Montgomery
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montgomery clear sky chart from 2005-11-06 to 2024-01-12.

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
55%
23557
23%
74422
19%
23502
61%
23502
29%
45565

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
33%
760
23%
2459
12%
757
47%
757
26%
1517
January11th to 20thNight
39%
727
25%
2269
16%
727
49%
727
25%
1444
January21st to endNight
34%
792
28%
2376
15%
792
46%
792
28%
1508
February1st to 10thNight
39%
720
23%
2160
15%
720
47%
720
26%
1406
February11th to 20thNight
35%
703
22%
2098
11%
699
44%
699
27%
1327
February21st to endNight
36%
592
22%
1776
12%
592
44%
592
27%
1151
March1st to 10thNight
43%
720
25%
2160
16%
720
51%
720
34%
1284
March11th to 20thNight
42%
720
22%
2033
13%
720
48%
720
29%
1318
March21st to endNight
45%
756
26%
2142
15%
756
53%
756
33%
1312
April1st to 10thNight
50%
540
25%
1800
21%
540
57%
540
29%
1055
April11th to 20thNight
49%
533
27%
1775
22%
533
58%
533
32%
1011
April21st to endNight
60%
540
29%
1800
25%
540
67%
540
39%
934
May1st to 10thNight
64%
540
27%
1656
22%
540
69%
540
39%
904
May11th to 20thNight
62%
531
18%
1592
15%
531
63%
531
29%
1002
May21st to endNight
70%
582
22%
1744
20%
582
73%
582
32%
1085
June1st to 10thNight
70%
540
13%
1620
12%
540
70%
540
24%
1103
June11th to 20thNight
76%
540
19%
1620
18%
540
76%
540
36%
949
June21st to endNight
73%
540
16%
1620
15%
540
74%
540
28%
1036
July1st to 10thNight
74%
525
10%
1575
10%
525
74%
525
22%
1109
July11th to 20thNight
78%
522
13%
1566
15%
522
78%
522
27%
1045
July21st to endNight
79%
591
16%
1733
16%
558
79%
558
31%
1074
August1st to 10thNight
75%
537
11%
1778
15%
534
75%
534
25%
1138
August11th to 20thNight
70%
534
14%
1776
16%
534
71%
534
23%
1161
August21st to endNight
68%
594
18%
1980
22%
594
68%
594
21%
1337
September1st to 10thNight
72%
599
19%
1859
20%
599
72%
599
25%
1234
September11th to 20thNight
66%
720
20%
1980
18%
720
67%
720
30%
1295
September21st to endNight
68%
720
27%
1980
23%
720
70%
720
35%
1216
October1st to 10thNight
69%
720
29%
1980
25%
720
71%
720
43%
1131
October11th to 20thNight
62%
720
36%
1980
29%
720
68%
720
41%
1132
October21st to endNight
57%
792
31%
2424
28%
792
63%
792
35%
1376
November1st to 10thNight
62%
740
28%
2406
28%
740
67%
740
37%
1286
November11th to 20thNight
53%
760
31%
2470
26%
760
63%
760
37%
1334
November21st to endNight
50%
760
26%
2470
22%
760
59%
760
30%
1455
December1st to 10thNight
46%
760
26%
2470
20%
760
56%
760
28%
1495
December11th to 20thNight
41%
759
24%
2904
19%
758
48%
758
21%
1750
December21st to endNight
38%
828
15%
4391
16%
817
45%
817
14%
2651

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
11%5%35%5%35%5%6%8%43%
74806
Night
11%5%25%5%35%5%6%8%46%
74914
TransparencyDay
37%8%12%19%18%6%
74533
Night
36%7%11%18%20%8%
74706
SeeingDay
12%7%18%24%24%16%
13521
Night
13%420%33%25%5%
23568

