Westport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Westport clear sky chart from 2005-11-06 to 2024-03-08.

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
26%
22855
13%
80844
8%
22767
35%
22767
14%
57841

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
14%
754
7%
4413
2%
737
21%
737
4%
3313
January11th to 20thNight
15%
758
7%
4413
4%
740
22%
740
4%
3470
January21st to endNight
18%
830
7%
4655
5%
814
27%
814
6%
3750
February1st to 10thNight
14%
760
10%
2470
3%
760
22%
760
9%
1912
February11th to 20thNight
14%
741
14%
2405
4%
740
27%
740
12%
1761
February21st to endNight
18%
628
14%
1894
5%
628
28%
628
13%
1420
March1st to 10thNight
17%
751
16%
2215
8%
751
27%
751
15%
1632
March11th to 20thNight
22%
720
16%
1979
6%
720
31%
720
16%
1438
March21st to endNight
23%
792
20%
2086
7%
792
33%
792
20%
1491
April1st to 10thNight
19%
720
17%
1800
4%
720
26%
720
19%
1311
April11th to 20thNight
22%
711
18%
1775
5%
711
29%
711
19%
1280
April21st to endNight
27%
641
15%
1721
6%
641
32%
641
19%
1263
May1st to 10thNight
32%
360
16%
1440
13%
360
42%
360
16%
945
May11th to 20thNight
31%
354
21%
1416
15%
354
47%
354
19%
855
May21st to endNight
34%
388
15%
1551
11%
388
46%
388
23%
895
June1st to 10thNight
33%
360
11%
1440
9%
360
44%
360
17%
952
June11th to 20thNight
37%
360
13%
1440
15%
360
47%
360
21%
860
June21st to endNight
42%
360
11%
1440
13%
360
48%
360
17%
928
July1st to 10thNight
46%
350
15%
1400
18%
350
54%
350
25%
785
July11th to 20thNight
49%
348
17%
1392
21%
348
56%
348
25%
810
July21st to endNight
48%
394
16%
1486
14%
372
55%
372
25%
847
August1st to 10thNight
48%
454
17%
1518
13%
452
53%
452
26%
923
August11th to 20thNight
51%
534
18%
1598
11%
534
55%
534
29%
1001
August21st to endNight
43%
787
18%
1975
8%
787
48%
787
32%
1310
September1st to 10thNight
41%
720
17%
1800
7%
720
46%
720
32%
1204
September11th to 20thNight
49%
720
24%
1800
13%
720
54%
720
36%
1150
September21st to endNight
40%
720
23%
2047
16%
720
45%
720
26%
1352
October1st to 10thNight
33%
720
16%
2160
11%
720
40%
720
19%
1499
October11th to 20thNight
23%
720
13%
2160
7%
720
32%
720
16%
1578
October21st to endNight
22%
792
13%
2479
5%
792
32%
792
13%
1845
November1st to 10thNight
24%
740
17%
2407
9%
740
34%
740
17%
1636
November11th to 20thNight
20%
760
17%
2659
9%
760
33%
760
14%
1843
November21st to endNight
19%
760
11%
2660
5%
760
27%
760
10%
2037
December1st to 10thNight
12%
760
8%
2660
2%
760
19%
760
7%
2147
December11th to 20thNight
14%
760
11%
3244
5%
759
23%
759
8%
2431
December21st to endNight
12%
828
5%
4846
1%
817
18%
817
4%
3967

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%10%47%6%35%5%5%6%32%
78414
Night
17%10%47%6%35%45%6%32%
81146
TransparencyDay
51%6%11%19%11%1
78119
Night
53%6%11%18%10%1
80975
SeeingDay
24%17%30%19%8%3
13551
Night
23%14%31%23%8%1
22880

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%16%6%8%8%45%445%26%
2517
11th to 20thDay
14%15%6%13%8%45%5%45%22%
2520
