Catoctin Mountain Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Catoctin Mountain Park clear sky chart from 2005-11-06 to 2024-03-28.

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%
23647
19%
80598
11%
23544
47%
23544
21%
51230

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
19%
755
19%
4310
8%
737
37%
737
12%
2580
January11th to 20thNight
22%
760
22%
3992
8%
740
37%
740
11%
2390
January21st to endNight
21%
830
13%
4475
8%
814
38%
814
12%
2892
February1st to 10thNight
27%
760
18%
2470
10%
760
39%
760
18%
1619
February11th to 20thNight
15%
742
18%
2382
4%
740
33%
740
16%
1553
February21st to endNight
17%
628
19%
1884
5%
628
33%
628
17%
1289
March1st to 10thNight
24%
760
23%
2114
9%
760
39%
760
25%
1363
March11th to 20thNight
24%
760
21%
2090
9%
760
36%
760
21%
1403
March21st to endNight
23%
821
19%
2232
7%
821
33%
821
24%
1502
April1st to 10thNight
25%
720
15%
1800
4%
720
32%
720
22%
1292
April11th to 20thNight
35%
711
20%
1775
7%
711
41%
711
30%
1181
April21st to endNight
32%
720
19%
1800
5%
720
39%
720
27%
1223
May1st to 10thNight
40%
552
17%
1632
10%
552
45%
552
23%
1096
May11th to 20thNight
41%
411
16%
1473
13%
411
47%
411
19%
976
May21st to endNight
51%
388
16%
1551
17%
388
56%
388
20%
950
June1st to 10thNight
51%
360
20%
1440
21%
360
59%
360
25%
822
June11th to 20thNight
53%
360
16%
1440
18%
360
57%
360
19%
889
June21st to endNight
61%
360
18%
1440
19%
360
67%
360
25%
821
July1st to 10thNight
59%
350
14%
1400
18%
350
62%
350
19%
874
July11th to 20thNight
69%
402
17%
1446
18%
402
72%
402
28%
826
July21st to endNight
68%
591
16%
1672
14%
558
71%
558
32%
1033
August1st to 10thNight
67%
537
16%
1600
14%
534
68%
534
28%
1026
August11th to 20thNight
61%
578
18%
1642
13%
578
63%
578
27%
1103
August21st to endNight
63%
792
20%
1980
12%
792
65%
792
33%
1295
September1st to 10thNight
56%
720
22%
1800
12%
720
60%
720
32%
1206
September11th to 20thNight
59%
720
30%
1800
22%
720
63%
720
39%
1131
September21st to endNight
49%
720
21%
2073
15%
720
55%
720
26%
1371
October1st to 10thNight
48%
720
18%
2160
16%
720
54%
720
26%
1420
October11th to 20thNight
42%
720
24%
2160
17%
720
53%
720
29%
1332
October21st to endNight
36%
792
26%
2376
16%
792
49%
792
28%
1464
November1st to 10thNight
40%
740
27%
2320
18%
740
53%
740
31%
1343
November11th to 20thNight
32%
760
22%
2533
13%
760
46%
760
23%
1528
November21st to endNight
32%
760
21%
2660
12%
760
46%
760
21%
1621
December1st to 10thNight
23%
760
17%
2660
6%
760
37%
760
16%
1771
December11th to 20thNight
26%
760
18%
3199
8%
759
40%
759
16%
1990
December21st to endNight
27%
827
12%
4817
9%
817
39%
817
11%
3055

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
15%6%35%5%35%5%6%8%40%
78798
Night
15%6%25%5%35%5%5%7%42%
81203
TransparencyDay
42%7%13%22%14%2
78508
Night
40%7%12%23%15%2
81012
SeeingDay
19%13%25%23%15%5%
14025
Night
18%10%29%30%12%1
23669

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%6%27%5%35%446%41%
2559
11th to 20thDay
