Grimes Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grimes Observing Site clear sky chart from 2005-11-06 to 2024-03-06.

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%
25022
21%
80145
10%
24930
45%
24930
28%
45708

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
26%
939
24%
4325
8%
926
40%
926
17%
2248
January11th to 20thNight
22%
944
22%
4324
8%
930
36%
930
16%
2379
January21st to endNight
18%
1036
15%
4564
4%
1023
33%
1023
17%
2147
February1st to 10thNight
20%
760
18%
2470
7%
760
34%
760
19%
1517
February11th to 20thNight
23%
740
19%
2260
6%
740
37%
740
23%
1375
February21st to endNight
25%
628
20%
1884
5%
628
39%
628
24%
1134
March1st to 10thNight
29%
742
21%
2226
7%
742
41%
742
26%
1320
March11th to 20thNight
34%
719
20%
2110
10%
719
43%
719
29%
1270
March21st to endNight
33%
594
16%
1980
10%
594
44%
594
21%
1262
April1st to 10thNight
29%
540
17%
1800
10%
540
41%
540
23%
1111
April11th to 20thNight
26%
533
18%
1777
8%
533
40%
533
20%
1112
April21st to endNight
34%
540
16%
1688
11%
540
43%
540
22%
1082
May1st to 10thNight
37%
540
16%
1561
11%
540
43%
540
26%
991
May11th to 20thNight
38%
531
15%
1418
8%
531
42%
531
28%
933
May21st to endNight
33%
583
16%
1552
7%
582
39%
582
26%
1034
June1st to 10thNight
46%
540
13%
1440
6%
540
49%
540
34%
903
June11th to 20thNight
37%
540
13%
1440
5%
540
41%
540
30%
918
June21st to endNight
48%
540
17%
1440
7%
540
54%
540
45%
800
July1st to 10thNight
56%
525
15%
1400
9%
525
59%
525
41%
832
July11th to 20thNight
55%
522
23%
1392
11%
522
61%
522
52%
746
July21st to endNight
60%
591
25%
1488
17%
558
64%
558
48%
823
August1st to 10thNight
55%
537
23%
1424
16%
534
59%
534
39%
861
August11th to 20thNight
60%
534
27%
1703
21%
534
69%
534
44%
850
August21st to endNight
61%
594
28%
1980
27%
594
69%
594
43%
972
September1st to 10thNight
55%
540
27%
1800
24%
540
66%
540
40%
906
September11th to 20thNight
52%
540
30%
1867
25%
540
63%
540
38%
943
September21st to endNight
46%
540
29%
1980
24%
540
56%
540
32%
1012
October1st to 10thNight
39%
638
24%
2078
16%
638
46%
638
26%
1237
October11th to 20thNight
36%
720
28%
2160
13%
720
48%
720
32%
1207
October21st to endNight
29%
988
24%
2572
7%
988
40%
988
34%
1557
November1st to 10thNight
31%
925
24%
2405
8%
925
41%
925
35%
1459
November11th to 20thNight
25%
950
30%
2470
8%
950
41%
950
33%
1432
November21st to endNight
28%
950
25%
2655
8%
950
43%
950
33%
1521
December1st to 10thNight
22%
950
24%
2660
5%
950
38%
950
28%
1554
December11th to 20thNight
27%
948
23%
3135
8%
948
40%
948
26%
1699
December21st to endNight
21%
1041
14%
4717
4%
1026
36%
1026
16%
2561

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
7%6%35%5%345%6%8%49%
78442
Night
5%6%35%5%35%5%6%8%51%
81127
TransparencyDay
31%8%16%26%16%4
78146
Night
29%8%16%26%17%4
80945
SeeingDay
12%19%35%24%9%1
14870
Night
9%17%35%29%9%1
25059

