Carter
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carter clear sky chart from 2005-11-06 to 2026-04-17.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	131713
	Night	13% 9% 3 8% 5% 4 4 4 5% 7% 37%	130480
Transparency	Day	46% 4 10% 23% 14% 2	135399
	Night	45% 4 10% 23% 15% 2	134863
Seeing	Day	21% 12% 27% 22% 13% 6%	16731
	Night	19% 11% 25% 28% 15% 2	26873

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	16% 17% 6% 11% 5% 4 3 3 4 6% 24%	5258
	11th to 20th	Day	11% 13% 6% 15% 6% 4 3 3 3 4 32%	5280
	21st to end	Day	18% 13% 5% 8% 8% 5% 5% 4 5% 5% 25%	5780
February	1st to 10th	Day	18% 14% 5% 10% 5% 3 4 3 4 5% 30%	1932
	11th to 20th	Day	20% 12% 3 10% 5% 4 4 3 5% 5% 29%	2048
	21st to end	Day	19% 13% 4 8% 3 3 3 4 4 6% 32%	1730
March	1st to 10th	Day	17% 14% 3 9% 4 4 4 3 4 6% 33%	4803
	11th to 20th	Day	12% 8% 3 6% 5% 4 5% 3 6% 7% 42%	5090
	21st to end	Day	17% 7% 3 7% 5% 4 4 4 5% 8% 36%	5586
April	1st to 10th	Day	13% 10% 3 8% 5% 4 4 3 5% 6% 38%	2348
	11th to 20th	Day	15% 8% 3 7% 4 4 4 3 5% 6% 41%	2561
	21st to end	Day	16% 8% 3 8% 5% 4 4 4 6% 6% 36%	2600
May	1st to 10th	Day	17% 9% 3 9% 5% 5% 6% 5% 7% 8% 27%	5862
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 31%	5861
	21st to end	Day	13% 6% 2 8% 5% 5% 6% 5% 7% 9% 33%	6433
June	1st to 10th	Day	10% 6% 2 7% 5% 4 6% 5% 6% 9% 41%	2600
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 8% 40%	2600
	21st to end	Day	8% 6% 3 5% 5% 6% 6% 5% 7% 10% 40%	2600
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 9% 43%	5900
	11th to 20th	Day	8% 6% 3 7% 6% 6% 7% 6% 9% 10% 33%	5900
	21st to end	Day	13% 9% 3 8% 6% 6% 6% 5% 7% 8% 29%	6424
August	1st to 10th	Day	7% 5% 3 7% 5% 5% 5% 5% 8% 10% 40%	4234
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 6% 11% 38%	4174
	21st to end	Day	5% 4 2 5% 3 4 4 4 6% 9% 55%	4489
September	1st to 10th	Day	13% 6% 2 5% 4 3 4 4 4 7% 48%	2200
	11th to 20th	Day	10% 6% 2 5% 3 4 3 4 5% 8% 50%	2200
	21st to end	Day	17% 7% 2 7% 4 4 3 3 4 6% 43%	2200
October	1st to 10th	Day	12% 4 2 5% 3 4 4 4 4 8% 52%	2170
	11th to 20th	Day	13% 6% 2 6% 4 4 3 3 4 6% 49%	2000
	21st to end	Day	18% 8% 3 7% 4 3 3 2 4 6% 42%	2170
November	1st to 10th	Day	11% 6% 2 5% 4 3 4 4 4 6% 50%	1852
	11th to 20th	Day	14% 11% 4 7% 5% 3 3 3 5% 6% 40%	1890
	21st to end	Day	16% 10% 4 7% 4 4 4 3 4 6% 37%	1890
December	1st to 10th	Day	17% 12% 3 8% 4 4 4 4 5% 4 36%	3020
	11th to 20th	Day	22% 14% 4 8% 5% 5% 4 3 4 4 27%	3463
	21st to end	Day	18% 15% 5% 11% 6% 5% 5% 3 4 6% 22%	4565
January	1st to 10th	Night	13% 14% 6% 15% 6% 5% 5% 3 5% 6% 24%	7635
	11th to 20th	Night	15% 12% 5% 13% 6% 4 4 3 4 5% 28%	7680
	21st to end	Night	16% 12% 4 10% 6% 4 4 3 4 5% 32%	8401
February	1st to 10th	Night	18% 13% 4 9% 5% 4 4 4 4 5% 30%	2683
	11th to 20th	Night	20% 12% 4 10% 5% 3 4 4 4 5% 29%	2458
	21st to end	Night	19% 12% 4 11% 4 4 4 3 4 5% 30%	2076
