Prettyboy Reservoir
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prettyboy Reservoir 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
32%
23337
20%
74673
10%
23286
44%
23286
22%
46872

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%
758
23%
2649
7%
757
36%
757
18%
1633
January11th to 20thNight
18%
737
22%
2414
7%
737
36%
737
18%
1543
January21st to endNight
15%
792
24%
2574
7%
792
36%
792
20%
1581
February1st to 10thNight
17%
720
17%
2340
6%
720
32%
720
18%
1508
February11th to 20thNight
10%
703
19%
2212
2%
700
32%
700
14%
1438
February21st to endNight
13%
592
23%
1776
6%
592
33%
592
16%
1190
March1st to 10thNight
19%
720
23%
2052
7%
720
37%
720
23%
1280
March11th to 20thNight
21%
720
21%
1980
8%
720
34%
720
19%
1316
March21st to endNight
18%
792
21%
2120
6%
792
31%
792
22%
1420
April1st to 10thNight
19%
720
18%
1800
3%
720
28%
720
20%
1249
April11th to 20thNight
27%
711
20%
1775
5%
711
35%
711
29%
1164
April21st to endNight
25%
720
19%
1800
4%
720
33%
720
24%
1217
May1st to 10thNight
34%
607
17%
1687
8%
607
40%
607
23%
1151
May11th to 20thNight
34%
355
17%
1417
12%
355
43%
355
17%
897
May21st to endNight
48%
388
15%
1551
13%
388
54%
388
21%
945
June1st to 10thNight
45%
360
19%
1440
18%
360
55%
360
24%
830
June11th to 20thNight
48%
360
16%
1440
17%
360
55%
360
22%
867
June21st to endNight
53%
360
17%
1440
17%
360
61%
360
26%
807
July1st to 10thNight
55%
350
14%
1400
15%
350
59%
350
19%
877
July11th to 20thNight
65%
348
19%
1392
21%
348
69%
348
27%
771
July21st to endNight
61%
577
18%
1659
12%
545
66%
545
32%
984
August1st to 10thNight
62%
537
17%
1600
13%
534
64%
534
29%
1020
August11th to 20thNight
56%
618
17%
1682
10%
618
57%
618
26%
1137
August21st to endNight
58%
792
19%
1980
10%
792
60%
792
33%
1306
September1st to 10thNight
51%
720
22%
1800
10%
720
56%
720
32%
1184
September11th to 20thNight
57%
720
31%
1800
20%
720
62%
720
38%
1119
September21st to endNight
44%
720
23%
2048
15%
720
51%
720
26%
1364
October1st to 10thNight
41%
720
17%
2160
14%
720
48%
720
24%
1412
October11th to 20thNight
37%
720
24%
2160
15%
720
50%
720
29%
1292
October21st to endNight
31%
792
26%
2376
13%
792
47%
792
26%
1455
November1st to 10thNight
35%
740
27%
2369
14%
740
52%
740
29%
1347
November11th to 20thNight
28%
760
25%
2484
11%
760
45%
760
22%
1482
November21st to endNight
27%
760
23%
2660
11%
760
45%
760
21%
1537
December1st to 10thNight
19%
760
18%
2660
5%
760
36%
760
16%
1704
December11th to 20thNight
20%
760
21%
3183
6%
759
38%
759
15%
1912
December21st to endNight
22%
828
14%
4793
8%
817
38%
817
11%
2933

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%35%5%35%5%6%8%40%
74717
Night
14%6%25%5%345%5%7%43%
75059
TransparencyDay
41%6%12%23%15%3
74426
Night
40%6%12%23%16%3
74869
SeeingDay
20%15%29%22%11%3
13808
Night
18%13%30%26%11%1
23348

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%8%35%5%445%5%6%42%
1517
11th to 20thDay
15%7%46%5%35%45%6%39%
1632
21st to endDay
