Frosty Drew Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Frosty Drew Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
27%
23081
19%
74583
8%
23040
40%
23040
20%
48306

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
17%
760
22%
2649
7%
757
36%
757
18%
1600
January11th to 20thNight
15%
739
18%
2583
4%
739
33%
739
13%
1735
January21st to endNight
18%
792
21%
2772
7%
792
36%
792
17%
1712
February1st to 10thNight
18%
720
18%
2212
5%
720
33%
720
16%
1491
February11th to 20thNight
11%
703
20%
2100
4%
700
31%
700
17%
1397
February21st to endNight
14%
592
25%
1776
7%
592
36%
592
16%
1187
March1st to 10thNight
18%
720
22%
2160
7%
720
38%
720
21%
1382
March11th to 20thNight
19%
720
19%
2076
6%
720
33%
720
19%
1405
March21st to endNight
19%
792
23%
2041
6%
792
32%
792
22%
1394
April1st to 10thNight
21%
720
20%
1800
5%
720
30%
720
21%
1265
April11th to 20thNight
23%
711
18%
1775
4%
711
31%
711
24%
1227
April21st to endNight
20%
563
19%
1643
6%
563
30%
563
20%
1121
May1st to 10thNight
22%
540
13%
1620
5%
540
29%
540
17%
1175
May11th to 20thNight
19%
532
17%
1594
6%
532
29%
532
19%
1108
May21st to endNight
36%
395
11%
1558
9%
395
42%
395
15%
1039
June1st to 10thNight
36%
360
15%
1440
12%
360
46%
360
17%
918
June11th to 20thNight
36%
360
14%
1440
14%
360
45%
360
18%
899
June21st to endNight
42%
360
14%
1440
12%
360
50%
360
22%
848
July1st to 10thNight
42%
350
13%
1400
15%
350
47%
350
19%
889
July11th to 20thNight
49%
348
13%
1392
16%
348
52%
348
20%
869
July21st to endNight
47%
394
17%
1486
18%
372
53%
372
21%
903
August1st to 10thNight
47%
508
16%
1572
12%
506
49%
506
28%
975
August11th to 20thNight
48%
611
17%
1675
10%
611
50%
611
27%
1128
August21st to endNight
50%
792
21%
1980
10%
792
54%
792
35%
1287
September1st to 10thNight
41%
720
19%
1800
8%
720
46%
720
29%
1250
September11th to 20thNight
43%
720
23%
1975
13%
720
51%
720
34%
1204
September21st to endNight
36%
720
22%
1980
13%
720
45%
720
25%
1362
October1st to 10thNight
33%
720
18%
1980
11%
720
40%
720
23%
1359
October11th to 20thNight
32%
720
23%
2174
10%
720
48%
720
27%
1339
October21st to endNight
25%
792
18%
2574
7%
792
38%
792
20%
1661
November1st to 10thNight
31%
740
22%
2407
11%
740
46%
740
25%
1452
November11th to 20thNight
22%
760
24%
2470
9%
760
40%
760
20%
1544
November21st to endNight
24%
760
23%
2470
8%
760
44%
760
21%
1497
December1st to 10thNight
20%
760
20%
2588
6%
760
36%
760
16%
1677
December11th to 20thNight
18%
760
20%
3198
5%
759
36%
759
14%
1949
December21st to endNight
15%
827
15%
4783
5%
817
35%
817
10%
3058

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
17%6%35%5%3445%7%41%
74826
Night
18%7%35%5%3445%6%41%
74945
TransparencyDay
43%5%11%22%16%3
74531
Night
44%411%22%15%3
74774
SeeingDay
23%16%32%20%7%2
14019
Night
22%13%31%25%8%1
23091

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
16%6%35%5%3445%6%45%
1517
11th to 20thDay
20%8%245%3445%7%38%
1472
21st to endDay
