Deerfield West Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerfield West Observatory clear sky chart from 2005-11-05 to 2019-06-02.

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
43%
18052
28%
53828
17%
18006
54%
18006
38%
29586

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
32%
1049
31%
2717
11%
1045
45%
1045
38%
1570
January16th to endNight
35%
1120
35%
2912
13%
1120
48%
1120
43%
1613
February1st to 15thNight
28%
925
25%
2573
8%
921
40%
921
33%
1524
February16th to endNight
25%
736
27%
2206
9%
736
39%
736
29%
1307
March1st to 15thNight
31%
652
28%
2332
15%
652
46%
652
26%
1305
March16th to endNight
28%
672
22%
2464
12%
672
42%
672
27%
1369
April1st to 15thNight
24%
629
25%
2293
12%
629
44%
629
29%
1205
April16th to endNight
31%
624
26%
1892
13%
624
49%
624
35%
1078
May1st to 15thNight
33%
630
25%
1890
15%
630
49%
630
31%
1121
May16th to endNight
46%
659
26%
1972
19%
657
58%
657
40%
1073
June1st to 15thNight
57%
588
24%
1764
18%
588
66%
588
47%
894
June16th to endNight
62%
585
26%
1755
21%
585
70%
585
52%
857
July1st to 15thNight
70%
555
21%
1665
21%
555
74%
555
42%
903
July16th to endNight
83%
612
29%
1738
34%
579
84%
579
55%
842
August1st to 15thNight
79%
575
30%
1717
34%
572
82%
572
47%
886
August16th to endNight
75%
621
28%
1979
31%
621
79%
621
46%
984
September1st to 15thNight
61%
585
26%
2145
28%
585
66%
585
33%
1152
September16th to endNight
61%
582
33%
2145
30%
582
71%
582
38%
1060
October1st to 15thNight
46%
669
30%
2229
22%
669
55%
669
36%
1189
October16th to endNight
46%
832
35%
2496
18%
832
59%
832
45%
1259
November1st to 15thNight
40%
932
31%
2572
13%
932
51%
932
43%
1402
November16th to endNight
36%
1050
33%
2730
14%
1050
48%
1050
42%
1561
December1st to 15thNight
35%
1050
31%
2730
11%
1050
47%
1050
37%
1621
December16th to endNight
32%
1120
29%
2912
11%
1120
45%
1120
33%
1811

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
9%5%24424447%51%
54505
Night
8%413323346%56%
54024
Cloud CoverDay
10%424323446%51%
54503
Night
9%413323346%56%
54024
TransparencyDay
32%410%25%21%5%
54203
Night
28%310%25%24%7%
53829
SeeingDay
11%7%26%30%18%4
7921
Night
11%9%32%32%13%1
18053

