Freeport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Freeport clear sky chart from 2005-11-06 to 2025-03-12.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	7% 5% 2 7% 6% 6% 7% 6% 9% 12% 33%	109048
	Night	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	109956
Transparency	Day	36% 12% 22% 20% 9% 1	112695
	Night	35% 10% 21% 22% 10% 1	114449
Seeing	Day	7% 3 11% 26% 32% 21%	16797
	Night	8% 3 12% 28% 34% 17%	26997

By Month

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 5% 8% 12% 42%	4056
	11th to 20th	Day	13% 8% 3 9% 7% 6% 6% 5% 7% 9% 26%	4060
	21st to end	Day	7% 6% 3 8% 6% 6% 6% 5% 7% 10% 36%	4466
February	1st to 10th	Day	8% 6% 2 6% 5% 4 5% 4 8% 11% 41%	1940
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 5% 7% 12% 44%	2143
	21st to end	Day	5% 4 2 6% 5% 5% 5% 5% 8% 10% 44%	1815
March	1st to 10th	Day	6% 6% 2 8% 7% 6% 7% 7% 10% 11% 31%	3545
	11th to 20th	Day	4 3 1 4 4 4 5% 4 7% 13% 51%	3491
	21st to end	Day	9% 5% 2 4 3 4 4 3 7% 11% 47%	3815
April	1st to 10th	Day	4 4 2 5% 4 5% 5% 6% 8% 13% 43%	2121
	11th to 20th	Day	6% 5% 2 5% 5% 5% 6% 6% 9% 12% 38%	2254
	21st to end	Day	7% 4 2 4 5% 5% 5% 6% 9% 12% 41%	2280
May	1st to 10th	Day	3 3 1 3 3 3 4 4 7% 14% 55%	3765
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 6% 10% 14% 32%	3764
	21st to end	Day	5% 5% 2 5% 5% 4 5% 5% 7% 12% 45%	4159
June	1st to 10th	Day	13% 9% 4 10% 7% 7% 7% 6% 9% 11% 19%	2470
	11th to 20th	Day	9% 7% 3 7% 6% 7% 8% 7% 11% 12% 23%	2470
	21st to end	Day	7% 6% 3 8% 7% 7% 8% 7% 10% 13% 23%	2470
July	1st to 10th	Day	5% 6% 3 7% 6% 6% 7% 6% 10% 13% 32%	4120
	11th to 20th	Day	6% 7% 2 7% 6% 6% 8% 7% 11% 14% 27%	4120
	21st to end	Day	3 3 2 6% 6% 7% 8% 7% 13% 17% 30%	4435
August	1st to 10th	Day	4 5% 3 9% 9% 10% 9% 8% 11% 12% 19%	3786
	11th to 20th	Day	4 4 2 7% 5% 6% 8% 7% 11% 15% 30%	3730
	21st to end	Day	5% 4 3 9% 8% 9% 10% 7% 12% 16% 17%	4180
September	1st to 10th	Day	8% 6% 2 8% 7% 8% 9% 8% 11% 13% 20%	2227
	11th to 20th	Day	7% 5% 3 10% 7% 9% 8% 6% 11% 12% 22%	2090
	21st to end	Day	8% 8% 3 12% 7% 7% 9% 6% 9% 10% 22%	2071
October	1st to 10th	Day	10% 6% 3 9% 6% 6% 7% 7% 10% 11% 25%	1900
	11th to 20th	Day	9% 6% 3 7% 6% 8% 7% 6% 10% 12% 27%	1900
	21st to end	Day	10% 5% 2 7% 5% 6% 5% 5% 7% 11% 35%	2090
November	1st to 10th	Day	8% 6% 2 7% 5% 7% 7% 5% 8% 11% 35%	1957
	11th to 20th	Day	10% 7% 3 8% 6% 6% 6% 5% 8% 9% 31%	2000
	21st to end	Day	9% 5% 2 6% 5% 6% 6% 4 8% 10% 38%	2000
December	1st to 10th	Day	7% 4 2 5% 4 4 5% 5% 9% 11% 46%	3260
	11th to 20th	Day	8% 6% 3 7% 6% 5% 7% 5% 8% 12% 33%	3632
	21st to end	Day	11% 7% 3 8% 5% 7% 6% 5% 8% 11% 29%	4466
January	1st to 10th	Night	6% 5% 2 6% 4 6% 7% 6% 8% 13% 39%	5889
	11th to 20th	Night	14% 8% 3 8% 6% 5% 6% 4 6% 8% 31%	5900
	21st to end	Night	10% 7% 3 8% 6% 6% 6% 4 6% 8% 35%	6490
February	1st to 10th	Night	7% 5% 2 6% 6% 5% 5% 4 6% 8% 45%	2450