14%7%34433448%45%
1584
February1st to 10thDay
20%6%35%435%45%7%38%
1744
11th to 20thDay
15%6%35%6%35%5%5%6%41%
1748
21st to endDay
22%9%45%42445%6%37%
1480
March1st to 10thDay
16%6%35%5%3335%7%44%
1797
11th to 20thDay
17%6%345%345%6%8%40%
1883
21st to endDay
19%9%35%5%24445%40%
2312
April1st to 10thDay
19%6%3443445%6%40%
2160
11th to 20thDay
18%6%35%424447%42%
2134
21st to endDay
21%6%35%5%35%5%5%7%37%
2317
May1st to 10thDay
24%9%35%5%3435%6%34%
2340
11th to 20thDay
19%6%35%5%3445%7%39%
2308
21st to endDay
17%6%244345%6%7%42%
2725
June1st to 10thDay
19%5%25%5%45%5%6%9%34%
2520
11th to 20thDay
17%6%35%5%26%5%6%8%37%
2520
21st to endDay
14%5%25%5%345%5%10%40%
2520
July1st to 10thDay
15%425%5%35%5%6%9%41%
2520
11th to 20thDay
15%5%245%345%6%10%40%
2520
21st to endDay
14%6%25%5%35%6%7%9%39%
2744
August1st to 10thDay
12%6%25%6%36%5%6%10%40%
2337
11th to 20thDay
14%5%25%6%35%6%6%7%41%
2223
21st to endDay
12%5%25%5%46%5%6%9%42%
2376
September1st to 10thDay
16%6%25%435%446%44%
2160
11th to 20thDay
13%5%24433447%51%
1984
21st to endDay
19%6%24434446%43%
1980
October1st to 10thDay
21%7%345%23345%43%
1980
11th to 20thDay
16%5%34325%45%7%46%
1782
21st to endDay
21%5%25%5%3335%5%43%
1782
November1st to 10thDay
16%6%25%5%3335%448%
1671
11th to 20thDay
17%5%244235%5%5%48%
1710
21st to endDay
18%5%35%5%3345%6%45%
1710
December1st to 10thDay
21%7%24435%45%6%39%
1588
11th to 20thDay
23%7%33323346%45%
1906
21st to endDay
21%10%36%5%2444436%
2772
January1st to 10thNight
17%7%24424446%45%
2649
11th to 20thNight
22%7%35%434445%39%
2583
21st to endNight
14%9%45%5%2445%6%43%
2772
February1st to 10thNight
16%10%36%6%24336%40%
2212
11th to 20thNight
19%6%35%5%24446%42%
2098
21st to endNight
19%8%35%4345%45%40%
1776
March1st to 10thNight
18%7%2442445%6%44%
2150
11th to 20thNight
16%7%36%5%35%5%47%39%
2075
21st to endNight
18%9%35%423446%41%
2041
April1st to 10thNight
20%8%35%5%34446%40%
1800
11th to 20thNight
19%7%35%43445%6%41%
1775
21st to endNight
23%7%35%5%33346%38%
1643
May1st to 10thNight
22%9%45%5%445%46%32%
1620
11th to 20thNight
19%8%36%5%3445%8%35%
1593
21st to endNight
19%7%36%6%35%6%5%6%34%
1557
June1st to 10thNight
20%8%36%4245%48%36%
1440
11th to 20thNight
21%7%245%3345%8%38%
1440
21st to endNight
17%8%25%4335%6%10%38%
1440
July1st to 10thNight
16%6%27%5%46%6%5%7%36%
1440
11th to 20thNight
16%6%35%6%445%7%8%36%
1440
21st to endNight
14%6%36%5%35%5%5%8%39%
1574
August1st to 10thNight
9%7%25%6%45%6%8%7%41%
1582
11th to 20thNight
10%6%35%6%35%6%7%9%37%
1675
21st to endNight
14%5%2443446%9%46%
1980
September1st to 10thNight
16%6%26%5%35%5%5%6%39%
1800
11th to 20thNight
15%6%24413346%51%
1975
21st to endNight
20%7%35%5%35%45%440%
1980
October1st to 10thNight
20%9%35%5%34346%40%
1980
11th to 20thNight
15%5%3443345%6%47%
2174
21st to endNight
20%7%25%434447%40%
2574
November1st to 10thNight
14%6%26%5%34446%47%
2407
11th to 20thNight
19%7%24424445%46%
2470
21st to endNight
