Morgan Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morgan Hill clear sky chart from 2005-11-05 to 2018-03-21.

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
69%
16179
27%
49237
25%
16143
72%
16143
38%
27407

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
65%
776
21%
2586
22%
776
67%
776
32%
1473
January16th to endNight
61%
832
25%
2704
26%
832
64%
832
30%
1603
February1st to 15thNight
63%
757
28%
2460
28%
757
68%
757
32%
1412
February16th to endNight
57%
684
25%
2051
22%
684
63%
684
32%
1238
March1st to 15thNight
59%
780
19%
2191
17%
780
62%
780
30%
1411
March16th to endNight
55%
792
21%
2142
17%
792
59%
792
32%
1371
April1st to 15thNight
57%
719
24%
1799
14%
719
60%
719
36%
1133
April16th to endNight
60%
720
26%
1800
13%
720
64%
720
46%
1031
May1st to 15thNight
71%
653
24%
1733
16%
653
72%
653
43%
987
May16th to endNight
69%
385
25%
1507
26%
385
74%
385
33%
753
June1st to 15thNight
74%
360
25%
1440
28%
360
79%
360
35%
697
June16th to endNight
85%
360
32%
1440
42%
360
86%
360
44%
609
July1st to 15thNight
89%
374
27%
1394
33%
374
90%
374
43%
632
July16th to endNight
81%
564
29%
1593
27%
531
82%
531
38%
868
August1st to 15thNight
75%
583
27%
1656
21%
580
75%
580
37%
954
August16th to endNight
84%
764
33%
1910
22%
764
84%
764
50%
1098
September1st to 15thNight
85%
720
37%
1800
27%
720
86%
720
59%
958
September16th to endNight
81%
716
41%
1950
38%
716
83%
716
56%
987
October1st to 15thNight
75%
720
31%
2160
33%
720
79%
720
48%
1089
October16th to endNight
75%
768
36%
2304
39%
768
77%
768
45%
1199
November1st to 15thNight
71%
760
29%
2381
30%
760
75%
760
42%
1244
November16th to endNight
69%
780
27%
2594
28%
780
73%
780
36%
1387
December1st to 15thNight
62%
780
25%
2730
25%
780
66%
780
30%
1559
December16th to endNight
55%
832
22%
2912
22%
832
61%
832
26%
1714

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
7%313323346%59%
49605
Night
8%424424447%54%
49426
TransparencyDay
27%28%20%25%16%
49292
Night
30%38%19%22%15%
49238
SeeingDay
8%7%20%33%22%7%
6615
Night
10%39%32%34%10%
16192

