Harford Community College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harford Community College Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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%
23337
20%
74649
10%
23285
45%
23285
22%
47053

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
16%
760
23%
2649
7%
757
37%
757
19%
1598
January11th to 20thNight
22%
729
21%
2415
9%
729
38%
729
18%
1562
January21st to endNight
18%
792
25%
2574
6%
792
39%
792
21%
1570
February1st to 10thNight
18%
720
17%
2340
5%
720
33%
720
17%
1533
February11th to 20thNight
12%
703
19%
2186
2%
700
33%
700
16%
1419
February21st to endNight
14%
592
23%
1776
7%
592
33%
592
17%
1179
March1st to 10thNight
20%
720
23%
2083
7%
720
39%
720
24%
1265
March11th to 20thNight
22%
720
21%
1980
8%
720
35%
720
21%
1300
March21st to endNight
22%
792
21%
2101
7%
792
34%
792
23%
1417
April1st to 10thNight
20%
720
19%
1800
3%
720
30%
720
21%
1238
April11th to 20thNight
30%
711
21%
1775
6%
711
37%
711
30%
1167
April21st to endNight
31%
720
19%
1800
5%
720
38%
720
26%
1233
May1st to 10thNight
33%
618
17%
1698
8%
618
39%
618
23%
1153
May11th to 20thNight
33%
354
17%
1416
12%
354
43%
354
16%
913
May21st to endNight
51%
389
15%
1551
15%
388
56%
388
19%
951
June1st to 10thNight
48%
360
19%
1440
18%
360
57%
360
24%
845
June11th to 20thNight
51%
360
15%
1440
16%
360
57%
360
21%
881
June21st to endNight
56%
360
17%
1440
17%
360
62%
360
25%
823
July1st to 10thNight
53%
350
13%
1400
14%
350
56%
350
19%
876
July11th to 20thNight
65%
348
17%
1392
20%
348
68%
348
26%
780
July21st to endNight
62%
545
17%
1629
13%
515
67%
515
30%
990
August1st to 10thNight
61%
537
17%
1600
13%
534
63%
534
28%
1016
August11th to 20thNight
55%
645
16%
1709
10%
645
56%
645
26%
1175
August21st to endNight
58%
792
18%
1980
9%
792
60%
792
31%
1338
September1st to 10thNight
50%
720
22%
1800
10%
720
55%
720
31%
1212
September11th to 20thNight
58%
720
30%
1800
20%
720
62%
720
39%
1117
September21st to endNight
45%
720
22%
2032
15%
720
53%
720
26%
1355
October1st to 10thNight
40%
720
17%
2160
14%
720
47%
720
24%
1419
October11th to 20thNight
38%
720
24%
2160
17%
720
51%
720
29%
1294
October21st to endNight
32%
792
27%
2376
13%
792
48%
792
26%
1462
November1st to 10thNight
35%
740
26%
2393
14%
740
53%
740
29%
1366
November11th to 20thNight
30%
760
25%
2470
13%
760
46%
760
22%
1488
November21st to endNight
29%
760
24%
2639
11%
760
46%
760
22%
1539
December1st to 10thNight
21%
760
19%
2660
6%
760
38%
760
16%
1708
December11th to 20thNight
21%
760
20%
3187
6%
759
39%
759
15%
1907
December21st to endNight
24%
828
14%
4798
9%
817
39%
817
11%
2964

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
14%6%25%5%35%5%6%8%42%
74710
Night
15%6%25%5%3445%7%43%
75024
TransparencyDay
40%7%12%23%16%3
74417
Night
40%6%12%23%17%3
74836
SeeingDay
19%15%28%23%12%4
13839
Night
19%13%29%27%11%1
23345

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
14%7%245%3445%8%43%
1517
11th to 20thDay
