De Forest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the De Forest clear sky chart from 2005-11-05 to 2018-10-27.

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
37%
17545
17%
51246
10%
17503
43%
17503
23%
34371

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
23%
975
14%
2716
5%
970
30%
970
18%
1984
January16th to endNight
22%
1040
12%
2863
4%
1040
28%
1040
17%
2157
February1st to 15thNight
24%
935
14%
2467
3%
935
32%
935
21%
1749
February16th to endNight
26%
683
18%
2049
8%
683
34%
683
18%
1435
March1st to 15thNight
32%
780
16%
2340
9%
780
37%
780
22%
1546
March16th to endNight
35%
624
17%
2165
15%
624
42%
624
18%
1481
April1st to 15thNight
27%
584
15%
1947
10%
584
37%
584
19%
1337
April16th to endNight
37%
579
19%
1879
13%
579
45%
579
23%
1234
May1st to 15thNight
31%
585
15%
1628
8%
585
37%
585
22%
1160
May16th to endNight
47%
610
15%
1626
8%
609
52%
609
31%
1052
June1st to 15thNight
47%
585
14%
1560
8%
585
50%
585
30%
1015
June16th to endNight
50%
585
15%
1560
9%
585
53%
585
34%
991
July1st to 15thNight
68%
555
19%
1480
12%
555
70%
555
45%
837
July16th to endNight
68%
612
20%
1545
13%
579
71%
579
43%
893
August1st to 15thNight
67%
575
20%
1625
17%
572
70%
572
37%
961
August16th to endNight
62%
621
19%
2070
21%
621
64%
621
31%
1205
September1st to 15thNight
61%
585
27%
1950
28%
585
66%
585
34%
1080
September16th to endNight
54%
741
25%
2109
18%
741
59%
741
35%
1241
October1st to 15thNight
39%
780
20%
2311
13%
780
45%
780
25%
1495
October16th to endNight
33%
816
18%
2568
11%
816
42%
816
22%
1671
November1st to 15thNight
32%
760
21%
2471
15%
760
40%
760
22%
1580
November16th to endNight
26%
920
16%
2675
8%
920
33%
920
18%
1862
December1st to 15thNight
19%
975
11%
2730
3%
975
26%
975
15%
2063
December16th to endNight
17%
1040
11%
2912
3%
1040
25%
1040
12%
2342

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
13%7%36%5%35%45%7%37%
52320
Night
13%8%35%5%2445%6%39%
51413
Cloud CoverDay
13%7%36%5%3445%7%37%
52328
Night
13%8%35%5%2445%6%39%
51418
TransparencyDay
45%6%13%22%11%1
52005
Night
44%5%12%22%13%1
51246
SeeingDay
16%7%27%27%15%5%
7543
Night
17%7%30%30%12%1
17549

