Idlewild Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Idlewild Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
61%
16835
29%
49532
21%
16795
67%
16795
44%
26480

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
58%
972
32%
2716
23%
970
66%
970
51%
1398
January16th to endNight
57%
877
35%
2749
28%
877
67%
877
44%
1405
February1st to 15thNight
50%
759
26%
2432
18%
758
61%
758
38%
1317
February16th to endNight
47%
684
33%
2050
18%
684
61%
684
43%
1093
March1st to 15thNight
56%
780
30%
2295
18%
780
65%
780
47%
1195
March16th to endNight
51%
731
28%
2187
18%
731
60%
731
41%
1189
April1st to 15thNight
47%
584
25%
1948
19%
584
58%
584
36%
1046
April16th to endNight
47%
558
23%
1859
19%
558
56%
558
29%
1094
May1st to 15thNight
57%
540
20%
1611
17%
540
61%
540
30%
1013
May16th to endNight
56%
562
18%
1498
12%
561
61%
561
39%
868
June1st to 15thNight
71%
540
23%
1440
17%
540
74%
540
52%
763
June16th to endNight
77%
540
26%
1440
22%
540
80%
540
56%
734
July1st to 15thNight
72%
510
18%
1360
16%
510
73%
510
37%
816
July16th to endNight
77%
564
26%
1441
23%
531
78%
531
46%
781
August1st to 15thNight
73%
539
19%
1674
20%
536
75%
536
37%
911
August16th to endNight
75%
573
29%
1910
32%
573
77%
573
40%
966
September1st to 15thNight
72%
540
29%
1800
30%
540
75%
540
41%
928
September16th to endNight
73%
537
37%
1935
37%
537
79%
537
46%
893
October1st to 15thNight
62%
703
30%
2143
21%
703
67%
703
45%
1118
October16th to endNight
68%
802
37%
2338
25%
802
73%
802
50%
1184
November1st to 15thNight
65%
950
33%
2470
21%
950
70%
950
55%
1299
November16th to endNight
64%
975
36%
2594
24%
975
69%
975
56%
1347
December1st to 15thNight
56%
975
27%
2730
17%
975
63%
975
47%
1472
December16th to endNight
54%
1040
29%
2912
20%
1040
62%
1040
42%
1650

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
5%42332445%8%53%
49997
Night
5%423323347%58%
49707
Cloud CoverDay
5%42332446%8%53%
49995
Night
5%42332335%7%58%
49707
TransparencyDay
27%410%24%22%9%
49674
Night
25%411%26%24%8%
49532
SeeingDay
9%6%25%31%20%7%
6541
Night
7%222%48%17%1
16844

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 15thDay
26%24312247%61%
1552
16th to endDay
15%23212349%62%
1836
February1st to 15thDay
25%26%324447%55%
1759
16th to endDay
16%25%423447%58%
1710
March1st to 15thDay
4424433348%56%
1992
16th to endDay
6%6%233235%5%9%51%
2388
April1st to 15thDay
7%5%1332345%8%53%
2330
16th to endDay
12%6%2342346%7%46%
2215
May1st to 15thDay
10%7%245%2446%7%43%
2337
16th to endDay
9%4245%25%6%6%10%43%
2616
June1st to 15thDay
5%214425%6%6%9%50%
2520
16th to endDay
2112325%6%7%9%54%
2520
July1st to 15thDay
7%3135%35%5%7%11%44%
2520
16th to endDay
5%3244346%8%10%46%
2626
August1st to 15thDay
5%3145%37%7%8%9%43%
2276
16th to endDay
5%213435%6%6%8%51%
2292
September1st to 15thDay
7%21432346%6%57%
2160
16th to endDay
5%412223346%63%
2023
October1st to 15thDay
6%31232335%7%60%
1815
16th to endDay
5%412212336%65%
1872
November1st to 15thDay
142331336%8%61%
1718
16th to endDay
242321235%8%62%
1696
December1st to 15thDay
25%25%32335%9%56%
1560
16th to endDay
35%34324447%57%
1664
January1st to 15thNight
1434322346%64%
2716
16th to endNight
26%24313236%61%
2749
February1st to 15thNight
36%2441435%7%55%
2422
16th to endNight
28%35%324335%57%
2050
March1st to 15thNight
35%1332345%6%59%
2295
16th to endNight
7%6%23223347%57%
2187
April1st to 15thNight
8%6%13323446%54%
1948
16th to endNight
14%6%14313345%49%
1859
May1st to 15thNight
14%5%1332445%8%45%
1610
16th to endNight
8%32432345%8%53%
1497
June1st to 15thNight
5%222135%6%9%60%
1440
16th to endNight
2122135%7%8%62%
1440
July1st to 15thNight
5%3135%35%37%10%49%
1440
16th to endNight
5%213325%5%7%10%52%
1539
August1st to 15thNight
33144245%7%10%52%
1683
16th to endNight
421342446%9%55%
1910
September1st to 15thNight
7%313323348%56%
1800
16th to endNight
6%212312236%66%
1935
October1st to 15thNight
8%413222345%61%
2143
16th to endNight
5%423312336%63%
2338
November1st to 15thNight
3312313346%65%
2470
16th to endNight
2413213336%65%
2594
December1st to 15thNight
25%24422348%58%
2730
16th to endNight
27%34324447%54%
2912

