Hanford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hanford clear sky chart from 2005-11-05 to 2018-01-20.

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
73%
16001
32%
48472
29%
15966
77%
15966
51%
23605

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
66%
776
20%
2670
23%
776
68%
776
29%
1551
January16th to endNight
66%
788
25%
2561
28%
788
68%
788
32%
1499
February1st to 15thNight
68%
700
27%
2157
29%
700
70%
700
36%
1209
February16th to endNight
63%
632
26%
1895
26%
632
67%
632
37%
1083
March1st to 15thNight
70%
720
23%
2121
23%
720
73%
720
43%
1137
March16th to endNight
65%
768
26%
2013
20%
768
69%
768
48%
1126
April1st to 15thNight
55%
719
29%
1799
15%
719
62%
719
48%
1024
April16th to endNight
62%
720
33%
1800
14%
720
69%
720
62%
904
May1st to 15thNight
68%
642
31%
1722
18%
642
72%
642
66%
796
May16th to endNight
61%
447
34%
1571
25%
447
72%
447
56%
632
June1st to 15thNight
61%
360
36%
1440
30%
360
77%
360
60%
496
June16th to endNight
81%
360
42%
1440
46%
360
88%
360
84%
403
July1st to 15thNight
88%
340
37%
1360
43%
340
93%
340
77%
404
July16th to endNight
90%
499
42%
1529
39%
467
92%
467
71%
582
August1st to 15thNight
88%
690
39%
1764
25%
687
90%
687
83%
768
August16th to endNight
94%
764
46%
1910
30%
764
94%
764
87%
823
September1st to 15thNight
91%
720
44%
1800
33%
720
93%
720
82%
806
September16th to endNight
85%
716
49%
1953
42%
716
89%
716
80%
812
October1st to 15thNight
78%
720
33%
2106
33%
720
83%
720
58%
973
October16th to endNight
81%
768
42%
2304
45%
768
84%
768
61%
1034
November1st to 15thNight
80%
760
32%
2464
36%
760
82%
760
51%
1149
November16th to endNight
73%
780
29%
2535
30%
780
76%
780
43%
1272
December1st to 15thNight
71%
780
25%
2646
27%
780
73%
780
33%
1469
December16th to endNight
65%
832
24%
2912
26%
832
68%
832
30%
1653

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%312212235%68%
49059
Night
6%212212235%67%
48655
TransparencyDay
19%38%19%26%21%
48740
Night
19%39%21%26%19%
48473
SeeingDay
6%211%24%33%20%
6283
Night
7%112%37%35%5%
16012