By Month

Percentage Cloud Cover SW (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%5%14324336%53%
1881
16th to endDay
9%5%24312236%56%
2016
February1st to 15thDay
10%8%25%423346%49%
1959
16th to endDay
13%7%25%41333449%
1840
March1st to 15thDay
12%5%24423345%48%
2286
16th to endDay
13%8%34323336%46%
2464
April1st to 15thDay
10%5%15%424346%51%
2315
16th to endDay
14%5%245%24346%46%
2670
May1st to 15thDay
14%6%34423445%45%
2721
16th to endDay
10%424435%5%5%7%44%
2846
June1st to 15thDay
6%42342435%8%54%
2549
16th to endDay
6%2134345%5%9%54%
2535
July1st to 15thDay
6%324436%6%6%10%44%
2535
16th to endDay
42123245%6%10%54%
2674
August1st to 15thDay
5%314335%6%6%7%51%
2486
16th to endDay
6%2144245%6%10%49%
2571
September1st to 15thDay
13%41444445%6%45%
2145
16th to endDay
9%41432345%6%53%
2145
October1st to 15thDay
12%5%1331223458%
2048
16th to endDay
8%31332233463%
2080
November1st to 15thDay
7%5%12213347%58%
1943
16th to endDay
9%412212335%62%
1890
December1st to 15thDay
11%6%15%323336%52%
1890
16th to endDay
13%7%34423335%47%
2016
January1st to 15thNight
8%5%23313345%58%
2717
16th to endNight
7%323312245%62%
2912
February1st to 15thNight
12%5%23323235%54%
2563
16th to endNight
12%6%34323345%51%
2206
March1st to 15thNight
11%5%25%42333453%
2332
16th to endNight
13%5%23323345%51%
2464
April1st to 15thNight
10%314323347%53%
2293
16th to endNight
11%413323346%54%
1892
May1st to 15thNight
10%423433347%51%
1889
16th to endNight
7%31332246%9%54%
1971
June1st to 15thNight
5%31231345%10%60%
1764
16th to endNight
4112323449%63%
1755
July1st to 15thNight
42135%25%6%6%9%52%
1755
16th to endNight
31122135%5%11%61%
1846
August1st to 15thNight
22133246%6%9%56%
1727
16th to endNight
311332447%10%57%
1979
September1st to 15thNight
10%5%24422246%53%
2145
16th to endNight
7%424312347%57%
2145
October1st to 15thNight
10%413323345%56%
2229
16th to endNight
7%212312335%65%
2496
November1st to 15thNight
7%41332233461%
2572
16th to endNight
9%42331223462%
2730
December1st to 15thNight
10%423322346%55%
2730
16th to endNight
13%6%24313335%52%
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
11%5%14313436%54%
1881
16th to endDay
9%5%24222236%57%
2016
February1st to 15thDay
11%6%35%423346%49%
1959
16th to endDay
13%6%25%313335%50%
1840
March1st to 15thDay
13%5%24423346%49%
2286
16th to endDay
14%8%24323336%47%
2462
April1st to 15thDay
10%424423446%51%
2315
16th to endDay
14%5%145%2435%5%46%
2670
May1st to 15thDay
15%6%25%423345%46%
2721
16th to endDay
10%424435%45%7%45%
2846
June1st to 15thDay
7%42342436%7%54%
2549
16th to endDay
6%2133345%48%54%
2535
July1st to 15thDay
7%224435%6%6%10%45%
2535
16th to endDay
5%213325%46%9%55%
2674
August1st to 15thDay
5%314335%6%5%7%52%
2486
16th to endDay
7%2144345%7%10%49%
2571
September1st to 15thDay
13%42443445%5%46%
2145
16th to endDay
9%315%42345%6%54%
2145
October1st to 15thDay
13%41331223458%
2048
16th to endDay
8%313322335%62%
2080
November1st to 15thDay
8%412213346%58%
1943
16th to endDay
8%5%1322233463%
1890
December1st to 15thDay
11%6%25%322336%52%
1890
16th to endDay
13%7%24423335%47%
2016
January1st to 15thNight
9%423313345%58%
2717
16th to endNight
8%323312245%62%
2912
February1st to 15thNight
12%6%13322335%55%
2563
16th to endNight
12%5%34323345%51%
2206
March1st to 15thNight
11%5%25%41433453%
2332
16th to endNight
13%5%23323345%52%
2464
April1st to 15thNight
10%31332345%7%53%
2293
16th to endNight
11%413223346%54%
1892
May1st to 15thNight
10%423433447%51%
1889
16th to endNight
8%31332346%9%54%
1971
June1st to 15thNight
6%212312449%60%
1764
16th to endNight
4111323449%63%
1755
July1st to 15thNight
42145%345%6%9%52%
1755
16th to endNight
32123135%5%11%61%
1846
August1st to 15thNight
2213325%6%6%9%57%
1727
16th to endNight
311332446%10%57%
1979
September1st to 15thNight
11%414423246%53%
2145
16th to endNight
7%414312346%58%
2145
October1st to 15thNight
11%413313345%56%
2229
16th to endNight
7%212222335%65%
2496
November1st to 15thNight
7%323322335%62%
2572
16th to endNight
9%42332223462%
2730