14%10%47%7%46%5%6%6%33%
2840
21st to endDay
17%11%46%5%35%45%6%32%
3124
February1st to 10thDay
14%8%37%6%446%5%6%37%
1710
11th to 20thDay
14%7%46%6%45%5%5%7%39%
1686
21st to endDay
18%8%46%5%35%36%5%38%
1570
March1st to 10thDay
13%7%345%35%35%7%46%
2061
11th to 20thDay
15%6%346%45%5%6%6%39%
2090
21st to endDay
18%7%37%6%345%46%38%
2278
April1st to 10thDay
13%7%37%6%46%5%6%7%38%
2160
11th to 20thDay
14%6%25%5%4445%8%43%
2134
21st to endDay
19%6%25%5%35%45%6%39%
2163
May1st to 10thDay
17%7%35%5%35%6%6%9%34%
2340
11th to 20thDay
20%6%35%5%35%5%6%7%36%
2419
21st to endDay
15%7%35%6%25%5%5%8%39%
2725
June1st to 10thDay
13%434435%6%7%11%40%
2520
11th to 20thDay
13%5%25%6%36%5%8%9%38%
2520
21st to endDay
12%3245%35%5%7%11%44%
2520
July1st to 10thDay
9%5%25%7%46%7%7%8%42%
2520
11th to 20thDay
7%4245%46%6%7%10%44%
2462
21st to endDay
10%6%35%6%47%6%6%9%37%
2547
August1st to 10thDay
9%5%27%6%5%7%6%7%10%37%
2327
11th to 20thDay
12%5%26%5%346%7%9%40%
2240
21st to endDay
12%5%35%5%346%6%9%41%
2376
September1st to 10thDay
17%6%14435%45%6%44%
2160
11th to 20thDay
13%5%245%245%5%9%47%
2160
21st to endDay
20%6%25%44445%7%40%
1883
October1st to 10thDay
16%6%245%3445%7%44%
1800
11th to 20thDay
17%5%25%42446%6%46%
1800
21st to endDay
14%6%36%4245%47%45%
1980
November1st to 10thDay
12%5%3443436%7%49%
1758
11th to 20thDay
16%5%234345%5%7%46%
1644
21st to endDay
15%5%26%5%2446%7%42%
1520
December1st to 10thDay
17%8%35%5%346%6%8%34%
1520
11th to 20thDay
16%6%26%6%35%5%6%7%38%
1910
21st to endDay
18%6%37%5%35%6%6%8%32%
2772
January1st to 10thNight
13%8%36%5%45%5%6%8%39%
4383
11th to 20thNight
18%8%35%5%35%445%41%
4120
21st to endNight
20%9%36%6%35%45%6%34%
4532
February1st to 10thNight
14%6%37%5%35%5%6%7%39%
2470
11th to 20thNight
17%7%36%5%25%5%47%40%
2380
21st to endNight
17%8%26%6%345%5%6%36%
1884
March1st to 10thNight
14%6%24435%5%5%6%46%
2114
11th to 20thNight
17%6%344245%5%7%43%
2090
21st to endNight
15%6%36%6%345%5%7%41%
2232
April1st to 10thNight
14%7%37%5%46%5%6%6%37%
1800
11th to 20thNight
13%6%25%5%3446%8%44%
1775
21st to endNight
19%6%344245%5%7%42%
1800
May1st to 10thNight
18%7%25%5%3445%8%38%
1632
11th to 20thNight
19%7%26%5%345%6%7%37%
1472
21st to endNight
13%7%35%5%35%5%6%9%40%
1550
June1st to 10thNight
12%4245%2446%8%48%
1440
11th to 20thNight
12%5%36%5%45%6%7%9%39%
1440
21st to endNight
9%425%5%35%47%10%45%
1440
July1st to 10thNight
11%426%6%35%6%6%10%40%
1440
11th to 20thNight
7%425%5%36%6%6%9%48%
1494
21st to endNight
9%424445%6%8%12%42%
1771
August1st to 10thNight
10%436%5%45%6%7%8%41%
1611
11th to 20thNight
11%5%26%7%36%5%6%7%42%
1642
21st to endNight
12%5%245%35%5%6%8%45%
1980
September1st to 10thNight
15%5%245%345%5%7%46%
1800
11th to 20thNight
13%5%25%323447%53%
1800
21st to endNight
20%5%13434447%43%
2073
October1st to 10thNight
20%5%34434436%44%
2160
11th to 20thNight
14%6%25%433446%49%
2160
21st to endNight
16%6%2442346%7%47%
2376
November1st to 10thNight
10%6%2443445%6%53%
2320
11th to 20thNight
14%7%245%3445%6%46%