21st to endDay
18%19%7%12%8%4443417%
2993
February1st to 10thDay
16%14%411%7%45%5%5%6%23%
1710
11th to 20thDay
13%14%5%10%7%36%45%5%28%
1663
21st to endDay
20%14%49%7%45%45%424%
1559
March1st to 10thDay
16%11%5%10%8%5%434430%
1903
11th to 20thDay
16%11%5%8%6%35%436%30%
1980
21st to endDay
19%12%37%42333438%
2269
April1st to 10thDay
20%13%46%5%2445%5%33%
2160
11th to 20thDay
20%9%35%5%24345%39%
2134
21st to endDay
22%10%37%5%34445%32%
2251
May1st to 10thDay
20%7%37%5%345%5%7%34%
2520
11th to 20thDay
16%6%36%5%35%35%8%38%
2478
21st to endDay
13%6%26%6%46%5%6%8%39%
2725
June1st to 10thDay
21%7%46%5%45%5%6%7%31%
2520
11th to 20thDay
16%6%35%5%26%5%6%9%38%
2520
21st to endDay
17%7%37%6%35%6%6%8%33%
2520
July1st to 10thDay
11%5%35%5%46%5%6%8%41%
2520
11th to 20thDay
13%6%35%5%35%5%6%10%38%
2520
21st to endDay
11%6%35%6%47%6%7%9%37%
2744
August1st to 10thDay
12%7%26%6%45%6%7%8%38%
2408
11th to 20thDay
12%6%26%5%35%6%7%9%38%
2290
21st to endDay
13%6%26%6%346%6%9%39%
2376
September1st to 10thDay
14%5%26%5%35%46%9%41%
2160
11th to 20thDay
12%6%245%2445%8%47%
2160
21st to endDay
19%5%25%5%45%45%6%40%
1909
October1st to 10thDay
21%8%36%5%3345%6%36%
1800
11th to 20thDay
21%8%48%6%45%5%6%7%28%
1800
21st to endDay
27%8%47%6%35%45%6%26%
1876
November1st to 10thDay
15%9%47%6%35%5%6%8%33%
1671
11th to 20thDay
17%11%5%8%6%44446%30%
1520
21st to endDay
20%14%5%9%7%36%45%5%22%
1520
December1st to 10thDay
23%16%5%10%6%35%5%5%5%18%
1520
11th to 20thDay
21%14%5%9%7%35%445%24%
1906
21st to endDay
27%16%6%12%6%3332320%
2772
January1st to 10thNight
18%14%6%10%8%45%5%5%6%20%
4429
11th to 20thNight
14%14%5%12%9%5%6%5%45%20%
4440
21st to endNight
20%16%7%11%7%45%43420%
4660
February1st to 10thNight
15%14%5%9%8%45%5%6%6%23%
2470
11th to 20thNight
13%14%6%8%7%45%445%30%
2403
21st to endNight
16%13%5%8%6%45%5%5%5%29%
1894
March1st to 10thNight
16%11%5%7%7%45%45%5%31%
2205
11th to 20thNight
17%14%5%6%5%3435%6%34%
1979
21st to endNight
17%8%47%5%3344440%
2086
April1st to 10thNight
21%8%5%6%5%2444436%
1800
11th to 20thNight
20%8%36%5%34445%37%
1775
21st to endNight
21%10%37%5%34447%32%
1721
May1st to 10thNight
22%7%25%5%435%5%5%36%
1440
11th to 20thNight
14%7%35%6%25%5%5%6%43%
1415
21st to endNight
12%426%5%345%6%9%45%
1550
June1st to 10thNight
16%7%36%6%36%6%7%8%33%
1440
11th to 20thNight
14%6%35%5%35%45%8%42%
1440
21st to endNight
16%6%26%5%35%5%6%9%36%
1440
July1st to 10thNight
9%5%35%5%35%5%5%9%46%
1440
11th to 20thNight
12%5%25%5%35%5%6%9%44%
1440
21st to endNight
9%5%245%345%6%8%48%
1574
August1st to 10thNight
9%5%36%5%45%6%5%7%45%
1528
11th to 20thNight
9%7%36%5%35%6%6%7%44%
1598
21st to endNight
10%5%25%6%345%7%8%44%
1975
September1st to 10thNight
12%6%25%6%345%5%8%46%
1800
11th to 20thNight
13%42433445%7%50%
1800
21st to endNight
16%7%25%5%25%446%43%
2047
October1st to 10thNight
19%7%36%6%45%45%6%37%
2160
11th to 20thNight
21%9%27%6%345%5%6%31%
2160
21st to endNight
23%10%37%6%4445%6%29%
2479
November1st to 10thNight