December1st to 15thNight
11%323322346%55%
2730
16th to endNight
13%6%14313335%52%
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
32%38%25%25%4
1882
16th to endDay
30%26%27%25%7%
2016
February1st to 15thDay
37%28%25%21%4
1960
16th to endDay
37%36%24%21%6%
1840
March1st to 15thDay
36%47%23%19%8%
2286
16th to endDay
40%311%23%16%4
2464
April1st to 15thDay
33%5%11%25%18%6%
2315
16th to endDay
38%49%22%20%4
2670
May1st to 15thDay
39%5%11%21%18%3
2721
16th to endDay
35%6%13%25%16%1
2850
June1st to 15thDay
27%5%14%29%19%2
2549
16th to endDay
26%5%14%25%23%4
2535
July1st to 15thDay
30%7%15%28%15%1
2396
16th to endDay
22%6%16%30%22%2
2519
August1st to 15thDay
27%5%16%23%18%7%
2472
16th to endDay
28%5%14%29%16%4
2571
September1st to 15thDay
37%5%8%23%17%7%
2145
16th to endDay
29%47%26%25%5%
2145
October1st to 15thDay
30%311%23%23%8%
2048
16th to endDay
25%37%23%29%10%
2080
November1st to 15thDay
25%39%26%25%8%
1943
16th to endDay
25%26%27%28%9%
1890
December1st to 15thDay
34%310%26%21%3
1890
16th to endDay
39%38%19%23%5%
2016
January1st to 15thNight
28%38%24%29%5%
2717
16th to endNight
24%27%25%29%8%
2912
February1st to 15thNight
33%38%25%22%6%
2573
16th to endNight
35%37%24%22%7%
2206
March1st to 15thNight
34%37%21%20%11%
2332
16th to endNight
33%411%26%18%5%
2464
April1st to 15thNight
30%411%24%20%9%
2293
16th to endNight
30%410%25%20%7%
1892
May1st to 15thNight
33%411%22%20%6%
1890
16th to endNight
26%5%15%30%18%3
1973
June1st to 15thNight
20%5%15%32%21%4
1764
16th to endNight
18%413%28%26%8%
1755
July1st to 15thNight
24%6%13%31%20%2
1665
16th to endNight
16%5%13%31%28%4
1738
August1st to 15thNight
21%6%13%25%25%7%
1717
16th to endNight
21%5%13%30%22%6%
1979
September1st to 15thNight
32%29%24%19%11%
2145
16th to endNight
26%38%25%27%8%
2145
October1st to 15thNight
29%312%21%21%11%
2229
16th to endNight
21%36%22%33%12%
2496
November1st to 15thNight
25%28%23%28%10%
2572
16th to endNight
27%25%24%30%9%
2730
December1st to 15thNight
30%49%23%25%7%
2730
16th to endNight
34%38%21%24%7%
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
21%12%37%21%6%
180
16th to endDay
11%16%44%20%5%1
192
February1st to 15thDay
13%18%49%13%4
180
16th to endDay
22%18%44%13%1
159
March1st to 15thDay
16%23%42%14%2
180
16th to endDay
13%18%39%18%8%1
192
April1st to 15thDay
14%18%32%31%2
194
16th to endDay
17%15%34%24%6%1
562
May1st to 15thDay
14%11%38%26%8%1
618
16th to endDay
12%9%32%26%14%3
677
June1st to 15thDay
7%325%38%19%5%
576
16th to endDay
6%222%42%20%6%
570
July1st to 15thDay
7%12%38%30%10%
550
16th to endDay
5%436%42%10%
595
August1st to 15thDay
7%9%40%36%5%
549
16th to endDay
7%111%40%31%7%
483
September1st to 15thDay
12%17%26%38%13%
180
16th to endDay
16%113%38%20%9%
180
October1st to 15thDay
15%8%28%26%16%4
180
16th to endDay
11%8%33%28%15%2
192
November1st to 15thDay
21%7%36%23%9%2
180
16th to endDay
17%13%32%25%8%2
180
December1st to 15thDay
10%12%49%19%7%1
180
16th to endDay
23%16%36%16%5%
192
January1st to 15thNight
12%15%37%28%6%
1050
16th to endNight
9%13%40%30%6%
1120
February1st to 15thNight
14%14%40%26%4
925
16th to endNight
16%15%39%24%4
736
March1st to 15thNight
13%14%37%30%4
652
16th to endNight
15%11%42%23%6%
672
April1st to 15thNight
12%14%45%22%4
629
16th to endNight
14%10%41%26%7%
624
May1st to 15thNight
12%9%40%27%8%
630
16th to endNight
9%5%35%30%16%2
659
June1st to 15thNight
6%327%42%17%1
588
16th to endNight
4127%44%18%3
585
July1st to 15thNight
416%48%27%2
555
16th to endNight
37%48%36%2
612
August1st to 15thNight
38%50%32%3
575
16th to endNight
313%44%34%4
621
September1st to 15thNight
13%114%39%27%3
585
16th to endNight
10%219%39%21%6%
582
October1st to 15thNight
13%432%30%16%2
669
16th to endNight
9%8%32%34%13%1
832
November1st to 15thNight
9%10%36%30%12%1
932
16th to endNight
12%12%36%29%9%
1050
December1st to 15thNight
14%13%34%29%7%
1050
16th to endNight
17%12%34%29%6%
1120
Page generated at 2019-06-02 18:43:08. Version ac04

Copyright 2019 A. Danko


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