Monsey Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monsey Observatory clear sky chart from 2005-11-05 to 2017-12-01.

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
33%
15299
20%
47774
10%
15268
45%
15268
23%
30311

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
23%
720
21%
2506
8%
716
40%
716
20%
1553
January16th to endNight
21%
768
21%
2601
7%
768
40%
768
19%
1615
February1st to 15thNight
21%
704
18%
2230
6%
701
36%
701
18%
1459
February16th to endNight
22%
631
27%
1893
9%
631
44%
631
21%
1191
March1st to 15thNight
22%
720
19%
2154
7%
720
37%
720
20%
1413
March16th to endNight
23%
768
23%
1992
8%
768
35%
768
25%
1314
April1st to 15thNight
25%
718
18%
1796
5%
718
32%
718
25%
1236
April16th to endNight
28%
701
19%
1781
4%
701
36%
701
26%
1201
May1st to 15thNight
28%
495
19%
1575
8%
495
39%
495
19%
1046
May16th to endNight
41%
374
16%
1497
13%
374
49%
374
19%
928
June1st to 15thNight
41%
360
14%
1440
12%
360
53%
360
19%
908
June16th to endNight
51%
360
15%
1440
14%
360
60%
360
26%
814
July1st to 15thNight
53%
340
13%
1360
15%
340
58%
340
22%
827
July16th to endNight
57%
376
16%
1418
18%
354
63%
354
25%
820
August1st to 15thNight
53%
543
19%
1614
13%
541
57%
541
29%
1010
August16th to endNight
57%
764
19%
1910
11%
764
59%
764
32%
1275
September1st to 15thNight
46%
720
23%
1800
12%
720
51%
720
34%
1165
September16th to endNight
52%
717
27%
1971
20%
717
58%
717
35%
1203
October1st to 15thNight
38%
720
21%
2106
14%
720
46%
720
25%
1354
October16th to endNight
30%
768
23%
2403
12%
768
46%
768
25%
1491
November1st to 15thNight
35%
760
22%
2472
12%
760
49%
760
24%
1503
November16th to endNight
28%
780
23%
2595
11%
780
44%
780
21%
1598
December1st to 15thNight
25%
724
16%
2532
7%
724
37%
724
17%
1640
December16th to endNight
19%
768
19%
2688
5%
768
36%
768
17%
1747

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
16%6%25%42445%7%39%
48656
Night
16%5%24424446%43%
47944
Cloud CoverDay
16%5%25%42445%7%40%
48665
Night
17%5%24424446%43%
47950
TransparencyDay
42%5%11%22%15%2
48344
Night
41%411%23%16%2
47774
SeeingDay
20%11%27%24%12%4
6028
Night
19%11%28%28%10%1
15300

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 15thDay
15%6%24435%5%45%41%
1432
16th to endDay
14%8%344245%5%7%40%
1620
February1st to 15thDay
15%6%35%6%34448%37%
1630
16th to endDay
15%6%25%6%2445%6%42%
1580
March1st to 15thDay
18%6%25%43446%7%36%
1793
16th to endDay
17%6%25%424435%42%
2232
April1st to 15thDay
19%7%34323346%41%
2152
16th to endDay
17%5%24424446%42%
2178
May1st to 15thDay
22%6%25%42335%7%33%
2387
16th to endDay
17%6%25%5%35%5%5%8%35%
2618
June1st to 15thDay
20%7%2442446%7%34%
2520
16th to endDay
13%5%25%5%35%6%6%9%36%
2520
July1st to 15thDay
12%6%25%5%35%5%6%9%36%
2520
16th to endDay
11%5%36%6%35%6%6%9%36%
2654
August1st to 15thDay
13%5%25%6%45%5%6%8%37%
2320
16th to endDay
13%5%25%43446%8%40%
2292
September1st to 15thDay
15%4245%345%46%43%
2160
16th to endDay
13%5%25%42445%6%45%
1989
October1st to 15thDay
18%5%24424346%42%
1851
16th to endDay
19%5%23423446%43%
1821
November1st to 15thDay
19%5%2431335%6%45%
1716
16th to endDay
17%5%23323447%45%
1693
December1st to 15thDay
17%7%35%41445%5%40%
1442
16th to endDay
20%7%35%324347%36%
1536
January1st to 15thNight
17%5%2432345%6%42%
2506
16th to endNight
15%7%34424347%41%
2601
February1st to 15thNight
14%7%35%424446%40%
2229
16th to endNight
16%5%245%24446%45%
1893
March1st to 15thNight
20%5%24423346%42%
2141
16th to endNight
16%7%24423345%44%
1992
April1st to 15thNight
18%6%3441445%7%39%
1796
16th to endNight
18%6%25%323346%43%
1781
May1st to 15thNight
19%7%25%423445%40%
1575
16th to endNight
18%6%2442345%8%39%
1495
June1st to 15thNight
20%5%2342445%7%38%
1440
16th to endNight
10%5%144345%6%8%45%
1440
July1st to 15thNight
13%325%435%5%6%8%40%
1440
16th to endNight
10%425%425%6%7%9%41%
1514
August1st to 15thNight
12%4144335%5%8%45%
1624
16th to endNight
14%4245%2445%7%44%
1910
September1st to 15thNight
15%423323446%48%
1800
16th to endNight
12%5%245%13346%51%
1971
October1st to 15thNight
18%6%25%42324445%
2106
16th to endNight
19%42432245%5%45%
2403
November1st to 15thNight
16%5%34323346%46%
2472
16th to endNight
17%5%23423446%43%
2595
December1st to 15thNight
20%6%235%24446%38%
2532
16th to endNight
19%7%3442435%7%38%
2688

