Lewiston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lewiston clear sky chart from 2005-11-06 to 2024-01-14.

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
55%
22878
16%
74924
16%
22844
57%
22844
24%
48097

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
34%
756
8%
2646
7%
756
36%
756
10%
2069
January11th to 20thNight
40%
734
7%
2568
7%
734
42%
734
13%
1955
January21st to endNight
40%
792
7%
2772
7%
792
42%
792
12%
2107
February1st to 10thNight
38%
720
7%
2501
7%
720
40%
720
12%
1866
February11th to 20thNight
44%
703
12%
2121
11%
700
47%
700
19%
1516
February21st to endNight
40%
592
12%
1776
12%
592
43%
592
17%
1300
March1st to 10thNight
47%
720
12%
2160
12%
720
50%
720
21%
1526
March11th to 20thNight
51%
720
15%
2098
13%
720
53%
720
24%
1445
March21st to endNight
49%
792
11%
2021
7%
792
51%
792
20%
1519
April1st to 10thNight
54%
720
15%
1800
8%
720
56%
720
28%
1253
April11th to 20thNight
46%
658
21%
1726
12%
658
50%
658
27%
1174
April21st to endNight
56%
540
17%
1620
14%
540
58%
540
26%
1055
May1st to 10thNight
63%
475
22%
1555
22%
475
67%
475
35%
850
May11th to 20thNight
66%
354
20%
1416
28%
354
68%
354
26%
778
May21st to endNight
63%
388
11%
1552
18%
388
65%
388
21%
937
June1st to 10thNight
63%
360
12%
1396
16%
360
66%
360
26%
783
June11th to 20thNight
56%
360
16%
1260
17%
360
61%
360
29%
716
June21st to endNight
75%
360
19%
1397
30%
360
78%
360
41%
630
July1st to 10thNight
85%
350
21%
1400
37%
350
88%
350
57%
515
July11th to 20thNight
84%
348
27%
1392
44%
348
89%
348
62%
484
July21st to endNight
85%
394
34%
1488
51%
372
88%
372
62%
511
August1st to 10thNight
85%
358
33%
1424
46%
356
87%
356
55%
539
August11th to 20thNight
86%
508
33%
1576
31%
508
87%
508
60%
699
August21st to endNight
78%
752
35%
1940
24%
752
80%
752
60%
986
September1st to 10thNight
80%
720
34%
1800
20%
720
82%
720
63%
918
September11th to 20thNight
77%
720
32%
1918
25%
720
78%
720
49%
1045
September21st to endNight
69%
720
27%
1980
24%
720
70%
720
43%
1134
October1st to 10thNight
64%
720
22%
2016
19%
720
67%
720
36%
1209
October11th to 20thNight
60%
720
21%
2263
22%
720
63%
720
30%
1325
October21st to endNight
55%
792
19%
2574
19%
792
59%
792
25%
1617
November1st to 10thNight
48%
740
14%
2405
14%
740
50%
740
19%
1695
November11th to 20thNight
44%
760
11%
2489
9%
760
47%
760
17%
1763
November21st to endNight
49%
774
12%
2674
11%
774
52%
774
20%
1774
December1st to 10thNight
49%
950
9%
2850
6%
950
51%
950
17%
2150
December11th to 20thNight
35%
948
4%
3472
3%
948
37%
948
9%
2802
December21st to endNight
30%
860
5%
4878
5%
853
33%
853
6%
3452

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
11%7%36%5%35%5%5%7%42%
74542
Night
13%8%36%6%45%5%5%7%38%
75187
TransparencyDay
42%313%23%15%5%
74245
Night
45%314%21%12%4
75005
SeeingDay
14%5%18%30%23%10%
13424
Night
17%312%39%25%4
22898

