Vassar
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vassar 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
34%
15503
14%
46493
9%
15462
40%
15462
20%
32788

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
16%
899
8%
2506
2%
895
22%
895
12%
2004
January16th to endNight
21%
891
8%
2619
2%
891
26%
891
11%
2107
February1st to 15thNight
18%
701
9%
2269
3%
701
25%
701
10%
1758
February16th to endNight
24%
631
13%
1893
6%
631
32%
631
13%
1436
March1st to 15thNight
27%
720
15%
2082
9%
720
31%
720
19%
1503
March16th to endNight
32%
768
18%
2112
10%
768
39%
768
22%
1492
April1st to 15thNight
26%
579
14%
1795
8%
579
32%
579
19%
1259
April16th to endNight
34%
540
19%
1620
8%
540
44%
540
24%
1079
May1st to 15thNight
35%
540
15%
1620
9%
540
41%
540
22%
1098
May16th to endNight
44%
562
15%
1639
9%
561
51%
561
29%
1061
June1st to 15thNight
46%
372
15%
1272
13%
372
52%
372
26%
771
June16th to endNight
53%
388
16%
1288
15%
388
59%
388
30%
758
July1st to 15thNight
62%
510
16%
1360
13%
510
64%
510
41%
818
July16th to endNight
63%
564
17%
1472
14%
531
66%
531
36%
898
August1st to 15thNight
63%
527
17%
1575
14%
524
67%
524
34%
947
August16th to endNight
60%
525
21%
1584
16%
525
64%
525
34%
914
September1st to 15thNight
55%
605
22%
1760
17%
605
58%
605
31%
1089
September16th to endNight
57%
657
21%
1815
16%
657
59%
657
32%
1136
October1st to 15thNight
43%
660
18%
1900
15%
660
48%
660
25%
1279
October16th to endNight
21%
704
11%
2216
6%
704
29%
704
14%
1651
November1st to 15thNight
32%
700
18%
2276
14%
700
38%
700
19%
1546
November16th to endNight
23%
720
11%
2435
6%
720
29%
720
12%
1818
December1st to 15thNight
15%
780
7%
2580
2%
780
20%
780
10%
2049
December16th to endNight
15%
960
7%
2805
1%
960
20%
960
9%
2317

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
14%8%46%6%35%45%7%33%
47466
Night
15%9%46%5%3445%6%34%
46669
Cloud CoverDay
14%8%36%6%35%45%7%33%
47476
Night
15%9%46%5%34446%34%
46673
TransparencyDay
49%6%12%19%10%1
47160
Night
49%5%12%19%10%1
46493
SeeingDay
18%8%27%24%14%6%
5725
Night
19%8%30%28%11%1
15508

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%15%6%8%8%45%445%18%
1432
16th to endDay
15%15%8%12%8%36%33416%
1605
February1st to 15thDay
12%15%6%9%9%46%5%46%18%
1591
16th to endDay
12%13%5%8%6%47%5%45%25%
1580
March1st to 15thDay
15%9%48%8%35%35%7%27%
1867
16th to endDay
16%10%5%7%6%34446%30%
2112
April1st to 15thDay
19%12%45%423447%31%
2163
16th to endDay
15%8%35%43445%5%38%
2340
May1st to 15thDay
19%7%25%5%34447%36%
2331
16th to endDay
13%5%36%4345%47%41%
2473
June1st to 15thDay
11%6%35%5%35%5%6%7%40%
2685
16th to endDay
10%5%36%6%35%5%7%8%37%
2668
July1st to 15thDay
6%325%5%45%6%6%8%44%
2520
16th to endDay
9%415%5%35%5%7%9%41%
2592
August1st to 15thDay
10%425%6%45%6%6%9%37%
2288
16th to endDay
10%6%25%5%35%5%5%8%41%
2264
September1st to 15thDay
12%6%345%345%7%8%38%
1858
16th to endDay
13%5%25%434449%40%
1815
October1st to 15thDay
16%7%45%5%33436%37%
1730
16th to endDay
23%9%37%5%34335%28%
1653
November1st to 15thDay
16%8%37%5%3445%7%33%
1582
16th to endDay
15%14%5%9%6%345%46%23%
1524
December1st to 15thDay
15%15%8%9%6%44445%21%
1377
16th to endDay
20%15%8%10%7%1345%5%16%
1416
January1st to 15thNight
21%13%5%9%6%3333423%
2506
16th to endNight
14%12%7%10%7%36%445%21%
2619
February1st to 15thNight
14%15%5%8%7%35%446%23%
2267
16th to endNight
16%11%5%7%7%45%446%25%
1893
March1st to 15thNight
15%11%46%6%33336%34%
2070
16th to endNight
16%8%46%5%3445%5%36%
2112
April1st to 15thNight
20%9%45%41335%7%33%
1795
16th to endNight
17%7%25%423347%40%
1620
May1st to 15thNight
15%7%26%7%2445%7%36%
1620
16th to endNight
12%5%245%25%45%7%43%
1637
June1st to 15thNight
11%325%435%5%5%8%43%
1272
16th to endNight
9%423425%5%6%10%44%
1288
July1st to 15thNight
8%42342345%8%52%
1440
16th to endNight
7%4234345%6%9%49%
1573
August1st to 15thNight
6%4146%35%6%6%8%45%
1586
16th to endNight
11%32442335%8%51%
1584
September1st to 15thNight
12%5%25%423446%48%
1760
16th to endNight
11%5%25%42335%7%46%
1815
October1st to 15thNight
16%7%25%5%2445%6%41%
1900
16th to endNight
22%10%37%6%33445%29%
2216
November1st to 15thNight
14%8%36%5%345%5%6%35%
2276
16th to endNight
20%13%46%6%3445%6%25%
2435
December1st to 15thNight
19%15%7%8%6%34335%22%
2580
16th to endNight
20%16%6%8%6%24345%18%
2805

