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 2026-07-16.

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	6% 5% 2 7% 5% 6% 6% 6% 9% 12% 36%	136903
	Night	6% 5% 2 6% 5% 5% 6% 5% 8% 11% 42%	135773
Transparency	Day	35% 10% 23% 21% 9% 1	140506
	Night	34% 9% 22% 23% 10% 2	140243
Seeing	Day	7% 3 12% 27% 32% 20%	18711
	Night	8% 3 12% 28% 34% 16%	28851

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	6% 4 2 5% 4 4 5% 5% 8% 12% 47%	5258
	11th to 20th	Day	12% 8% 3 9% 7% 6% 7% 6% 8% 10% 25%	5280
	21st to end	Day	7% 5% 3 8% 6% 6% 6% 5% 7% 11% 37%	5780
February	1st to 10th	Day	8% 6% 2 6% 5% 4 5% 4 7% 11% 42%	2037
	11th to 20th	Day	7% 4 2 5% 5% 4 5% 4 7% 12% 45%	2253
	21st to end	Day	5% 4 2 5% 5% 5% 5% 5% 8% 11% 45%	1903
March	1st to 10th	Day	4 5% 2 7% 6% 5% 6% 6% 9% 10% 41%	5045
	11th to 20th	Day	4 3 1 3 3 3 4 4 6% 11% 57%	5090
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 8% 10% 45%	5586
April	1st to 10th	Day	5% 4 2 4 4 4 5% 6% 8% 14% 43%	2345
	11th to 20th	Day	5% 5% 2 5% 5% 5% 6% 6% 9% 12% 40%	2494
	21st to end	Day	6% 3 2 4 5% 5% 5% 6% 8% 12% 44%	2520
May	1st to 10th	Day	5% 3 1 4 3 3 4 4 7% 13% 52%	7021
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 6% 9% 12% 38%	7030
	21st to end	Day	3 3 1 5% 4 5% 6% 5% 9% 15% 43%	7794
June	1st to 10th	Day	12% 9% 4 10% 7% 7% 7% 5% 8% 11% 20%	2730
	11th to 20th	Day	8% 6% 3 7% 6% 6% 8% 7% 11% 13% 26%	2730
	21st to end	Day	7% 6% 2 8% 7% 6% 8% 8% 11% 13% 25%	2730
July	1st to 10th	Day	4 6% 3 9% 7% 7% 8% 6% 10% 13% 27%	6030
	11th to 20th	Day	5% 7% 3 7% 6% 6% 8% 6% 10% 14% 29%	5965
	21st to end	Day	2 3 1 5% 5% 6% 7% 6% 12% 16% 35%	6379
August	1st to 10th	Day	4 5% 3 9% 9% 10% 9% 8% 11% 12% 20%	3906
	11th to 20th	Day	4 4 2 7% 5% 6% 8% 7% 11% 15% 31%	3850
	21st to end	Day	5% 4 3 9% 8% 9% 10% 7% 12% 16% 17%	4312
September	1st to 10th	Day	8% 6% 2 8% 7% 8% 9% 8% 12% 13% 20%	2344
	11th to 20th	Day	8% 6% 3 10% 7% 8% 8% 6% 11% 12% 22%	2200
	21st to end	Day	9% 8% 3 12% 8% 7% 9% 6% 9% 10% 21%	2180
October	1st to 10th	Day	10% 6% 3 9% 6% 6% 7% 7% 10% 12% 24%	2000
	11th to 20th	Day	8% 6% 3 7% 6% 7% 7% 6% 10% 12% 28%	2000
	21st to end	Day	10% 5% 2 7% 5% 6% 5% 5% 7% 12% 36%	2200
November	1st to 10th	Day	7% 6% 2 7% 5% 7% 7% 5% 8% 11% 34%	2057
	11th to 20th	Day	9% 6% 3 8% 6% 6% 6% 5% 8% 8% 32%	2100
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 4 8% 11% 38%	2100
December	1st to 10th	Day	7% 4 2 5% 4 4 5% 4 9% 12% 46%	3360
	11th to 20th	Day	8% 6% 3 7% 6% 5% 7% 5% 8% 12% 33%	3729
	21st to end	Day	10% 6% 3 8% 5% 7% 6% 5% 8% 11% 30%	4565
January	1st to 10th	Night	5% 4 2 5% 4 5% 6% 5% 7% 11% 47%	7635
	11th to 20th	Night	13% 8% 3 8% 6% 6% 6% 5% 7% 9% 29%	7680
	21st to end	Night	9% 6% 3 7% 6% 6% 6% 4 6% 8% 38%	8401
February	1st to 10th	Night	7% 5% 2 6% 6% 5% 5% 4 6% 8% 46%	2573
	11th to 20th	Night	6% 4 2 5% 5% 4 5% 4 6% 8% 50%	2253