13%9%35%7%36%5%5%6%38%
1782
February1st to 10thDay
14%8%37%5%45%5%7%7%36%
1620
11th to 20thDay
17%7%35%5%45%5%5%7%39%
1636
21st to endDay
19%10%36%5%34346%38%
1480
March1st to 10thDay
13%6%35%434446%47%
1903
11th to 20thDay
15%7%36%5%345%5%7%40%
1980
21st to endDay
18%7%47%6%34446%37%
2236
April1st to 10thDay
14%7%35%5%446%6%7%39%
2160
11th to 20thDay
14%5%25%6%345%5%7%44%
2134
21st to endDay
18%5%35%5%345%5%7%40%
2160
May1st to 10thDay
17%7%35%5%35%5%6%8%36%
2288
11th to 20thDay
20%7%346%35%5%5%7%35%
2473
21st to endDay
13%6%26%6%35%5%6%8%39%
2725
June1st to 10thDay
13%5%25%5%46%5%7%10%39%
2520
11th to 20thDay
13%6%36%6%45%6%6%8%38%
2520
21st to endDay
11%3246%35%6%7%10%42%
2520
July1st to 10thDay
10%5%35%5%46%6%7%10%41%
2520
11th to 20thDay
6%425%5%46%6%9%10%42%
2520
21st to endDay
9%6%26%6%47%7%7%9%36%
2557
August1st to 10thDay
10%5%25%7%47%7%7%9%36%
2327
11th to 20thDay
10%6%36%7%45%7%6%8%38%
2201
21st to endDay
12%5%25%5%36%6%6%9%40%
2376
September1st to 10thDay
15%6%35%5%345%5%7%44%
2160
11th to 20thDay
12%5%25%5%2446%8%48%
2160
21st to endDay
17%7%25%6%4445%8%39%
1908
October1st to 10thDay
18%6%25%42445%6%44%
1800
11th to 20thDay
17%6%2443445%6%46%
1800
21st to endDay
15%6%36%42445%6%44%
1980
November1st to 10thDay
13%6%24423448%50%
1707
11th to 20thDay
16%6%243235%5%6%48%
1693
21st to endDay
15%5%35%426%447%44%
1520
December1st to 10thDay
17%8%35%5%3445%8%37%
1520
11th to 20thDay
17%6%25%6%3436%7%40%
1910
21st to endDay
17%7%36%6%35%5%5%8%35%
2772
January1st to 10thNight
14%7%35%5%35%45%6%43%
2649
11th to 20thNight
18%7%36%5%3345%7%40%
2414
21st to endNight
14%7%36%5%3445%7%44%
2574
February1st to 10thNight
16%8%46%5%3446%7%39%
2340
11th to 20thNight
17%8%36%5%245%45%41%
2210
21st to endNight
16%7%36%5%3445%5%40%
1776
March1st to 10thNight
13%5%245%25%5%5%6%47%
2052
11th to 20thNight
16%7%35%5%345%5%6%43%
1980
21st to endNight
16%7%36%5%34446%43%
2120
April1st to 10thNight
15%8%36%6%45%45%7%39%
1800
11th to 20thNight
14%5%26%43445%9%44%
1775
21st to endNight
18%8%3442445%6%43%
1800
May1st to 10thNight
17%7%36%5%3445%8%39%
1687
11th to 20thNight
18%7%36%43445%7%38%
1416
21st to endNight
13%7%245%35%5%6%9%41%
1550
June1st to 10thNight
12%5%25%5%3447%8%45%
1440
11th to 20thNight
11%5%25%5%45%6%7%9%40%
1440
21st to endNight
10%4245%35%5%7%11%44%
1440
July1st to 10thNight
9%438%5%37%7%7%9%38%
1440
11th to 20thNight
6%425%445%6%7%11%47%
1440
21st to endNight
7%425%5%35%5%6%10%46%
1757
August1st to 10thNight
10%425%5%35%6%8%10%41%
1611
11th to 20thNight
11%6%36%7%45%6%6%7%40%
1682
21st to endNight
12%5%25%5%25%46%9%44%
1980
September1st to 10thNight
14%6%345%2446%8%45%
1800
11th to 20thNight
11%5%245%23448%52%
1800
21st to endNight
17%6%35%5%34446%43%
2048
October1st to 10thNight
19%6%35%423445%44%
2160
11th to 20thNight
16%5%2442335%6%50%
2160
21st to endNight
17%5%2442445%6%47%
2376
November1st to 10thNight
12%5%2442345%6%53%
2369
11th to 20thNight
15%7%25%424446%48%
2484
21st to endNight