	11th to 20th	Night	7% 5% 2 5% 5% 4 5% 4 6% 8% 50%	2143
	21st to end	Night	6% 4 2 4 5% 3 5% 4 7% 9% 50%	1815
March	1st to 10th	Night	7% 5% 2 7% 5% 6% 6% 5% 8% 11% 37%	3528
	11th to 20th	Night	3 2 1 3 3 4 4 4 8% 9% 58%	3498
	21st to end	Night	5% 3 1 4 3 4 5% 5% 6% 10% 52%	3817
April	1st to 10th	Night	5% 3 1 4 3 3 4 4 6% 12% 55%	2057
	11th to 20th	Night	7% 3 2 4 3 4 5% 5% 9% 11% 47%	1875
	21st to end	Night	6% 5% 1 5% 4 4 4 5% 8% 10% 50%	1900
May	1st to 10th	Night	3 2 1 3 2 4 4 4 6% 10% 62%	3130
	11th to 20th	Night	6% 4 2 6% 5% 4 6% 5% 9% 13% 39%	3130
	21st to end	Night	5% 4 1 4 4 4 5% 4 7% 12% 50%	3408
June	1st to 10th	Night	11% 8% 3 9% 7% 5% 7% 6% 7% 11% 26%	1710
	11th to 20th	Night	8% 7% 3 8% 6% 6% 6% 6% 9% 11% 30%	1710
	21st to end	Night	5% 5% 2 6% 6% 5% 6% 6% 10% 13% 35%	1710
July	1st to 10th	Night	4 4 2 5% 4 5% 5% 5% 8% 13% 46%	2840
	11th to 20th	Night	5% 5% 2 5% 5% 5% 7% 5% 10% 15% 36%	2840
	21st to end	Night	2 2 1 4 4 5% 5% 5% 9% 14% 48%	3087
August	1st to 10th	Night	3 4 2 8% 6% 7% 8% 7% 10% 13% 32%	3139
	11th to 20th	Night	2 2 1 4 5% 4 6% 5% 8% 16% 47%	3097
	21st to end	Night	4 4 1 7% 7% 7% 9% 8% 13% 17% 23%	3476
September	1st to 10th	Night	7% 5% 2 7% 6% 6% 6% 6% 10% 13% 30%	1946
	11th to 20th	Night	4 5% 3 8% 8% 6% 7% 6% 10% 13% 31%	2090
	21st to end	Night	8% 7% 3 10% 7% 6% 7% 5% 9% 10% 27%	2107
October	1st to 10th	Night	9% 7% 3 9% 6% 5% 6% 6% 8% 10% 31%	2280
	11th to 20th	Night	9% 6% 3 7% 5% 6% 6% 5% 7% 10% 36%	2280
	21st to end	Night	10% 6% 3 7% 5% 5% 4 3 6% 9% 41%	2508
November	1st to 10th	Night	7% 5% 3 6% 5% 4 6% 4 7% 10% 42%	2341
	11th to 20th	Night	8% 6% 3 7% 7% 5% 6% 5% 7% 11% 34%	2400
	21st to end	Night	7% 5% 2 6% 5% 6% 7% 4 7% 11% 40%	2400
December	1st to 10th	Night	6% 4 2 5% 4 4 5% 4 6% 11% 49%	3920
	11th to 20th	Night	11% 6% 3 7% 5% 5% 6% 5% 7% 9% 37%	4555
	21st to end	Night	9% 7% 3 9% 6% 6% 6% 5% 8% 11% 30%	6490

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	31% 7% 12% 29% 20% 1	4057
	11th to 20th	Day	51% 9% 15% 19% 6%	4060
	21st to end	Day	39% 8% 12% 26% 14% 1	4466
February	1st to 10th	Day	32% 7% 15% 28% 15% 1	1940
	11th to 20th	Day	29% 8% 16% 28% 18% 2	2153
	21st to end	Day	28% 9% 17% 22% 22% 3	1815
March	1st to 10th	Day	35% 16% 19% 18% 10% 1	3545
	11th to 20th	Day	20% 10% 26% 33% 9% 2	3491
	21st to end	Day	26% 8% 18% 31% 14% 4	3815
April	1st to 10th	Day	23% 11% 24% 28% 13% 2	2121
	11th to 20th	Day	29% 13% 23% 21% 13% 1	2254
	21st to end	Day	26% 10% 18% 24% 19% 3	2280
May	1st to 10th	Day	13% 9% 25% 36% 14% 2	3800
	11th to 20th	Day	30% 17% 33% 16% 4	3768
	21st to end	Day	24% 12% 21% 30% 12%	4172
June	1st to 10th	Day	51% 16% 21% 11% 2	2470
	11th to 20th	Day	42% 19% 23% 14% 1	2470
	21st to end	Day	40% 23% 28% 9% 1	2470
July	1st to 10th	Day	38% 12% 35% 15% 1	4055
	11th to 20th	Day	39% 14% 35% 12%	4051
	21st to end	Day	31% 16% 39% 14% 1	4294