	21st to end	Night	5% 4 2 4 5% 3 5% 4 7% 9% 52%	1903
March	1st to 10th	Night	5% 4 2 6% 4 5% 5% 5% 7% 10% 47%	5028
	11th to 20th	Night	3 2 1 3 3 3 4 4 7% 8% 61%	5090
	21st to end	Night	5% 3 1 6% 4 5% 5% 5% 7% 10% 49%	5588
April	1st to 10th	Night	5% 3 1 4 3 3 4 4 6% 11% 55%	2273
	11th to 20th	Night	6% 3 2 4 3 4 5% 5% 8% 10% 50%	2075
	21st to end	Night	6% 5% 1 5% 4 4 4 4 7% 10% 51%	2100
May	1st to 10th	Night	4 3 1 3 2 4 4 4 7% 11% 57%	5833
	11th to 20th	Night	5% 4 2 7% 5% 4 6% 5% 8% 11% 42%	5830
	21st to end	Night	3 3 1 4 4 5% 6% 5% 8% 16% 45%	6384
June	1st to 10th	Night	11% 8% 3 9% 7% 5% 7% 6% 7% 11% 26%	1890
	11th to 20th	Night	7% 6% 2 7% 5% 6% 6% 6% 9% 12% 34%	1890
	21st to end	Night	4 5% 2 6% 6% 5% 6% 6% 10% 13% 36%	1890
July	1st to 10th	Night	3 5% 3 8% 5% 5% 5% 5% 8% 13% 41%	4148
	11th to 20th	Night	5% 5% 2 6% 5% 5% 6% 5% 8% 13% 40%	4102
	21st to end	Night	1 2 1 3 4 5% 5% 5% 8% 13% 53%	4427
August	1st to 10th	Night	3 4 2 8% 6% 7% 8% 7% 10% 13% 33%	3239
	11th to 20th	Night	2 2 1 4 4 4 6% 5% 8% 16% 48%	3197
	21st to end	Night	4 4 1 7% 7% 7% 9% 8% 13% 17% 23%	3586
September	1st to 10th	Night	7% 5% 2 8% 6% 7% 7% 6% 10% 13% 29%	2049
	11th to 20th	Night	4 5% 3 8% 7% 6% 7% 7% 10% 13% 30%	2200
	21st to end	Night	8% 7% 3 10% 7% 6% 7% 5% 9% 10% 27%	2218
October	1st to 10th	Night	8% 7% 3 9% 6% 5% 6% 6% 9% 10% 31%	2400
	11th to 20th	Night	9% 6% 3 7% 6% 6% 6% 5% 7% 10% 36%	2400
	21st to end	Night	9% 6% 3 7% 5% 5% 4 4 6% 9% 42%	2640
November	1st to 10th	Night	7% 6% 3 6% 5% 4 6% 4 7% 10% 42%	2461
	11th to 20th	Night	8% 6% 3 7% 7% 5% 6% 5% 7% 11% 36%	2520
	21st to end	Night	7% 5% 2 6% 5% 5% 7% 4 8% 10% 41%	2520
December	1st to 10th	Night	6% 4 2 5% 4 4 5% 4 6% 11% 48%	4040
	11th to 20th	Night	11% 6% 3 7% 5% 4 6% 5% 7% 9% 37%	4677
	21st to end	Night	8% 7% 3 9% 6% 6% 6% 5% 8% 11% 32%	6633

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	28% 5% 11% 36% 19%	5259
	11th to 20th	Day	51% 8% 16% 18% 6% 2	5280
	21st to end	Day	39% 7% 12% 27% 15% 1	5780
February	1st to 10th	Day	32% 7% 15% 28% 16% 3	2037
	11th to 20th	Day	28% 8% 15% 29% 17% 2	2263
	21st to end	Day	27% 8% 17% 22% 23% 2	1903
March	1st to 10th	Day	31% 11% 15% 24% 17% 1	5045
	11th to 20th	Day	19% 7% 18% 29% 19% 8%	5090
	21st to end	Day	30% 6% 16% 31% 15% 2	5586
April	1st to 10th	Day	24% 10% 23% 28% 15% 2	2345
	11th to 20th	Day	28% 11% 22% 20% 16% 3	2494
	21st to end	Day	25% 9% 17% 26% 20% 2	2520
May	1st to 10th	Day	21% 5% 26% 35% 11% 1	7053
	11th to 20th	Day	32% 10% 30% 23% 5%	7034
	21st to end	Day	25% 8% 34% 24% 9%	7808
June	1st to 10th	Day	51% 15% 21% 12% 2	2730
	11th to 20th	Day	40% 17% 25% 15% 2	2730
	21st to end	Day	39% 21% 29% 10% 1	2730
July	1st to 10th	Day	44% 11% 34% 10%	5965
	11th to 20th	Day	40% 11% 35% 14%	5896
	21st to end	Day	30% 12% 38% 20% 1	6196