By Month

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 10thDay
16%7%345%3435%6%44%
1706
11th to 20thDay
12%9%45%6%33437%44%
1718
21st to endDay
16%7%35%42445%5%45%
1980
February1st to 10thDay
15%8%36%5%3445%7%39%
1800
11th to 20thDay
18%8%3443345%6%42%
1748
21st to endDay
16%7%37%5%3445%8%38%
1480
March1st to 10thDay
14%5%25%5%34346%48%
1800
11th to 20thDay
14%6%46%5%35%46%8%40%
1926
21st to endDay
11%6%25%5%35%5%6%7%45%
2227
April1st to 10thDay
10%5%35%5%35%45%7%47%
2160
11th to 20thDay
12%5%245%335%6%8%46%
2134
21st to endDay
7%4235%345%5%7%54%
2160
May1st to 10thDay
8%4245%35%5%6%7%52%
2302
11th to 20thDay
6%5%26%5%45%6%6%9%44%
2301
21st to endDay
8%5%26%5%35%5%6%8%46%
2531
June1st to 10thDay
7%6%47%6%46%7%7%10%36%
2340
11th to 20thDay
6%425%446%6%8%12%43%
2340
21st to endDay
6%436%6%48%8%8%12%37%
2340
July1st to 10thDay
9%435%6%5%7%8%9%13%31%
2340
11th to 20thDay
6%436%7%6%8%8%10%11%31%
2340
21st to endDay
5%426%7%6%7%8%9%11%35%
2478
August1st to 10thDay
6%425%7%5%7%7%10%14%33%
2148
11th to 20thDay
10%7%26%7%46%8%8%10%32%
2125
21st to endDay
10%5%36%7%5%7%7%8%9%33%
2376
September1st to 10thDay
9%5%37%6%46%6%6%8%40%
2081
11th to 20thDay
12%6%36%6%35%46%8%42%
1980
21st to endDay
9%426%6%35%45%8%49%
1980
October1st to 10thDay
10%415%5%3445%5%54%
1980
11th to 20thDay
11%5%2342345%7%55%
1980
21st to endDay
11%5%24424446%55%
1926
November1st to 10thDay
10%5%34424435%56%
1672
11th to 20thDay
11%6%35%323347%53%
1710
21st to endDay
14%6%25%4345%5%7%46%
1710
December1st to 10thDay
14%7%35%5%35%346%44%
1710
11th to 20thDay
16%9%35%5%34445%42%
2153
21st to endDay
19%7%36%5%34346%39%
3124
January1st to 10thNight
16%6%35%5%23436%47%
2459
11th to 20thNight
15%7%36%42445%6%43%
2269
21st to endNight
16%6%35%5%2445%5%45%
2376
February1st to 10thNight
15%7%35%7%345%46%43%
2160
11th to 20thNight
19%6%2432444447%
2098
21st to endNight
16%6%45%5%2445%8%41%
1776
March1st to 10thNight
12%6%245%34448%50%
2160
11th to 20thNight
13%5%245%35%6%7%8%42%
2033
21st to endNight
11%6%25%42445%8%49%
2142
April1st to 10thNight
9%5%25%5%45%47%8%46%
1800
11th to 20thNight
12%426%42346%9%48%
1775
21st to endNight
6%42443446%9%54%
1800
May1st to 10thNight
7%3244245%5%9%55%
1656
11th to 20thNight
7%5%26%8%5%5%5%6%9%44%
1592
21st to endNight
6%5%35%6%35%6%6%10%45%
1744
June1st to 10thNight
6%5%37%6%5%8%7%9%11%34%
1620
11th to 20thNight
5%4246%35%47%13%46%
1620
21st to endNight
4436%7%47%7%8%13%38%
1620
July1st to 10thNight
5%5%26%7%5%8%9%9%12%31%
1620
11th to 20thNight
4425%7%48%7%8%12%38%
1620
21st to endNight
4426%6%46%7%8%13%41%
1835
August1st to 10thNight
5%5%25%7%46%7%9%14%37%
1790
11th to 20thNight
7%5%36%7%447%9%12%37%
1776
21st to endNight
9%6%36%7%5%5%6%7%8%37%
1980
September1st to 10thNight
6%6%26%5%5%6%7%8%9%40%
1859
11th to 20thNight
11%6%25%5%45%5%6%9%43%
1980
21st to endNight
7%5%25%6%35%5%6%8%48%
1980
October1st to 10thNight
8%42443445%6%58%
1980
11th to 20thNight
10%32442435%6%56%
1980
21st to endNight
13%425%324345%55%
2424
November1st to 10thNight
9%324434445%59%
2406
11th to 20thNight
12%423424346%57%
2470
21st to endNight
13%5%245%34446%50%
2470
December1st to 10thNight
15%5%25%42445%6%47%
2470
11th to 20thNight
16%8%35%5%33335%47%
3042
21st to endNight
17%7%36%5%3445%8%37%
4532

