Strawbridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strawbridge Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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
33%
24189
18%
96789
10%
23915
45%
23915
19%
59519

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
18%
755
24%
4342
9%
737
38%
737
13%
2395
January11th to 20thNight
23%
760
25%
4255
7%
740
40%
740
12%
2426
January21st to endNight
20%
832
15%
4479
7%
814
40%
814
12%
2855
February1st to 10thNight
21%
760
18%
2470
7%
760
35%
760
19%
1576
February11th to 20thNight
14%
743
19%
2264
5%
740
33%
740
18%
1480
February21st to endNight
17%
628
23%
1884
8%
628
36%
628
20%
1217
March1st to 10thNight
22%
757
19%
3670
9%
744
40%
744
13%
2400
March11th to 20thNight
21%
757
24%
3454
8%
740
35%
740
17%
1748
March21st to endNight
21%
832
14%
3488
7%
814
33%
814
17%
2113
April1st to 10thNight
20%
760
20%
1900
4%
760
30%
760
24%
1300
April11th to 20thNight
27%
751
19%
1875
6%
751
33%
751
27%
1278
April21st to endNight
31%
760
19%
1900
5%
760
39%
760
28%
1270
May1st to 10thNight
29%
620
14%
2849
6%
616
35%
616
12%
1996
May11th to 20thNight
30%
370
11%
2485
10%
364
42%
364
10%
1674
May21st to endNight
47%
407
11%
2719
13%
399
53%
399
13%
1403
June1st to 10thNight
42%
380
19%
1520
17%
380
53%
380
22%
883
June11th to 20thNight
47%
380
15%
1520
18%
380
53%
380
22%
917
June21st to endNight
54%
380
16%
1520
17%
380
60%
380
24%
856
July1st to 10thNight
52%
365
13%
2384
16%
360
57%
360
12%
1378
July11th to 20thNight
60%
362
11%
2285
16%
358
64%
358
15%
1360
July21st to endNight
54%
460
12%
2541
17%
427
61%
427
15%
1625
August1st to 10thNight
59%
557
11%
2746
12%
545
62%
545
16%
1836
August11th to 20thNight
54%
714
16%
2766
10%
703
56%
703
19%
1766
August21st to endNight
55%
824
14%
3055
7%
814
58%
814
24%
1769
September1st to 10thNight
47%
760
23%
1900
11%
760
53%
760
33%
1268
September11th to 20thNight
56%
760
29%
1927
20%
760
60%
760
39%
1174
September21st to endNight
45%
760
22%
2090
15%
760
51%
760
26%
1409
October1st to 10thNight
40%
760
12%
2976
12%
740
47%
740
17%
2096
October11th to 20thNight
42%
760
21%
2446
16%
740
53%
740
28%
1470
October21st to endNight
33%
836
22%
2880
15%
814
47%
814
24%
1698
November1st to 10thNight
35%
771
26%
2505
14%
771
53%
771
31%
1411
November11th to 20thNight
30%
760
25%
2470
13%
760
45%
760
23%
1509
November21st to endNight
29%
760
22%
2591
10%
760
46%
760
24%
1522
December1st to 10thNight
22%
760
19%
2660
7%
760
38%
760
18%
1681
December11th to 20thNight
23%
760
20%
3186
7%
759
38%
759
16%
1907
December21st to endNight
24%
828
14%
4787
8%
817
39%
817
12%
2853

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
16%6%26%44446%8%40%
101344
Night
17%7%26%44435%7%42%
97770
TransparencyDay
41%5%12%23%16%2
104890
Night
40%5%12%23%17%3
102312
SeeingDay
20%14%28%23%12%3
15009
Night
19%11%31%28%10%1
24276

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 10thDay
15%6%25%44435%6%46%
2517
11th to 20thDay