13%425%5%3446%7%47%
2660
December1st to 10thNight
17%7%26%5%345%5%6%38%
2660
11th to 20thNight
17%6%25%5%35%46%7%42%
3285
21st to endNight
16%6%26%6%46%6%7%8%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
42%6%11%23%14%4
1518
11th to 20thDay
44%413%23%12%3
1632
21st to endDay
47%5%10%22%13%3
1782
February1st to 10thDay
45%7%13%24%10%2
1620
11th to 20thDay
44%5%10%25%13%2
1645
21st to endDay
49%49%21%13%4
1480
March1st to 10thDay
39%313%26%17%2
1903
11th to 20thDay
43%6%11%18%17%6%
1980
21st to endDay
49%5%8%19%17%3
2236
April1st to 10thDay
41%7%12%19%16%5%
2160
11th to 20thDay
39%6%11%22%18%5%
2134
21st to endDay
42%7%9%20%18%3
2160
May1st to 10thDay
45%6%11%21%14%2
2288
11th to 20thDay
48%7%12%18%13%3
2477
21st to endDay
41%7%15%23%12%2
2725
June1st to 10thDay
39%7%15%23%14%2
2520
11th to 20thDay
41%8%14%22%13%2
2520
21st to endDay
34%8%14%26%16%1
2520
July1st to 10thDay
37%10%13%21%15%3
2450
11th to 20thDay
32%9%14%28%15%2
2445
21st to endDay
41%9%12%21%15%2
2414
August1st to 10thDay
40%8%14%25%13%
2314
11th to 20thDay
40%8%13%22%15%2
2201
21st to endDay
38%7%14%24%14%3
2376
September1st to 10thDay
41%6%12%20%18%4
2160
11th to 20thDay
34%5%11%27%21%3
2160
21st to endDay
45%5%8%19%20%2
1908
October1st to 10thDay
41%5%10%25%17%2
1800
11th to 20thDay
39%6%11%22%20%3
1800
21st to endDay
41%5%10%25%18%2
1980
November1st to 10thDay
34%413%26%20%4
1707
11th to 20thDay
36%5%11%24%20%3
1693
21st to endDay
41%5%11%29%12%2
1520
December1st to 10thDay
46%5%14%23%11%1
1520
11th to 20thDay
42%6%10%31%10%1
1906
21st to endDay
46%5%16%21%11%1
2772
January1st to 10thNight
41%5%10%25%16%4
2649
11th to 20thNight
44%5%13%25%13%1
2414
21st to endNight
40%49%27%16%3
2574
February1st to 10thNight
44%414%24%12%1
2340
11th to 20thNight
45%49%21%17%4
2212
21st to endNight
46%49%20%16%5%
1776
March1st to 10thNight
37%5%11%27%18%2
2052
11th to 20thNight
42%6%10%22%17%3
1980
21st to endNight
43%411%21%16%5%
2120
April1st to 10thNight
44%5%10%19%18%4
1800
11th to 20thNight
38%5%12%21%19%5%
1775
21st to endNight
41%5%10%21%17%5%
1800
May1st to 10thNight
43%6%10%22%14%4
1687
11th to 20thNight
45%6%13%15%18%2
1417
21st to endNight
37%11%17%21%12%3
1551
June1st to 10thNight
35%8%12%26%17%2
1440
11th to 20thNight
39%7%15%22%16%2
1440
21st to endNight
34%7%14%26%16%2
1440
July1st to 10thNight
41%9%16%19%12%3
1400
11th to 20thNight
29%11%15%26%16%2
1392
21st to endNight
32%8%18%23%18%2
1659
August1st to 10thNight
36%9%17%24%13%1
1600
11th to 20thNight
41%8%13%21%15%2
1682
21st to endNight
37%7%14%24%15%4
1980
September1st to 10thNight
38%6%12%21%19%5%
1800
11th to 20thNight
32%6%10%25%25%3
1800
21st to endNight
43%6%9%20%20%3
2048
October1st to 10thNight
43%5%11%22%17%3
2160
11th to 20thNight
36%411%28%18%2
2160
21st to endNight
37%5%10%26%20%2
2376
November1st to 10thNight
33%5%10%27%21%5%
2369
11th to 20thNight
39%49%25%20%5%
2484
21st to endNight
36%5%12%27%18%2
2660
December1st to 10thNight
45%5%12%24%13%1
2660
