New Haven
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New Haven clear sky chart from 2005-11-05 to 2018-04-23.

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
38%
16361
15%
49500
10%
16325
44%
16325
21%
34391

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
19%
970
10%
2716
5%
970
24%
970
14%
2130
January16th to endNight
21%
881
9%
2753
4%
881
27%
881
11%
2166
February1st to 15thNight
19%
761
9%
2481
2%
761
26%
761
11%
1920
February16th to endNight
25%
683
14%
2049
6%
683
32%
683
15%
1525
March1st to 15thNight
27%
780
15%
2230
9%
780
32%
780
18%
1640
March16th to endNight
36%
832
19%
2288
11%
832
43%
832
24%
1594
April1st to 15thNight
32%
669
15%
1969
7%
669
39%
669
20%
1399
April16th to endNight
41%
558
20%
1672
9%
558
49%
558
26%
1092
May1st to 15thNight
42%
540
14%
1620
9%
540
48%
540
23%
1115
May16th to endNight
52%
549
16%
1672
14%
549
56%
549
29%
1052
June1st to 15thNight
56%
360
17%
1292
17%
360
63%
360
27%
772
June16th to endNight
60%
366
19%
1266
20%
366
65%
366
29%
735
July1st to 15thNight
67%
510
17%
1360
15%
510
69%
510
41%
800
July16th to endNight
70%
564
17%
1531
15%
531
72%
531
38%
888
August1st to 15thNight
69%
539
19%
1609
16%
536
71%
536
34%
957
August16th to endNight
65%
573
24%
1719
19%
573
69%
573
34%
1020
September1st to 15thNight
59%
687
22%
1931
16%
687
63%
687
33%
1186
September16th to endNight
61%
717
23%
1980
18%
717
64%
717
33%
1221
October1st to 15thNight
46%
720
18%
2091
15%
720
50%
720
26%
1369
October16th to endNight
29%
768
16%
2379
10%
768
38%
768
18%
1698
November1st to 15thNight
38%
760
19%
2471
15%
760
45%
760
22%
1633
November16th to endNight
26%
780
14%
2662
9%
780
34%
780
15%
1886
December1st to 15thNight
19%
780
7%
2730
3%
780
25%
780
11%
2108
December16th to endNight
16%
1014
8%
3029
2%
1014
21%
1014
10%
2485

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%8%47%6%35%5%5%7%33%
49997
Night
14%8%46%5%3445%6%35%
49681
Cloud CoverDay
13%8%47%6%35%5%5%7%33%
50007
Night
15%8%36%5%3445%6%35%
49685
TransparencyDay
48%7%12%20%10%1
49696
Night
47%6%11%20%11%1
49500
SeeingDay
17%424%27%17%7%
6474
Night
18%5%28%30%13%1
16371

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%13%6%10%8%35%445%20%
1552
16th to endDay
15%17%7%10%8%36%44417%
1820
February1st to 15thDay
16%13%7%10%8%35%446%18%
1710
16th to endDay
13%13%5%10%8%34445%24%
1710
March1st to 15thDay
16%12%5%8%6%34446%27%
2049
16th to endDay
18%10%47%6%34445%30%
2288
April1st to 15thDay
18%10%47%5%2435%6%30%
2318
16th to endDay
16%8%35%5%23347%37%
2402
May1st to 15thDay
17%7%36%5%345%47%33%
2331
16th to endDay
12%5%35%5%35%448%39%
2440
June1st to 15thDay
9%436%5%35%5%7%10%38%
2665
16th to endDay
8%5%25%5%46%5%6%10%37%
2690
July1st to 15thDay
7%425%6%35%6%5%9%43%
2520
16th to endDay
7%435%5%36%6%7%11%38%
2528
August1st to 15thDay
7%426%6%36%6%7%10%37%
2340
16th to endDay
10%425%5%35%5%6%8%40%
2483
September1st to 15thDay
10%5%345%346%5%9%40%
2016
16th to endDay
11%5%345%35%5%5%8%41%
1980
October1st to 15thDay
12%8%26%5%34447%39%
1869
16th to endDay
19%10%47%5%24345%32%
1842
November1st to 15thDay
14%8%26%5%245%47%37%
1717
16th to endDay
16%10%47%7%345%5%6%28%
1626
December1st to 15thDay
17%12%5%10%6%3436%6%22%
1560
16th to endDay
20%15%6%8%6%3445%6%17%
1541
January1st to 15thNight
22%11%5%8%6%34446%23%
2716
16th to endNight
13%13%7%9%7%445%45%23%
2753
February1st to 15thNight
14%14%6%10%6%345%35%25%
2479
16th to endNight
16%12%5%8%6%44445%28%
2049
March1st to 15thNight
17%10%5%6%6%35%445%32%
2218
16th to endNight
17%7%25%5%335%5%7%36%
2288
April1st to 15thNight
19%9%35%5%34447%33%
1969
16th to endNight
14%6%3443346%8%40%
1672
May1st to 15thNight
16%6%35%6%3446%7%36%
1620
16th to endNight
10%426%42445%7%45%
1670
June1st to 15thNight
7%425%5%246%6%8%45%
1292
16th to endNight
8%5%244246%6%9%45%
1266
July1st to 15thNight
7%32342435%8%52%
1440
16th to endNight
5%3233245%7%9%51%
1637
August1st to 15thNight
5%425%4346%6%8%48%
1620
16th to endNight
7%5%245%33445%53%
1719
September1st to 15thNight
9%5%3443335%6%49%
1931
16th to endNight
10%425%42345%7%48%
1980
October1st to 15thNight
15%6%26%42445%6%42%
2091
16th to endNight
19%8%36%5%345%5%5%32%
2379
November1st to 15thNight
14%7%35%43446%7%37%
2471
16th to endNight
19%10%46%5%2445%7%30%
2662
December1st to 15thNight
19%12%5%8%5%245%46%24%
2730
16th to endNight
21%14%7%9%6%3444420%
3029

