NAA Ransom
Clear Sky Chart
History

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

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	13% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	126796
	Night	13% 9% 4 8% 5% 4 4 3 5% 6% 38%	123509
Transparency	Day	44% 6% 12% 23% 14% 2	130329
	Night	44% 6% 11% 22% 15% 2	128050
Seeing	Day	15% 10% 28% 26% 16% 6%	17150
	Night	17% 10% 30% 30% 12% 1	26942

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	12% 12% 6% 13% 7% 6% 5% 4 5% 6% 25%	3617
	11th to 20th	Day	10% 10% 6% 14% 8% 7% 5% 5% 7% 5% 25%	3620
	21st to end	Day	16% 16% 7% 10% 5% 4 4 3 4 6% 26%	4230
February	1st to 10th	Day	17% 12% 4 9% 7% 6% 4 4 5% 6% 27%	1835
	11th to 20th	Day	14% 11% 4 7% 7% 5% 5% 3 6% 6% 32%	1948
	21st to end	Day	14% 13% 5% 10% 5% 4 3 3 5% 7% 31%	1650
March	1st to 10th	Day	19% 13% 3 6% 3 3 2 2 4 4 40%	4480
	11th to 20th	Day	8% 7% 3 7% 5% 4 4 5% 6% 8% 42%	4712
	21st to end	Day	18% 12% 5% 11% 6% 5% 5% 4 6% 6% 23%	5967
April	1st to 10th	Day	17% 13% 3 7% 6% 4 4 3 5% 6% 33%	2400
	11th to 20th	Day	14% 10% 3 6% 6% 5% 5% 4 4 7% 36%	2374
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 3 5% 6% 34%	2465
May	1st to 10th	Day	18% 7% 3 7% 4 5% 5% 4 7% 8% 33%	5862
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 5% 7% 41%	6175
	21st to end	Day	13% 6% 2 7% 5% 4 5% 4 6% 9% 38%	6935
June	1st to 10th	Day	10% 4 2 6% 5% 5% 4 4 6% 8% 46%	2800
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 9% 44%	2800
	21st to end	Day	10% 6% 2 6% 6% 5% 5% 5% 7% 8% 41%	2800
July	1st to 10th	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 38%	6360
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 8% 10% 40%	6360
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	6924
August	1st to 10th	Day	7% 4 2 6% 5% 5% 6% 4 7% 10% 46%	4384
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 7% 11% 43%	3849
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 7% 10% 47%	4312
September	1st to 10th	Day	11% 5% 2 5% 3 4 5% 4 5% 7% 50%	2400
	11th to 20th	Day	11% 4 1 4 3 3 4 4 5% 8% 52%	2290
	21st to end	Day	9% 7% 3 7% 4 4 4 3 5% 7% 47%	2200
October	1st to 10th	Day	11% 6% 2 6% 5% 3 4 4 5% 6% 47%	2123
	11th to 20th	Day	15% 8% 2 7% 4 4 5% 3 5% 7% 40%	2000
	21st to end	Day	18% 9% 3 7% 4 3 5% 4 5% 5% 38%	2005
November	1st to 10th	Day	11% 9% 2 5% 4 3 3 3 6% 7% 46%	1780
	11th to 20th	Day	15% 11% 4 7% 5% 4 4 3 4 6% 35%	1800
	21st to end	Day	17% 11% 5% 9% 3 4 4 3 4 5% 35%	1739
December	1st to 10th	Day	9% 8% 4 9% 5% 4 4 3 4 6% 45%	2610
	11th to 20th	Day	11% 16% 5% 11% 6% 6% 5% 4 5% 6% 23%	3008
	21st to end	Day	24% 19% 8% 13% 6% 4 4 3 3 4 13%	3982
January	1st to 10th	Night	14% 13% 6% 12% 5% 4 4 3 4 4 30%	6348
	11th to 20th	Night	12% 15% 6% 13% 8% 6% 5% 3 5% 4 22%	6360
	21st to end	Night	18% 14% 5% 9% 4 4 4 3 3 3 31%	6743
February	1st to 10th	Night	16% 14% 4 8% 6% 4 4 3 4 6% 31%	2564
	11th to 20th	Night	14% 10% 4 8% 5% 5% 4 3 5% 6% 36%	2338
	21st to end	Night	17% 11% 4 8% 3 4 5% 3 4 6% 35%	1980
March	1st to 10th	Night	17% 11% 5% 6% 3 4 3 3 4 5% 41%	5373
	11th to 20th	Night	11% 6% 3 6% 4 4 4 3 5% 6% 47%	5292
	21st to end	Night	18% 10% 5% 10% 5% 5% 5% 4 5% 5% 28%	4962
April	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 5% 7% 38%	2000
	11th to 20th	Night	18% 8% 3 5% 4 5% 3 3 5% 6% 41%	1975
	21st to end	Night	18% 7% 3 6% 5% 4 4 4 6% 7% 36%	1935
May	1st to 10th	Night	18% 9% 3 7% 5% 4 4 3 6% 7% 34%	4033
	11th to 20th	Night	12% 5% 2 6% 4 5% 5% 4 6% 9% 42%	3730
	21st to end	Night	13% 7% 3 8% 4 5% 5% 4 6% 7% 38%	3942
June	1st to 10th	Night	10% 5% 2 6% 3 4 4 4 5% 6% 52%	1600
	11th to 20th	Night	9% 5% 2 6% 5% 3 4 4 7% 11% 45%	1600
	21st to end	Night	8% 6% 3 5% 5% 5% 4 4 5% 10% 44%	1600
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 6% 8% 49%	3617
	21st to end	Night	8% 6% 3 8% 5% 5% 5% 4 7% 7% 43%	3947
August	1st to 10th	Night	6% 4 2 5% 4 5% 4 4 7% 10% 50%	2770
	11th to 20th	Night	7% 4 1 5% 3 4 5% 4 7% 8% 51%	3200
	21st to end	Night	6% 4 2 5% 4 4 4 3 5% 9% 53%	3586
September	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 55%	2000
	11th to 20th	Night	8% 4 2 4 4 4 4 3 5% 7% 56%	2090
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 6% 7% 45%	2200
October	1st to 10th	Night	10% 5% 2 5% 3 4 3 3 5% 6% 54%	2274
	11th to 20th	Night	15% 8% 2 6% 3 3 3 3 4 6% 48%	2400
	21st to end	Night	19% 7% 3 7% 4 3 4 3 4 6% 39%	2835
November	1st to 10th	Night	11% 8% 2 5% 4 4 3 3 5% 6% 49%	2563
	11th to 20th	Night	14% 8% 4 8% 5% 4 5% 3 5% 6% 39%	2600
	21st to end	Night	16% 10% 3 8% 5% 4 3 3 4 6% 38%	2659
December	1st to 10th	Night	11% 9% 3 8% 4 4 4 3 5% 6% 44%	4580
	11th to 20th	Night	15% 14% 5% 10% 5% 4 4 3 4 5% 32%	5199
	21st to end	Night	24% 18% 6% 10% 6% 5% 4 3 4 5% 15%	6996