16%5%25%434446%47%
2470
December1st to 10thNight
21%6%35%434346%40%
2588
11th to 20thNight
20%7%24434346%43%
3288
21st to endNight
21%11%46%42333439%
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
41%310%26%16%4
1518
11th to 20thDay
46%6%12%20%13%3
1472
21st to endDay
39%5%10%25%19%3
1584
February1st to 10thDay
48%313%19%14%3
1744
11th to 20thDay
43%5%10%23%16%4
1757
21st to endDay
50%39%20%14%4
1480
March1st to 10thDay
43%312%23%15%5%
1800
11th to 20thDay
42%5%10%24%16%4
1883
21st to endDay
47%48%19%17%5%
2312
April1st to 10thDay
44%5%10%20%17%3
2160
11th to 20thDay
43%48%23%20%3
2134
21st to endDay
48%49%20%14%4
2317
May1st to 10thDay
52%5%8%20%13%3
2340
11th to 20thDay
44%5%9%22%17%3
2312
21st to endDay
40%6%16%23%13%2
2725
June1st to 10thDay
46%7%13%23%11%1
2520
11th to 20thDay
45%6%13%21%14%1
2520
21st to endDay
41%7%14%25%13%1
2520
July1st to 10thDay
41%6%13%24%14%2
2450
11th to 20thDay
42%5%14%28%10%2
2445
21st to endDay
40%6%15%21%15%3
2591
August1st to 10thDay
40%6%16%23%13%1
2323
11th to 20thDay
41%6%14%25%13%1
2223
21st to endDay
39%7%11%22%18%2
2376
September1st to 10thDay
41%6%10%22%19%2
2160
11th to 20thDay
34%410%24%24%3
1984
21st to endDay
43%47%21%22%2
1980
October1st to 10thDay
46%39%22%17%4
1980
11th to 20thDay
38%5%11%29%17%2
1782
21st to endDay
44%311%21%16%4
1782
November1st to 10thDay
41%413%21%20%2
1671
11th to 20thDay
39%5%9%23%21%4
1710
21st to endDay
42%411%28%13%3
1710
December1st to 10thDay
47%313%18%17%2
1588
11th to 20thDay
44%312%18%18%5%
1906
21st to endDay
51%49%25%11%1
2772
January1st to 10thNight
41%412%23%17%3
2649
11th to 20thNight
49%5%12%20%11%3
2583
21st to endNight
43%310%22%19%3
2772
February1st to 10thNight
48%412%22%13%2
2212
11th to 20thNight
45%49%21%15%5%
2100
21st to endNight
47%37%23%16%4
1776
March1st to 10thNight
42%410%24%16%4
2160
11th to 20thNight
46%49%19%17%4
2076
21st to endNight
45%37%19%19%6%
2041
April1st to 10thNight
47%48%21%17%3
1800
11th to 20thNight
45%49%21%19%2
1775
21st to endNight
48%49%21%14%4
1643
May1st to 10thNight
54%410%17%13%3
1620
11th to 20thNight
48%5%10%20%14%3
1594
21st to endNight
48%8%15%18%11%1
1558
June1st to 10thNight
46%6%12%21%14%1
1440
11th to 20thNight
45%5%12%25%12%1
1440
21st to endNight
41%416%26%12%1
1440
July1st to 10thNight
45%6%13%23%12%1
1400
11th to 20thNight
42%7%15%26%9%1
1392
21st to endNight
41%6%14%25%12%2
1486
August1st to 10thNight
37%7%17%25%12%2
1572
11th to 20thNight
41%8%15%25%11%
1675
21st to endNight
36%6%12%25%20%2
1980
September1st to 10thNight
44%5%10%24%16%2
1800
11th to 20thNight
35%411%23%25%2
1975
21st to endNight
46%47%19%20%3
1980
October1st to 10thNight
47%5%9%22%14%4
1980
11th to 20thNight
38%5%12%29%15%1
2174
21st to endNight
46%312%22%15%2
2574
November1st to 10thNight
39%412%22%19%4
2407
11th to 20thNight
42%49%23%19%4
2470
21st to endNight
39%414%28%13%2
2470
December1st to 10thNight
47%412%21%15%1
2588
11th to 20thNight
43%5%12%20%18%2