March	1st to 10th	Night	18% 11% 3 7% 4 4 3 3 4 6% 37%	5269
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 6% 8% 44%	5090
	21st to end	Night	13% 10% 3 8% 6% 5% 5% 4 6% 7% 33%	5588
April	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 6% 7% 39%	2289
	11th to 20th	Night	14% 6% 2 5% 5% 5% 5% 4 6% 8% 41%	1920
	21st to end	Night	15% 8% 2 7% 4 5% 5% 3 6% 7% 38%	1800
May	1st to 10th	Night	18% 10% 3 8% 5% 5% 5% 4 6% 7% 29%	4033
	11th to 20th	Night	16% 7% 2 7% 5% 5% 6% 4 6% 9% 33%	4032
	21st to end	Night	12% 7% 2 8% 5% 4 5% 4 6% 10% 37%	4421
June	1st to 10th	Night	8% 5% 2 5% 5% 6% 5% 4 7% 9% 45%	1800
	11th to 20th	Night	6% 4 2 8% 4 4 5% 4 7% 11% 45%	1800
	21st to end	Night	7% 5% 2 4 5% 4 5% 5% 7% 11% 46%	1800
July	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 4 7% 9% 45%	4058
	11th to 20th	Night	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 38%	4057
	21st to end	Night	10% 8% 3 8% 5% 5% 5% 4 7% 8% 36%	4427
August	1st to 10th	Night	7% 6% 3 6% 5% 5% 5% 4 7% 9% 42%	2915
	11th to 20th	Night	8% 5% 2 7% 4 5% 5% 4 6% 8% 43%	2875
	21st to end	Night	4 2 1 4 3 3 4 4 6% 9% 58%	3405
September	1st to 10th	Night	10% 4 2 5% 4 4 4 3 5% 8% 50%	2180
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	2200
	21st to end	Night	13% 7% 2 5% 4 4 4 3 6% 7% 46%	2200
October	1st to 10th	Night	10% 5% 1 5% 3 3 3 3 5% 7% 54%	2229
	11th to 20th	Night	12% 7% 2 5% 4 4 4 3 4 7% 49%	2400
	21st to end	Night	17% 8% 2 6% 4 4 4 3 4 5% 44%	2668
November	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 4 5% 50%	2666
	11th to 20th	Night	13% 9% 3 6% 4 4 4 4 5% 6% 42%	2730
	21st to end	Night	18% 11% 3 6% 5% 3 4 3 4 6% 37%	2730
December	1st to 10th	Night	15% 12% 4 9% 5% 4 4 3 4 5% 36%	4380
	11th to 20th	Night	18% 12% 6% 10% 5% 4 3 3 4 5% 30%	4952
	21st to end	Night	17% 15% 6% 10% 6% 6% 5% 4 5% 6% 21%	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	62% 3 10% 17% 7%	5259
	11th to 20th	Day	57% 3 6% 19% 13% 2	5280
	21st to end	Day	61% 3 7% 22% 6% 2	5780
February	1st to 10th	Day	58% 3 8% 18% 11% 1	1932
	11th to 20th	Day	58% 3 7% 19% 12% 2	2058
	21st to end	Day	53% 3 8% 23% 11% 2	1730
March	1st to 10th	Day	53% 3 6% 19% 14% 5%	4803
	11th to 20th	Day	42% 3 9% 25% 19% 3	5090
	21st to end	Day	47% 4 9% 26% 14% 1	5586
April	1st to 10th	Day	47% 3 11% 25% 12% 3	2348
	11th to 20th	Day	44% 3 10% 23% 17% 4	2561
	21st to end	Day	47% 5% 10% 23% 12% 3	2600
May	1st to 10th	Day	53% 5% 12% 19% 10% 1	5897
	11th to 20th	Day	53% 5% 9% 23% 10% 1	5865
	21st to end	Day	44% 6% 13% 22% 13% 2	6447
June	1st to 10th	Day	39% 5% 12% 25% 18% 1	2600
	11th to 20th	Day	40% 5% 14% 22% 17% 2	2600
	21st to end	Day	38% 7% 14% 23% 15% 4	2600
July	1st to 10th	Day	37% 7% 13% 26% 17% 1	5835
	11th to 20th	Day	40% 10% 14% 25% 9% 1	5831
	21st to end	Day	49% 8% 11% 19% 12% 1	6240
August	1st to 10th	Day	35% 7% 15% 31% 11% 1	4221