14%10%38%5%4445%6%37%
2594
21st to endDay
21%8%27%44435%6%35%
3124
February1st to 10thDay
16%7%26%5%5%435%7%39%
1710
11th to 20thDay
16%8%27%44346%6%41%
1800
21st to endDay
18%9%36%44335%7%37%
1570
March1st to 10thDay
25%6%26%44435%6%37%
3134
11th to 20thDay
10%5%25%5%5%5%46%7%46%
3480
21st to endDay
22%6%36%433246%43%
4033
April1st to 10thDay
15%8%26%445%45%8%40%
2280
11th to 20thDay
15%7%25%5%4445%8%42%
2254
21st to endDay
17%5%25%5%45%46%7%39%
2280
May1st to 10thDay
27%9%26%44435%7%28%
4053
11th to 20thDay
25%9%37%5%5%446%6%27%
4398
21st to endDay
13%5%16%435%46%10%44%
4837
June1st to 10thDay
13%5%25%45%5%47%9%39%
2660
11th to 20thDay
12%6%26%5%5%5%5%7%10%37%
2660
21st to endDay
10%5%25%45%5%5%7%10%42%
2660
July1st to 10thDay
7%6%26%5%6%7%6%9%11%36%
4440
11th to 20thDay
10%6%26%45%6%5%7%10%39%
4440
21st to endDay
12%8%38%5%5%5%6%6%8%33%
4725
August1st to 10thDay
19%5%27%5%5%5%46%8%33%
4104
11th to 20thDay
12%5%25%44446%9%43%
3735
21st to endDay
11%5%25%44446%8%48%
4180
September1st to 10thDay
15%6%16%45%445%6%45%
2280
11th to 20thDay
13%5%1433336%8%50%
2252
21st to endDay
19%8%36%345%45%6%37%
2087
October1st to 10thDay
19%5%26%33345%6%44%
1900
11th to 20thDay
16%5%2433435%7%49%
1900
21st to endDay
18%6%3433336%6%46%
2028
November1st to 10thDay
13%6%24333346%53%
1734
11th to 20thDay
17%5%25%33336%6%47%
1710
21st to endDay
15%6%25%33435%7%46%
1587
December1st to 10thDay
18%7%26%43436%7%39%
1520
11th to 20thDay
20%7%2423335%7%43%
1906
21st to endDay
17%6%26%5%5%6%5%6%7%36%
2772
January1st to 10thNight
17%6%26%444345%45%
4429
11th to 20thNight
18%9%25%434245%44%
4362
21st to endNight
24%8%25%434346%36%
4532
February1st to 10thNight
17%9%36%344446%41%
2470
11th to 20thNight
18%8%36%444346%41%
2263
21st to endNight
18%7%36%43335%5%42%
1884
March1st to 10thNight
22%9%26%343346%37%
3704
11th to 20thNight
11%6%35%444345%51%
3479
21st to endNight
17%9%36%43323445%
3597
April1st to 10thNight
16%7%26%44446%7%40%
1900
11th to 20thNight
15%7%36%44445%6%42%
1875
21st to endNight
18%6%25%33335%7%43%
1900
May1st to 10thNight
23%10%37%44445%8%29%
2913
11th to 20thNight
24%9%37%5%4336%6%29%
2495
21st to endNight
14%6%25%5%4346%10%43%
2738
June1st to 10thNight
16%6%35%44337%8%42%
1520
11th to 20thNight
11%5%26%5%5%6%5%6%9%40%
1520
21st to endNight
10%415%445%5%8%11%41%
1520
July1st to 10thNight
8%6%36%6%5%6%5%8%10%38%
2520
11th to 20thNight
12%6%26%45%5%5%7%10%37%
2520
21st to endNight
15%7%36%5%4448%8%36%
2824
August1st to 10thNight
21%7%26%445%46%8%33%
2825
11th to 20thNight
14%6%26%45%436%7%42%
3059
21st to endNight
11%425%44436%8%49%
3476
September1st to 10thNight
14%7%35%43435%6%47%
1900
11th to 20thNight
14%5%2333425%6%53%
1927
21st to endNight
19%6%26%43445%7%40%
2090
October1st to 10thNight
19%6%36%433346%43%
2280
11th to 20thNight
15%5%15%333346%51%
2280
21st to endNight
17%7%24333245%49%
2570
November1st to 10thNight
11%6%25%333346%54%
2505
11th to 20thNight
17%6%26%333335%48%
2470
21st to endNight