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
10%12%6%7%6%25%45%8%29%
1552
16th to endDay
11%12%6%12%6%45%5%6%6%22%
1713
February1st to 15thDay
13%12%5%7%5%34446%33%
1726
16th to endDay
13%11%38%5%36%446%32%
1710
March1st to 15thDay
13%8%35%4346%5%6%36%
1952
16th to endDay
16%8%46%5%35%346%35%
2411
April1st to 15thDay
17%10%45%6%3446%6%29%
2331
16th to endDay
18%8%36%5%33446%35%
2356
May1st to 15thDay
18%7%37%5%35%5%6%7%29%
2649
16th to endDay
13%5%25%5%35%46%7%39%
2841
June1st to 15thDay
12%5%25%6%35%5%5%9%39%
2730
16th to endDay
10%5%245%35%47%10%39%
2730
July1st to 15thDay
6%4244345%7%10%46%
2730
16th to endDay
7%425%5%36%6%6%9%42%
2879
August1st to 15thDay
7%5%25%435%5%7%10%42%
2575
16th to endDay
11%5%25%5%35%5%5%7%42%
2484
September1st to 15thDay
12%4245%25%446%47%
2340
16th to endDay
10%6%35%424448%45%
2167
October1st to 15thDay
18%7%35%424336%40%
1979
16th to endDay
16%9%35%5%3345%6%36%
1911
November1st to 15thDay
12%8%45%5%245%5%5%39%
1717
16th to endDay
14%10%5%7%6%24336%37%
1613
December1st to 15thDay
15%13%48%6%33346%29%
1560
16th to endDay
17%14%7%8%6%4445%6%19%
1664
January1st to 15thNight
14%11%5%8%5%3435%5%33%
2716
16th to endNight
12%10%6%10%6%35%446%28%
2863
February1st to 15thNight
11%12%46%5%245%5%5%36%
2464
16th to endNight
15%10%37%5%24346%34%
2049
March1st to 15thNight
15%9%25%42345%5%40%
2327
16th to endNight
16%7%35%5%345%5%7%34%
2165
April1st to 15thNight
20%8%25%43345%7%34%
1947
16th to endNight
18%7%24423446%39%
1879
May1st to 15thNight
19%6%25%435%45%6%34%
1628
16th to endNight
10%5%245%3446%10%41%
1624
June1st to 15thNight
11%6%25%5%24349%43%
1560
16th to endNight
8%5%235%2445%8%46%
1560
July1st to 15thNight
5%3133245%6%8%55%
1560
16th to endNight
5%22442445%8%54%
1641
August1st to 15thNight
5%315%5%25%5%7%7%50%
1634
16th to endNight
10%425%423448%48%
2070
September1st to 15thNight
10%21342335%6%54%
1950
16th to endNight
8%5%2442345%7%50%
2109
October1st to 15thNight
16%6%25%323337%44%
2311
16th to endNight
15%6%25%5%3445%6%40%
2568
November1st to 15thNight
13%8%345%24335%43%
2471
16th to endNight
17%8%35%435%45%5%36%
2675
December1st to 15thNight
17%11%47%6%35%345%29%
2730
16th to endNight
20%13%5%7%6%34445%23%
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
10%12%6%7%5%35%45%8%29%
1552
16th to endDay
11%12%6%12%7%35%5%6%6%22%
1713
February1st to 15thDay
13%11%5%6%5%34446%33%
1726
16th to endDay
12%11%38%5%36%5%46%32%
1710
March1st to 15thDay
14%8%45%425%5%5%6%36%
1962
16th to endDay
16%8%36%5%25%446%35%
2409
April1st to 15thDay
17%10%46%6%3445%7%29%
2331
16th to endDay
19%7%36%5%33346%35%
2356
May1st to 15thDay
18%8%26%5%35%5%6%7%29%
2649
16th to endDay
13%5%245%26%45%8%39%
2841
June1st to 15thDay
12%425%6%35%6%5%9%39%
2730
16th to endDay
10%5%245%35%47%11%39%
2730
July1st to 15thDay
6%4245%345%7%10%46%
2730
16th to endDay
7%4245%36%5%7%9%43%
2879
August1st to 15thDay
7%5%25%5%35%6%7%9%42%
2575
16th to endDay
11%5%25%5%345%6%7%42%
2484
September1st to 15thDay
12%424425%45%7%47%
2340
16th to endDay
9%6%35%42445%7%45%
2167
October1st to 15thDay
18%7%35%423336%40%
1979
16th to endDay
16%8%35%5%3345%6%36%
1911
November1st to 15thDay
13%8%46%5%2445%6%39%
1717
16th to endDay
13%11%46%6%24236%36%
1613
December1st to 15thDay
15%13%5%7%7%3335%6%29%
1560
16th to endDay
18%14%7%8%7%345%47%19%
1664
January1st to 15thNight
14%10%5%8%5%24445%33%
2716
16th to endNight
12%10%6%10%7%3445%6%28%
2863
February1st to 15thNight
12%12%46%5%2445%5%36%
2457
16th to endNight
15%11%37%5%23347%34%
2049
March1st to 15thNight
15%9%25%42345%6%40%
2340
16th to endNight
16%7%26%5%35%5%47%34%
2165
April1st to 15thNight
20%9%24434447%34%
1947
16th to endNight
18%7%25%423446%39%
1879
May1st to 15thNight
20%6%25%436%46%5%34%
1627
16th to endNight
10%5%245%35%45%9%42%
1624
June1st to 15thNight
10%6%25%5%3445%8%43%
1560
16th to endNight
8%6%245%245%5%9%45%
1560
July1st to 15thNight
5%2143245%5%8%56%
1560
16th to endNight
5%22442445%8%54%
1641
August1st to 15thNight
5%325%5%345%6%7%50%
1634
16th to endNight
10%5%25%424447%48%
2070
September1st to 15thNight
10%31332335%6%55%
1950
16th to endNight
8%42442445%7%50%
2109
October1st to 15thNight
16%6%25%423346%44%
