Three Forks Visitor's Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Three Forks Visitor's Center clear sky chart from 2005-11-05 to 2017-09-24.

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
29%
13466
5%
46647
3%
13438
31%
13438
7%
38907

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
38%
776
9%
3044
6%
776
40%
776
10%
2264
January16th to endNight
30%
803
8%
2907
5%
803
31%
803
7%
2397
February1st to 15thNight
33%
678
7%
2568
5%
675
35%
675
10%
1975
February16th to endNight
23%
501
8%
2054
5%
501
28%
501
5%
1673
March1st to 15thNight
34%
570
11%
2151
11%
570
37%
570
11%
1580
March16th to endNight
39%
602
10%
2081
10%
602
40%
602
12%
1581
April1st to 15thNight
26%
539
4%
1640
3%
539
27%
539
7%
1406
April16th to endNight
37%
522
2%
1476
1%
522
38%
522
9%
1248
May1st to 15thNight
37%
359
0%
1254
0%
359
37%
359
8%
1028
May16th to endNight
40%
375
0%
1080
0%
374
40%
374
10%
904
June1st to 15thNight
32%
360
0%
900
0%
360
32%
360
7%
804
June16th to endNight
37%
360
0%
900
0%
360
37%
360
8%
797
July1st to 15thNight
41%
340
0%
850
0%
340
41%
340
8%
760
July16th to endNight
22%
376
0%
1097
0%
354
22%
354
4%
1001
August1st to 15thNight
29%
358
0%
1253
0%
356
29%
356
3%
1139
August16th to endNight
22%
562
2%
1652
2%
562
22%
562
4%
1507
September1st to 15thNight
21%
540
1%
1716
1%
540
21%
540
3%
1569
September16th to endNight
22%
553
3%
1919
4%
553
23%
553
5%
1695
October1st to 15thNight
26%
525
4%
1997
4%
525
27%
525
5%
1740
October16th to endNight
26%
687
4%
2415
4%
687
26%
687
5%
2117
November1st to 15thNight
23%
730
3%
2561
3%
730
23%
730
4%
2295
November16th to endNight
30%
750
6%
2880
3%
750
33%
750
8%
2273
December1st to 15thNight
29%
768
5%
2988
4%
768
30%
768
6%
2489
December16th to endNight
24%
832
6%
3264
4%
832
26%
832
7%
2665

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
18%16%6%9%7%46%5%5%5%15%
48340
Night
11%14%5%9%8%47%6%5%6%18%
46769
TransparencyDay
70%10%8%7%2
47962
Night
64%12%9%7%41
46652
SeeingDay
27%12%22%20%13%3
9264
Night
20%13%24%21%15%4
13472