By Month

Percentage Cloud Cover SW (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
19%12%5%8%8%47%6%6%8%18%
1519
11th to 20thDay
18%11%6%9%8%47%5%6%7%18%
1464
21st to endDay
15%13%49%8%47%7%5%8%20%
1584
February1st to 10thDay
17%13%5%7%8%35%6%5%8%25%
1458
11th to 20thDay
16%16%47%6%36%5%46%26%
1727
21st to endDay
14%15%48%5%446%7%8%26%
1480
March1st to 10thDay
14%10%5%8%7%5%5%6%6%9%27%
1800
11th to 20thDay
13%9%48%7%47%6%7%8%26%
1862
21st to endDay
13%14%48%8%47%6%6%7%23%
2331
April1st to 10thDay
13%9%36%6%37%6%7%10%28%
2160
11th to 20thDay
11%9%46%6%45%46%8%36%
2181
21st to endDay
13%8%37%5%46%5%6%8%36%
2340
May1st to 10thDay
8%6%35%5%35%5%6%8%46%
2402
11th to 20thDay
10%6%36%6%46%6%6%9%40%
2477
21st to endDay
12%7%36%6%46%5%6%8%36%
2723
June1st to 10thDay
14%6%26%6%45%6%6%8%37%
2556
11th to 20thDay
12%6%25%5%35%6%5%8%42%
2700
21st to endDay
5%42343345%6%62%
2551
July1st to 10thDay
221322345%6%69%
2520
11th to 20thDay
2112223346%74%
2520
21st to endDay
1121234481%
2741
August1st to 10thDay
3213323346%71%
2507
11th to 20thDay
3212223348%70%
2325
21st to endDay
431332345%6%65%
2412
September1st to 10thDay
421331335%6%71%
2160
11th to 20thDay
7%324435%46%7%55%
2041
21st to endDay
7%415%435%5%6%8%52%
1980
October1st to 10thDay
11%6%36%6%3445%7%44%
1940
11th to 20thDay
10%5%25%6%36%5%6%8%45%
1696
21st to endDay
14%9%47%7%445%5%6%35%
1782
November1st to 10thDay
22%7%36%7%46%5%5%7%27%
1674
11th to 20thDay
18%9%5%9%8%46%6%6%7%24%
1688
21st to endDay
15%9%5%10%8%46%7%7%8%23%
1482
December1st to 10thDay
18%10%48%7%5%7%6%5%6%23%
1330
11th to 20thDay
19%14%5%9%8%7%6%6%6%6%15%
1685
21st to endDay
16%12%49%8%5%6%6%6%9%19%
2744
January1st to 10thNight
21%15%5%9%6%46%6%6%7%15%
2646
11th to 20thNight
19%11%5%9%7%46%6%5%7%20%
2568
21st to endNight
16%12%5%11%8%46%5%5%6%21%
2772
February1st to 10thNight
19%14%5%7%6%35%5%5%6%25%
2501
11th to 20thNight
16%13%47%5%45%45%6%31%
2120
21st to endNight
14%13%48%7%35%6%5%6%28%
1776
March1st to 10thNight
15%10%36%6%46%7%5%8%30%
2160
11th to 20thNight
13%9%37%7%35%6%6%8%34%
2098
21st to endNight
15%10%36%7%46%7%7%8%27%
2021
April1st to 10thNight
13%10%35%6%36%6%7%10%33%
1800
11th to 20thNight
14%8%37%6%44446%40%
1726
21st to endNight
12%8%26%5%36%6%5%7%40%
1620
May1st to 10thNight
8%5%245%346%6%6%50%
1555
11th to 20thNight
11%5%245%345%6%9%45%
1416
21st to endNight
12%6%35%5%46%6%7%8%39%
1552
June1st to 10thNight
9%5%35%445%47%11%42%
1396
11th to 20thNight
11%5%25%5%345%6%8%46%
1260
21st to endNight
5%314425%5%5%7%61%
1397
July1st to 10thNight
2212213448%71%
1440
11th to 20thNight
212212346%77%
1440
21st to endNight
2112222235%78%
1576
August1st to 10thNight
321232235%7%70%
1432
11th to 20thNight
2123235%46%70%
1576
21st to endNight
431322235%6%69%
1940
September1st to 10thNight
431222335%6%69%
1800
11th to 20thNight
6%3235%3445%7%58%
1918
21st to endNight
11%42443445%6%55%
1980
October1st to 10thNight
9%5%35%5%345%5%6%49%
2016
11th to 20thNight
13%6%35%5%345%5%8%45%
2263
21st to endNight
14%7%25%6%45%6%6%5%40%
2574
November1st to 10thNight
21%9%36%7%45%5%5%7%29%
2405
11th to 20thNight
20%9%46%7%45%5%6%6%28%
2489
21st to endNight
16%10%36%6%46%6%6%7%30%
2674
December1st to 10thNight
17%10%38%7%47%6%7%7%26%
2850
11th to 20thNight
20%14%5%9%9%5%7%6%6%6%14%
3506
21st to endNight
17%11%410%9%7%8%7%5%6%16%
4924