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
26%23312247%61%
1552
16th to endDay
15%23213249%61%
1836
February1st to 15thDay
25%36%324438%54%
1759
16th to endDay
25%2442335%7%57%
1710
March1st to 15thDay
3424423348%56%
1992
16th to endDay
6%6%2332345%9%51%
2386
April1st to 15thDay
7%5%2332345%8%53%
2330
16th to endDay
12%6%2342446%7%46%
2215
May1st to 15thDay
10%6%24425%46%7%43%
2337
16th to endDay
8%424425%6%6%10%43%
2616
June1st to 15thDay
6%314425%5%7%9%50%
2520
16th to endDay
2113425%6%8%10%54%
2520
July1st to 15thDay
7%3145%35%5%7%11%45%
2520
16th to endDay
4314435%6%8%10%46%
2626
August1st to 15thDay
5%3245%36%7%8%10%43%
2276
16th to endDay
5%213435%6%7%8%51%
2292
September1st to 15thDay
7%21342345%7%57%
2160
16th to endDay
5%412223346%63%
2023
October1st to 15thDay
6%31232345%6%60%
1815
16th to endDay
5%412212336%65%
1872
November1st to 15thDay
141331425%9%61%
1718
16th to endDay
242221235%9%62%
1696
December1st to 15thDay
25%3432345%9%56%
1560
16th to endDay
35%35%31435%7%57%
1664
January1st to 15thNight
1334323346%63%
2716
16th to endNight
25%25%323236%61%
2749
February1st to 15thNight
36%25%41445%7%54%
2422
16th to endNight
28%34424335%57%
2050
March1st to 15thNight
35%1332345%6%59%
2295
16th to endNight
6%6%23323347%56%
2187
April1st to 15thNight
7%6%23323446%54%
1948
16th to endNight
14%6%24322345%49%
1859
May1st to 15thNight
14%5%1343445%8%45%
1610
16th to endNight
8%31432245%8%53%
1497
June1st to 15thNight
5%222135%6%8%60%
1440
16th to endNight
21122145%7%9%62%
1440
July1st to 15thNight
5%3145%35%47%10%48%
1440
16th to endNight
42124246%8%10%51%
1539
August1st to 15thNight
42144246%7%9%52%
1683
16th to endNight
421343436%9%55%
1910
September1st to 15thNight
7%22333335%8%56%
1800
16th to endNight
6%213313336%65%
1935
October1st to 15thNight
8%5%12313345%61%
2143
16th to endNight
5%422312236%63%
2338
November1st to 15thNight
3313313446%65%
2470
16th to endNight
2423223336%64%
2594
December1st to 15thNight
25%24422348%58%
2730
16th to endNight
37%3432445%7%54%
2912