By Month

Percentage Cloud Cover NW (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
412%49%8%38%9%8%8%22%
895
16th to endDay
312%5%9%7%38%8%8%8%23%
1315
February1st to 15thDay
411%5%8%8%48%7%9%9%22%
1296
16th to endDay
6%17%7%10%9%47%5%5%7%17%
1419
March1st to 15thDay
410%5%8%10%48%10%6%6%24%
1808
16th to endDay
5%16%5%11%10%49%6%5%419%
2137
April1st to 15thDay
8%20%8%11%9%45%44417%
2305
16th to endDay
6%17%8%11%8%46%5%5%5%18%
2484
May1st to 15thDay
12%19%8%9%8%24435%21%
2697
16th to endDay
10%16%6%9%8%46%5%5%7%19%
3033
June1st to 15thDay
20%17%6%8%7%34445%14%
3060
16th to endDay
28%13%6%9%7%34345%12%
3060
July1st to 15thDay
28%15%5%8%7%44445%10%
3060
16th to endDay
40%15%5%7%6%342338%
2993
August1st to 15thDay
34%14%5%7%7%45%4448%
2700
16th to endDay
42%15%5%8%4233237%
2547
September1st to 15thDay
31%17%5%9%8%343429%
2244
16th to endDay
30%20%6%8%5%3343211%
1898
October1st to 15thDay
16%21%8%9%7%4444314%
1631
16th to endDay
10%16%5%16%9%35%5%5%416%
1456
November1st to 15thDay
12%18%7%12%9%38%5%45%11%
1293
16th to endDay
6%13%37%7%8%14%6%6%7%16%
1080
December1st to 15thDay
7%12%7%9%7%5%8%8%7%7%17%
969
16th to endDay
5%14%5%7%9%5%8%9%9%8%15%
960
January1st to 15thNight
311%5%7%7%5%8%8%8%8%25%
3044
16th to endNight
5%13%6%9%8%48%8%7%6%19%
2907
February1st to 15thNight
311%48%6%48%9%7%9%24%
2557
16th to endNight
5%15%6%9%9%46%7%5%6%22%
2054
March1st to 15thNight
410%6%10%7%48%9%6%6%25%
2151
16th to endNight
212%6%12%11%47%6%5%5%24%
2081
April1st to 15thNight
7%18%7%11%10%46%35%5%18%
1640
16th to endNight
5%13%6%9%9%47%6%7%5%24%
1476
May1st to 15thNight
9%19%6%7%6%34447%25%
1253
16th to endNight
12%12%38%7%25%6%6%9%22%
1079
June1st to 15thNight
19%12%48%9%46%45%7%16%
900
16th to endNight
21%13%47%9%46%45%5%18%
900
July1st to 15thNight
22%11%37%6%47%7%6%6%16%
900
16th to endNight
35%15%5%6%5%3443411%
1175
August1st to 15thNight
26%14%48%7%46%45%5%12%
1260
16th to endNight
36%13%48%6%3444311%
1652
September1st to 15thNight
24%16%5%9%8%345%45%11%
1716
16th to endNight
30%19%37%6%3433314%
1919
October1st to 15thNight
14%18%7%9%7%35%447%15%
1997
16th to endNight
13%16%5%14%9%35%445%17%
2415
November1st to 15thNight
11%21%6%11%9%46%5%5%412%
2561
16th to endNight
5%12%5%9%10%6%11%8%5%6%16%
2880
December1st to 15thNight
7%14%6%9%8%49%7%6%6%18%
2988
16th to endNight
414%6%10%10%5%9%8%7%7%16%
3264

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
51%13%11%10%8%3
895
16th to endDay
53%16%10%9%6%2
1315
February1st to 15thDay
54%14%8%10%7%4
1296
16th to endDay
64%14%7%6%41
1419
March1st to 15thDay
52%10%10%12%10%4
1808
16th to endDay
60%7%9%10%7%4
2137
April1st to 15thDay
70%9%5%8%5%
2305
16th to endDay
66%11%8%10%2
2484
May1st to 15thDay
66%7%8%13%3
2697
16th to endDay
64%12%11%9%1
3037
June1st to 15thDay
71%10%10%7%
3060
16th to endDay
73%10%11%3
3060
July1st to 15thDay
74%11%9%4
2881
16th to endDay
82%5%6%5%
2808
August1st to 15thDay
79%10%6%3
2682
16th to endDay
82%7%6%2
2547
September1st to 15thDay
81%7%5%4
2244
16th to endDay
80%447%2
1898
October1st to 15thDay
76%7%5%7%3
1631
16th to endDay
71%10%6%6%3
1456
November1st to 15thDay
73%13%7%41
1293
16th to endDay
62%11%12%8%4
1080
December1st to 15thDay
62%13%11%7%41
969
16th to endDay
61%13%10%9%31
960
January1st to 15thNight
50%14%10%10%10%2
3044
16th to endNight
60%14%7%6%7%2
2907
February1st to 15thNight
55%12%9%9%8%3
2568
16th to endNight
59%15%9%6%7%1
2054
March1st to 15thNight
53%10%8%13%10%3
2151
16th to endNight
56%9%11%11%7%4
2086
April1st to 15thNight
67%10%6%8%5%
1640
16th to endNight
62%14%9%10%4
1476
May1st to 15thNight
63%11%9%13%2
1254
16th to endNight
60%13%15%7%2
1080
June1st to 15thNight
69%13%8%8%
900
16th to endNight
68%12%12%5%1
900
July1st to 15thNight
68%12%12%5%
850
16th to endNight
77%9%9%3
1097
August1st to 15thNight
74%13%8%3
1253
16th to endNight
78%8%7%5%
1652
September1st to 15thNight
76%11%7%4
1716
16th to endNight
76%6%6%6%3
1919
October1st to 15thNight
71%10%6%7%3
1997
16th to endNight
69%12%6%5%31
2415
November1st to 15thNight
71%13%6%6%2
2561
16th to endNight
60%10%13%7%6%1
2880
December1st to 15thNight
63%13%9%7%4
2988
16th to endNight
64%10%9%8%5%1
3264

