Port Isabel Lighthouse State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Isabel Lighthouse State Historic Site clear sky chart from 2005-11-05 to 2018-10-08.

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
0%
5744
0%
30601
0%
4527
0%
4527
26%
31294

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
0%
532
0%
1639
0%
420
0%
420
18%
1837
January16th to endNight
0%
395
0%
1493
0%
307
0%
307
24%
1731
February1st to 15thNight
0%
387
0%
1332
0%
273
0%
273
22%
1460
February16th to endNight
0%
289
0%
1078
0%
207
0%
207
23%
1180
March1st to 15thNight
0%
295
0%
1268
0%
211
0%
211
19%
1284
March16th to endNight
0%
246
0%
1292
0%
206
0%
206
25%
1294
April1st to 15thNight
0%
278
0%
1274
0%
202
0%
202
20%
1249
April16th to endNight
0%
252
0%
1265
0%
203
0%
203
20%
1279
May1st to 15thNight
0%
219
0%
1216
0%
194
0%
194
22%
1168
May16th to endNight
0%
188
0%
1063
0%
144
0%
144
29%
1085
June1st to 15thNight
0%
101
0%
855
0%
58
0%
58
37%
931
June16th to endNight
0%
124
0%
1097
0%
112
0%
112
31%
1041
July1st to 15thNight
0%
91
0%
1187
0%
89
0%
89
30%
1019
July16th to endNight
0%
111
0%
1082
0%
75
0%
75
47%
867
August1st to 15thNight
0%
63
0%
1065
0%
59
0%
59
47%
871
August16th to endNight
0%
97
0%
1498
0%
94
0%
94
28%
1264
September1st to 15thNight
0%
106
0%
1458
0%
94
0%
94
22%
1337
September16th to endNight
0%
127
0%
1497
0%
125
0%
125
18%
1402
October1st to 15thNight
0%
81
0%
976
0%
71
0%
71
36%
1081
October16th to endNight
0%
188
0%
1003
0%
149
0%
149
36%
1319
November1st to 15thNight
0%
268
0%
1360
0%
232
0%
232
24%
1471
November16th to endNight
0%
305
0%
1235
0%
194
0%
194
28%
1432
December1st to 15thNight
0%
436
0%
1636
0%
378
0%
378
23%
1797
December16th to endNight
0%
565
0%
1732
0%
430
0%
430
20%
1895

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
TransparencyDay
33%7%19%23%12%3
51650
Night
36%6%16%22%12%5%
51172
SeeingDay
9%6%6%23%38%15%
6369
Night
12%14%7%24%30%9%
16450