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
13%424433446%47%
1679
16th to endDay
16%6%2442335%5%45%
1872
February1st to 15thDay
15%5%24423336%47%
1732
16th to endDay
17%5%36%5%34335%41%
1709
March1st to 15thDay
15%5%245%36%5%6%9%36%
2096
16th to endDay
12%5%36%5%34447%41%
2209
April1st to 15thDay
13%6%25%424347%44%
2149
16th to endDay
7%313313437%58%
2160
May1st to 15thDay
3413213346%64%
2214
16th to endDay
5%5%24423346%56%
2602
June1st to 15thDay
3423313447%61%
2520
16th to endDay
111212235%76%
2520
July1st to 15thDay
112213235%75%
2480
16th to endDay
111212236%75%
2468
August1st to 15thDay
213323226%71%
2295
16th to endDay
112212235%75%
2292
September1st to 15thDay
121112226%76%
2160
16th to endDay
222212245%71%
2005
October1st to 15thDay
5%21222335%6%65%
1800
16th to endDay
6%313323445%61%
1920
November1st to 15thDay
8%313424446%54%
1806
16th to endDay
11%42332345%7%51%
1693
December1st to 15thDay
14%5%25%5%24435%46%
1560
16th to endDay
15%5%35%42435%6%42%
1664
January1st to 15thNight
12%41342445%7%47%
2586
16th to endNight
15%5%23313346%48%
2704
February1st to 15thNight
13%42341445%7%48%
2449
16th to endNight
14%5%24323347%46%
2051
March1st to 15thNight
14%6%25%42445%7%42%
2191
16th to endNight
13%5%25%424348%45%
2142
April1st to 15thNight
12%42441445%6%47%
1799
16th to endNight
6%413313448%58%
1800
May1st to 15thNight
2324426%448%56%
1733
16th to endNight
343342445%8%55%
1507
June1st to 15thNight
232442435%8%58%
1440
16th to endNight
212423335%68%
1440
July1st to 15thNight
112225%45%7%63%
1477
16th to endNight
315%5%27%6%5%8%54%
1701
August1st to 15thNight
436%5%35%45%8%53%
1665
16th to endNight
114335%448%61%
1910
September1st to 15thNight
1213313346%68%
1800
16th to endNight
2313213146%69%
1950
October1st to 15thNight
5%412322336%63%
2160
16th to endNight
5%313423346%61%
2304
November1st to 15thNight
7%41331335%6%58%
2381
16th to endNight
8%414423447%53%
2594
December1st to 15thNight
14%5%23423347%49%
2730
16th to endNight
17%5%14323347%45%
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
37%411%20%16%9%
1679
16th to endDay
40%39%15%19%12%
1872
February1st to 15thDay
37%27%23%20%8%
1732
16th to endDay
44%29%23%16%3
1709
March1st to 15thDay
42%411%20%15%5%
2096
16th to endDay
41%315%19%16%3
2209
April1st to 15thDay
39%311%22%19%2
2149
16th to endDay
27%312%25%21%8%
2160
May1st to 15thDay
21%210%30%28%7%
2214
16th to endDay
29%211%27%22%6%
2606
June1st to 15thDay
24%310%23%24%13%
2520
16th to endDay
13%1417%36%25%
2520
July1st to 15thDay
14%228%25%46%
2334
16th to endDay
12%2310%31%38%
2313
August1st to 15thDay
19%1111%31%33%
2279
16th to endDay
14%2113%37%31%
2292
September1st to 15thDay
13%2115%34%32%
2160
16th to endDay
16%1226%33%18%
2005
October1st to 15thDay
19%27%22%24%23%
1800
16th to endDay
24%38%22%23%18%
1920
November1st to 15thDay
29%310%24%24%7%
1806
16th to endDay
32%210%21%28%4
1693
December1st to 15thDay
39%210%17%19%10%
1560
16th to endDay
41%212%17%19%6%
1664
January1st to 15thNight
35%212%23%17%8%
2586
16th to endNight
36%411%15%16%15%
2704
February1st to 15thNight
36%18%22%21%8%
2460
16th to endNight
37%212%27%15%4
2051
March1st to 15thNight
41%213%19%15%6%
2191
16th to endNight
39%312%21%16%6%
2142
April1st to 15thNight
35%313%25%18%3
1799
16th to endNight
24%412%28%20%9%
1800
May1st to 15thNight
28%39%21%26%10%
1734
16th to endNight
27%411%26%23%5%
1507
June1st to 15thNight
25%5%9%19%22%16%
1440
16th to endNight
21%2213%32%28%
1440
July1st to 15thNight
21%416%23%42%
1394
16th to endNight
29%339%20%33%
1593
August1st to 15thNight
32%319%23%29%
1656
16th to endNight
25%319%31%29%
1910
September1st to 15thNight
18%3210%31%34%
1800
16th to endNight
19%2219%36%19%
1950
October1st to 15thNight
23%16%22%21%24%
2160
16th to endNight
26%16%22%23%20%
2304
November1st to 15thNight
26%311%24%25%8%
2381
16th to endNight
29%310%22%24%9%
2594
December1st to 15thNight
36%28%19%19%12%
2730
16th to endNight
39%213%17%18%7%
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
20%8%17%32%16%5%
217
16th to endDay
16%7%20%27%21%7%
304
February1st to 15thDay
12%10%21%28%20%6%
287
16th to endDay
16%12%26%24%17%2
290
March1st to 15thDay
18%12%23%26%15%4
330
16th to endDay
15%12%32%26%11%1
311
April1st to 15thDay
17%15%31%23%10%2
269
16th to endDay
11%16%32%25%11%3
270
May1st to 15thDay
8%13%30%31%12%3
288
16th to endDay
8%10%22%32%20%5%
330
June1st to 15thDay
6%6%31%35%13%6%
315
16th to endDay
1217%41%26%10%
315
July1st to 15thDay
12%43%30%11%
305
16th to endDay
18%44%31%14%
327
August1st to 15thDay
413%39%31%10%
315
16th to endDay
110%40%31%15%
332
September1st to 15thDay
2114%40%28%12%
315
16th to endDay
4416%34%29%10%
315
October1st to 15thDay
5%7%25%33%22%6%
315
16th to endDay
8%418%31%27%8%
336
November1st to 15thDay
7%5%14%30%26%15%
222
16th to endDay
9%6%17%34%30%1
121
December1st to 15thDay
14%8%15%26%24%10%
90
16th to endDay
10%10%5%29%33%11%
96
January1st to 15thNight
14%110%35%30%8%
780
16th to endNight
17%27%32%28%10%
832
February1st to 15thNight
15%310%32%29%8%
764
16th to endNight
17%414%37%21%5%
684
March1st to 15thNight
15%5%11%32%29%6%
780
16th to endNight
15%6%13%36%24%4
792
April1st to 15thNight
13%7%14%37%23%3
719
16th to endNight
8%6%17%34%25%8%
720
May1st to 15thNight
4114%39%32%7%
654
16th to endNight
5%49%34%38%7%
386
June1st to 15thNight
3310%39%38%4
360
16th to endNight
21337%49%6%
360
July1st to 15thNight
2218%59%15%
374
16th to endNight
23317%51%21%
564
August1st to 15thNight
44424%49%13%
583
16th to endNight
215%23%52%14%
764
September1st to 15thNight
2427%48%15%
720
16th to endNight
416%29%43%13%
716
October1st to 15thNight
8%27%34%32%15%
720
16th to endNight
7%28%29%32%19%
768
November1st to 15thNight
9%29%36%31%11%
760
16th to endNight
9%28%37%30%11%
780
December1st to 15thNight
16%29%35%27%8%
780
16th to endNight
19%412%34%24%5%
832
Page generated at 2018-03-22 08:34:25. Version ac04

Copyright 2018 A. Danko


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