2533
21st to endNight
13%5%25%5%35%5%6%7%44%
2660
December1st to 10thNight
16%8%36%5%35%5%5%6%37%
2660
11th to 20thNight
17%5%245%35%5%6%7%40%
3285
21st to endNight
16%6%25%6%36%6%7%9%33%
4884

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
43%6%13%26%9%3
2560
11th to 20thDay
50%6%12%17%12%2
2840
21st to endDay
51%7%11%22%8%2
3124
February1st to 10thDay
47%7%13%22%10%2
1710
11th to 20thDay
45%6%11%22%14%2
1695
21st to endDay
49%5%11%20%12%4
1570
March1st to 10thDay
39%6%12%24%17%2
2061
11th to 20thDay
44%6%12%18%15%5%
2090
21st to endDay
48%6%10%19%15%3
2278
April1st to 10thDay
44%6%12%18%16%4
2160
11th to 20thDay
40%6%12%20%18%4
2134
21st to endDay
44%6%10%20%16%3
2163
May1st to 10thDay
44%8%12%19%14%2
2340
11th to 20thDay
47%8%12%18%13%3
2423
21st to endDay
42%8%14%23%12%2
2725
June1st to 10thDay
37%9%15%23%15%1
2520
11th to 20thDay
40%11%13%21%13%2
2520
21st to endDay
33%9%15%28%15%1
2520
July1st to 10thDay
37%11%13%21%15%3
2450
11th to 20thDay
32%10%14%25%16%2
2387
21st to endDay
41%9%13%20%15%2
2405
August1st to 10thDay
40%10%14%24%12%
2314
11th to 20thDay
39%9%14%23%14%2
2240
21st to endDay
38%8%14%24%13%3
2376
September1st to 10thDay
40%6%12%20%18%4
2160
11th to 20thDay
34%6%11%25%20%3
2160
21st to endDay
45%5%10%19%20%2
1883
October1st to 10thDay
40%7%11%23%17%2
1800
11th to 20thDay
38%6%11%24%20%1
1800
21st to endDay
38%6%11%24%18%2
1980
November1st to 10thDay
34%5%14%24%19%4
1758
11th to 20thDay
37%5%14%22%18%3
1644
21st to endDay
41%6%12%28%12%1
1520
December1st to 10thDay
47%8%14%22%9%1
1520
11th to 20thDay
44%7%13%27%7%2
1906
21st to endDay
47%9%17%17%10%
2772
January1st to 10thNight
42%8%13%23%12%2
4383
11th to 20thNight
43%6%14%24%11%2
4120
21st to endNight
48%6%12%24%8%1
4532
February1st to 10thNight
43%7%13%23%12%1
2470
11th to 20thNight
44%6%10%20%17%2
2382
21st to endNight
47%6%12%19%12%5%
1884
March1st to 10thNight
38%6%11%28%15%2
2114
11th to 20thNight
42%7%10%22%17%3
2090
21st to endNight
43%5%11%21%16%5%
2232
April1st to 10thNight
45%8%12%17%15%3
1800
11th to 20thNight
37%6%12%21%18%6%
1775
21st to endNight
40%6%12%23%15%4
1800
May1st to 10thNight
44%6%11%21%13%4
1632
11th to 20thNight
45%8%11%17%17%2
1473
21st to endNight
39%9%15%23%11%2
1551
June1st to 10thNight
34%8%11%27%17%3
1440
11th to 20thNight
40%10%13%22%14%2
1440
21st to endNight
34%9%13%25%17%2
1440
July1st to 10thNight
39%11%15%19%13%3
1400
11th to 20thNight
31%10%15%24%18%3
1446
21st to endNight
31%11%19%22%16%2
1672
August1st to 10thNight
37%9%17%23%13%1
1600
11th to 20thNight
39%9%13%21%16%1
1642
21st to endNight
36%7%14%24%16%3
1980
September1st to 10thNight
37%8%12%19%19%4
1800
11th to 20thNight
33%6%10%27%23%3
1800
21st to endNight
42%6%10%21%19%3
2073
October1st to 10thNight
43%6%10%22%17%2
2160
11th to 20thNight
36%6%10%27%19%2
2160
21st to endNight
37%5%10%26%20%2
2376
November1st to 10thNight
32%6%11%26%20%5%
2320
11th to 20thNight
38%6%10%23%20%4
2533
21st to endNight
38%7%12%24%16%2
2660