August	1st to 10th	Day	48% 15% 25% 11% 1	3894
	11th to 20th	Day	34% 13% 31% 21%	3886
	21st to end	Day	46% 16% 30% 7% 1	4312
September	1st to 10th	Day	43% 23% 23% 11% 1	2344
	11th to 20th	Day	44% 19% 23% 12% 2	2200
	21st to end	Day	49% 17% 16% 12% 5% 1	2180
October	1st to 10th	Day	44% 11% 22% 17% 5%	3260
	11th to 20th	Day	46% 9% 17% 17% 12%	3240
	21st to end	Day	37% 5% 11% 25% 20% 3	3538
November	1st to 10th	Day	37% 11% 16% 17% 15% 4	2057
	11th to 20th	Day	43% 9% 12% 19% 15% 3	2100
	21st to end	Day	35% 10% 16% 21% 15% 2	2100
December	1st to 10th	Day	29% 6% 21% 24% 19%	3360
	11th to 20th	Day	41% 7% 13% 22% 15% 3	3726
	21st to end	Day	44% 8% 18% 19% 10% 1	4565
January	1st to 10th	Night	29% 7% 11% 35% 17% 1	7636
	11th to 20th	Night	50% 6% 19% 15% 8% 2	7680
	21st to end	Night	41% 7% 11% 29% 10% 2	8401
February	1st to 10th	Night	35% 7% 13% 24% 18% 3	2573
	11th to 20th	Night	28% 8% 15% 27% 19% 4	2254
	21st to end	Night	26% 7% 15% 25% 23% 4	1903
March	1st to 10th	Night	31% 9% 15% 28% 15% 2	5028
	11th to 20th	Night	19% 7% 18% 28% 18% 10%	5090
	21st to end	Night	27% 7% 16% 29% 19% 1	5588
April	1st to 10th	Night	21% 8% 22% 30% 15% 3	2273
	11th to 20th	Night	26% 10% 21% 19% 19% 4	2075
	21st to end	Night	27% 8% 16% 26% 20% 4	2100
May	1st to 10th	Night	20% 5% 28% 33% 13% 1	5863
	11th to 20th	Night	32% 9% 25% 27% 6%	5831
	21st to end	Night	26% 8% 35% 23% 7%	6394
June	1st to 10th	Night	50% 14% 22% 12% 3	1890
	11th to 20th	Night	39% 16% 24% 18% 3	1890
	21st to end	Night	33% 15% 36% 14% 1	1890
July	1st to 10th	Night	34% 11% 40% 13% 2	4105
	11th to 20th	Night	34% 9% 43% 14%	4051
	21st to end	Night	21% 10% 44% 24% 2	4297
August	1st to 10th	Night	39% 15% 32% 13% 1	3227
	11th to 20th	Night	23% 13% 36% 27% 1	3227
	21st to end	Night	41% 18% 34% 7% 1	3586
September	1st to 10th	Night	42% 18% 25% 14% 1	2049
	11th to 20th	Night	39% 20% 26% 12% 3	2200
	21st to end	Night	48% 15% 16% 13% 7%	2218
October	1st to 10th	Night	45% 11% 25% 16% 4	3920
	11th to 20th	Night	48% 6% 16% 17% 13%	3899
	21st to end	Night	35% 4 10% 31% 16% 3	4252
November	1st to 10th	Night	36% 10% 15% 20% 16% 4	2461
	11th to 20th	Night	40% 9% 14% 22% 12% 3	2520
	21st to end	Night	36% 9% 17% 20% 16% 2	2520
December	1st to 10th	Night	30% 6% 17% 29% 16%	4040
	11th to 20th	Night	42% 5% 15% 21% 15% 3	4679
	21st to end	Night	44% 8% 19% 19% 9% 1	6633

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	6% 7% 23% 37% 25% 2	330
	11th to 20th	Day	15% 7% 25% 30% 21% 3	330
	21st to end	Day	10% 9% 33% 34% 13% 1	363
February	1st to 10th	Day	7% 8% 17% 39% 25% 4	435
	11th to 20th	Day	6% 5% 21% 35% 28% 4	536
	21st to end	Day	5% 4 19% 39% 27% 5%	446
March	1st to 10th	Day	4 4 23% 45% 22% 3	540
	11th to 20th	Day	6% 5% 20% 40% 26% 2	540
	21st to end	Day	5% 2 19% 37% 32% 5%	594
April	1st to 10th	Day	5% 3 21% 44% 26% 2	540
	11th to 20th	Day	5% 2 14% 43% 31% 4	532