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
18%14%7%8%8%45%445%19%
1432
16th to endDay
16%16%8%12%8%35%43416%
1605
February1st to 15thDay
12%16%6%9%9%5%6%445%18%
1591
16th to endDay
13%14%5%8%6%47%44425%
1580
March1st to 15thDay
16%9%48%7%4445%7%27%
1878
16th to endDay
17%10%47%6%34345%31%
2111
April1st to 15thDay
20%12%35%423446%31%
2163
16th to endDay
16%7%35%43445%5%38%
2340
May1st to 15thDay
20%6%35%5%24447%36%
2331
16th to endDay
13%5%26%5%345%47%40%
2473
June1st to 15thDay
11%6%245%35%5%5%7%40%
2685
16th to endDay
11%5%26%6%35%5%6%9%37%
2668
July1st to 15thDay
7%325%6%35%5%7%8%44%
2520
16th to endDay
10%325%5%35%5%7%9%41%
2592
August1st to 15thDay
11%426%6%45%5%6%8%38%
2288
16th to endDay
12%5%25%5%345%5%8%41%
2264
September1st to 15thDay
12%6%25%5%25%5%6%9%37%
1858
16th to endDay
14%5%25%435%45%9%40%
1815
October1st to 15thDay
17%7%36%434445%37%
1730
16th to endDay
24%9%37%5%34336%28%
1653
November1st to 15thDay
17%8%36%5%2445%7%33%
1582
16th to endDay
16%14%5%9%6%25%5%36%23%
1524
December1st to 15thDay
16%16%7%9%7%43445%21%
1377
16th to endDay
20%16%8%10%7%23346%17%
1416
January1st to 15thNight
21%13%6%8%6%3433423%
2506
16th to endNight
14%13%7%10%7%36%445%21%
2619
February1st to 15thNight
14%15%6%8%6%46%445%24%
2260
16th to endNight
16%11%5%8%6%45%45%6%25%
1893
March1st to 15thNight
15%11%46%6%33336%33%
2082
16th to endNight
16%8%46%5%24446%36%
2112
April1st to 15thNight
20%9%45%41235%7%33%
1795
16th to endNight
16%7%25%5%23347%40%
1620
May1st to 15thNight
15%7%26%6%24448%36%
1619
16th to endNight
12%5%24425%45%7%44%
1637
June1st to 15thNight
12%324427%5%5%8%43%
1272
16th to endNight
10%423435%46%10%44%
1288
July1st to 15thNight
8%32342345%7%53%
1440
16th to endNight
7%4135%345%7%9%49%
1573
August1st to 15thNight
7%3145%35%6%6%8%45%
1586
16th to endNight
11%414413448%51%
1584
September1st to 15thNight
13%425%334347%47%
1760
16th to endNight
11%6%2442335%7%46%
1815
October1st to 15thNight
16%6%25%5%3335%6%41%
1900
16th to endNight
23%9%37%6%23345%29%
2216
November1st to 15thNight
15%9%35%5%35%45%6%36%
2276
16th to endNight
20%13%46%6%34446%25%
2435
December1st to 15thNight
19%15%7%8%6%24335%22%
2580
16th to endNight
20%16%7%9%6%34345%18%
2805