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 10thDay
16%36%445%5%7%9%51%
2538
11th to 20thDay
25%48%5%45%5%6%9%48%
2540
21st to endDay
26%25%423447%59%
2808
February1st to 10thDay
49%47%6%37%5%5%8%42%
1710
11th to 20thDay
48%48%6%35%46%7%45%
1806
21st to endDay
28%47%6%45%6%5%8%45%
1570
March1st to 10thDay
48%36%5%345%5%8%48%
1850
11th to 20thDay
5%7%47%5%35%45%8%48%
1844
21st to endDay
10%11%37%5%35%5%7%8%36%
2376
April1st to 10thDay
9%11%5%5%4345%6%7%41%
2160
11th to 20thDay
12%11%46%6%35%5%6%6%36%
2131
21st to endDay
15%10%47%5%345%6%7%36%
2272
May1st to 10thDay
12%8%38%6%45%6%5%7%36%
2397
11th to 20thDay
16%10%35%5%345%6%8%35%
2478
21st to endDay
16%8%35%5%45%6%6%9%34%
2724
June1st to 10thDay
8%5%35%435%6%6%10%46%
2520
11th to 20thDay
9%425%43447%10%47%
2520
21st to endDay
5%3133345%8%8%55%
2520
July1st to 10thDay
5%325%435%6%7%10%50%
2520
11th to 20thDay
42135%245%6%9%60%
2520
21st to endDay
6%324435%5%7%8%55%
2742
August1st to 10thDay
5%324435%6%7%11%48%
2507
11th to 20thDay
42234346%7%8%57%
2194
21st to endDay
5%32442446%8%60%
2376
September1st to 10thDay
7%42332335%7%62%
2160
11th to 20thDay
7%423324446%60%
2093
21st to endDay
10%5%23413337%60%
1980
October1st to 10thDay
11%8%24413446%53%
1877
11th to 20thDay
8%6%25%43345%7%54%
1782
21st to endDay
6%7%2442445%8%54%
1782
November1st to 10thDay
45%24435%6%6%8%52%
1673
11th to 20thDay
25%35%5%345%5%8%55%
1710
21st to endDay
37%36%3245%6%10%51%
1522
December1st to 10thDay
35%36%5%26%5%5%8%51%
1520
11th to 20thDay
2424435%5%6%11%54%
1926
21st to endDay
39%47%5%35%45%7%49%
2794
January1st to 10thNight
1438%6%45%5%6%8%50%
4417
11th to 20thNight
1337%7%46%5%7%9%49%
4430
21st to endNight
1435%5%3445%8%58%
4873
February1st to 10thNight
38%47%6%35%5%6%7%45%
2470
11th to 20thNight
26%36%6%45%5%6%7%47%
2260
21st to endNight
28%47%5%25%6%5%8%48%
1884
March1st to 10thNight
5%6%36%5%246%6%8%49%
2226
11th to 20thNight
47%35%5%45%5%6%7%48%
2110
21st to endNight
8%9%36%5%46%6%6%8%38%
1980
April1st to 10thNight
10%7%45%5%25%5%7%7%43%
1800
11th to 20thNight
11%10%35%5%34447%44%
1777
21st to endNight
12%7%36%5%35%5%47%43%
1688
May1st to 10thNight
11%7%35%5%35%6%5%7%44%
1561
11th to 20thNight
11%7%35%5%345%5%9%42%
1417
21st to endNight
15%8%3433445%7%43%
1552
June1st to 10thNight
8%5%245%35%5%6%11%46%
1440
11th to 20thNight
9%5%24436%5%7%8%45%
1440
21st to endNight
5%3134445%5%9%58%
1440
July1st to 10thNight
6%4246%346%6%8%52%
1440
11th to 20thNight
421332447%9%62%
1440
21st to endNight
3313425%5%6%8%60%
1576
August1st to 10thNight
45%246%46%5%6%7%51%
1432
11th to 20thNight
42144245%6%8%60%
1703
21st to endNight
43134335%6%8%59%
1980
September1st to 10thNight
7%424324446%61%
1800
11th to 20thNight
6%41343445%8%58%
1867
21st to endNight
10%6%14323345%59%
1980
October1st to 10thNight
11%8%25%424446%50%
2078
11th to 20thNight
8%6%25%424446%55%
2160
21st to endNight
6%7%25%43345%7%53%
2572
November1st to 10thNight
5%6%25%4346%6%8%50%
2405
11th to 20thNight
46%3442446%7%56%
2470
21st to endNight
46%35%425%5%6%8%52%
2655
December1st to 10thNight
26%35%5%3445%8%54%
2660
11th to 20thNight
25%36%425%6%5%9%53%
3271
21st to endNight
28%48%6%3445%7%49%
4873

