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 2005-11-05 to 2017-09-18.

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
36%
15171
20%
46887
10%
15130
47%
15130
24%
29647

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 15thNight
21%
720
21%
2477
8%
716
38%
716
18%
1560
January16th to endNight
18%
768
23%
2496
6%
768
38%
768
21%
1562
February1st to 15thNight
16%
704
18%
2287
4%
701
34%
701
18%
1454
February16th to endNight
16%
631
24%
1893
5%
631
38%
631
20%
1191
March1st to 15thNight
25%
720
20%
2049
8%
720
38%
720
23%
1308
March16th to endNight
24%
768
21%
2059
8%
768
35%
768
25%
1374
April1st to 15thNight
24%
718
19%
1796
5%
718
33%
718
27%
1200
April16th to endNight
36%
720
18%
1800
5%
720
42%
720
30%
1231
May1st to 15thNight
36%
531
17%
1611
9%
531
42%
531
22%
1081
May16th to endNight
48%
375
16%
1497
15%
374
54%
374
19%
907
June1st to 15thNight
51%
360
17%
1440
17%
360
59%
360
24%
841
June16th to endNight
57%
360
16%
1440
17%
360
62%
360
25%
834
July1st to 15thNight
50%
340
12%
1360
13%
340
53%
340
18%
886
July16th to endNight
68%
477
15%
1511
13%
447
72%
447
31%
860
August1st to 15thNight
62%
554
18%
1624
13%
551
63%
551
31%
1015
August16th to endNight
62%
764
19%
1910
11%
764
64%
764
34%
1248
September1st to 15thNight
52%
720
25%
1800
13%
720
57%
720
32%
1193
September16th to endNight
55%
669
24%
1822
19%
669
59%
669
32%
1177
October1st to 15thNight
41%
660
22%
1980
17%
660
50%
660
26%
1258
October16th to endNight
35%
704
26%
2112
14%
704
51%
704
30%
1238
November1st to 15thNight
35%
700
24%
2269
14%
700
50%
700
24%
1379
November16th to endNight
30%
720
22%
2446
11%
720
44%
720
19%
1507
December1st to 15thNight
23%
720
17%
2520
6%
720
37%
720
16%
1631
December16th to endNight
21%
768
20%
2688
6%
768
40%
768
18%
1712

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%5%25%43445%7%41%
47905
Night
15%5%2442445%7%43%
47066
Cloud CoverDay
14%5%2443445%7%41%
47915
Night
15%5%2442445%7%43%
47071
TransparencyDay
40%6%12%22%15%2
47602
Night
39%5%11%22%16%2
46887
SeeingDay
18%10%25%25%15%5%
5709
Night
17%11%29%27%12%1
15171

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 15thDay
16%5%245%25%5%47%40%
1459
16th to endDay
14%7%35%5%34445%42%
1728
February1st to 15thDay
14%7%25%5%2445%6%40%
1575
16th to endDay
13%8%35%424436%41%
1580
March1st to 15thDay
15%5%25%433346%43%
1899
16th to endDay
18%6%25%424346%40%
2163
April1st to 15thDay
15%5%34434347%42%
2152
16th to endDay
16%424433446%44%
2160
May1st to 15thDay
18%5%25%4345%5%6%37%
2350
16th to endDay
16%425%425%5%5%8%38%
2618
June1st to 15thDay
13%4246%35%5%6%10%37%
2520
16th to endDay
12%4244245%6%10%42%
2520
July1st to 15thDay
8%5%36%5%35%6%7%9%40%
2520
16th to endDay
6%325%6%46%7%8%11%38%
2552
August1st to 15thDay
11%425%5%35%6%6%8%39%
2313
16th to endDay
10%424435%6%8%8%41%
2292
September1st to 15thDay
14%3245%3345%7%45%
2160
16th to endDay
16%425%43435%6%42%
1859
October1st to 15thDay
17%5%1342345%6%44%
1650
16th to endDay
16%5%2432335%5%45%
1760
November1st to 15thDay
16%5%1342445%5%45%
1587
16th to endDay
17%5%25%323445%43%
1512
December1st to 15thDay
17%6%245%2435%7%40%
1440
16th to endDay
17%6%25%42445%6%39%
1536
January1st to 15thNight
17%5%2442435%7%41%
2477
16th to endNight
16%6%25%42335%6%43%
2496
February1st to 15thNight
14%7%35%5%24446%42%
2285
16th to endNight
15%5%34424345%45%
1893
March1st to 15thNight
17%423423446%45%
2037
16th to endNight
15%5%25%5%24436%44%
2059
April1st to 15thNight
16%6%2342445%7%42%
1796
16th to endNight
19%42432335%6%45%
1800
May1st to 15thNight
20%5%24424445%39%
1611
16th to endNight
16%6%15%42345%8%42%
1495
June1st to 15thNight
12%424424448%45%
1440
16th to endNight
10%425%5%245%7%10%41%
1440
July1st to 15thNight
10%436%6%46%5%6%9%35%
1440
16th to endNight
6%324435%5%6%11%46%
1615
August1st to 15thNight
10%4245%3447%9%43%
1635
16th to endNight
11%325%4246%5%8%45%
1910
September1st to 15thNight
12%5%25%424446%47%
1800
16th to endNight
14%6%24323447%45%
1822
October1st to 15thNight
19%424423345%45%
1980
16th to endNight
16%313323346%51%
2112
November1st to 15thNight
13%6%24323335%49%
2269
16th to endNight
16%5%145%25%35%6%43%
2446
December1st to 15thNight
17%6%35%43445%5%38%
2520
16th to endNight
17%6%2442445%7%39%
2688