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
67%5%10%12%3
1433
16th to endDay
71%6%8%9%4
1605
February1st to 15thDay
66%6%10%13%3
1593
16th to endDay
60%6%10%15%6%
1580
March1st to 15thDay
56%6%13%16%6%
1878
16th to endDay
54%6%12%17%7%1
2112
April1st to 15thDay
53%5%9%21%9%
2163
16th to endDay
45%6%14%16%14%1
2340
May1st to 15thDay
48%5%11%21%10%2
2331
16th to endDay
41%7%13%21%14%1
2477
June1st to 15thDay
40%7%13%22%14%
2685
16th to endDay
41%7%14%20%15%
2668
July1st to 15thDay
34%7%12%26%17%2
2371
16th to endDay
37%8%14%21%14%3
2430
August1st to 15thDay
39%9%14%22%13%1
2275
16th to endDay
38%8%12%26%13%2
2264
September1st to 15thDay
41%8%15%24%9%1
1858
16th to endDay
40%6%13%26%12%
1815
October1st to 15thDay
47%6%12%20%12%1
1730
16th to endDay
58%5%14%16%4
1653
November1st to 15thDay
49%7%12%20%9%
1582
16th to endDay
61%6%12%14%4
1524
December1st to 15thDay
65%6%12%11%3
1377
16th to endDay
69%5%11%10%2
1416
January1st to 15thNight
64%411%12%7%
2506
16th to endNight
63%6%13%13%2
2619
February1st to 15thNight
61%6%9%16%6%
2269
16th to endNight
58%5%11%17%6%
1893
March1st to 15thNight
52%411%21%8%1
2082
16th to endNight
48%5%11%22%11%1
2112
April1st to 15thNight
49%5%9%20%13%
1795
16th to endNight
43%5%11%18%17%3
1620
May1st to 15thNight
46%5%11%20%13%3
1620
16th to endNight
38%6%12%22%15%4
1639
June1st to 15thNight
37%7%13%23%17%1
1272
16th to endNight
33%7%16%24%17%1
1288
July1st to 15thNight
29%6%10%29%21%2
1360
16th to endNight
29%8%16%23%19%2
1472
August1st to 15thNight
32%7%15%27%15%1
1575
16th to endNight
31%5%13%30%17%2
1584
September1st to 15thNight
36%5%12%28%15%
1760
16th to endNight
35%6%12%30%13%
1815
October1st to 15thNight
43%6%11%23%14%1
1900
16th to endNight
56%5%12%18%6%
2216
November1st to 15thNight
47%6%14%21%9%
2276
16th to endNight
59%415%15%4
2435
December1st to 15thNight
64%5%12%11%5%
2580
16th to endNight
68%5%11%10%3
2805

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
22%17%38%21%
90
16th to endDay
36%9%37%15%1
96
February1st to 15thDay
24%24%42%7%1
90
16th to endDay
16%18%39%19%6%
81
March1st to 15thDay
30%16%22%25%5%
168
16th to endDay
26%6%30%21%12%2
288
April1st to 15thDay
28%8%31%20%8%2
270
16th to endDay
22%10%28%20%13%4
270
May1st to 15thDay
24%9%29%20%11%4
288
16th to endDay
17%9%27%24%13%7%
373
June1st to 15thDay
13%8%30%30%11%4
495
16th to endDay
12%8%32%24%17%5%
495
July1st to 15thDay
9%5%26%30%18%9%
475
16th to endDay
10%325%31%19%9%
452
August1st to 15thDay
9%120%26%24%17%
297
16th to endDay
16%414%22%23%17%
268
September1st to 15thDay
16%220%23%25%12%
255
16th to endDay
16%417%26%22%12%
254
October1st to 15thDay
19%7%26%25%18%2
255
16th to endDay
29%12%31%20%6%
165
November1st to 15thDay
14%16%31%26%8%2
90
16th to endDay
18%24%36%12%8%
74
December1st to 15thDay
26%21%35%15%1
60
16th to endDay
30%32%30%6%
76
January1st to 15thNight
26%13%34%18%5%
900
16th to endNight
19%10%37%27%5%
891
February1st to 15thNight
22%13%37%21%4
704
16th to endNight
22%13%31%27%4
631
March1st to 15thNight
20%11%33%28%5%
720
16th to endNight
18%10%31%29%8%1
768
April1st to 15thNight
22%12%35%23%5%
579
16th to endNight
20%8%32%27%8%1
540
May1st to 15thNight
19%6%31%33%9%1
540
16th to endNight
14%428%33%16%2
563
June1st to 15thNight
12%333%40%10%
372
16th to endNight
10%327%42%16%1
388
July1st to 15thNight
11%117%42%24%2
510
16th to endNight
8%120%43%23%1
564
August1st to 15thNight
10%17%43%25%3
527
16th to endNight
11%319%34%28%4
525
September1st to 15thNight
15%220%33%21%5%
605
16th to endNight
13%5%18%34%23%4
657
October1st to 15thNight
19%6%26%31%15%1
660
16th to endNight
28%11%33%21%4
704
November1st to 15thNight
19%11%32%25%10%
700
16th to endNight
26%12%33%21%6%
720
December1st to 15thNight
27%13%35%20%3
780
16th to endNight
29%11%35%20%2
960
Page generated at 2017-08-13 14:16:54. Version ac04

Copyright 2017 A. Danko


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