18%9%45%5%345%6%6%35%
2407
11th to 20thNight
18%10%47%5%35%5%5%7%32%
2659
21st to endNight
21%12%38%6%45%45%6%25%
2660
December1st to 10thNight
20%15%5%11%7%35%45%5%20%
2660
11th to 20thNight
21%14%48%6%3434427%
3288
21st to endNight
30%15%49%6%4444417%
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
59%7%14%12%6%2
2518
11th to 20thDay
66%5%11%10%8%
2520
21st to endDay
71%6%8%9%5%1
2993
February1st to 10thDay
62%5%8%17%6%1
1710
11th to 20thDay
58%411%16%9%1
1672
21st to endDay
64%5%9%12%9%1
1559
March1st to 10thDay
59%410%16%10%2
1906
11th to 20thDay
56%5%10%14%12%3
1980
21st to endDay
51%47%19%14%6%
2269
April1st to 10thDay
54%47%19%13%3
2160
11th to 20thDay
48%47%21%17%2
2134
21st to endDay
54%49%15%14%4
2251
May1st to 10thDay
50%5%9%16%16%3
2520
11th to 20thDay
44%5%10%23%15%2
2482
21st to endDay
42%8%14%21%13%3
2725
June1st to 10thDay
51%8%10%19%12%1
2520
11th to 20thDay
43%6%10%25%14%2
2520
21st to endDay
47%8%13%19%11%1
2520
July1st to 10thDay
37%8%12%28%15%1
2450
11th to 20thDay
40%7%16%27%10%
2445
21st to endDay
41%9%16%23%11%
2591
August1st to 10thDay
41%7%15%26%11%1
2394
11th to 20thDay
40%8%15%25%11%1
2290
21st to endDay
40%7%13%27%13%1
2376
September1st to 10thDay
39%7%14%27%12%1
2160
11th to 20thDay
36%6%12%29%15%1
2160
21st to endDay
44%7%12%27%10%
1909
October1st to 10thDay
49%5%11%22%12%1
1800
11th to 20thDay
54%6%13%19%7%1
1800
21st to endDay
60%5%10%18%7%
1876
November1st to 10thDay
48%7%14%21%9%1
1671
11th to 20thDay
55%7%10%17%10%1
1520
21st to endDay
63%7%11%11%8%
1520
December1st to 10thDay
67%7%11%11%41
1520
11th to 20thDay
64%6%14%12%4
1906
21st to endDay
71%47%14%4
2772
January1st to 10thNight
63%7%14%12%4
4429
11th to 20thNight
66%7%11%11%5%
4440
21st to endNight
68%6%9%10%6%1
4660
February1st to 10thNight
62%6%10%15%6%1
2470
11th to 20thNight
57%411%19%9%
2405
21st to endNight
57%6%9%17%10%1
1894
March1st to 10thNight
55%410%18%11%1
2215
11th to 20thNight
53%411%19%12%2
1980
21st to endNight
50%5%6%20%17%4
2086
April1st to 10thNight
51%48%21%14%2
1800
11th to 20thNight
48%6%7%19%18%2
1775
21st to endNight
53%49%16%15%3
1721
May1st to 10thNight
49%5%8%17%16%4
1440
11th to 20thNight
41%6%9%24%17%3
1416
21st to endNight
37%7%16%18%19%3
1551
June1st to 10thNight
46%8%12%21%12%1
1440
11th to 20thNight
40%6%12%21%19%2
1440
21st to endNight
43%10%13%21%12%1
1440
July1st to 10thNight
34%8%11%26%19%3
1400
11th to 20thNight
36%7%13%30%14%
1392
21st to endNight
33%9%16%28%13%1
1486
August1st to 10thNight
36%8%15%27%13%1
1518
11th to 20thNight
37%7%15%26%13%1
1598
21st to endNight
35%9%14%28%13%1
1975
September1st to 10thNight
37%7%13%28%14%1
1800
11th to 20thNight
33%7%14%32%13%2
1800
21st to endNight
41%6%10%31%11%1
2047
October1st to 10thNight
48%6%10%21%14%1
2160
11th to 20thNight
53%6%13%19%9%1
2160
21st to endNight
57%5%13%15%9%
2479
November1st to 10thNight
48%6%14%21%10%1
2407
11th to 20thNight
51%5%12%19%11%2
2659
21st to endNight
60%7%12%16%6%