August	1st to 10th	Day	48% 16% 25% 10% 1	3774
	11th to 20th	Day	35% 14% 31% 20%	3766
	21st to end	Day	46% 17% 30% 6% 1	4180
September	1st to 10th	Day	42% 23% 23% 11% 1	2227
	11th to 20th	Day	43% 20% 23% 11% 2	2090
	21st to end	Day	49% 17% 16% 12% 5% 1	2071
October	1st to 10th	Day	44% 11% 22% 17% 6%	3160
	11th to 20th	Day	46% 9% 17% 16% 11%	3140
	21st to end	Day	37% 6% 11% 24% 19% 2	3428
November	1st to 10th	Day	36% 11% 17% 17% 16% 3	1957
	11th to 20th	Day	44% 10% 12% 18% 13% 3	2000
	21st to end	Day	36% 10% 17% 20% 16% 2	2000
December	1st to 10th	Day	30% 6% 21% 24% 19%	3260
	11th to 20th	Day	41% 7% 13% 21% 15% 3	3629
	21st to end	Day	44% 8% 18% 19% 10% 1	4466
January	1st to 10th	Night	34% 8% 13% 28% 16%	5889
	11th to 20th	Night	50% 8% 18% 16% 8%	5900
	21st to end	Night	42% 9% 12% 27% 8% 1	6490
February	1st to 10th	Night	35% 8% 14% 25% 17% 2	2450
	11th to 20th	Night	29% 8% 14% 26% 19% 4	2144
	21st to end	Night	27% 8% 15% 24% 22% 4	1815
March	1st to 10th	Night	37% 13% 17% 20% 12% 2	3528
	11th to 20th	Night	18% 10% 25% 35% 10% 2	3498
	21st to end	Night	22% 9% 18% 28% 20% 2	3817
April	1st to 10th	Night	20% 9% 23% 31% 14% 3	2057
	11th to 20th	Night	27% 11% 23% 20% 18% 1	1875
	21st to end	Night	28% 9% 16% 25% 19% 4	1900
May	1st to 10th	Night	14% 9% 21% 38% 16% 3	3160
	11th to 20th	Night	29% 15% 28% 22% 5%	3131
	21st to end	Night	25% 11% 24% 30% 10%	3416
June	1st to 10th	Night	49% 15% 21% 12% 3	1710
	11th to 20th	Night	42% 17% 22% 16% 2	1710
	21st to end	Night	35% 16% 35% 13% 1	1710
July	1st to 10th	Night	30% 12% 38% 19% 3	2795
	11th to 20th	Night	34% 11% 41% 14%	2786
	21st to end	Night	23% 14% 47% 16% 1	2988
August	1st to 10th	Night	39% 15% 31% 13% 1	3127
	11th to 20th	Night	23% 14% 35% 27% 1	3127
	21st to end	Night	41% 18% 34% 7% 1	3476
September	1st to 10th	Night	40% 19% 25% 15% 1	1946
	11th to 20th	Night	38% 20% 26% 13% 3	2090
	21st to end	Night	48% 15% 16% 14% 7%	2107
October	1st to 10th	Night	45% 11% 24% 16% 4	3800
	11th to 20th	Night	48% 6% 16% 17% 13%	3779
	21st to end	Night	36% 4 10% 30% 16% 3	4120
November	1st to 10th	Night	35% 10% 15% 19% 16% 4	2341
	11th to 20th	Night	42% 10% 15% 21% 11% 3	2400
	21st to end	Night	36% 10% 17% 19% 15% 2	2400
December	1st to 10th	Night	30% 7% 17% 30% 16%	3920
	11th to 20th	Night	42% 5% 15% 20% 15% 3	4557
	21st to end	Night	45% 9% 19% 19% 8% 1	6490

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 7% 23% 37% 24% 2	300
	11th to 20th	Day	13% 6% 25% 30% 23% 3	300
	21st to end	Day	9% 8% 31% 37% 14% 2	330
February	1st to 10th	Day	7% 7% 15% 39% 27% 5%	400
	11th to 20th	Day	6% 5% 20% 35% 29% 5%	496
	21st to end	Day	5% 3 19% 38% 29% 6%	414
March	1st to 10th	Day	3 5% 25% 44% 21% 3	500
	11th to 20th	Day	6% 4 17% 41% 30% 2	464
	21st to end	Day	5% 2 16% 38% 34% 5%	506
April	1st to 10th	Day	4 3 18% 44% 28% 2	460