2311
16th to endNight
15%6%25%5%2345%7%40%
2568
November1st to 15thNight
13%8%35%5%24336%43%
2471
16th to endNight
17%8%35%435%45%5%36%
2675
December1st to 15thNight
17%12%47%5%35%45%5%29%
2730
16th to endNight
20%13%5%7%6%34445%23%
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
52%6%13%18%9%
1553
16th to endDay
60%5%12%14%6%
1713
February1st to 15thDay
52%414%19%8%
1727
16th to endDay
51%7%11%19%8%1
1710
March1st to 15thDay
45%6%14%21%9%1
1962
16th to endDay
50%5%14%21%7%
2411
April1st to 15thDay
53%6%11%19%9%
2331
16th to endDay
50%5%11%20%11%1
2356
May1st to 15thDay
51%6%14%20%6%
2649
16th to endDay
42%7%11%23%13%1
2845
June1st to 15thDay
40%8%14%23%12%
2730
16th to endDay
38%8%16%22%13%
2730
July1st to 15thDay
32%8%14%26%15%2
2581
16th to endDay
35%8%16%22%14%2
2712
August1st to 15thDay
35%7%15%28%12%1
2560
16th to endDay
38%7%14%24%14%1
2484
September1st to 15thDay
35%6%10%26%18%1
2340
16th to endDay
36%5%13%29%13%
2167
October1st to 15thDay
45%410%24%14%
1979
16th to endDay
47%5%12%24%9%
1911
November1st to 15thDay
44%413%23%11%1
1717
16th to endDay
50%417%21%5%
1613
December1st to 15thDay
55%5%14%17%6%
1560
16th to endDay
65%5%10%9%7%
1664
January1st to 15thNight
52%5%9%19%11%
2716
16th to endNight
55%5%14%16%7%
2863
February1st to 15thNight
48%5%12%21%11%1
2467
16th to endNight
49%5%11%22%9%1
2049
March1st to 15thNight
44%414%21%12%1
2340
16th to endNight
49%5%12%23%8%1
2165
April1st to 15thNight
49%5%8%21%14%
1947
16th to endNight
44%5%10%22%14%3
1879
May1st to 15thNight
48%6%13%19%12%
1628
16th to endNight
36%7%14%23%15%2
1626
June1st to 15thNight
37%6%12%25%16%
1560
16th to endNight
34%6%15%23%18%2
1560
July1st to 15thNight
24%6%13%29%21%4
1480
16th to endNight
25%7%15%30%17%3
1545
August1st to 15thNight
30%7%13%27%18%2
1625
16th to endNight
34%5%13%27%16%2
2070
September1st to 15thNight
28%7%10%26%24%2
1950
16th to endNight
31%5%11%32%18%
2109
October1st to 15thNight
41%5%9%23%18%1
2311
16th to endNight
42%5%12%24%13%
2568
November1st to 15thNight
42%5%10%23%15%2
2471
16th to endNight
48%5%14%21%8%1
2675
December1st to 15thNight
57%411%18%7%
2730
16th to endNight
63%5%10%13%6%
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
17%8%32%31%9%
135
16th to endDay
20%9%36%29%5%
144
February1st to 15thDay
17%10%45%20%6%
135
16th to endDay
28%13%35%15%5%
120
March1st to 15thDay
22%12%35%20%6%2
135
16th to endDay
27%427%25%10%3
267
April1st to 15thDay
24%11%32%23%8%
330
16th to endDay
23%8%23%25%14%4
319
May1st to 15thDay
23%9%30%23%10%2
471
16th to endDay
17%9%24%25%17%5%
597
June1st to 15thDay
12%5%26%33%18%3
570
16th to endDay
12%6%28%30%15%5%
570
July1st to 15thDay
8%421%32%22%12%
550
16th to endDay
9%125%32%23%8%
595
August1st to 15thDay
10%121%31%23%10%
524
16th to endDay
15%6%16%26%21%12%
396
September1st to 15thDay
12%419%28%23%12%
375
16th to endDay
13%6%23%29%21%6%
374
October1st to 15thDay
28%11%25%22%10%1
209
16th to endDay
21%14%33%24%6%
178
November1st to 15thDay
13%13%31%25%11%5%
135
16th to endDay
26%12%34%20%5%
135
December1st to 15thDay
15%15%46%17%21
135
16th to endDay
22%20%41%13%2
144
January1st to 15thNight
19%13%36%22%7%
975
16th to endNight
18%9%39%28%3
1040
February1st to 15thNight
18%9%37%27%5%
938
16th to endNight
20%11%35%26%5%
683
March1st to 15thNight
20%9%32%26%9%
780
16th to endNight
21%6%29%31%9%1
624
April1st to 15thNight
25%9%34%25%4
584
16th to endNight
22%6%30%30%8%1
579
May1st to 15thNight
23%5%33%27%9%
585
16th to endNight
13%328%37%16%
611
June1st to 15thNight
13%327%40%14%
585
16th to endNight
11%427%39%16%
585
July1st to 15thNight
8%118%40%29%3
555
16th to endNight
5%118%46%26%1
612
August1st to 15thNight
6%116%47%25%2
575
16th to endNight
12%215%42%23%4
621
September1st to 15thNight
10%221%31%27%5%
585
16th to endNight
11%5%24%33%23%2
741
October1st to 15thNight
20%7%28%28%14%1
780
16th to endNight
19%10%30%28%8%
816
November1st to 15thNight
19%9%35%25%10%
760
16th to endNight
20%13%34%23%8%
920
December1st to 15thNight
23%12%37%21%5%
975
16th to endNight
27%11%33%22%3
1040
Page generated at 2018-10-28 07:41:05. Version ac04

Copyright 2018 A. Danko


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