2660
December1st to 10thNight
67%6%10%14%4
2660
11th to 20thNight
61%5%11%15%7%1
3288
21st to endNight
71%6%8%12%3
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
26%23%35%12%41
180
11th to 20thDay
36%17%29%16%21
180
21st to endDay
27%22%31%17%4
260
February1st to 10thDay
34%26%29%10%1
270
11th to 20thDay
29%28%37%6%
270
21st to endDay
35%20%33%11%2
371
March1st to 10thDay
26%22%33%15%5%
448
11th to 20thDay
30%20%32%13%4
420
21st to endDay
33%21%26%13%5%1
462
April1st to 10thDay
30%22%28%14%6%
420
11th to 20thDay
33%19%22%16%8%2
412
21st to endDay
28%22%31%11%5%2
420
May1st to 10thDay
25%18%30%18%6%2
423
11th to 20thDay
19%16%36%20%7%2
447
21st to endDay
20%14%33%21%10%2
485
June1st to 10thDay
24%12%36%20%6%2
450
11th to 20thDay
18%16%33%20%10%3
450
21st to endDay
20%14%30%24%9%3
450
July1st to 10thDay
14%10%28%30%15%4
445
11th to 20thDay
15%13%30%24%14%4
444
21st to endDay
13%10%35%28%10%4
488
August1st to 10thDay
13%10%30%29%14%4
446
11th to 20thDay
15%6%27%30%15%7%
439
21st to endDay
15%11%33%24%11%7%
495
September1st to 10thDay
14%14%32%22%12%7%
450
11th to 20thDay
13%11%26%24%16%10%
450
21st to endDay
20%11%29%23%13%4
450
October1st to 10thDay
26%18%25%16%11%4
450
11th to 20thDay
30%19%29%16%5%2
450
21st to endDay
31%19%27%18%4
443
November1st to 10thDay
25%19%29%20%7%
365
11th to 20thDay
32%19%31%13%42
180
21st to endDay
29%23%31%13%3
180
December1st to 10thDay
35%19%32%10%4
180
11th to 20thDay
35%22%32%8%31
180
21st to endDay
34%21%32%10%31
198
January1st to 10thNight
29%20%29%19%3
760
11th to 20thNight
29%18%29%19%4
760
21st to endNight
20%17%36%22%5%
836
February1st to 10thNight
24%21%35%18%2
760
11th to 20thNight
22%22%37%16%3
743
21st to endNight
25%20%35%18%3
628
March1st to 10thNight
24%17%35%21%3
751
11th to 20thNight
27%21%28%20%41
720
21st to endNight
23%16%33%20%8%
792
April1st to 10thNight
27%16%33%22%3
720
11th to 20thNight
24%20%30%18%7%1
711
21st to endNight
26%14%29%22%8%1
641
May1st to 10thNight
26%10%26%27%10%1
360
11th to 20thNight
16%10%36%31%6%
354
21st to endNight
13%8%40%28%11%1
389
June1st to 10thNight
16%8%33%34%9%1
360
11th to 20thNight
14%12%31%30%12%1
360
21st to endNight
17%7%26%36%13%1
360
July1st to 10thNight
10%6%31%37%15%
350
11th to 20thNight
11%332%37%15%1
348
21st to endNight
10%5%32%41%11%1
394
August1st to 10thNight
13%5%28%34%20%1
454
11th to 20thNight
13%5%24%33%24%2
534
21st to endNight
12%6%32%33%15%2
787
September1st to 10thNight
14%7%33%29%16%2
720
11th to 20thNight
15%8%24%28%21%4
720
21st to endNight
20%10%25%25%18%2
720
October1st to 10thNight
22%14%27%20%15%2
720
11th to 20thNight
26%15%30%21%7%1
720
21st to endNight
29%15%28%24%5%
792
November1st to 10thNight
27%14%31%21%7%
740
11th to 20thNight
26%18%32%15%9%
760
21st to endNight
29%20%28%18%6%
760
December1st to 10thNight
30%20%31%16%3
760
11th to 20thNight
27%20%33%17%31
760
21st to endNight
35%17%30%17%1
836
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