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
26%7%20%29%16%1
2539
11th to 20thDay
29%10%19%22%16%4
2540
21st to endDay
22%8%20%33%13%4
2808
February1st to 10thDay
40%8%15%22%13%2
1710
11th to 20thDay
36%8%16%23%13%4
1816
21st to endDay
34%8%17%22%15%4
1570
March1st to 10thDay
32%7%16%29%13%3
1850
11th to 20thDay
32%7%16%28%15%2
1844
21st to endDay
43%9%15%23%9%1
2376
April1st to 10thDay
40%7%17%22%10%4
2160
11th to 20thDay
46%6%13%20%13%2
2134
21st to endDay
44%8%15%24%9%
2272
May1st to 10thDay
42%10%15%23%9%1
2397
11th to 20thDay
45%8%18%22%7%
2482
21st to endDay
43%10%17%21%7%1
2724
June1st to 10thDay
32%10%20%26%11%2
2520
11th to 20thDay
30%9%18%26%13%5%
2520
21st to endDay
22%8%17%28%21%5%
2520
July1st to 10thDay
25%9%16%29%18%4
2451
11th to 20thDay
20%6%12%26%25%12%
2445
21st to endDay
23%7%13%26%21%9%
2590
August1st to 10thDay
26%9%16%27%15%7%
2491
11th to 20thDay
21%7%15%29%19%8%
2194
21st to endDay
22%5%12%24%26%11%
2376
September1st to 10thDay
23%411%26%25%11%
2160
11th to 20thDay
25%5%11%26%25%8%
2093
21st to endDay
26%5%11%34%23%2
1980
October1st to 10thDay
31%6%13%25%22%3
1877
11th to 20thDay
29%413%30%18%6%
1782
21st to endDay
28%8%18%25%17%4
1782
November1st to 10thDay
26%9%15%25%21%4
1673
11th to 20thDay
25%7%13%29%19%6%
1710
21st to endDay
27%7%18%29%16%4
1522
December1st to 10thDay
29%8%18%26%17%2
1520
11th to 20thDay
23%8%21%33%13%2
1924
21st to endDay
34%7%10%24%23%4
2794
January1st to 10thNight
30%8%15%28%17%2
4417
11th to 20thNight
28%12%19%24%14%3
4430
21st to endNight
23%9%21%30%15%2
4873
February1st to 10thNight
35%9%18%23%12%3
2470
11th to 20thNight
33%9%17%25%14%3
2260
21st to endNight
32%9%14%25%15%5%
1884
March1st to 10thNight
30%9%17%26%17%2
2226
11th to 20thNight
33%6%17%24%16%3
2110
21st to endNight
39%8%19%21%11%2
1980
April1st to 10thNight
37%8%16%23%13%3
1800
11th to 20thNight
40%6%15%22%13%3
1777
21st to endNight
40%8%15%23%13%1
1688
May1st to 10thNight
36%8%16%27%12%
1561
11th to 20thNight
38%8%21%25%8%
1418
21st to endNight
39%8%16%27%10%1
1552
June1st to 10thNight
30%9%24%24%11%1
1440
11th to 20thNight
33%10%20%22%13%3
1440
21st to endNight
22%7%19%28%19%5%
1440
July1st to 10thNight
27%8%16%29%18%3
1400
11th to 20thNight
18%6%15%27%23%11%
1392
21st to endNight
19%9%15%29%21%7%
1488
August1st to 10thNight
29%8%15%27%17%4
1424
11th to 20thNight
20%7%12%31%24%7%
1703
21st to endNight
20%7%12%25%28%8%
1980
September1st to 10thNight
25%49%26%27%9%
1800
11th to 20thNight
24%5%13%25%25%7%
1867
21st to endNight
29%48%28%25%6%
1980
October1st to 10thNight
36%6%11%21%23%3
2078
11th to 20thNight
29%5%11%28%20%7%
2160
21st to endNight
29%7%17%22%20%6%
2572
November1st to 10thNight
28%8%17%22%19%6%
2405
11th to 20thNight
27%5%15%29%19%5%
2470
21st to endNight
27%6%15%28%20%4
2655
December1st to 10thNight
27%8%17%26%18%4
2660
11th to 20thNight
24%9%18%35%12%2
3272
21st to endNight
33%7%14%26%16%4
4873