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 15thDay
16%5%25%434447%40%
1459
16th to endDay
14%6%35%434346%42%
1728
February1st to 15thDay
14%7%25%42445%6%40%
1575
16th to endDay
14%8%45%5%23447%40%
1580
March1st to 15thDay
14%6%26%43435%6%43%
1910
16th to endDay
18%6%25%425%346%40%
2162
April1st to 15thDay
15%5%34434346%43%
2152
16th to endDay
16%414433447%44%
2160
May1st to 15thDay
17%6%25%4345%5%7%37%
2350
16th to endDay
15%4245%345%7%8%38%
2618
June1st to 15thDay
12%3246%35%5%7%10%38%
2520
16th to endDay
11%4244345%6%9%42%
2520
July1st to 15thDay
8%435%5%25%6%7%9%39%
2520
16th to endDay
5%325%5%37%6%9%11%38%
2552
August1st to 15thDay
11%5%25%5%35%6%6%8%39%
2313
16th to endDay
10%4245%346%8%9%40%
2292
September1st to 15thDay
14%324424448%45%
2160
16th to endDay
15%5%25%5%2445%7%42%
1859
October1st to 15thDay
17%5%1442345%6%44%
1650
16th to endDay
16%42433345%6%45%
1760
November1st to 15thDay
16%5%233245%46%45%
1587
16th to endDay
17%6%25%323446%44%
1512
December1st to 15thDay
17%6%2442435%7%41%
1440
16th to endDay
18%6%25%434447%38%
1536
January1st to 15thNight
17%5%25%42435%6%41%
2477
16th to endNight
17%5%2433335%6%43%
2496
February1st to 15thNight
13%7%25%5%23446%42%
2278
16th to endNight
14%6%24434345%46%
1893
March1st to 15thNight
17%413434446%45%
2049
16th to endNight
15%5%25%5%33436%44%
2059
April1st to 15thNight
15%7%24325%45%7%42%
1796
16th to endNight
18%42342445%6%45%
1800
May1st to 15thNight
20%6%24424346%39%
1611
16th to endNight
15%6%25%41345%8%42%
1495
June1st to 15thNight
12%4245%245%48%45%
1440
16th to endNight
9%325%5%345%7%10%41%
1440
July1st to 15thNight
9%5%26%7%46%5%6%9%35%
1440
16th to endNight
5%3245%26%5%7%11%44%
1615
August1st to 15thNight
9%5%245%3447%10%43%
1635
16th to endNight
11%3244245%5%8%45%
1910
September1st to 15thNight
12%5%25%5%24447%46%
1800
16th to endNight
13%6%14323447%44%
1822
October1st to 15thNight
18%424423346%44%
1980
16th to endNight
16%313313436%51%
2112
November1st to 15thNight
13%6%25%413335%49%
2269
16th to endNight
16%5%145%24347%43%
2446
December1st to 15thNight
17%6%26%43445%5%38%
2520
16th to endNight
17%6%25%5%2445%7%40%
2688