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
23%111%31%25%6%
1553
16th to endDay
21%37%34%24%7%
1836
February1st to 15thDay
29%212%33%16%5%
1760
16th to endDay
25%27%27%28%7%
1710
March1st to 15thDay
25%29%26%26%9%
1992
16th to endDay
29%5%12%25%21%6%
2388
April1st to 15thDay
29%411%26%20%8%
2330
16th to endDay
35%5%11%22%18%5%
2215
May1st to 15thDay
40%5%11%23%15%4
2337
16th to endDay
34%7%12%23%13%6%
2620
June1st to 15thDay
27%6%13%20%19%12%
2520
16th to endDay
21%6%10%19%28%12%
2520
July1st to 15thDay
32%6%11%21%16%12%
2371
16th to endDay
29%8%12%24%16%7%
2461
August1st to 15thDay
32%7%13%19%15%10%
2261
16th to endDay
26%5%10%24%24%8%
2292
September1st to 15thDay
25%5%9%21%21%15%
2160
16th to endDay
21%46%20%36%10%
2023
October1st to 15thDay
23%311%20%29%12%
1815
16th to endDay
21%27%26%29%13%
1872
November1st to 15thDay
19%38%28%27%12%
1718
16th to endDay
20%17%24%34%11%
1696
December1st to 15thDay
24%311%31%22%6%
1560
16th to endDay
26%313%27%22%6%
1664
January1st to 15thNight
21%310%32%25%6%
2716
16th to endNight
25%27%28%27%8%
2749
February1st to 15thNight
28%411%32%19%4
2432
16th to endNight
27%27%26%26%10%
2050
March1st to 15thNight
23%38%26%29%8%
2295
16th to endNight
27%310%25%26%5%
2187
April1st to 15thNight
28%411%24%21%8%
1948
16th to endNight
36%410%23%18%6%
1859
May1st to 15thNight
36%6%14%21%15%5%
1611
16th to endNight
28%5%21%24%12%7%
1498
June1st to 15thNight
18%6%17%29%15%12%
1440
16th to endNight
16%5%11%24%29%12%
1440
July1st to 15thNight
28%8%15%21%16%9%
1360
16th to endNight
22%6%16%29%19%5%
1441
August1st to 15thNight
26%7%16%24%16%8%
1674
16th to endNight
24%5%11%25%25%7%
1910
September1st to 15thNight
26%412%22%21%13%
1800
16th to endNight
21%37%25%34%8%
1935
October1st to 15thNight
24%311%20%27%12%
2143
16th to endNight
22%27%24%29%12%
2338
November1st to 15thNight
19%38%26%28%13%
2470
16th to endNight
20%29%25%31%11%
2594
December1st to 15thNight
25%312%30%21%7%
2730
16th to endNight
28%414%27%22%3
2912

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
6%5%20%46%16%3
135
16th to endDay
6%226%46%16%1
144
February1st to 15thDay
38%41%39%7%
135
16th to endDay
4332%45%14%
120
March1st to 15thDay
5%9%32%38%12%1
177
16th to endDay
15%19%34%23%7%
352
April1st to 15thDay
13%17%35%22%8%2
329
16th to endDay
23%16%32%17%9%1
288
May1st to 15thDay
15%8%25%30%17%2
426
16th to endDay
16%7%21%27%19%7%
517
June1st to 15thDay
7%324%32%22%9%
495
16th to endDay
4424%29%27%9%
495
July1st to 15thDay
9%216%24%34%12%
475
16th to endDay
6%114%26%35%14%
485
August1st to 15thDay
11%323%31%20%10%
315
16th to endDay
8%221%34%21%10%
332
September1st to 15thDay
10%425%30%20%9%
315
16th to endDay
7%326%31%17%11%
178
October1st to 15thDay
8%5%18%33%20%14%
135
16th to endDay
8%322%33%24%7%
144
November1st to 15thDay
1216%44%25%8%
135
16th to endDay
7%5%28%43%12%1
135
December1st to 15thDay
6%438%40%9%
135
16th to endDay
4229%50%11%2
144
January1st to 15thNight
3228%53%10%2
975
16th to endNight
5%227%53%10%1
877
February1st to 15thNight
6%231%52%6%
764
16th to endNight
7%333%49%6%
684
March1st to 15thNight
5%230%49%11%
780
16th to endNight
10%329%48%8%
731
April1st to 15thNight
12%5%30%43%7%
584
16th to endNight
18%425%39%11%
558
May1st to 15thNight
17%219%45%14%1
540
16th to endNight
10%223%38%23%1
563
June1st to 15thNight
6%117%47%24%1
540
16th to endNight
4112%50%31%
540
July1st to 15thNight
6%19%38%40%3
510
16th to endNight
5%7%37%44%4
564
August1st to 15thNight
5%19%41%38%2
539
16th to endNight
6%10%42%36%2
573
September1st to 15thNight
8%110%43%29%6%
540
16th to endNight
5%115%45%29%3
537
October1st to 15thNight
11%119%46%17%3
703
16th to endNight
8%215%50%20%2
802
November1st to 15thNight
4221%52%15%2
950
16th to endNight
4124%53%14%1
975
December1st to 15thNight
5%228%53%9%
975
16th to endNight
6%227%51%10%1
1040
Page generated at 2018-04-24 08:03:05. Version ac04

Copyright 2018 A. Danko


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