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
12%18%23%19%20%7%
210
16th to endDay
12%21%30%20%11%4
224
February1st to 15thDay
11%16%33%18%11%8%
209
16th to endDay
18%21%29%16%10%2
211
March1st to 15thDay
10%17%31%26%12%1
341
16th to endDay
12%13%27%28%14%2
448
April1st to 15thDay
17%19%26%21%12%2
419
16th to endDay
14%14%30%21%14%4
442
May1st to 15thDay
22%11%20%24%18%3
468
16th to endDay
20%14%24%23%14%3
560
June1st to 15thDay
27%8%20%21%18%4
675
16th to endDay
27%6%17%24%18%5%
675
July1st to 15thDay
34%6%15%23%17%3
645
16th to endDay
45%7%15%17%11%3
577
August1st to 15thDay
38%7%17%21%11%3
494
16th to endDay
51%8%14%18%5%1
488
September1st to 15thDay
42%12%18%13%10%2
450
16th to endDay
45%8%20%15%6%4
399
October1st to 15thDay
33%17%18%16%9%4
225
16th to endDay
24%15%26%18%11%3
240
November1st to 15thDay
25%20%22%15%10%5%
220
16th to endDay
18%17%28%17%14%4
210
December1st to 15thDay
16%15%28%17%16%5%
210
16th to endDay
14%22%29%19%10%4
224
January1st to 15thNight
7%17%27%26%16%4
780
16th to endNight
13%15%29%25%11%4
803
February1st to 15thNight
12%16%26%24%14%4
678
16th to endNight
13%19%29%19%13%3
501
March1st to 15thNight
10%15%26%28%15%3
570
16th to endNight
6%8%25%33%21%5%
603
April1st to 15thNight
17%14%25%24%13%4
539
16th to endNight
10%12%28%25%16%5%
522
May1st to 15thNight
17%6%22%23%25%3
360
16th to endNight
19%9%22%23%20%4
375
June1st to 15thNight
25%8%19%22%19%5%
360
16th to endNight
30%413%16%29%6%
360
July1st to 15thNight
29%6%12%20%24%6%
340
16th to endNight
40%6%16%15%15%6%
376
August1st to 15thNight
34%6%19%16%18%4
358
16th to endNight
43%8%14%18%13%1
562
September1st to 15thNight
35%11%22%14%13%2
540
16th to endNight
42%7%20%13%11%3
553
October1st to 15thNight
29%16%19%16%14%4
525
16th to endNight
24%14%23%21%12%2
687
November1st to 15thNight
24%17%21%18%12%4
730
16th to endNight
15%15%28%22%13%4
750
December1st to 15thNight
16%18%26%20%13%5%
768
16th to endNight
14%19%31%22%9%2
832
Page generated at 2017-09-25 05:02:20. Version ac04

Copyright 2017 A. Danko


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