11th to 20thNight
41%5%11%23%17%3
3288
21st to endNight
45%7%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
28%28%29%11%41
180
11th to 20thDay
32%25%31%11%1
240
21st to endDay
24%33%30%10%3
264
February1st to 10thDay
29%25%35%8%3
240
11th to 20thDay
32%29%36%31
303
21st to endDay
33%24%31%10%1
346
March1st to 10thDay
23%27%31%17%2
420
11th to 20thDay
26%23%32%14%32
420
21st to endDay
25%23%31%15%5%1
462
April1st to 10thDay
23%23%35%13%5%1
420
11th to 20thDay
19%22%29%18%10%2
412
21st to endDay
26%15%39%12%7%1
420
May1st to 10thDay
26%20%28%17%8%1
423
11th to 20thDay
24%14%31%22%8%1
447
21st to endDay
17%7%26%28%20%3
485
June1st to 10thDay
14%13%31%22%15%4
450
11th to 20thDay
18%9%31%26%12%3
450
21st to endDay
12%9%31%30%14%3
450
July1st to 10thDay
13%421%31%20%10%
445
11th to 20thDay
5%422%37%25%7%
444
21st to endDay
12%429%32%18%4
488
August1st to 10thDay
11%5%23%31%22%7%
446
11th to 20thDay
10%6%22%34%21%8%
439
21st to endDay
11%5%23%32%19%10%
495
September1st to 10thDay
18%8%21%21%21%10%
450
11th to 20thDay
12%6%24%30%19%9%
450
21st to endDay
23%13%23%25%13%3
450
October1st to 10thDay
23%8%24%24%14%6%
450
11th to 20thDay
19%15%28%25%12%2
450
21st to endDay
17%18%39%18%7%2
495
November1st to 10thDay
18%14%33%23%10%2
383
11th to 20thDay
20%22%32%17%8%
353
21st to endDay
27%16%37%16%4
180
December1st to 10thDay
26%23%35%12%31
180
11th to 20thDay
31%23%29%13%4
180
21st to endDay
25%21%34%14%7%
198
January1st to 10thNight
20%21%39%17%3
760
11th to 20thNight
25%18%33%20%3
737
21st to endNight
18%21%42%18%1
792
February1st to 10thNight
21%20%38%19%2
720
11th to 20thNight
25%25%35%14%1
703
21st to endNight
24%22%38%14%3
592
March1st to 10thNight
20%21%37%20%3
720
11th to 20thNight
21%21%35%18%5%
720
21st to endNight
20%18%40%17%41
792
April1st to 10thNight
20%24%34%18%4
720
11th to 20thNight
17%16%36%23%7%
711
21st to endNight
23%16%32%23%7%
720
May1st to 10thNight
21%10%31%28%9%1
607
11th to 20thNight
23%6%30%32%8%1
355
21st to endNight
17%5%22%37%17%2
389
June1st to 10thNight
12%332%33%20%
360
11th to 20thNight
13%427%39%16%1
360
21st to endNight
11%325%46%15%
360
July1st to 10thNight
8%320%39%26%4
350
11th to 20thNight
8%318%41%28%3
348
21st to endNight
9%320%39%27%2
577
August1st to 10thNight
11%414%46%23%2
537
11th to 20thNight
12%5%16%38%26%2
618
21st to endNight
14%417%36%26%4
792
September1st to 10thNight
16%421%32%23%4
720
11th to 20thNight
12%419%36%25%4
720
21st to endNight
21%5%23%31%18%2
720
October1st to 10thNight
22%8%22%27%18%4
720
11th to 20thNight
18%12%28%30%11%1
720
21st to endNight
21%13%32%23%11%
792
November1st to 10thNight
14%12%34%28%10%1
740
11th to 20thNight
19%20%30%24%7%1
760
21st to endNight
16%18%35%23%7%1
760
December1st to 10thNight
23%18%36%17%7%
760
11th to 20thNight
19%17%40%20%4
760
21st to endNight
21%19%34%25%2
836
Page generated at 2024-01-11 22:33:46. Version ac07

Copyright 2024 Attilla Danko


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