13%6%25%45%436%7%46%
2591
December1st to 10thNight
19%8%25%44435%6%39%
2660
11th to 20thNight
17%6%26%44435%7%42%
3288
21st to endNight
17%7%36%5%4446%7%37%
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
38%414%26%14%3
2518
11th to 20thDay
45%412%23%13%2
2594
21st to endDay
49%5%12%22%10%1
3124
February1st to 10thDay
44%5%14%24%11%2
1710
11th to 20thDay
43%311%25%16%2
1809
21st to endDay
46%411%23%12%4
1570
March1st to 10thDay
47%5%9%27%9%2
3137
11th to 20thDay
33%6%11%31%17%3
3480
21st to endDay
44%49%19%21%3
4033
April1st to 10thDay
41%5%11%22%16%5%
2280
11th to 20thDay
39%5%12%23%16%4
2254
21st to endDay
41%6%11%20%18%4
2280
May1st to 10thDay
54%6%11%17%10%2
4065
11th to 20thDay
54%6%13%17%8%1
4402
21st to endDay
34%7%13%27%16%2
4837
June1st to 10thDay
38%7%14%24%15%1
2660
11th to 20thDay
40%8%13%25%11%3
2660
21st to endDay
36%7%14%25%17%1
2660
July1st to 10thDay
40%8%16%19%14%3
4370
11th to 20thDay
40%6%15%24%14%2
4365
21st to endDay
47%6%10%19%16%1
4574
August1st to 10thDay
48%6%14%22%9%1
4091
11th to 20thDay
37%5%12%31%15%1
3771
21st to endDay
34%5%10%27%21%2
4180
September1st to 10thDay
39%6%11%20%22%3
2280
11th to 20thDay
32%410%26%24%4
2252
21st to endDay
47%5%7%18%20%2
2087
October1st to 10thDay
36%39%19%28%5%
3160
11th to 20thDay
24%311%25%30%7%
3140
21st to endDay
25%311%28%28%5%
3318
November1st to 10thDay
33%313%26%21%3
1734
11th to 20thDay
37%5%10%25%20%3
1710
21st to endDay
37%414%31%12%2
1587
December1st to 10thDay
44%5%16%22%13%1
1520
11th to 20thDay
43%412%28%11%2
1906
21st to endDay
44%7%13%23%12%1
2772
January1st to 10thNight
41%410%29%13%4
4429
11th to 20thNight
44%411%26%13%3
4362
21st to endNight
49%49%24%12%2
4532
February1st to 10thNight
44%413%25%12%2
2470
11th to 20thNight
45%49%20%18%5%
2265
21st to endNight
43%49%23%16%5%
1884
March1st to 10thNight
48%5%9%23%13%2
3714
11th to 20thNight
34%5%13%28%17%3
3480
21st to endNight
43%47%17%24%5%
3597
April1st to 10thNight
42%5%10%21%17%4
1900
11th to 20thNight
41%6%10%20%20%3
1875
21st to endNight
40%5%10%21%19%5%
1900
May1st to 10thNight
52%6%10%19%11%1
2920
11th to 20thNight
53%7%14%15%10%2
2496
21st to endNight
36%8%17%20%16%3
2739
June1st to 10thNight
38%6%12%22%20%2
1520
11th to 20thNight
39%8%12%26%14%1
1520
21st to endNight
34%8%15%26%15%2
1520
July1st to 10thNight
39%9%20%17%13%2
2480
11th to 20thNight
40%7%18%24%11%1
2472
21st to endNight
44%6%15%19%15%1
2734
August1st to 10thNight
48%6%18%18%9%1
2814
11th to 20thNight
40%5%12%26%15%1
3089
21st to endNight
33%5%11%29%21%2
3476
September1st to 10thNight
38%6%11%20%22%3
1900
11th to 20thNight
32%5%9%23%27%4
1927
21st to endNight
43%5%9%20%21%2
2090
October1st to 10thNight
41%410%21%21%3
3800
11th to 20thNight
24%310%29%29%5%
3779
21st to endNight
27%211%32%24%4
4230
November1st to 10thNight
33%411%25%20%6%
2505
11th to 20thNight
40%49%22%20%5%
2470
21st to endNight
37%413%28%16%2
2591
December1st to 10thNight
44%5%12%24%14%1
2660
11th to 20thNight