By Month

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
55%47%13%12%6%
1747
16th to endDay
44%411%18%12%6%
2022
February1st to 15thDay
43%5%10%17%15%7%
1901
16th to endDay
35%5%16%21%15%5%
1778
March1st to 15thDay
37%418%19%14%5%
2145
16th to endDay
31%6%19%20%14%7%
2288
April1st to 15thDay
32%6%18%24%13%4
2136
16th to endDay
36%7%15%21%14%4
2198
May1st to 15thDay
30%8%22%21%12%4
2450
16th to endDay
23%8%21%28%18%1
2642
June1st to 15thDay
17%7%21%35%17%1
2535
16th to endDay
28%10%25%28%7%
2535
July1st to 15thDay
31%9%31%24%3
2396
16th to endDay
20%10%31%35%2
2519
August1st to 15thDay
16%9%34%35%3
2352
16th to endDay
31%11%29%22%3
2309
September1st to 15thDay
39%10%21%19%8%
2145
16th to endDay
42%11%19%13%10%2
2145
October1st to 15thDay
28%7%13%26%20%3
2031
16th to endDay
32%5%10%20%22%8%
1920
November1st to 15thDay
41%5%12%21%13%4
1908
16th to endDay
38%5%11%17%17%9%
1921
December1st to 15thDay
47%5%12%18%11%4
1755
16th to endDay
49%6%12%15%12%3
1872
January1st to 15thNight
50%5%9%15%12%7%
2522
16th to endNight
44%5%8%18%14%8%
2564
February1st to 15thNight
41%411%17%15%8%
2292
16th to endNight
37%412%21%17%6%
1980
March1st to 15thNight
40%413%20%14%5%
2145
16th to endNight
33%6%16%18%17%7%
2288
April1st to 15thNight
39%415%22%13%4
2142
16th to endNight
42%6%13%18%12%6%
2033
May1st to 15thNight
40%6%18%15%12%5%
1827
16th to endNight
30%8%18%24%16%1
1829
June1st to 15thNight
20%8%19%32%15%3
1755
16th to endNight
30%8%23%28%8%
1755
July1st to 15thNight
30%10%29%24%4
1665
16th to endNight
16%7%37%32%4
1738
August1st to 15thNight
14%9%33%38%3
1832
16th to endNight
29%9%27%27%5%
2242
September1st to 15thNight
37%10%20%23%6%2
2145
16th to endNight
42%10%17%18%9%2
2145
October1st to 15thNight
26%6%14%27%20%5%
2084
16th to endNight
28%6%8%23%23%10%
2304
November1st to 15thNight
39%6%13%20%14%5%
2280
16th to endNight
34%5%12%20%14%12%
2366
December1st to 15thNight
46%5%11%17%13%4
2535
16th to endNight
45%5%12%16%13%5%
2704

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%16%31%26%1
135
16th to endDay
18%6%19%34%19%
144
February1st to 15thDay
15%114%41%25%2
135
16th to endDay
13%20%50%15%
120
March1st to 15thDay
20%215%42%18%
135
16th to endDay
9%321%48%17%
144
April1st to 15thDay
14%213%46%22%
135
16th to endDay
16%6%19%35%19%3
210
May1st to 15thDay
7%11%12%43%23%
467
16th to endDay
5%10%10%40%30%1
597
June1st to 15thDay
211%21%54%10%
570
16th to endDay
6%10%115%45%20%
570
July1st to 15thDay
6%7%113%48%22%
550
16th to endDay
310%153%30%
595
August1st to 15thDay
6%447%40%
431
16th to endDay
411447%41%
221
September1st to 15thDay
15%8%38%36%
180
16th to endDay
11%18%46%32%
180
October1st to 15thDay
5%6%54%33%
157
16th to endDay
16%1424%40%11%
144
November1st to 15thDay
23%2425%39%5%
135
16th to endDay
15%213%27%28%12%
135
December1st to 15thDay
28%9%31%22%8%
135
16th to endDay
33%411%31%17%2
144
January1st to 15thNight
25%18%10%29%14%1
975
16th to endNight
15%16%11%37%16%1
900
February1st to 15thNight
18%16%15%30%18%
764
16th to endNight
15%18%13%37%14%
614
March1st to 15thNight
17%18%13%31%17%
585
16th to endNight
10%18%10%41%16%2
624
April1st to 15thNight
14%17%15%36%15%
584
16th to endNight
12%18%13%38%17%1
579
May1st to 15thNight
10%16%10%41%20%
585
16th to endNight
8%16%6%36%29%2
611
June1st to 15thNight
115%20%53%8%
585
16th to endNight
5%15%14%45%18%
585
July1st to 15thNight
410%11%49%22%
555
16th to endNight
215%351%26%
612
August1st to 15thNight
18%250%35%
575
16th to endNight
5%8%1440%39%
621
September1st to 15thNight
9%8%6%43%31%
585
16th to endNight
11%8%18%50%18%
582
October1st to 15thNight
28%216%50%19%
580
16th to endNight
7%9%6%25%41%7%
768
November1st to 15thNight
15%13%6%25%33%5%
760
16th to endNight
12%16%8%29%28%4
806
December1st to 15thNight
18%17%8%26%24%4
975
16th to endNight
22%18%13%25%16%2
1040
Page generated at 2018-10-09 09:39:16. Version ac04

Copyright 2018 A. Danko


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