15%7%36%5%4445%7%42%
1586
21st to endDay
15%7%36%7%35%446%39%
1782
February1st to 10thDay
15%8%35%5%345%6%7%38%
1620
11th to 20thDay
17%7%35%5%3445%8%40%
1662
21st to endDay
19%10%45%4335%5%5%39%
1480
March1st to 10thDay
12%6%25%435%446%48%
1875
11th to 20thDay
16%7%26%43345%7%42%
1980
21st to endDay
19%7%26%5%36%446%39%
2254
April1st to 10thDay
14%6%35%5%35%5%5%8%42%
2160
11th to 20thDay
13%6%35%5%35%45%7%45%
2134
21st to endDay
18%5%25%4345%5%8%40%
2160
May1st to 10thDay
17%7%36%5%35%5%6%7%38%
2275
11th to 20thDay
20%6%245%35%5%6%7%36%
2478
21st to endDay
14%6%245%345%7%8%40%
2725
June1st to 10thDay
12%5%25%6%35%6%6%11%39%
2520
11th to 20thDay
13%5%35%5%46%5%7%9%39%
2520
21st to endDay
10%4245%347%7%11%43%
2520
July1st to 10thDay
9%5%25%5%35%6%8%10%42%
2520
11th to 20thDay
5%325%5%35%8%9%11%44%
2520
21st to endDay
8%5%26%6%47%6%9%11%35%
2589
August1st to 10thDay
9%5%35%6%36%7%8%9%39%
2327
11th to 20thDay
10%5%25%5%45%7%8%10%39%
2174
21st to endDay
11%5%246%45%6%8%9%41%
2376
September1st to 10thDay
15%5%25%5%35%5%5%7%44%
2160
11th to 20thDay
12%425%5%3445%8%50%
2160
21st to endDay
18%6%35%5%3446%8%39%
1924
October1st to 10thDay
17%6%25%5%245%47%44%
1800
11th to 20thDay
18%43433345%7%47%
1800
21st to endDay
16%6%25%434445%46%
1980
November1st to 10thDay
13%5%244145%47%51%
1681
11th to 20thDay
16%5%2433445%6%48%
1710
21st to endDay
15%5%35%434447%45%
1539
December1st to 10thDay
18%7%245%25%5%5%7%40%
1520
11th to 20thDay
19%6%25%44345%8%41%
1910
21st to endDay
16%6%37%5%45%5%5%7%37%
2772
January1st to 10thNight
16%6%2443435%6%46%
2649
11th to 20thNight
19%6%35%435%45%7%40%
2415
21st to endNight
15%6%25%43445%7%45%
2574
February1st to 10thNight
16%8%35%6%335%46%39%
2340
11th to 20thNight
16%8%36%434445%43%
2184
21st to endNight
17%7%36%5%34445%42%
1776
March1st to 10thNight
15%4234345%46%49%
2083
11th to 20thNight
17%6%25%43445%6%44%
1980
21st to endNight
17%6%35%5%345%46%43%
2101
April1st to 10thNight
16%7%25%436%45%8%40%
1800
11th to 20thNight
14%6%35%42445%7%45%
1775
21st to endNight
20%5%2442445%6%45%
1800
May1st to 10thNight
18%7%25%5%345%5%7%40%
1698
11th to 20thNight
20%7%346%25%45%7%37%
1415
21st to endNight
16%6%25%4245%6%11%39%
1550
June1st to 10thNight
13%435%6%345%5%8%45%
1440
11th to 20thNight
11%6%36%6%45%5%7%9%40%
1440
21st to endNight
11%3245%347%7%10%42%
1440
July1st to 10thNight
10%5%26%6%45%6%6%10%38%
1440
11th to 20thNight
6%425%5%36%6%7%10%45%
1440
21st to endNight
9%435%5%36%5%7%11%42%
1725
August1st to 10thNight
9%5%25%6%446%8%11%40%
1611
11th to 20thNight
10%6%37%6%35%6%6%8%39%
1709
21st to endNight
13%5%25%435%6%5%9%42%
1980
September1st to 10thNight
14%6%35%5%3445%7%44%
1800
11th to 20thNight
11%6%25%424437%53%
1800
21st to endNight
17%7%25%444447%41%
2032
October1st to 10thNight
20%6%25%5%34346%42%
2160
11th to 20thNight
17%5%14423347%49%
2160
21st to endNight
18%5%24324446%48%
2376
November1st to 10thNight
12%5%24423446%53%
2393
11th to 20thNight
16%6%25%423345%49%
2470
21st to endNight