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
423%35%23%11%3
270
11th to 20thDay
13%25%35%17%9%1
270
21st to endDay
11%35%38%11%31
297
February1st to 10thDay
11%30%46%12%1
270
11th to 20thDay
9%32%43%14%1
270
21st to endDay
13%30%43%13%1
225
March1st to 10thDay
7%33%40%14%5%1
255
11th to 20thDay
14%23%42%15%6%1
284
21st to endDay
20%28%30%16%5%1
462
April1st to 10thDay
21%30%35%12%2
420
11th to 20thDay
22%32%37%8%1
412
21st to endDay
21%20%30%22%7%1
532
May1st to 10thDay
18%22%32%18%8%2
603
11th to 20thDay
22%16%27%24%10%2
625
21st to endDay
19%18%31%22%9%1
679
June1st to 10thDay
9%13%32%30%14%3
630
11th to 20thDay
12%17%39%24%8%
630
21st to endDay
9%11%35%31%13%1
630
July1st to 10thDay
6%5%34%38%15%2
621
11th to 20thDay
47%41%35%12%1
618
21st to endDay
6%7%31%38%16%2
684
August1st to 10thDay
6%6%31%40%15%1
626
11th to 20thDay
5%7%34%39%13%3
475
21st to endDay
5%10%33%38%13%2
495
September1st to 10thDay
8%12%35%31%10%2
450
11th to 20thDay
10%10%33%30%13%4
383
21st to endDay
17%16%35%19%9%4
270
October1st to 10thDay
19%17%25%25%11%3
270
11th to 20thDay
17%25%33%17%5%3
270
21st to endDay
10%31%31%20%5%2
297
November1st to 10thDay
11%27%35%19%6%2
270
11th to 20thDay
12%27%36%20%5%
270
21st to endDay
11%24%43%15%7%1
270
December1st to 10thDay
12%29%34%18%6%
270
11th to 20thDay
11%31%44%11%3
270
21st to endDay
12%30%38%14%6%
297
January1st to 10thNight
7%25%36%22%9%1
950
11th to 20thNight
430%39%19%6%1
950
21st to endNight
6%31%38%21%4
1045
February1st to 10thNight
8%26%41%21%5%
760
11th to 20thNight
6%23%42%22%6%1
744
21st to endNight
8%20%41%25%5%1
628
March1st to 10thNight
9%22%35%26%6%1
742
11th to 20thNight
8%16%36%32%7%1
719
21st to endNight
15%14%32%30%8%
594
April1st to 10thNight
16%14%36%30%3
540
11th to 20thNight
19%18%33%26%4
533
21st to endNight
18%15%29%26%12%
540
May1st to 10thNight
14%12%32%31%10%1
540
11th to 20thNight
18%9%31%29%13%1
531
21st to endNight
21%11%32%28%8%
584
June1st to 10thNight
11%10%30%35%13%
540
11th to 20thNight
12%13%35%32%7%
540
21st to endNight
6%7%35%44%8%1
540
July1st to 10thNight
6%428%40%20%1
525
11th to 20thNight
6%434%46%9%1
522
21st to endNight
4130%53%12%
591
August1st to 10thNight
6%428%49%12%1
537
11th to 20thNight
5%327%46%18%1
534
21st to endNight
6%5%24%47%18%1
594
September1st to 10thNight
9%6%26%42%16%1
540
11th to 20thNight
9%9%25%39%16%2
540
21st to endNight
14%13%25%34%13%1
540
October1st to 10thNight
16%14%28%29%12%1
638
11th to 20thNight
13%15%32%29%9%1
720
21st to endNight
11%17%39%23%8%2
988
November1st to 10thNight
9%17%40%26%6%2
925
11th to 20thNight
10%21%39%24%5%1
950
21st to endNight
7%21%39%27%5%
950
December1st to 10thNight
7%28%40%20%5%1
950
11th to 20thNight
5%23%40%26%6%
950
21st to endNight
9%26%38%20%6%1
1045
Page generated at 2024-03-03 04:28:54. Version ac07

Copyright © 2024 Attilla Danko.


Grimes Observing Site Clear Sky Chart |Charts Home