December1st to 10thNight
47%7%12%23%11%1
2660
11th to 20thNight
43%7%12%22%14%2
3288
21st to endNight
44%11%17%18%10%
4884

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
25%29%27%15%5%
194
11th to 20thDay
28%30%28%11%3
270
21st to endDay
21%29%33%13%31
297
February1st to 10thDay
22%25%37%13%3
270
11th to 20thDay
31%27%34%7%1
293
21st to endDay
29%20%30%17%3
382
March1st to 10thDay
23%23%27%23%5%
460
11th to 20thDay
24%22%30%17%5%1
460
21st to endDay
24%19%31%19%6%1
490
April1st to 10thDay
19%20%30%23%6%2
420
11th to 20thDay
17%17%29%18%15%4
412
21st to endDay
26%15%28%21%8%3
420
May1st to 10thDay
26%13%29%19%10%3
423
11th to 20thDay
21%13%28%22%12%3
447
21st to endDay
18%7%19%25%22%8%
485
June1st to 10thDay
16%7%26%25%19%6%
450
11th to 20thDay
17%6%26%27%18%6%
450
21st to endDay
12%5%25%31%22%5%
450
July1st to 10thDay
12%418%28%24%13%
445
11th to 20thDay
6%418%29%31%12%
444
21st to endDay
11%5%18%30%26%9%
488
August1st to 10thDay
11%317%26%30%13%
446
11th to 20thDay
13%218%31%24%13%
439
21st to endDay
13%416%29%24%14%
495
September1st to 10thDay
18%6%17%23%23%13%
450
11th to 20thDay
15%317%27%25%12%
450
21st to endDay
24%8%22%24%17%5%
450
October1st to 10thDay
19%7%22%25%20%6%
450
11th to 20thDay
17%14%26%27%14%2
450
21st to endDay
16%13%33%27%8%2
495
November1st to 10thDay
17%12%27%28%13%3
408
11th to 20thDay
20%17%29%23%10%1
304
21st to endDay
19%23%32%18%7%1
180
December1st to 10thDay
24%24%29%17%32
180
11th to 20thDay
22%23%28%21%7%
180
21st to endDay
23%18%29%23%6%
198
January1st to 10thNight
17%17%43%20%2
760
11th to 20thNight
23%16%33%26%3
760
21st to endNight
18%16%39%25%1
836
February1st to 10thNight
18%17%34%29%3
760
11th to 20thNight
24%21%36%17%1
743
21st to endNight
24%18%36%19%2
628
March1st to 10thNight
19%16%38%23%4
760
11th to 20thNight
23%17%33%22%5%
760
21st to endNight
19%15%38%23%5%1
821
April1st to 10thNight
19%19%33%25%4
720
11th to 20thNight
15%12%34%30%9%
711
21st to endNight
22%10%31%28%8%
720
May1st to 10thNight
24%7%24%32%13%
552
11th to 20thNight
22%6%24%35%12%1
411
21st to endNight
16%421%37%21%1
389
June1st to 10thNight
13%226%33%24%1
360
11th to 20thNight
13%5%20%44%18%2
360
21st to endNight
8%319%50%19%
360
July1st to 10thNight
12%215%40%27%3
350
11th to 20thNight
7%115%40%34%3
402
21st to endNight
10%214%42%30%3
591
August1st to 10thNight
11%19%44%32%2
537
11th to 20thNight
12%313%40%29%3
578
21st to endNight
14%213%39%28%4
792
September1st to 10thNight
17%217%34%27%3
720
11th to 20thNight
14%318%33%28%4
720
21st to endNight
23%219%33%20%1
720
October1st to 10thNight
21%421%30%21%3
720
11th to 20thNight
16%9%30%32%12%1
720
21st to endNight
20%9%32%29%10%1
792
November1st to 10thNight
13%7%33%35%9%2
740
11th to 20thNight
19%15%31%28%8%
760
21st to endNight
15%14%35%29%7%
760
December1st to 10thNight
21%14%36%22%6%
760
11th to 20thNight
18%10%41%26%5%
760
21st to endNight
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836
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