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 15thDay
16%6%14425%446%42%
1432
16th to endDay
15%6%2441445%7%41%
1620
February1st to 15thDay
16%6%35%43445%5%39%
1630
16th to endDay
15%5%25%5%24445%43%
1580
March1st to 15thDay
18%6%25%5%24447%36%
1803
16th to endDay
17%6%24424345%42%
2231
April1st to 15thDay
19%7%34413347%41%
2152
16th to endDay
17%424324447%43%
2178
May1st to 15thDay
22%6%244245%5%6%35%
2387
16th to endDay
17%6%346%245%5%7%36%
2618
June1st to 15thDay
20%6%34425%46%7%35%
2520
16th to endDay
12%5%25%5%35%5%6%9%37%
2520
July1st to 15thDay
12%5%35%5%35%5%6%9%37%
2520
16th to endDay
11%5%35%5%45%5%6%9%36%
2654
August1st to 15thDay
13%426%5%36%6%5%7%38%
2320
16th to endDay
12%5%245%3446%9%40%
2292
September1st to 15thDay
13%425%5%24446%44%
2160
16th to endDay
13%436%42345%6%45%
1989
October1st to 15thDay
18%6%34324336%43%
1851
16th to endDay
19%5%14323345%45%
1821
November1st to 15thDay
19%5%2332335%5%45%
1716
16th to endDay
17%6%13323346%46%
1693
December1st to 15thDay
17%7%35%423446%40%
1442
16th to endDay
21%8%25%324437%37%
1536
January1st to 15thNight
18%5%24324446%42%
2506
16th to endNight
15%7%34424347%41%
2601
February1st to 15thNight
14%7%36%434445%41%
2222
16th to endNight
16%5%24424436%45%
1893
March1st to 15thNight
19%6%24424446%42%
2154
16th to endNight
16%7%25%323345%44%
1992
April1st to 15thNight
19%6%25%32346%7%40%
1796
16th to endNight
19%5%24414246%43%
1781
May1st to 15thNight
18%6%35%424446%39%
1575
16th to endNight
18%6%24333448%39%
1495
June1st to 15thNight
21%42442345%7%39%
1440
16th to endNight
10%4236%3445%9%45%
1440
July1st to 15thNight
12%425%6%3447%9%39%
1440
16th to endNight
10%423436%5%6%9%41%
1514
August1st to 15thNight
12%3145%2445%7%46%
1624
16th to endNight
14%415%6%3445%7%44%
1910
September1st to 15thNight
15%423423437%48%
1800
16th to endNight
12%5%25%423336%50%
1971
October1st to 15thNight
17%7%25%322335%46%
2106
16th to endNight
19%5%14322345%46%
2403
November1st to 15thNight
17%5%24314345%47%
2472
16th to endNight
18%5%24423445%45%
2595
December1st to 15thNight
21%6%24423446%39%
2532
16th to endNight
20%6%24434445%39%
2688