	21st to end	Day	4 2 12% 41% 36% 5%	540
May	1st to 10th	Day	5% 1 10% 33% 39% 10%	543
	11th to 20th	Day	8% 2 11% 33% 34% 11%	567
	21st to end	Day	8% 1 6% 20% 42% 22%	617
June	1st to 10th	Day	13% 2 6% 21% 39% 19%	570
	11th to 20th	Day	7% 2 4 16% 38% 33%	570
	21st to end	Day	5% 3 14% 33% 45%	570
July	1st to 10th	Day	4 3 12% 28% 53%	565
	11th to 20th	Day	6% 1 1 11% 33% 49%	544
	21st to end	Day	4 1 11% 36% 48%	576
August	1st to 10th	Day	7% 1 4 12% 37% 39%	526
	11th to 20th	Day	3 1 9% 34% 52%	519
	21st to end	Day	7% 1 3 13% 35% 41%	583
September	1st to 10th	Day	9% 1 2 12% 30% 47%	530
	11th to 20th	Day	7% 3 12% 33% 45%	530
	21st to end	Day	8% 2 7% 16% 30% 37%	530
October	1st to 10th	Day	10% 2 7% 22% 42% 17%	530
	11th to 20th	Day	9% 2 8% 28% 38% 14%	530
	21st to end	Day	8% 4 15% 27% 34% 12%	583
November	1st to 10th	Day	8% 2 17% 32% 30% 11%	535
	11th to 20th	Day	8% 5% 15% 36% 30% 7%	540
	21st to end	Day	4 4 19% 36% 30% 6%	540
December	1st to 10th	Day	9% 3 18% 32% 34% 4	540
	11th to 20th	Day	8% 5% 17% 32% 31% 6%	484
	21st to end	Day	10% 6% 14% 35% 28% 7%	363
January	1st to 10th	Night	8% 4 19% 35% 30% 4	840
	11th to 20th	Night	11% 7% 20% 40% 21% 2	840
	21st to end	Night	11% 8% 21% 41% 19% 1	924
February	1st to 10th	Night	8% 5% 18% 39% 27% 3	840
	11th to 20th	Night	7% 5% 22% 36% 27% 3	823
	21st to end	Night	7% 4 17% 42% 28% 1	692
March	1st to 10th	Night	4 4 22% 42% 26% 2	840
	11th to 20th	Night	6% 4 17% 40% 31% 2	840
	21st to end	Night	5% 3 18% 40% 30% 4	924
April	1st to 10th	Night	5% 2 13% 44% 33% 3	840
	11th to 20th	Night	6% 4 14% 40% 34% 2	831
	21st to end	Night	7% 2 12% 40% 37% 2	840
May	1st to 10th	Night	5% 1 10% 34% 43% 7%	840
	11th to 20th	Night	9% 1 11% 37% 34% 8%	829
	21st to end	Night	9% 1 6% 22% 47% 16%	903
June	1st to 10th	Night	13% 1 5% 22% 39% 19%	630
	11th to 20th	Night	8% 2 5% 12% 39% 34%	630
	21st to end	Night	6% 3 10% 39% 43%	630
July	1st to 10th	Night	7% 3 8% 33% 49%	615
	11th to 20th	Night	5% 2 8% 41% 44%	597
	21st to end	Night	4 2 6% 36% 52%	657
August	1st to 10th	Night	5% 3 11% 40% 41%	792
	11th to 20th	Night	3 1 7% 37% 52%	790
	21st to end	Night	7% 1 2 12% 36% 41%	880
September	1st to 10th	Night	8% 1 4 10% 31% 46%	800
	11th to 20th	Night	6% 1 3 12% 33% 46%	800
	21st to end	Night	10% 2 6% 15% 36% 33%	800
October	1st to 10th	Night	10% 2 7% 20% 43% 17%	800
	11th to 20th	Night	12% 2 7% 27% 37% 15%	800
	21st to end	Night	12% 2 14% 28% 35% 9%	880
November	1st to 10th	Night	9% 4 15% 31% 33% 8%	820
	11th to 20th	Night	9% 4 14% 33% 35% 5%	840
	21st to end	Night	6% 4 20% 33% 33% 4	840
December	1st to 10th	Night	8% 3 14% 33% 37% 4	840
	11th to 20th	Night	11% 5% 17% 32% 29% 6%	840
	21st to end	Night	9% 5% 15% 34% 31% 6%	924

Page generated at 2026-07-13 03:14:54. Version ac07

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