	11th to 20th	Day	38% 6% 11% 31% 14%	4213
	21st to end	Day	26% 5% 14% 32% 21% 2	4488
September	1st to 10th	Day	36% 4 12% 22% 20% 6%	2200
	11th to 20th	Day	34% 3 10% 28% 24% 1	2200
	21st to end	Day	43% 3 7% 24% 21% 2	2200
October	1st to 10th	Day	24% 3 8% 27% 37% 2	3534
	11th to 20th	Day	27% 3 8% 31% 28% 4	3240
	21st to end	Day	33% 3 10% 28% 23% 3	3484
November	1st to 10th	Day	37% 3 8% 28% 21% 4	1852
	11th to 20th	Day	46% 2 7% 23% 18% 3	1890
	21st to end	Day	50% 3 9% 21% 16% 1	1890
December	1st to 10th	Day	51% 3 8% 24% 15%	3020
	11th to 20th	Day	61% 3 7% 17% 10% 1	3460
	21st to end	Day	64% 3 10% 17% 6%	4565
January	1st to 10th	Night	62% 3 10% 18% 7%	7636
	11th to 20th	Night	58% 3 5% 19% 12% 3	7680
	21st to end	Night	55% 2 8% 22% 11% 1	8401
February	1st to 10th	Night	57% 3 9% 21% 10% 1	2683
	11th to 20th	Night	57% 3 7% 21% 11% 1	2459
	21st to end	Night	58% 2 9% 17% 10% 3	2076
March	1st to 10th	Night	49% 3 5% 25% 15% 3	5269
	11th to 20th	Night	37% 4 8% 29% 21% 1	5090
	21st to end	Night	50% 3 8% 24% 14% 1	5588
April	1st to 10th	Night	44% 3 10% 23% 17% 2	2289
	11th to 20th	Night	40% 4 11% 23% 17% 6%	1920
	21st to end	Night	46% 4 11% 22% 15% 2	1800
May	1st to 10th	Night	53% 6% 11% 19% 9% 2	4060
	11th to 20th	Night	47% 6% 14% 22% 10% 1	4033
	21st to end	Night	42% 6% 15% 22% 13% 3	4429
June	1st to 10th	Night	33% 6% 14% 25% 19% 3	1800
	11th to 20th	Night	33% 6% 16% 22% 20% 3	1800
	21st to end	Night	31% 7% 15% 25% 18% 3	1800
July	1st to 10th	Night	34% 9% 11% 25% 19% 3	4015
	11th to 20th	Night	37% 10% 16% 23% 12% 1	4006
	21st to end	Night	43% 7% 11% 23% 13% 2	4297
August	1st to 10th	Night	35% 7% 15% 29% 12% 1	2904
	11th to 20th	Night	37% 6% 11% 27% 18% 1	2902
	21st to end	Night	21% 6% 14% 32% 23% 3	3405
September	1st to 10th	Night	33% 5% 12% 22% 20% 8%	2180
	11th to 20th	Night	32% 4 10% 23% 27% 3	2200
	21st to end	Night	38% 4 9% 22% 24% 2	2200
October	1st to 10th	Night	24% 3 7% 26% 37% 3	3645
	11th to 20th	Night	26% 3 8% 27% 30% 7%	3899
	21st to end	Night	31% 2 7% 24% 27% 8%	4304
November	1st to 10th	Night	38% 2 8% 25% 23% 4	2666
	11th to 20th	Night	43% 3 7% 21% 21% 5%	2730
	21st to end	Night	50% 2 8% 24% 14% 1	2730
December	1st to 10th	Night	52% 3 11% 22% 12% 1	4380
	11th to 20th	Night	56% 3 10% 21% 9% 1	4954
	21st to end	Night	64% 3 9% 16% 7%	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	29% 21% 34% 12% 3 1	330
	11th to 20th	Day	38% 24% 28% 8% 1	330
	21st to end	Day	34% 27% 28% 8% 3	363
February	1st to 10th	Day	32% 22% 33% 12% 2	330
	11th to 20th	Day	42% 23% 28% 5% 2 1	330
	21st to end	Day	36% 18% 38% 8%	273
March	1st to 10th	Day	34% 20% 29% 12% 4 1	423
	11th to 20th	Day	28% 22% 33% 13% 4 1	540
	21st to end	Day	31% 19% 32% 14% 4	594
April	1st to 10th	Day	25% 20% 29% 18% 6% 1	540
	11th to 20th	Day	22% 17% 34% 17% 7% 3	516
	21st to end	Day	24% 16% 34% 19% 5% 2	500