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 15thDay
42%6%13%21%12%3
1460
16th to endDay
42%411%24%13%3
1728
February1st to 15thDay
43%5%12%24%11%2
1577
16th to endDay
43%411%25%12%2
1580
March1st to 15thDay
41%411%23%15%1
1910
16th to endDay
45%49%19%17%2
2163
April1st to 15thDay
42%410%21%16%4
2152
16th to endDay
39%410%18%21%5%
2160
May1st to 15thDay
44%7%11%19%15%2
2350
16th to endDay
41%8%14%21%12%2
2622
June1st to 15thDay
39%8%12%25%13%1
2520
16th to endDay
35%8%14%22%17%1
2520
July1st to 15thDay
37%9%12%22%14%3
2371
16th to endDay
34%10%14%25%12%2
2393
August1st to 15thDay
39%9%12%20%17%1
2300
16th to endDay
35%8%12%22%17%3
2292
September1st to 15thDay
37%6%10%22%19%3
2160
16th to endDay
41%5%8%20%22%2
1859
October1st to 15thDay
38%5%11%24%16%2
1650
16th to endDay
38%410%26%18%1
1760
November1st to 15thDay
39%413%20%18%4
1587
16th to endDay
41%48%27%14%2
1512
December1st to 15thDay
42%5%15%23%11%1
1440
16th to endDay
44%6%13%21%12%
1536
January1st to 15thNight
42%5%11%21%15%3
2477
16th to endNight
41%311%26%15%1
2496
February1st to 15thNight
42%412%23%14%2
2287
16th to endNight
40%310%23%19%2
1893
March1st to 15thNight
39%413%24%15%1
2049
16th to endNight
42%411%21%17%3
2059
April1st to 15thNight
40%411%20%19%4
1796
16th to endNight
39%6%9%18%20%6%
1800
May1st to 15thNight
45%5%10%19%16%2
1611
16th to endNight
39%8%15%18%15%3
1497
June1st to 15thNight
37%6%13%24%17%
1440
16th to endNight
35%7%13%25%15%2
1440
July1st to 15thNight
43%9%13%17%11%3
1360
16th to endNight
30%8%19%22%17%1
1511
August1st to 15thNight
34%7%13%22%18%1
1624
16th to endNight
35%7%12%23%19%3
1910
September1st to 15thNight
38%5%9%21%21%3
1800
16th to endNight
37%5%9%20%23%3
1822
October1st to 15thNight
41%410%23%17%2
1980
16th to endNight
34%310%28%19%2
2112
November1st to 15thNight
38%48%23%17%7%
2269
16th to endNight
41%49%25%16%2
2446
December1st to 15thNight
46%411%22%12%1
2520
16th to endNight
42%5%15%22%12%1
2688

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 15thDay
23%35%29%10%1
65
16th to endDay
20%30%31%16%1
96
February1st to 15thDay
22%34%34%7%1
90
16th to endDay
17%22%44%13%2
239
March1st to 15thDay
17%20%29%25%6%
270
16th to endDay
21%15%37%17%43
288
April1st to 15thDay
20%15%34%19%7%2
270
16th to endDay
21%9%27%24%12%4
270
May1st to 15thDay
29%13%27%15%12%2
288
16th to endDay
21%6%18%26%22%5%
331
June1st to 15thDay
16%7%25%25%20%5%
315
16th to endDay
16%6%27%28%16%4
315
July1st to 15thDay
12%22%35%22%5%
305
16th to endDay
6%216%38%28%7%
326
August1st to 15thDay
14%18%31%24%10%
313
16th to endDay
10%114%33%24%15%
332
September1st to 15thDay
15%7%19%24%20%13%
315
16th to endDay
22%216%25%19%12%
262
October1st to 15thDay
21%5%19%29%16%7%
255
16th to endDay
14%16%31%25%11%1
272
November1st to 15thDay
19%11%28%23%15%2
236
16th to endDay
20%18%28%20%10%1
132
December1st to 15thDay
25%26%23%11%11%1
60
16th to endDay
32%7%43%10%4
64
January1st to 15thNight
20%18%35%21%4
720
16th to endNight
21%17%38%20%1
768
February1st to 15thNight
17%19%40%20%1
704
16th to endNight
17%23%38%17%2
631
March1st to 15thNight
20%18%33%22%5%
720
16th to endNight
17%13%39%20%7%
768
April1st to 15thNight
18%15%37%22%5%
718
16th to endNight
19%10%29%29%10%
720
May1st to 15thNight
23%8%27%31%8%1
531
16th to endNight
18%421%34%20%
375
June1st to 15thNight
13%325%36%19%1
360
16th to endNight
8%222%46%18%1
360
July1st to 15thNight
12%222%37%24%1
340
16th to endNight
6%114%43%27%5%
477
August1st to 15thNight
13%15%38%28%2
554
16th to endNight
14%113%38%28%4
764
September1st to 15thNight
14%321%30%26%2
720
16th to endNight
16%319%31%25%4
669
October1st to 15thNight
20%7%22%27%17%3
660
16th to endNight
18%12%30%26%11%
704
November1st to 15thNight
16%11%32%26%11%1
700
16th to endNight
18%19%29%22%9%
720
December1st to 15thNight
22%15%33%19%7%
720
16th to endNight
20%17%36%23%3
768
Page generated at 2017-09-19 07:32:26. Version ac04

Copyright 2017 A. Danko


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