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
10%8%46%5%45%45%7%37%
1594
16th to endDay
15%9%46%424347%37%
1766
February1st to 15thDay
14%6%24324337%46%
1703
16th to endDay
12%424424346%48%
1579
March1st to 15thDay
7%3143345%6%8%51%
1836
16th to endDay
8%314314436%56%
2211
April1st to 15thDay
8%313222335%61%
2149
16th to endDay
5%112213245%67%
2160
May1st to 15thDay
1112212235%76%
2226
16th to endDay
211212235%75%
2540
June1st to 15thDay
21111222479%
2520
16th to endDay
1111289%
2520
July1st to 15thDay
1111112385%
2520
16th to endDay
1111112381%
2531
August1st to 15thDay
111289%
2187
16th to endDay
111111288%
2292
September1st to 15thDay
1111386%
2160
16th to endDay
111122384%
2007
October1st to 15thDay
3211111236%72%
1853
16th to endDay
222312335%72%
1920
November1st to 15thDay
7%323314346%59%
1725
16th to endDay
8%5%24423345%53%
1755
December1st to 15thDay
9%7%35%42445%7%45%
1641
16th to endDay
12%7%36%42345%7%42%
1664
January1st to 15thNight
11%7%24322347%48%
2670
16th to endNight
12%6%24423347%49%
2561
February1st to 15thNight
9%5%23323346%55%
2146
16th to endNight
13%413223346%54%
1895
March1st to 15thNight
7%213423347%58%
2121
16th to endNight
7%313322347%59%
2013
April1st to 15thNight
7%313323346%61%
1799
16th to endNight
3112212325%73%
1800
May1st to 15thNight
211112227%75%
1722
16th to endNight
31122123376%
1570
June1st to 15thNight
21111123479%
1440
16th to endNight
292%
1440
July1st to 15thNight
111112385%
1440
16th to endNight
11111123381%
1635
August1st to 15thNight
11111188%
1773
16th to endNight
112288%
1910
September1st to 15thNight
111111386%
1800
16th to endNight
111112385%
1953
October1st to 15thNight
3112212326%72%
2106
16th to endNight
32221223474%
2304
November1st to 15thNight
5%212212345%67%
2464
16th to endNight
6%323322346%60%
2535
December1st to 15thNight
8%5%2421345%7%52%
2646
16th to endNight
13%424314346%51%
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
43%8%12%17%15%2
1594
16th to endDay
46%6%12%15%14%5%
1766
February1st to 15thDay
38%5%13%22%16%2
1703
16th to endDay
35%7%11%31%12%1
1579
March1st to 15thDay
28%7%17%24%17%3
1836
16th to endDay
28%5%14%26%20%4
2211
April1st to 15thDay
25%410%30%21%6%
2149
16th to endDay
18%412%27%28%9%
2160
May1st to 15thDay
11%28%25%37%13%
2226
16th to endDay
12%27%28%35%12%
2543
June1st to 15thDay
9%26%18%31%30%
2520
16th to endDay
5%17%32%52%
2520
July1st to 15thDay
6%126%23%59%
2371
16th to endDay
10%229%23%52%
2374
August1st to 15thDay
5%19%30%51%
2171
16th to endDay
5%27%38%45%
2292
September1st to 15thDay
7%1312%32%43%
2160
16th to endDay
7%1219%45%24%
2007
October1st to 15thDay
14%26%25%28%22%
1853
16th to endDay
15%48%26%27%17%
1920
November1st to 15thDay
25%5%12%28%25%2
1725
16th to endDay
31%6%12%26%19%4
1755
December1st to 15thDay
37%7%10%20%19%4
1641
16th to endDay
40%7%13%22%14%1
1664
January1st to 15thNight
34%6%11%25%17%3
2670
16th to endNight
34%5%13%18%19%8%
2561
February1st to 15thNight
30%412%27%20%4
2157
16th to endNight
31%412%29%18%3
1895
March1st to 15thNight
24%5%15%26%22%5%
2121
16th to endNight
24%316%28%22%5%
2013
April1st to 15thNight
24%311%31%21%7%
1799
16th to endNight
14%313%27%32%9%
1800
May1st to 15thNight
11%27%25%34%18%
1723
16th to endNight
14%27%22%38%15%
1571
June1st to 15thNight
10%25%19%30%31%
1440
16th to endNight
316%28%60%
1440
July1st to 15thNight
4126%21%61%
1360
16th to endNight
9%138%21%55%
1529
August1st to 15thNight
6%18%27%55%
1764
16th to endNight
418%34%49%
1910
September1st to 15thNight
7%1310%30%47%
1800
16th to endNight
6%1218%42%29%
1953
October1st to 15thNight
14%36%22%26%25%
2106
16th to endNight
14%26%25%32%18%
2304
November1st to 15thNight
18%412%29%29%5%
2464
16th to endNight
24%312%25%27%5%
2535
December1st to 15thNight
30%6%12%23%19%8%
2646
16th to endNight
34%414%23%18%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
19%12%28%22%15%
132
16th to endDay
17%211%23%27%17%
269
February1st to 15thDay
18%113%22%24%20%
258
16th to endDay
13%417%27%24%12%
238
March1st to 15thDay
10%417%24%27%16%
270
16th to endDay
11%420%26%25%11%
288
April1st to 15thDay
14%7%23%21%21%12%
269
16th to endDay
410%26%24%23%10%
270
May1st to 15thDay
3414%29%29%19%
288
16th to endDay
25%14%26%31%19%
330
June1st to 15thDay
2213%27%37%17%
315
16th to endDay
6%20%38%32%
315
July1st to 15thDay
2319%43%31%
305
16th to endDay
2214%45%34%
327
August1st to 15thDay
1425%47%20%
315
16th to endDay
1421%42%30%
332
September1st to 15thDay
425%47%21%
315
16th to endDay
111%26%40%18%
315
October1st to 15thDay
1117%33%29%16%
315
16th to endDay
339%26%32%24%
336
November1st to 15thDay
5%9%18%31%34%
141
16th to endDay
8%211%27%34%15%
135
December1st to 15thDay
10%39%24%37%14%
109
16th to endDay
14%111%20%30%21%
96
January1st to 15thNight
16%6%34%33%7%
780
16th to endNight
15%19%34%31%7%
788
February1st to 15thNight
12%110%33%33%7%
704
16th to endNight
15%113%38%25%5%
632
March1st to 15thNight
7%212%39%32%4
720
16th to endNight
8%219%38%29%1
768
April1st to 15thNight
7%427%36%21%1
719
16th to endNight
4425%35%27%2
720
May1st to 15thNight
2223%40%27%2
643
16th to endNight
5%425%38%24%
449
June1st to 15thNight
35%28%45%18%
360
16th to endNight
1116%55%24%1
360
July1st to 15thNight
8%47%41%
340
16th to endNight
1331%57%5%
499
August1st to 15thNight
26%36%49%5%
690
16th to endNight
328%62%5%
764
September1st to 15thNight
5%33%53%6%
720
16th to endNight
119%36%43%7%
716
October1st to 15thNight
4111%38%38%5%
720
16th to endNight
418%30%40%14%
768
November1st to 15thNight
6%7%36%38%10%
760
16th to endNight
8%9%35%36%9%
780
December1st to 15thNight
11%17%41%32%6%
780
16th to endNight
13%210%41%27%4
832
Page generated at 2018-01-21 09:19:30. Version ac04

Copyright 2018 A. Danko


Hanford Clear Sky Chart |Charts Home