Amherst
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Amherst clear sky chart from 2005-11-06 to 2024-01-10.

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
19%
23467
13%
74556
4%
23401
28%
23401
13%
54744

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
11%
849
11%
2835
2%
846
21%
846
8%
2166
January11th to 20thNight
14%
786
10%
2503
2%
786
23%
786
8%
1947
January21st to endNight
17%
792
17%
2574
5%
792
31%
792
12%
1833
February1st to 10thNight
13%
720
12%
2340
3%
720
23%
720
10%
1752
February11th to 20thNight
12%
703
10%
2276
1%
700
23%
700
8%
1744
February21st to endNight
17%
592
15%
1920
4%
592
30%
592
13%
1391
March1st to 10thNight
15%
720
16%
1985
4%
720
25%
720
13%
1521
March11th to 20thNight
18%
720
13%
1980
4%
720
26%
720
13%
1503
March21st to endNight
16%
792
14%
2178
4%
792
26%
792
15%
1646
April1st to 10thNight
14%
551
11%
1811
4%
551
22%
551
9%
1397
April11th to 20thNight
17%
534
16%
1676
7%
534
26%
534
15%
1195
April21st to endNight
17%
540
12%
1620
4%
540
25%
540
13%
1228
May1st to 10thNight
22%
540
13%
1545
6%
540
28%
540
14%
1168
May11th to 20thNight
22%
532
14%
1417
4%
532
31%
532
17%
1046
May21st to endNight
15%
583
11%
1551
3%
582
21%
582
18%
1140
June1st to 10thNight
19%
490
8%
1390
4%
490
23%
490
13%
1073
June11th to 20thNight
21%
360
12%
1260
4%
360
31%
360
16%
878
June21st to endNight
23%
360
6%
1260
2%
360
27%
360
13%
934
July1st to 10thNight
22%
350
11%
1225
3%
350
32%
350
17%
829
July11th to 20thNight
26%
437
10%
1307
5%
437
31%
437
19%
915
July21st to endNight
26%
590
10%
1528
6%
558
30%
558
18%
1155
August1st to 10thNight
29%
538
10%
1600
5%
534
33%
534
22%
1085
August11th to 20thNight
28%
532
11%
1596
5%
532
32%
532
17%
1157
August21st to endNight
34%
594
15%
1856
7%
594
41%
594
23%
1188
September1st to 10thNight
27%
540
15%
1800
8%
540
38%
540
22%
1162
September11th to 20thNight
34%
614
19%
1874
11%
614
43%
614
23%
1210
September21st to endNight
28%
720
20%
2030
9%
720
37%
720
23%
1357
October1st to 10thNight
30%
720
17%
2160
9%
720
38%
720
22%
1443
October11th to 20thNight
23%
720
19%
2160
7%
720
33%
720
18%
1501
October21st to endNight
16%
792
14%
2376
4%
792
26%
792
11%
1773
November1st to 10thNight
17%
827
12%
2584
4%
827
25%
827
11%
1942
November11th to 20thNight
18%
850
14%
2660
5%
850
27%
850
11%
1996
November21st to endNight
15%
850
12%
2660
3%
850
24%
850
10%
1985
December1st to 10thNight
12%
850
13%
2660
2%
850
23%
850
8%
2065
December11th to 20thNight
9%
850
12%
3244
2%
849
20%
849
7%
2568
December21st to endNight
12%
929
6%
5115
2%
907
22%
907
4%
3851

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
19%10%47%6%3445%7%31%
74858
Night
19%11%47%6%3445%6%31%
74803
TransparencyDay
54%6%11%19%9%1
74555
Night
55%6%11%18%9%1
74641
SeeingDay
27%22%31%15%41
15852
Night
26%18%31%19%5%
23473