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%13%5%10%6%5%4445%20%
1552
16th to endDay
15%17%7%9%9%35%44417%
1820
February1st to 15thDay
16%13%6%10%8%35%446%19%
1710
16th to endDay
13%14%6%9%8%35%5%45%24%
1710
March1st to 15thDay
17%12%5%7%6%34446%27%
2060
16th to endDay
18%10%47%6%34445%30%
2287
April1st to 15thDay
18%9%47%6%2445%6%30%
2318
16th to endDay
17%8%26%5%33347%37%
2402
May1st to 15thDay
17%6%36%5%35%5%47%33%
2331
16th to endDay
12%5%36%5%35%45%8%40%
2440
June1st to 15thDay
9%436%5%35%47%9%39%
2665
16th to endDay
8%5%35%6%46%6%6%10%38%
2690
July1st to 15thDay
7%425%6%25%5%5%9%44%
2520
16th to endDay
7%425%5%36%6%8%10%39%
2528
August1st to 15thDay
7%427%5%35%7%7%10%37%
2340
16th to endDay
11%425%5%36%46%8%41%
2483
September1st to 15thDay
11%5%25%5%345%5%9%40%
2016
16th to endDay
11%5%34425%5%6%8%42%
1980
October1st to 15thDay
13%8%35%5%34447%39%
1869
16th to endDay
19%9%47%5%24435%32%
1842
November1st to 15thDay
15%7%36%4345%5%6%37%
1717
16th to endDay
17%10%47%7%3445%6%28%
1626
December1st to 15thDay
17%12%6%10%6%3446%5%23%
1560
16th to endDay
21%15%6%8%5%345%47%17%
1541
January1st to 15thNight
21%11%5%7%6%34446%24%
2716
16th to endNight
13%13%8%9%7%44445%23%
2753
February1st to 15thNight
14%14%6%10%6%345%45%25%
2472
16th to endNight
16%12%5%8%6%35%345%28%
2049
March1st to 15thNight
17%10%46%6%34446%31%
2230
16th to endNight
17%7%25%5%335%5%7%36%
2288
April1st to 15thNight
20%8%35%5%34447%33%
1969
16th to endNight
14%6%3442446%7%40%
1672
May1st to 15thNight
16%6%36%6%2445%7%36%
1619
16th to endNight
11%436%43445%7%45%
1670
June1st to 15thNight
7%425%5%345%5%8%46%
1292
16th to endNight
8%5%244236%5%9%45%
1266
July1st to 15thNight
8%3135%1445%8%52%
1440
16th to endNight
5%4233245%7%9%52%
1637
August1st to 15thNight
5%315%435%5%5%8%48%
1620
16th to endNight
8%5%24424446%52%
1719
September1st to 15thNight
9%5%3442435%6%49%
1931
16th to endNight
10%42442345%7%48%
1980
October1st to 15thNight
15%6%26%424346%42%
2091
16th to endNight
20%7%36%5%345%46%32%
2379
November1st to 15thNight
15%7%36%42446%7%37%
2471
16th to endNight
19%10%46%5%2445%6%30%
2662
December1st to 15thNight
20%12%5%8%6%25%445%24%
2730
16th to endNight
21%14%6%9%5%35%44420%
3029