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
42%5%13%22%12%3
1433
16th to endDay
41%5%12%23%14%2
1620
February1st to 15thDay
45%412%22%13%2
1633
16th to endDay
41%411%25%15%1
1580
March1st to 15thDay
46%414%21%11%2
1803
16th to endDay
43%49%20%18%3
2232
April1st to 15thDay
43%49%22%15%4
2152
16th to endDay
41%48%20%21%3
2178
May1st to 15thDay
47%5%8%20%15%2
2387
16th to endDay
45%6%12%20%13%1
2622
June1st to 15thDay
46%6%12%21%12%
2520
16th to endDay
41%6%13%23%14%1
2520
July1st to 15thDay
42%6%11%21%16%1
2371
16th to endDay
40%7%12%23%12%2
2487
August1st to 15thDay
41%7%13%19%17%
2306
16th to endDay
39%5%9%25%18%1
2292
September1st to 15thDay
39%5%10%21%21%1
2160
16th to endDay
38%39%22%23%2
1989
October1st to 15thDay
42%410%22%17%2
1851
16th to endDay
40%49%25%17%2
1821
November1st to 15thDay
40%312%21%18%2
1716
16th to endDay
38%310%27%16%2
1693
December1st to 15thDay
43%5%15%20%13%1
1442
16th to endDay
47%414%22%10%
1536
January1st to 15thNight
42%312%23%14%3
2506
16th to endNight
42%311%25%15%2
2601
February1st to 15thNight
44%5%11%22%13%2
2230
16th to endNight
39%47%26%18%3
1893
March1st to 15thNight
43%413%21%13%3
2154
16th to endNight
40%311%20%18%4
1992
April1st to 15thNight
42%410%22%16%2
1796
16th to endNight
42%48%19%22%2
1781
May1st to 15thNight
46%49%20%17%2
1575
16th to endNight
42%6%15%18%14%2
1497
June1st to 15thNight
43%6%12%21%14%1
1440
16th to endNight
34%6%15%27%15%
1440
July1st to 15thNight
38%8%12%22%15%2
1360
16th to endNight
35%7%16%22%15%2
1418
August1st to 15thNight
35%8%11%25%16%2
1614
16th to endNight
38%6%10%23%19%1
1910
September1st to 15thNight
36%5%10%27%18%1
1800
16th to endNight
35%37%23%27%1
1971
October1st to 15thNight
41%410%24%16%2
2106
16th to endNight
39%312%26%16%1
2403
November1st to 15thNight
39%311%22%19%3
2472
16th to endNight
41%311%26%14%2
2595
December1st to 15thNight
45%414%21%13%
2532
16th to endNight
46%412%22%12%1
2688

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
23%20%35%18%3
60
16th to endDay
20%16%41%16%5%
78
February1st to 15thDay
21%24%34%17%2
146
16th to endDay
17%23%32%20%5%
239
March1st to 15thDay
21%23%25%23%4
270
16th to endDay
22%16%31%20%6%2
288
April1st to 15thDay
25%11%32%18%11%2
270
16th to endDay
21%10%38%14%11%4
270
May1st to 15thDay
31%14%25%17%7%3
288
16th to endDay
21%9%25%29%12%3
331
June1st to 15thDay
24%12%25%22%13%1
315
16th to endDay
17%9%28%26%14%2
315
July1st to 15thDay
14%8%25%31%16%2
305
16th to endDay
13%422%32%24%2
326
August1st to 15thDay
13%420%37%16%8%
313
16th to endDay
14%418%29%21%10%
332
September1st to 15thDay
14%9%26%21%16%10%
315
16th to endDay
15%5%24%24%14%16%
314
October1st to 15thDay
23%5%22%24%18%5%
315
16th to endDay
21%14%30%19%13%1
311
November1st to 15thDay
23%11%26%25%10%2
280
16th to endDay
21%18%29%22%6%2
223
December1st to 15thDay
20%21%38%11%5%3
60
16th to endDay
32%15%39%12%
64
January1st to 15thNight
20%14%36%22%5%
720
16th to endNight
19%16%36%24%2
768
February1st to 15thNight
18%17%34%27%1
704
16th to endNight
20%19%34%22%3
631
March1st to 15thNight
24%15%31%23%4
720
16th to endNight
20%15%34%22%6%
768
April1st to 15thNight
20%15%35%23%4
718
16th to endNight
20%14%31%24%7%
701
May1st to 15thNight
22%13%28%27%7%
495
16th to endNight
20%6%23%37%10%1
375
June1st to 15thNight
20%6%25%35%12%
360
16th to endNight
10%326%43%15%
360
July1st to 15thNight
15%319%43%17%
340
16th to endNight
10%320%39%24%1
376
August1st to 15thNight
15%119%40%21%1
543
16th to endNight
15%214%36%28%3
764
September1st to 15thNight
17%5%23%34%17%2
720
16th to endNight
15%320%32%22%4
717
October1st to 15thNight
21%8%24%26%15%2
720
16th to endNight
22%11%30%25%9%
768
November1st to 15thNight
20%11%26%26%13%1
760
16th to endNight
21%13%30%24%9%1
780
December1st to 15thNight
25%11%31%24%6%
724
16th to endNight
24%14%35%21%2
768
Page generated at 2017-12-02 09:14:27. Version ac04

Copyright 2017 A. Danko


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