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
40%47%19%25%5%
1707
11th to 20thDay
42%5%7%17%22%7%
1718
21st to endDay
40%47%17%25%7%
1980
February1st to 10thDay
45%48%17%18%7%
1800
11th to 20thDay
43%5%5%17%22%8%
1758
21st to endDay
44%5%8%15%19%9%
1480
March1st to 10thDay
37%5%7%19%21%11%
1800
11th to 20thDay
42%6%12%16%16%8%
1926
21st to endDay
37%6%12%18%22%4
2227
April1st to 10thDay
36%6%11%21%18%8%
2160
11th to 20thDay
35%6%9%22%20%8%
2134
21st to endDay
29%6%9%24%28%5%
2160
May1st to 10thDay
29%7%11%23%25%5%
2302
11th to 20thDay
33%10%15%21%18%3
2305
21st to endDay
35%8%11%22%21%3
2531
June1st to 10thDay
40%9%15%22%12%2
2340
11th to 20thDay
31%10%18%25%14%2
2340
21st to endDay
35%14%18%19%11%3
2340
July1st to 10thDay
39%16%22%14%7%1
2275
11th to 20thDay
40%16%19%18%6%1
2271
21st to endDay
35%15%22%21%7%1
2339
August1st to 10thDay
35%13%23%22%7%
2136
11th to 20thDay
43%12%18%14%9%3
2125
21st to endDay
43%11%16%17%9%3
2376
September1st to 10thDay
40%9%13%16%16%5%
2081
11th to 20thDay
39%7%13%17%19%5%
1980
21st to endDay
33%6%10%19%24%7%
1980
October1st to 10thDay
31%5%11%18%23%12%
1980
11th to 20thDay
29%5%8%22%26%11%
1980
21st to endDay
31%5%6%16%30%13%
1926
November1st to 10thDay
32%47%17%28%12%
1672
11th to 20thDay
32%47%17%27%13%
1710
21st to endDay
38%5%9%17%22%9%
1710
December1st to 10thDay
41%5%10%17%20%6%
1710
11th to 20thDay
45%46%15%24%6%
2150
21st to endDay
46%46%22%19%3
3124
January1st to 10thNight
40%5%6%18%25%7%
2459
11th to 20thNight
41%5%6%18%22%7%
2269
21st to endNight
41%45%15%26%10%
2376
February1st to 10thNight
43%47%17%19%10%
2160
11th to 20thNight
40%5%6%15%22%11%
2099
21st to endNight
40%6%9%17%15%13%
1776
March1st to 10thNight
35%48%18%21%14%
2160
11th to 20thNight
38%7%11%16%19%9%
2033
21st to endNight
34%6%8%20%24%8%
2142
April1st to 10thNight
35%6%12%17%21%10%
1800
11th to 20thNight
32%6%7%20%24%10%
1775
21st to endNight
26%5%11%26%24%9%
1800
May1st to 10thNight
27%6%11%21%27%8%
1656
11th to 20thNight
36%9%17%19%14%6%
1593
21st to endNight
32%10%13%21%20%5%
1745
June1st to 10thNight
39%13%16%18%13%1
1620
11th to 20thNight
28%9%20%26%15%2
1620
21st to endNight
34%11%18%21%11%4
1620
July1st to 10thNight
38%17%22%15%6%2
1575
11th to 20thNight
34%15%24%19%7%1
1566
21st to endNight
30%12%25%23%9%1
1733
August1st to 10thNight
32%15%23%23%6%1
1778
11th to 20thNight
37%14%21%14%10%4
1776
21st to endNight
42%11%14%16%13%4
1980
September1st to 10thNight
36%14%15%15%14%7%
1859
11th to 20thNight
36%9%13%19%16%7%
1980
21st to endNight
32%8%11%18%22%9%
1980
October1st to 10thNight
27%6%10%19%24%14%
1980
11th to 20thNight
28%5%7%19%29%12%
1980
21st to endNight
32%46%14%28%17%
2424
November1st to 10thNight
28%5%7%17%26%17%
2406
11th to 20thNight
30%45%19%28%14%
2470
21st to endNight
36%5%7%19%21%12%
2470
December1st to 10thNight
37%6%10%19%23%6%
2470
11th to 20thNight
41%46%14%29%6%
3044
21st to endNight
44%6%8%19%21%3
4532