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
63%7%17%11%2
1519
11th to 20thDay
64%5%15%13%2
1464
21st to endDay
62%5%17%14%21
1584
February1st to 10thDay
59%6%19%12%4
1458
11th to 20thDay
60%415%16%6%
1737
21st to endDay
56%5%13%19%6%1
1480
March1st to 10thDay
55%316%20%6%1
1800
11th to 20thDay
55%317%21%4
1862
21st to endDay
62%415%15%4
2331
April1st to 10thDay
52%415%21%7%1
2160
11th to 20thDay
47%314%23%11%2
2184
21st to endDay
47%312%25%12%1
2340
May1st to 10thDay
37%312%33%14%1
2402
11th to 20thDay
42%315%25%13%1
2480
21st to endDay
47%314%26%9%1
2724
June1st to 10thDay
45%413%28%10%1
2556
11th to 20thDay
40%313%28%14%3
2700
21st to endDay
24%210%33%25%5%
2551
July1st to 10thDay
16%27%24%33%17%
2451
11th to 20thDay
14%29%17%34%24%
2445
21st to endDay
10%1319%44%23%
2589
August1st to 10thDay
17%16%22%38%15%
2490
11th to 20thDay
16%18%26%34%15%
2325
21st to endDay
21%28%31%29%8%
2412
September1st to 10thDay
16%28%32%29%13%
2160
11th to 20thDay
30%212%27%22%7%
2041
21st to endDay
31%316%32%15%3
1980
October1st to 10thDay
41%214%29%13%1
1940
11th to 20thDay
36%218%30%13%1
1696
21st to endDay
49%416%23%8%
1782
November1st to 10thDay
55%416%21%31
1674
11th to 20thDay
58%417%17%31
1688
21st to endDay
55%6%19%16%3
1482
December1st to 10thDay
60%6%15%16%4
1330
11th to 20thDay
68%417%10%1
1684
21st to endDay
62%218%16%2
2744
January1st to 10thNight
65%415%14%21
2646
11th to 20thNight
61%418%15%2
2568
21st to endNight
62%417%14%31
2772
February1st to 10thNight
61%417%14%41
2501
11th to 20thNight
54%317%21%5%
2121
21st to endNight
57%316%16%6%1
1776
March1st to 10thNight
52%415%22%7%1
2160
11th to 20thNight
49%216%28%5%
2098
21st to endNight
55%5%17%19%5%
2021
April1st to 10thNight
46%316%26%9%
1800
11th to 20thNight
47%29%25%14%3
1726
21st to endNight
44%313%22%16%2
1620
May1st to 10thNight
33%211%34%18%1
1555
11th to 20thNight
36%313%31%14%2
1416
21st to endNight
43%415%26%11%1
1552
June1st to 10thNight
37%413%31%14%1
1396
11th to 20thNight
37%311%30%15%4
1260
21st to endNight
25%210%30%26%8%
1397
July1st to 10thNight
14%17%23%34%22%
1400
11th to 20thNight
11%27%20%33%27%
1392
21st to endNight
12%1216%37%32%
1488
August1st to 10thNight
15%16%17%39%21%
1424
11th to 20thNight
16%110%18%36%19%
1576
21st to endNight
18%27%26%35%12%
1940
September1st to 10thNight
17%27%28%31%15%
1800
11th to 20thNight
26%29%28%27%8%
1918
21st to endNight
31%113%31%17%7%
1980
October1st to 10thNight
35%312%33%16%1
2016
11th to 20thNight
38%214%28%16%1
2263
21st to endNight
43%314%27%11%1
2574
November1st to 10thNight
54%314%23%6%
2405
11th to 20thNight
55%319%19%31
2489
21st to endNight
50%219%24%5%
2674
December1st to 10thNight
56%7%17%17%4
2850
11th to 20thNight
69%417%10%1
3507
21st to endNight
63%220%12%4
4924