41%5%13%20%17%4
3288
21st to endNight
44%6%14%24%11%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
22%28%33%13%22
180
11th to 20thDay
21%37%29%10%3
203
21st to endDay
24%30%26%14%5%
297
February1st to 10thDay
26%26%33%12%4
270
11th to 20thDay
28%23%35%12%2
408
21st to endDay
28%22%32%15%3
382
March1st to 10thDay
22%24%31%19%4
460
11th to 20thDay
22%25%33%15%32
460
21st to endDay
27%20%31%16%5%1
506
April1st to 10thDay
25%22%33%13%7%1
460
11th to 20thDay
21%21%33%17%6%2
452
21st to endDay
25%17%31%20%5%2
460
May1st to 10thDay
29%17%28%15%9%2
463
11th to 20thDay
23%11%30%24%10%2
487
21st to endDay
19%6%24%28%18%4
529
June1st to 10thDay
13%14%28%26%16%3
490
11th to 20thDay
15%10%28%29%16%3
490
21st to endDay
13%11%29%29%14%5%
490
July1st to 10thDay
13%320%33%23%7%
485
11th to 20thDay
9%322%35%26%6%
484
21st to endDay
14%426%34%18%5%
532
August1st to 10thDay
12%325%31%21%6%
486
11th to 20thDay
13%419%35%20%8%
479
21st to endDay
13%7%23%29%18%9%
539
September1st to 10thDay
18%10%21%27%18%7%
490
11th to 20thDay
15%5%25%28%17%9%
490
21st to endDay
26%12%20%25%12%4
490
October1st to 10thDay
25%7%24%22%14%7%
490
11th to 20thDay
16%16%29%25%13%2
490
21st to endDay
21%14%32%20%10%3
506
November1st to 10thDay
17%13%32%24%12%3
386
11th to 20thDay
20%19%32%22%6%1
370
21st to endDay
18%19%35%21%6%1
247
December1st to 10thDay
24%25%34%9%7%
180
11th to 20thDay
31%22%32%11%4
180
21st to endDay
27%21%32%11%9%1
198
January1st to 10thNight
19%18%38%21%4
760
11th to 20thNight
24%16%31%24%4
760
21st to endNight
19%18%38%23%2
836
February1st to 10thNight
22%15%38%24%1
760
11th to 20thNight
24%20%38%17%1
743
21st to endNight
22%19%38%18%3
628
March1st to 10thNight
20%18%35%23%3
760
11th to 20thNight
21%19%36%19%5%1
760
21st to endNight
20%13%39%21%6%
836
April1st to 10thNight
21%18%38%18%5%
760
11th to 20thNight
19%13%36%26%6%
751
21st to endNight
21%11%33%29%6%
760
May1st to 10thNight
24%10%31%28%6%
624
11th to 20thNight
20%10%33%30%6%
374
21st to endNight
18%6%21%40%14%2
411
June1st to 10thNight
18%5%27%38%11%1
380
11th to 20thNight
11%6%30%42%11%1
380
21st to endNight
11%326%46%15%
380
July1st to 10thNight
12%422%42%19%2
370
11th to 20thNight
8%220%45%23%2
368
21st to endNight
10%424%40%20%2
465
August1st to 10thNight
13%217%43%23%2
567
11th to 20thNight
15%218%38%25%2
724
21st to endNight
14%418%39%23%2
836
September1st to 10thNight
17%425%34%17%3
760
11th to 20thNight
15%419%36%22%4
760
21st to endNight
23%422%32%18%1
760
October1st to 10thNight
23%7%23%26%17%4
760
11th to 20thNight
17%10%28%32%12%1
760
21st to endNight
21%10%32%27%10%
836
November1st to 10thNight
15%8%37%28%11%1
771
11th to 20thNight
21%14%30%27%8%1
760
21st to endNight
16%16%34%26%7%1
760
December1st to 10thNight
25%15%33%21%6%1
760
11th to 20thNight
19%15%36%24%6%
760
21st to endNight
22%14%35%26%3
836
Page generated at 2024-11-05 08:15:52. Version ac07

Copyright © 2024 Attilla Danko.


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