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%17%5%8%6%44445%27%
1320
11th to 20thDay
20%14%6%10%7%35%34422%
1450
21st to endDay
12%11%5%8%7%35%6%5%7%32%
1782
February1st to 10thDay
18%11%5%8%6%44446%30%
1620
11th to 20thDay
18%14%49%6%345%5%6%27%
1573
21st to endDay
10%12%6%7%7%45%5%5%8%31%
1336
March1st to 10thDay
16%16%6%8%6%4445%5%26%
1966
11th to 20thDay
14%11%6%10%7%3445%5%30%
1980
21st to endDay
18%16%6%8%6%34335%29%
2178
April1st to 10thDay
21%13%5%8%6%25%45%5%26%
2148
11th to 20thDay
20%12%36%5%345%5%7%30%
2230
21st to endDay
23%11%37%5%35%45%7%27%
2340
May1st to 10thDay
24%10%48%6%3445%6%25%
2413
11th to 20thDay
23%9%35%5%2445%6%33%
2478
21st to endDay
20%10%47%5%245%5%7%31%
2724
June1st to 10thDay
27%9%46%5%35%5%5%7%26%
2582
11th to 20thDay
22%7%46%5%35%5%5%6%31%
2700
21st to endDay
27%8%46%43445%7%29%
2700
July1st to 10thDay
17%7%35%5%45%46%9%35%
2700
11th to 20thDay
15%6%37%6%35%5%6%9%35%
2591
21st to endDay
18%8%46%6%45%6%6%8%30%
2698
August1st to 10thDay
16%6%36%5%346%7%8%36%
2327
11th to 20thDay
17%6%36%6%45%6%7%8%32%
2304
21st to endDay
13%7%26%5%345%5%8%41%
2498
September1st to 10thDay
17%5%35%43445%8%41%
2160
11th to 20thDay
17%9%36%5%34447%38%
2084
21st to endDay
19%6%25%5%23446%44%
1928
October1st to 10thDay
18%8%26%5%3445%7%38%
1800
11th to 20thDay
19%9%36%7%34447%34%
1800
21st to endDay
18%11%47%5%45%446%31%
1980
November1st to 10thDay
20%11%37%7%44445%31%
1489
11th to 20thDay
18%14%47%6%345%46%30%
1520
21st to endDay
18%13%49%6%34445%29%
1520
December1st to 10thDay
23%13%5%6%5%33347%27%
1520
11th to 20thDay
18%18%6%10%6%3334426%
1906
21st to endDay
19%13%7%13%6%3444424%
2513
January1st to 10thNight
18%14%5%9%6%35%43428%
2835
11th to 20thNight
19%13%5%10%7%4445%5%26%
2503
21st to endNight
13%12%48%6%4445%7%33%
2574
February1st to 10thNight
17%12%5%8%6%45%5%5%6%27%
2340
11th to 20thNight
17%15%48%6%45%445%27%
2273
21st to endNight
12%13%6%8%7%35%45%5%32%
1920
March1st to 10thNight
16%15%49%6%35%45%5%29%
1976
11th to 20thNight
16%12%5%7%7%4446%5%29%
1979
21st to endNight
18%15%5%7%6%2434432%
2178
April1st to 10thNight
24%13%48%5%35%445%25%
1811
11th to 20thNight
22%12%36%425%446%33%
1676
21st to endNight
23%12%46%5%2435%6%28%
1620
May1st to 10thNight
26%9%346%45%447%28%
1545
11th to 20thNight
24%9%35%6%3345%6%33%
1416
21st to endNight
18%9%36%6%345%5%7%32%
1550
June1st to 10thNight
26%10%36%6%345%48%25%
1390
11th to 20thNight
23%7%36%6%35%448%33%
1260
21st to endNight
23%8%37%6%35%5%5%9%26%
1260
July1st to 10thNight
17%7%46%5%36%5%8%7%32%
1260
11th to 20thNight
14%7%36%7%36%6%7%9%30%
1350
21st to endNight
16%8%37%6%46%7%6%8%29%
1617
August1st to 10thNight
14%6%27%7%35%6%7%8%37%
1612
11th to 20thNight
15%9%37%6%36%5%7%9%30%
1596
21st to endNight
16%6%25%4345%6%8%41%
1856
September1st to 10thNight
17%6%35%5%345%5%8%40%
1800
11th to 20thNight
16%7%35%5%34447%44%
1874
21st to endNight
18%8%25%5%3345%6%42%
2030
October1st to 10thNight
19%7%25%6%3345%7%40%
2160
11th to 20thNight
19%8%35%5%3445%7%36%
2160
21st to endNight
25%10%46%5%43445%31%
2376
November1st to 10thNight
22%10%47%5%345%46%30%
2584
11th to 20thNight
20%10%5%7%6%445%5%5%30%
2660
21st to endNight
21%12%47%5%34446%30%
2660
December1st to 10thNight
24%11%5%8%5%3445%6%25%
2660
11th to 20thNight
23%16%5%8%6%2333426%
3293
21st to endNight
24%14%6%10%42333427%
5149