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%413%28%23%8%
180
11th to 20thDay
28%412%29%17%9%
166
21st to endDay
22%416%36%18%5%
176
February1st to 10thDay
26%421%34%13%2
178
11th to 20thDay
26%7%17%29%18%3
405
21st to endDay
25%7%19%30%16%3
346
March1st to 10thDay
20%6%25%28%17%4
420
11th to 20thDay
18%6%19%25%24%8%
420
21st to endDay
16%10%23%30%16%5%
462
April1st to 10thDay
19%11%21%28%15%6%
420
11th to 20thDay
17%9%27%26%13%7%
412
21st to endDay
18%9%20%25%22%6%
420
May1st to 10thDay
11%10%18%31%24%5%
423
11th to 20thDay
16%7%15%27%21%14%
448
21st to endDay
12%5%19%26%26%13%
485
June1st to 10thDay
14%6%17%27%25%12%
486
11th to 20thDay
14%6%20%33%21%6%
630
21st to endDay
6%5%19%30%29%11%
481
July1st to 10thDay
3422%32%29%11%
446
11th to 20thDay
2324%33%26%11%
444
21st to endDay
1319%33%30%14%
487
August1st to 10thDay
4317%31%28%18%
447
11th to 20thDay
3314%27%32%22%
437
21st to endDay
7%5%16%28%27%16%
495
September1st to 10thDay
6%219%26%30%17%
450
11th to 20thDay
9%5%13%30%29%14%
450
21st to endDay
11%416%29%31%10%
450
October1st to 10thDay
13%7%11%30%26%13%
450
11th to 20thDay
12%5%14%27%28%13%
346
21st to endDay
23%414%33%21%6%
297
November1st to 10thDay
27%414%33%21%1
270
11th to 20thDay
19%5%18%30%22%6%
259
21st to endDay
18%113%38%24%5%
180
December1st to 10thDay
21%312%35%19%11%
180
11th to 20thDay
31%7%11%33%15%3
180
21st to endDay
25%212%38%18%5%
198
January1st to 10thNight
27%5%15%34%16%4
760
11th to 20thNight
24%414%36%18%4
734
21st to endNight
22%5%11%37%22%3
792
February1st to 10thNight
26%6%14%38%15%2
720
11th to 20thNight
23%415%36%20%3
704
21st to endNight
20%5%16%40%17%2
592
March1st to 10thNight
21%316%40%18%3
720
11th to 20thNight
15%5%17%37%24%2
720
21st to endNight
20%413%46%15%3
792
April1st to 10thNight
18%413%39%24%2
720
11th to 20thNight
18%5%18%40%16%3
658
21st to endNight
14%415%42%23%2
540
May1st to 10thNight
10%5%15%41%27%2
475
11th to 20thNight
14%5%5%34%38%5%
354
21st to endNight
15%27%35%34%6%
389
June1st to 10thNight
12%310%44%28%4
360
11th to 20thNight
13%5%16%37%26%3
360
21st to endNight
6%19%46%35%3
360
July1st to 10thNight
218%47%38%4
350
11th to 20thNight
219%53%33%2
348
21st to endNight
226%44%42%4
394
August1st to 10thNight
315%45%41%5%
358
11th to 20thNight
216%39%44%7%
508
21st to endNight
5%29%39%39%6%
752
September1st to 10thNight
5%19%44%34%7%
720
11th to 20thNight
7%16%37%40%9%
720
21st to endNight
11%28%41%32%6%
720
October1st to 10thNight
11%210%45%28%4
720
11th to 20thNight
15%311%38%28%6%
720
21st to endNight
17%314%40%21%5%
792
November1st to 10thNight
24%311%42%18%1
740
11th to 20thNight
23%6%14%36%18%3
760
21st to endNight
21%411%37%21%5%
774
December1st to 10thNight
22%312%40%20%4
950
11th to 20thNight
29%411%36%17%2
950
21st to endNight
31%415%35%13%2
872
Page generated at 2024-01-11 01:22:42. Version ac07

Copyright 2024 Attilla Danko


Lewiston Clear Sky Chart |Charts Home