13%5%245%3445%7%48%
2639
December1st to 10thNight
18%7%25%5%34446%40%
2660
11th to 20thNight
18%5%25%5%35%45%7%42%
3285
21st to endNight
16%7%36%5%35%5%6%8%35%
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
40%6%12%22%16%4
1518
11th to 20thDay
43%6%13%22%13%3
1586
21st to endDay
46%5%10%22%13%3
1782
February1st to 10thDay
45%5%13%24%11%2
1620
11th to 20thDay
44%410%26%14%3
1671
21st to endDay
47%5%9%21%13%5%
1480
March1st to 10thDay
38%5%11%26%18%2
1875
11th to 20thDay
42%5%12%18%18%6%
1980
21st to endDay
47%5%8%19%17%3
2254
April1st to 10thDay
40%6%11%20%17%5%
2160
11th to 20thDay
38%6%11%21%17%6%
2134
21st to endDay
41%6%12%19%19%4
2160
May1st to 10thDay
44%7%10%20%16%3
2275
11th to 20thDay
45%8%12%19%13%3
2482
21st to endDay
39%8%16%23%12%2
2725
June1st to 10thDay
38%9%12%24%15%2
2520
11th to 20thDay
40%9%12%23%13%2
2520
21st to endDay
32%10%15%24%18%1
2520
July1st to 10thDay
35%10%14%22%15%3
2450
11th to 20thDay
28%12%16%27%14%3
2445
21st to endDay
39%10%13%22%15%2
2444
August1st to 10thDay
37%11%14%25%13%1
2314
11th to 20thDay
37%11%14%21%15%2
2174
21st to endDay
37%8%13%23%15%4
2376
September1st to 10thDay
39%8%12%20%17%4
2160
11th to 20thDay
33%6%9%27%21%4
2160
21st to endDay
44%6%8%19%20%2
1924
October1st to 10thDay
40%6%10%24%18%2
1800
11th to 20thDay
37%6%11%22%21%2
1800
21st to endDay
41%5%9%26%18%2
1980
November1st to 10thDay
33%5%13%25%20%4
1681
11th to 20thDay
37%5%10%23%22%3
1710
21st to endDay
39%5%11%30%13%3
1539
December1st to 10thDay
44%5%14%23%12%2
1520
11th to 20thDay
42%5%11%30%10%2
1906
21st to endDay
45%8%14%20%12%
2772
January1st to 10thNight
40%410%24%17%4
2649
11th to 20thNight
44%5%12%24%13%1
2415
21st to endNight
39%410%27%18%3
2574
February1st to 10thNight
45%5%13%23%12%1
2340
11th to 20thNight
44%410%20%18%4
2186
21st to endNight
45%49%19%16%5%
1776
March1st to 10thNight
35%413%26%19%3
2083
11th to 20thNight
42%5%11%21%18%4
1980
21st to endNight
43%5%10%19%18%5%
2101
April1st to 10thNight
42%6%10%18%19%5%
1800
11th to 20thNight
38%5%12%20%19%6%
1775
21st to endNight
40%6%10%20%18%5%
1800
May1st to 10thNight
44%6%10%20%16%4
1698
11th to 20thNight
46%7%12%15%18%2
1416
21st to endNight
38%10%16%21%12%3
1551
June1st to 10thNight
37%7%12%24%18%2
1440
11th to 20thNight
39%8%14%22%15%2
1440
21st to endNight
34%9%13%27%15%3
1440
July1st to 10thNight
41%9%17%17%13%3
1400
11th to 20thNight
31%11%17%24%15%2
1392
21st to endNight
33%10%17%22%18%1
1629
August1st to 10thNight
34%11%16%23%15%1
1600
11th to 20thNight
40%10%14%19%15%2
1709
21st to endNight
37%8%13%22%16%3
1980
September1st to 10thNight
39%7%10%21%18%5%
1800
11th to 20thNight
32%5%10%25%25%4
1800
21st to endNight
43%5%9%19%20%3
2032
October1st to 10thNight
45%411%22%17%2
2160
11th to 20thNight
36%411%28%18%3
2160
21st to endNight
37%5%9%26%19%3
2376
November1st to 10thNight
33%5%10%27%20%5%
2393
11th to 20thNight
38%49%23%20%5%
2470
21st to endNight
36%5%11%27%18%2
2639
December1st to 10thNight
45%5%11%24%14%1
2660