	11th to 20th	Day	6% 2 14% 41% 33% 4	452
	21st to end	Day	4 2 11% 40% 38% 5%	460
May	1st to 10th	Day	5% 1 8% 31% 44% 11%	463
	11th to 20th	Day	9% 2 9% 31% 37% 12%	487
	21st to end	Day	9% 2 5% 15% 44% 25%	529
June	1st to 10th	Day	13% 2 6% 18% 40% 21%	490
	11th to 20th	Day	8% 2 5% 14% 34% 37%	490
	21st to end	Day	5% 3 10% 30% 51%	490
July	1st to 10th	Day	4 2 9% 26% 58%	485
	11th to 20th	Day	5% 1 9% 31% 54%	484
	21st to end	Day	3 1 10% 36% 50%	532
August	1st to 10th	Day	7% 1 4 12% 36% 40%	486
	11th to 20th	Day	3 1 8% 34% 54%	479
	21st to end	Day	7% 1 3 12% 34% 42%	539
September	1st to 10th	Day	9% 1 2 12% 29% 49%	490
	11th to 20th	Day	6% 3 12% 33% 47%	490
	21st to end	Day	8% 1 7% 17% 29% 38%	490
October	1st to 10th	Day	9% 2 7% 21% 43% 18%	490
	11th to 20th	Day	10% 2 8% 27% 38% 15%	490
	21st to end	Day	8% 4 14% 26% 36% 12%	539
November	1st to 10th	Day	8% 2 15% 32% 31% 12%	495
	11th to 20th	Day	8% 5% 15% 35% 29% 8%	500
	21st to end	Day	5% 4 19% 36% 31% 6%	500
December	1st to 10th	Day	8% 3 17% 32% 35% 5%	500
	11th to 20th	Day	9% 5% 17% 32% 32% 6%	447
	21st to end	Day	11% 6% 14% 34% 28% 7%	330
January	1st to 10th	Night	8% 4 20% 35% 29% 4	800
	11th to 20th	Night	10% 7% 19% 40% 22% 2	800
	21st to end	Night	11% 8% 20% 41% 19% 1	880
February	1st to 10th	Night	7% 5% 18% 38% 29% 3	800
	11th to 20th	Night	7% 5% 22% 36% 28% 3	783
	21st to end	Night	7% 3 17% 43% 29% 1	660
March	1st to 10th	Night	4 4 23% 42% 25% 2	800
	11th to 20th	Night	5% 4 15% 41% 32% 3	767
	21st to end	Night	5% 2 17% 41% 30% 4	836
April	1st to 10th	Night	5% 2 12% 44% 34% 3	760
	11th to 20th	Night	6% 4 14% 39% 34% 2	751
	21st to end	Night	8% 2 12% 40% 36% 2	760
May	1st to 10th	Night	5% 1 9% 33% 45% 7%	760
	11th to 20th	Night	10% 1 9% 38% 34% 9%	749
	21st to end	Night	9% 1 6% 19% 48% 17%	816
June	1st to 10th	Night	12% 1 5% 22% 40% 19%	570
	11th to 20th	Night	8% 2 5% 12% 36% 36%	570
	21st to end	Night	5% 4 9% 37% 45%	570
July	1st to 10th	Night	7% 3 8% 33% 49%	555
	11th to 20th	Night	5% 2 7% 40% 46%	552
	21st to end	Night	4 2 6% 35% 53%	624
August	1st to 10th	Night	6% 3 11% 39% 40%	752
	11th to 20th	Night	3 1 6% 37% 53%	750
	21st to end	Night	8% 1 3 12% 35% 42%	836
September	1st to 10th	Night	8% 1 4 10% 32% 46%	760
	11th to 20th	Night	6% 1 3 12% 32% 47%	760
	21st to end	Night	10% 1 5% 15% 36% 33%	760
October	1st to 10th	Night	10% 2 7% 19% 44% 18%	760
	11th to 20th	Night	12% 2 8% 26% 37% 15%	760
	21st to end	Night	12% 2 13% 28% 36% 9%	836
November	1st to 10th	Night	8% 4 15% 30% 34% 8%	780
	11th to 20th	Night	10% 4 15% 33% 34% 5%	800
	21st to end	Night	6% 4 20% 34% 33% 3	800
December	1st to 10th	Night	8% 3 14% 33% 37% 4	800
	11th to 20th	Night	11% 5% 17% 32% 30% 6%	800
	21st to end	Night	9% 5% 15% 35% 30% 6%	880

Page generated at 2025-03-09 08:08:45. Version ac07

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