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
62%7%9%12%9%1
1321
11th to 20thDay
67%6%7%12%8%1
1450
21st to endDay
52%6%10%16%15%1
1782
February1st to 10thDay
58%5%10%15%11%1
1620
11th to 20thDay
61%5%9%15%9%1
1581
21st to endDay
53%412%18%11%2
1336
March1st to 10thDay
61%48%17%8%1
1970
11th to 20thDay
57%411%17%10%2
1980
21st to endDay
61%48%15%9%3
2178
April1st to 10thDay
62%5%7%14%10%3
2148
11th to 20thDay
55%5%9%19%12%1
2230
21st to endDay
58%5%9%17%9%2
2340
May1st to 10thDay
61%6%8%15%9%1
2413
11th to 20thDay
52%7%8%21%11%1
2482
21st to endDay
53%7%13%19%8%1
2724
June1st to 10thDay
59%6%10%19%5%
2582
11th to 20thDay
53%7%10%20%9%1
2700
21st to endDay
56%6%11%17%9%1
2700
July1st to 10thDay
45%8%15%22%9%1
2625
11th to 20thDay
44%9%16%22%8%1
2511
21st to endDay
51%9%14%20%6%
2547
August1st to 10thDay
43%10%14%26%7%
2314
11th to 20thDay
49%10%13%23%6%
2304
21st to endDay
40%7%16%25%11%
2498
September1st to 10thDay
41%7%15%24%13%
2160
11th to 20thDay
45%6%11%24%12%1
2084
21st to endDay
44%49%28%14%1
1928
October1st to 10thDay
46%6%11%27%10%1
1800
11th to 20thDay
52%5%13%22%7%1
1800
21st to endDay
56%6%10%18%10%
1980
November1st to 10thDay
57%6%9%18%10%
1489
11th to 20thDay
56%7%12%15%10%1
1520
21st to endDay
58%6%12%16%8%
1520
December1st to 10thDay
60%8%10%16%6%
1520
11th to 20thDay
64%5%8%15%6%1
1905
21st to endDay
66%7%11%11%6%1
2513
January1st to 10thNight
61%6%10%16%7%1
2835
11th to 20thNight
61%6%10%13%8%1
2503
21st to endNight
52%7%10%20%10%2
2574
February1st to 10thNight
58%5%9%12%13%2
2340
11th to 20thNight
60%6%9%12%11%1
2276
21st to endNight
55%5%8%17%13%2
1920
March1st to 10thNight
59%48%16%11%1
1985
11th to 20thNight
57%6%9%16%10%3
1980
21st to endNight
57%48%17%11%2
2178
April1st to 10thNight
62%5%8%11%10%3
1811
11th to 20thNight
54%49%20%12%1
1676
21st to endNight
58%5%10%15%11%1
1620
May1st to 10thNight
57%5%9%18%10%1
1545
11th to 20thNight
53%5%9%23%9%1
1417
21st to endNight
51%6%14%19%9%1
1551
June1st to 10thNight
58%7%10%17%8%
1390
11th to 20thNight
52%5%10%23%9%1
1260
21st to endNight
56%8%13%13%9%1
1260
July1st to 10thNight
46%9%16%22%7%
1225
11th to 20thNight
46%10%14%22%8%
1307
21st to endNight
51%11%14%17%7%
1528
August1st to 10thNight
42%10%17%24%7%
1600
11th to 20thNight
48%10%15%21%5%
1596
21st to endNight
40%8%17%26%9%
1856
September1st to 10thNight
41%8%12%29%10%
1800
11th to 20thNight
42%5%12%26%14%
1874
21st to endNight
43%6%11%27%12%1
2030
October1st to 10thNight
44%6%13%26%11%
2160
11th to 20thNight
47%7%12%26%7%
2160
21st to endNight
56%6%10%17%10%1
2376
November1st to 10thNight
56%7%11%16%9%1
2584
11th to 20thNight
56%8%11%15%10%1
2660
21st to endNight
57%6%13%16%8%
2660
December1st to 10thNight
61%7%9%16%7%
2660
11th to 20thNight
64%5%7%15%9%
3295
21st to endNight
64%6%12%12%5%1
5149