11th to 20thNight
41%5%12%21%17%3
3288
21st to endNight
43%9%15%22%10%1
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
24%31%28%14%21
180
11th to 20thDay
24%32%29%14%1
222
21st to endDay
23%33%29%11%31
264
February1st to 10thDay
25%30%32%10%3
240
11th to 20thDay
29%25%40%6%1
329
21st to endDay
29%26%30%12%2
346
March1st to 10thDay
21%25%32%19%3
420
11th to 20thDay
26%24%30%14%41
420
21st to endDay
25%22%32%16%5%1
462
April1st to 10thDay
20%24%36%14%5%1
420
11th to 20thDay
19%23%28%20%8%3
412
21st to endDay
26%18%34%16%5%1
420
May1st to 10thDay
29%16%29%17%9%1
423
11th to 20thDay
22%15%30%22%10%1
447
21st to endDay
20%7%22%27%19%5%
485
June1st to 10thDay
14%10%31%27%14%4
450
11th to 20thDay
18%9%26%28%16%4
450
21st to endDay
14%8%29%31%14%5%
450
July1st to 10thDay
12%220%33%24%9%
445
11th to 20thDay
4421%40%24%7%
444
21st to endDay
11%7%23%32%22%5%
488
August1st to 10thDay
12%422%33%23%7%
446
11th to 20thDay
11%5%16%34%25%9%
439
21st to endDay
12%5%23%31%20%9%
495
September1st to 10thDay
18%8%19%24%21%10%
450
11th to 20thDay
15%5%23%30%17%9%
450
21st to endDay
24%12%21%26%15%2
450
October1st to 10thDay
23%9%23%24%15%6%
450
11th to 20thDay
19%15%26%25%13%2
450
21st to endDay
19%17%35%20%7%3
495
November1st to 10thDay
17%13%35%21%12%3
370
11th to 20thDay
19%22%30%22%7%1
370
21st to endDay
22%19%32%20%7%1
199
December1st to 10thDay
23%24%34%13%41
180
11th to 20thDay
29%24%29%14%4
180
21st to endDay
24%19%33%16%8%
198
January1st to 10thNight
20%20%40%17%3
760
11th to 20thNight
25%16%32%23%4
729
21st to endNight
20%21%37%20%1
792
February1st to 10thNight
22%20%35%21%2
720
11th to 20thNight
24%22%38%14%1
703
21st to endNight
23%22%36%16%3
592
March1st to 10thNight
20%20%36%19%4
720
11th to 20thNight
23%18%34%19%6%
720
21st to endNight
19%15%39%21%5%1
792
April1st to 10thNight
22%21%34%19%5%
720
11th to 20thNight
17%14%35%27%7%
711
21st to endNight
23%13%29%27%7%
720
May1st to 10thNight
23%11%28%29%8%1
618
11th to 20thNight
23%8%31%29%10%
354
21st to endNight
19%5%19%38%19%2
389
June1st to 10thNight
14%428%37%16%1
360
11th to 20thNight
13%7%23%39%18%1
360
21st to endNight
11%223%46%18%1
360
July1st to 10thNight
11%320%39%23%4
350
11th to 20thNight
8%217%41%29%3
348
21st to endNight
9%317%44%24%3
545
August1st to 10thNight
12%216%39%27%3
537
11th to 20thNight
14%316%33%30%3
645
21st to endNight
14%416%38%25%4
792
September1st to 10thNight
17%5%20%30%24%4
720
11th to 20thNight
13%418%34%25%5%
720
21st to endNight
20%5%23%31%19%2
720
October1st to 10thNight
23%7%23%26%17%5%
720
11th to 20thNight
19%11%27%31%12%1
720
21st to endNight
20%14%31%23%12%
792
November1st to 10thNight
15%11%34%27%11%1
740
11th to 20thNight
20%17%29%25%8%1
760
21st to endNight
16%19%32%24%8%1
760
December1st to 10thNight
24%16%33%19%7%1
760
11th to 20thNight
19%17%37%22%5%
760
21st to endNight
20%18%33%26%3
836
Page generated at 2024-01-10 01:25:06. Version ac07

Copyright 2024 Attilla Danko


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