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
16%19%30%27%7%1
270
11th to 20thDay
17%15%28%23%14%4
243
21st to endDay
17%19%34%23%6%1
264
February1st to 10thDay
19%16%37%20%8%
240
11th to 20thDay
27%15%32%20%5%
240
21st to endDay
14%20%38%23%5%
198
March1st to 10thDay
18%14%32%27%8%1
240
11th to 20thDay
15%11%33%27%12%1
366
21st to endDay
16%10%31%32%11%1
462
April1st to 10thDay
14%12%25%29%16%4
420
11th to 20thDay
12%11%25%29%17%6%
412
21st to endDay
10%8%23%28%24%7%
420
May1st to 10thDay
8%7%21%29%28%8%
423
11th to 20thDay
6%316%28%30%17%
447
21st to endDay
11%412%23%30%21%
485
June1st to 10thDay
9%27%26%30%25%
450
11th to 20thDay
9%110%18%30%32%
450
21st to endDay
8%28%22%27%33%
450
July1st to 10thDay
6%15%15%33%40%
445
11th to 20thDay
6%1316%30%45%
444
21st to endDay
41413%38%40%
488
August1st to 10thDay
9%16%15%32%36%
446
11th to 20thDay
10%25%15%37%31%
439
21st to endDay
13%26%17%34%28%
495
September1st to 10thDay
8%35%22%36%26%
450
11th to 20thDay
12%47%21%38%17%
450
21st to endDay
11%210%25%34%17%
450
October1st to 10thDay
10%319%32%26%10%
450
11th to 20thDay
11%7%13%28%31%9%
450
21st to endDay
13%10%21%26%24%5%
387
November1st to 10thDay
17%420%33%19%8%
270
11th to 20thDay
16%6%31%30%14%3
270
21st to endDay
12%10%29%29%18%2
270
December1st to 10thDay
20%10%34%21%13%2
270
11th to 20thDay
23%13%27%28%8%
270
21st to endDay
25%11%25%27%11%
297
January1st to 10thNight
20%9%33%32%7%
760
11th to 20thNight
19%7%28%36%10%
727
21st to endNight
18%8%34%35%4
792
February1st to 10thNight
18%8%29%39%7%
720
11th to 20thNight
21%7%33%32%7%
703
21st to endNight
18%10%33%36%4
592
March1st to 10thNight
13%8%32%38%9%
720
11th to 20thNight
14%6%33%32%13%
720
21st to endNight
14%7%30%36%13%1
756
April1st to 10thNight
9%9%27%37%17%
540
11th to 20thNight
14%6%27%34%19%2
533
21st to endNight
9%422%40%24%1
540
May1st to 10thNight
8%320%40%26%3
540
11th to 20thNight
8%213%40%30%6%
531
21st to endNight
8%28%34%39%8%
584
June1st to 10thNight
8%18%34%43%6%
540
11th to 20thNight
5%27%23%51%12%
540
21st to endNight
5%5%29%45%15%
540
July1st to 10thNight
8%321%54%14%
525
11th to 20thNight
5%1219%49%24%
522
21st to endNight
5%1422%53%16%
591
August1st to 10thNight
6%1322%48%20%
537
11th to 20thNight
8%15%19%51%15%
534
21st to endNight
10%27%23%43%15%
594
September1st to 10thNight
8%17%24%48%12%
599
11th to 20thNight
13%19%31%39%7%
720
21st to endNight
8%110%35%41%4
720
October1st to 10thNight
9%212%41%32%4
720
11th to 20thNight
11%317%36%30%3
720
21st to endNight
14%5%18%37%25%2
792
November1st to 10thNight
10%5%17%42%24%2
740
11th to 20thNight
12%5%27%39%16%1
760
21st to endNight
14%6%25%39%14%1
760
December1st to 10thNight
16%6%27%36%14%1
760
11th to 20thNight
22%5%27%35%10%1
760
21st to endNight
22%7%27%35%8%
836
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