28%23%9%2
396
November1st to 10thDay
16%15%30%24%12%2
365
11th to 20thDay
22%18%33%21%6%
370
21st to endDay
21%20%29%20%9%1
370
December1st to 10thDay
21%15%37%21%6%
285
11th to 20thDay
26%23%33%14%4
180
21st to endDay
24%16%37%14%6%3
198
January1st to 10thNight
21%21%36%19%3
760
11th to 20thNight
28%21%33%16%3
760
21st to endNight
22%21%35%18%3
836
February1st to 10thNight
21%19%36%21%3
760
11th to 20thNight
24%20%39%15%2
743
21st to endNight
23%18%36%18%4
628
March1st to 10thNight
22%18%34%23%4
760
11th to 20thNight
20%14%38%24%4
752
21st to endNight
23%11%36%23%7%1
792
April1st to 10thNight
24%11%35%26%4
720
11th to 20thNight
22%8%36%26%7%
701
21st to endNight
24%8%32%28%7%1
540
May1st to 10thNight
28%6%31%26%9%1
540
11th to 20thNight
23%9%34%27%7%1
532
21st to endNight
26%318%36%16%1
431
June1st to 10thNight
25%5%20%34%15%1
360
11th to 20thNight
22%421%40%14%
360
21st to endNight
25%215%44%14%
360
July1st to 10thNight
19%319%39%19%1
350
11th to 20thNight
16%217%41%24%1
348
21st to endNight
17%317%41%21%1
395
August1st to 10thNight
12%121%44%20%1
538
11th to 20thNight
13%318%44%21%1
563
21st to endNight
17%215%37%24%5%
792
September1st to 10thNight
16%323%35%20%3
720
11th to 20thNight
18%423%29%22%3
720
21st to endNight
24%5%22%31%16%3
720
October1st to 10thNight
26%9%24%23%15%3
720
11th to 20thNight
19%12%29%26%12%2
720
21st to endNight
24%14%31%22%9%1
792
November1st to 10thNight
20%11%31%25%11%2
740
11th to 20thNight
21%21%31%19%7%1
760
21st to endNight
18%22%30%21%7%1
760
December1st to 10thNight
26%21%29%18%6%1
760
11th to 20thNight
24%23%32%17%3
760
21st to endNight
26%20%34%16%4
836
Page generated at 2024-03-15 14:01:41. Version ac07

Copyright © 2024 Attilla Danko.


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