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
64%6%11%10%5%
1553
16th to endDay
69%5%10%9%4
1820
February1st to 15thDay
66%5%8%14%5%
1712
16th to endDay
60%6%10%15%6%
1710
March1st to 15thDay
58%6%11%15%7%
2060
16th to endDay
54%6%9%20%8%1
2288
April1st to 15thDay
53%5%10%19%10%
2318
16th to endDay
46%5%12%17%14%2
2402
May1st to 15thDay
49%6%10%20%10%2
2331
16th to endDay
41%7%11%23%14%1
2444
June1st to 15thDay
38%8%13%24%13%1
2665
16th to endDay
39%8%15%21%14%1
2690
July1st to 15thDay
34%7%10%26%18%2
2371
16th to endDay
34%9%16%22%13%2
2371
August1st to 15thDay
35%10%14%24%12%1
2327
16th to endDay
37%8%12%25%14%1
2483
September1st to 15thDay
37%8%14%25%12%
2016
16th to endDay
37%8%12%29%12%
1980
October1st to 15thDay
44%5%13%23%12%1
1869
16th to endDay
53%6%14%17%8%
1842
November1st to 15thDay
44%8%12%23%10%1
1717
16th to endDay
55%7%13%15%6%
1626
December1st to 15thDay
62%6%11%13%5%
1560
16th to endDay
66%7%11%10%4
1541
January1st to 15thNight
60%5%10%14%7%
2716
16th to endNight
62%6%12%13%4
2753
February1st to 15thNight
60%6%10%14%6%
2481
16th to endNight
57%5%11%19%7%
2049
March1st to 15thNight
53%6%9%20%10%1
2230
16th to endNight
46%5%11%24%10%1
2288
April1st to 15thNight
50%410%19%13%1
1969
16th to endNight
40%6%10%19%17%4
1672
May1st to 15thNight
45%6%11%19%13%2
1620
16th to endNight
37%6%11%23%17%3
1672
June1st to 15thNight
35%8%11%27%15%1
1292
16th to endNight
33%6%13%24%19%1
1266
July1st to 15thNight
29%5%10%30%21%2
1360
16th to endNight
26%9%17%24%19%3
1531
August1st to 15thNight
30%7%13%31%13%3
1609
16th to endNight
32%6%10%29%18%2
1719
September1st to 15thNight
34%5%12%28%16%1
1931
16th to endNight
33%7%11%31%15%
1980
October1st to 15thNight
42%5%11%21%18%
2091
16th to endNight
50%6%12%21%7%
2379
November1st to 15thNight
44%6%12%23%11%1
2471
16th to endNight
53%5%14%19%6%
2662
December1st to 15thNight
60%7%12%12%6%
2730
16th to endNight
66%6%10%11%5%
3029

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
25%7%42%17%6%
135
16th to endDay
36%6%36%16%3
144
February1st to 15thDay
26%7%42%21%1
135
16th to endDay
20%13%41%20%4
120
March1st to 15thDay
26%9%33%23%8%
245
16th to endDay
24%425%33%8%2
352
April1st to 15thDay
21%8%32%26%9%2
330
16th to endDay
23%324%25%14%7%
289
May1st to 15thDay
23%226%24%19%3
288
16th to endDay
17%321%30%19%8%
331
June1st to 15thDay
11%125%36%20%5%
460
16th to endDay
9%227%35%18%5%
495
July1st to 15thDay
8%118%35%24%10%
475
16th to endDay
7%215%34%27%11%
388
August1st to 15thDay
7%111%34%26%18%
313
16th to endDay
14%314%24%25%18%
332
September1st to 15thDay
10%220%18%31%17%
315
16th to endDay
14%213%23%28%17%
314
October1st to 15thDay
17%425%24%19%8%
315
16th to endDay
24%8%31%27%6%1
258
November1st to 15thDay
18%8%21%32%16%2
135
16th to endDay
22%18%32%20%6%
105
December1st to 15thDay
22%16%40%12%8%
90
16th to endDay
25%12%46%12%2
110
January1st to 15thNight
27%8%35%22%5%
975
16th to endNight
20%8%37%28%5%
881
February1st to 15thNight
20%7%42%25%3
764
16th to endNight
22%7%34%29%5%
683
March1st to 15thNight
21%7%34%28%6%
780
16th to endNight
19%431%30%11%1
832
April1st to 15thNight
23%6%31%31%5%
669
16th to endNight
17%332%33%11%1
558
May1st to 15thNight
19%325%36%14%
540
16th to endNight
11%223%37%21%3
551
June1st to 15thNight
9%124%46%18%
360
16th to endNight
11%117%45%24%
366
July1st to 15thNight
9%114%39%31%4
510
16th to endNight
5%115%45%28%3
564
August1st to 15thNight
7%12%40%33%4
539
16th to endNight
9%114%36%33%4
573
September1st to 15thNight
11%317%32%27%6%
687
16th to endNight
13%215%33%28%7%
717
October1st to 15thNight
19%422%30%19%3
720
16th to endNight
24%8%33%27%5%
768
November1st to 15thNight
17%7%30%28%14%1
760
16th to endNight
25%12%31%22%8%
780
December1st to 15thNight
27%11%34%20%5%
780
16th to endNight
27%8%37%22%3
1014
Page generated at 2018-04-24 10:03:00. Version ac04

Copyright 2018 A. Danko


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