May	1st to 10th	Day	24% 16% 32% 17% 9% 2	503
	11th to 20th	Day	22% 11% 30% 23% 9% 5%	527
	21st to end	Day	17% 10% 24% 27% 14% 8%	573
June	1st to 10th	Day	12% 8% 25% 31% 17% 7%	530
	11th to 20th	Day	12% 7% 27% 30% 15% 8%	530
	21st to end	Day	11% 5% 27% 28% 18% 12%	530
July	1st to 10th	Day	16% 4 14% 27% 17% 22%	525
	11th to 20th	Day	9% 6% 21% 33% 19% 11%	524
	21st to end	Day	15% 3 18% 30% 23% 11%	576
August	1st to 10th	Day	11% 3 19% 29% 25% 12%	526
	11th to 20th	Day	14% 3 16% 34% 23% 9%	519
	21st to end	Day	9% 3 17% 31% 26% 14%	583
September	1st to 10th	Day	16% 4 15% 27% 27% 12%	530
	11th to 20th	Day	13% 2 13% 30% 29% 13%	530
	21st to end	Day	22% 7% 22% 25% 21% 5%	530
October	1st to 10th	Day	14% 6% 23% 30% 20% 7%	530
	11th to 20th	Day	15% 14% 30% 22% 14% 4	530
	21st to end	Day	23% 14% 31% 22% 10%	553
November	1st to 10th	Day	21% 13% 36% 22% 8% 1	330
	11th to 20th	Day	29% 18% 30% 17% 5% 2	330
	21st to end	Day	29% 17% 35% 15% 3 1	330
December	1st to 10th	Day	32% 19% 33% 12% 5%	330
	11th to 20th	Day	28% 20% 34% 13% 4 1	330
	21st to end	Day	35% 18% 33% 13% 2 1	363
January	1st to 10th	Night	26% 19% 32% 19% 4	840
	11th to 20th	Night	31% 19% 30% 17% 3	840
	21st to end	Night	24% 20% 34% 19% 2	924
February	1st to 10th	Night	28% 15% 33% 22% 2	840
	11th to 20th	Night	32% 19% 29% 19% 1	823
	21st to end	Night	31% 18% 30% 20% 1	692
March	1st to 10th	Night	26% 16% 31% 23% 4	840
	11th to 20th	Night	25% 18% 31% 19% 7%	840
	21st to end	Night	21% 15% 32% 25% 6%	924
April	1st to 10th	Night	23% 12% 33% 24% 8%	819
	11th to 20th	Night	18% 11% 31% 28% 10% 1	611
	21st to end	Night	18% 9% 37% 27% 8% 1	600
May	1st to 10th	Night	20% 10% 28% 27% 12% 2	600
	11th to 20th	Night	18% 6% 24% 35% 16% 2	591
	21st to end	Night	11% 5% 19% 33% 27% 5%	650
June	1st to 10th	Night	10% 3 22% 41% 22% 3	600
	11th to 20th	Night	7% 4 19% 39% 27% 5%	600
	21st to end	Night	8% 3 21% 37% 28% 4	600
July	1st to 10th	Night	12% 3 13% 31% 31% 10%	585
	11th to 20th	Night	5% 3 14% 37% 36% 4	582
	21st to end	Night	11% 3 12% 35% 32% 6%	657
August	1st to 10th	Night	9% 2 11% 37% 35% 6%	597
	11th to 20th	Night	9% 3 9% 38% 35% 7%	594
	21st to end	Night	8% 2 13% 34% 35% 9%	660
September	1st to 10th	Night	12% 3 12% 33% 34% 6%	780
	11th to 20th	Night	12% 2 13% 32% 34% 7%	800
	21st to end	Night	15% 7% 20% 30% 26% 2	800
October	1st to 10th	Night	13% 5% 17% 34% 28% 4	800
	11th to 20th	Night	16% 8% 28% 29% 17% 2	800
	21st to end	Night	22% 10% 29% 25% 13% 1	880
November	1st to 10th	Night	16% 12% 25% 31% 15% 2	820
	11th to 20th	Night	21% 15% 28% 27% 8% 1	840
	21st to end	Night	26% 14% 25% 26% 9% 1	840
December	1st to 10th	Night	29% 16% 28% 24% 4	840
	11th to 20th	Night	24% 14% 31% 24% 5% 1	840
	21st to end	Night	30% 15% 28% 23% 3	924

Page generated at 2026-04-14 01:44:27. Version ac07

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