3288
21st to endNight
51%48%24%13%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%27%31%17%2
180
11th to 20thDay
24%33%30%8%5%
168
21st to endDay
22%30%37%8%31
176
February1st to 10thDay
31%24%31%13%1
376
11th to 20thDay
27%27%35%10%2
416
21st to endDay
29%22%35%11%3
346
March1st to 10thDay
25%23%32%17%2
420
11th to 20thDay
25%25%34%12%31
420
21st to endDay
32%19%31%14%32
462
April1st to 10thDay
31%24%27%12%6%
420
11th to 20thDay
26%24%32%14%3
412
21st to endDay
32%18%32%12%41
420
May1st to 10thDay
33%21%30%12%4
423
11th to 20thDay
23%14%45%14%31
447
21st to endDay
21%9%33%29%6%2
485
June1st to 10thDay
19%15%34%23%7%2
450
11th to 20thDay
20%14%36%22%7%1
450
21st to endDay
19%11%36%26%6%2
450
July1st to 10thDay
19%6%31%30%13%1
445
11th to 20thDay
16%7%31%30%13%2
444
21st to endDay
14%10%38%27%10%1
488
August1st to 10thDay
16%8%33%30%11%3
446
11th to 20thDay
18%8%31%27%12%4
439
21st to endDay
13%7%35%26%14%6%
495
September1st to 10thDay
21%10%27%25%15%4
450
11th to 20thDay
16%10%32%24%12%6%
450
21st to endDay
23%9%35%20%9%4
450
October1st to 10thDay
27%11%27%21%10%4
450
11th to 20thDay
21%15%31%21%11%1
414
21st to endDay
27%14%31%20%7%2
396
November1st to 10thDay
18%18%32%22%8%2
365
11th to 20thDay
24%24%28%18%6%
370
21st to endDay
24%19%30%19%8%1
370
December1st to 10thDay
25%25%31%16%4
248
11th to 20thDay
32%26%32%8%3
180
21st to endDay
25%23%34%12%5%2
198
January1st to 10thNight
22%21%34%20%3
760
11th to 20thNight
29%18%32%17%3
739
21st to endNight
21%23%33%21%2
792
February1st to 10thNight
23%20%33%22%2
720
11th to 20thNight
26%21%38%14%2
703
21st to endNight
25%22%34%17%2
592
March1st to 10thNight
24%19%36%18%3
720
11th to 20thNight
23%16%37%20%3
720
21st to endNight
25%17%35%19%41
792
April1st to 10thNight
27%15%32%22%3
720
11th to 20thNight
22%13%37%22%5%
711
21st to endNight
25%13%34%22%41
563
May1st to 10thNight
28%11%32%23%7%1
540
11th to 20thNight
22%14%38%22%5%
532
21st to endNight
22%6%27%35%9%2
396
June1st to 10thNight
21%5%28%35%11%
360
11th to 20thNight
24%6%26%34%10%
360
21st to endNight
21%226%40%11%
360
July1st to 10thNight
19%323%37%17%1
350
11th to 20thNight
18%319%44%15%2
348
21st to endNight
16%423%44%13%1
394
August1st to 10thNight
13%429%41%13%1
508
11th to 20thNight
15%425%37%18%1
611
21st to endNight
15%421%38%19%3
792
September1st to 10thNight
19%428%31%17%2
720
11th to 20thNight
17%6%26%31%16%4
720
21st to endNight
22%6%28%27%15%2
720
October1st to 10thNight
24%10%28%24%12%2
720
11th to 20thNight
19%11%32%26%10%2
720
21st to endNight
25%12%34%21%8%1
792
November1st to 10thNight
17%13%32%24%12%1
740
11th to 20thNight
23%18%33%19%7%1
760
21st to endNight
21%20%31%21%7%1
760
December1st to 10thNight
27%17%31%21%41
760
11th to 20thNight
24%20%32%19%4
760
21st to endNight
25%18%36%18%3
836
Page generated at 2024-01-12 07:31:53. Version ac07

Copyright 2024 Attilla Danko


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