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
32%29%28%10%1
178
11th to 20thDay
31%24%28%12%4
323
21st to endDay
20%26%37%14%3
374
February1st to 10thDay
28%26%31%11%3
340
11th to 20thDay
32%29%26%11%21
336
21st to endDay
22%26%35%14%3
280
March1st to 10thDay
29%29%29%11%21
416
11th to 20thDay
26%27%30%12%31
420
21st to endDay
31%30%25%10%31
462
April1st to 10thDay
38%31%21%8%2
420
11th to 20thDay
32%29%25%12%3
412
21st to endDay
30%26%28%11%4
420
May1st to 10thDay
33%27%24%12%31
496
11th to 20thDay
30%21%28%15%41
624
21st to endDay
29%20%33%15%3
680
June1st to 10thDay
34%19%29%14%4
630
11th to 20thDay
25%20%33%17%4
630
21st to endDay
27%14%32%20%6%1
630
July1st to 10thDay
23%17%37%17%5%1
620
11th to 20thDay
17%11%41%23%6%1
618
21st to endDay
23%14%38%19%5%
638
August1st to 10thDay
14%15%40%23%7%
446
11th to 20thDay
21%15%34%23%7%
439
21st to endDay
17%18%33%24%6%2
495
September1st to 10thDay
17%18%39%20%6%1
450
11th to 20thDay
25%19%31%17%6%2
450
21st to endDay
21%22%30%18%7%1
423
October1st to 10thDay
24%16%32%18%8%2
360
11th to 20thDay
24%24%28%17%6%1
360
21st to endDay
26%26%27%15%5%1
396
November1st to 10thDay
29%24%29%10%6%1
365
11th to 20thDay
30%26%25%13%42
370
21st to endDay
33%26%26%11%3
370
December1st to 10thDay
34%25%27%11%21
370
11th to 20thDay
37%28%23%11%1
370
21st to endDay
29%27%30%11%21
241
January1st to 10thNight
27%24%29%16%4
849
11th to 20thNight
29%23%29%16%3
786
21st to endNight
21%23%33%18%5%
792
February1st to 10thNight
28%22%32%16%2
720
11th to 20thNight
30%26%28%13%21
703
21st to endNight
21%22%35%17%41
592
March1st to 10thNight
25%23%33%16%3
720
11th to 20thNight
27%19%29%18%5%1
720
21st to endNight
28%19%31%17%5%
792
April1st to 10thNight
32%21%29%16%3
551
11th to 20thNight
30%18%31%15%5%
534
21st to endNight
32%17%30%16%41
540
May1st to 10thNight
30%17%27%21%5%1
540
11th to 20thNight
27%18%28%22%5%
532
21st to endNight
24%16%40%16%2
583
June1st to 10thNight
32%13%32%20%4
490
11th to 20thNight
26%12%35%23%4
360
21st to endNight
24%9%36%25%5%1
360
July1st to 10thNight
20%6%47%19%7%
350
11th to 20thNight
17%11%42%26%4
437
21st to endNight
20%9%39%28%5%
590
August1st to 10thNight
17%10%41%24%8%
538
11th to 20thNight
16%11%39%27%6%1
532
21st to endNight
17%11%32%30%8%1
594
September1st to 10thNight
19%9%41%25%6%
540
11th to 20thNight
20%13%29%29%9%
614
21st to endNight
22%14%32%24%8%
720
October1st to 10thNight
22%13%31%25%8%1
720
11th to 20thNight
23%15%35%20%6%1
720
21st to endNight
31%23%26%16%4
792
November1st to 10thNight
30%21%27%17%5%1
827
11th to 20thNight
28%23%25%17%5%1
850
21st to endNight
31%22%27%15%3
850
December1st to 10thNight
32%20%29%15%3
850
11th to 20thNight
32%26%28%12%3
850
21st to endNight
32%23%25%16%31
935
Page generated at 2024-01-07 11:06:57. Version ac07

Copyright 2024 Attilla Danko


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