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	60% 6% 10% 16% 8% 1	3618
	11th to 20th	Day	59% 5% 9% 11% 13% 3	3620
	21st to end	Day	60% 4 11% 17% 8%	4230
February	1st to 10th	Day	58% 4 12% 16% 7% 2	1835
	11th to 20th	Day	51% 6% 11% 21% 9% 1	1958
	21st to end	Day	54% 5% 10% 21% 8% 2	1650
March	1st to 10th	Day	49% 4 8% 24% 14% 2	4480
	11th to 20th	Day	37% 6% 11% 33% 12%	4712
	21st to end	Day	58% 8% 11% 15% 7% 1	5969
April	1st to 10th	Day	51% 6% 11% 20% 12%	2400
	11th to 20th	Day	48% 6% 9% 22% 11% 3	2374
	21st to end	Day	49% 6% 13% 19% 11% 2	2465
May	1st to 10th	Day	46% 8% 11% 21% 13% 1	5897
	11th to 20th	Day	41% 8% 10% 27% 12% 2	6179
	21st to end	Day	40% 7% 12% 23% 15% 3	6949
June	1st to 10th	Day	34% 8% 12% 26% 17% 3	2800
	11th to 20th	Day	36% 8% 11% 22% 21% 3	2800
	21st to end	Day	38% 8% 14% 21% 16% 3	2800
July	1st to 10th	Day	38% 7% 13% 25% 15% 2	6291
	11th to 20th	Day	36% 9% 15% 26% 14% 1	6285
	21st to end	Day	39% 9% 17% 20% 13% 2	6728
August	1st to 10th	Day	31% 8% 18% 29% 13% 1	4369
	11th to 20th	Day	33% 7% 14% 30% 15% 1	3885
	21st to end	Day	30% 7% 12% 31% 16% 3	4311
September	1st to 10th	Day	32% 6% 12% 26% 20% 4	2400
	11th to 20th	Day	29% 7% 11% 27% 23% 4	2290
	21st to end	Day	35% 6% 9% 26% 21% 2	2200
October	1st to 10th	Day	26% 4 8% 26% 34% 2	3461
	11th to 20th	Day	30% 4 11% 23% 30% 2	3240
	21st to end	Day	40% 4 9% 26% 18% 2	3217
November	1st to 10th	Day	36% 5% 14% 25% 17% 2	1780
	11th to 20th	Day	50% 4 12% 21% 12% 1	1800
	21st to end	Day	52% 5% 11% 22% 10%	1739
December	1st to 10th	Day	42% 4 13% 32% 9%	2610
	11th to 20th	Day	60% 6% 11% 18% 5%	3005
	21st to end	Day	77% 5% 7% 7% 4	3982
January	1st to 10th	Night	57% 5% 9% 19% 9%	6348
	11th to 20th	Night	64% 4 10% 10% 12% 1	6360
	21st to end	Night	58% 4 9% 17% 11% 1	6743
February	1st to 10th	Night	55% 4 11% 17% 11% 2	2564
	11th to 20th	Night	49% 6% 10% 22% 12% 1	2339
	21st to end	Night	50% 5% 11% 19% 11% 3	1980
March	1st to 10th	Night	46% 4 9% 25% 11% 4	5373
	11th to 20th	Night	38% 5% 12% 25% 16% 3	5292
	21st to end	Night	56% 7% 8% 20% 7% 1	4962
April	1st to 10th	Night	45% 6% 12% 22% 14% 2	2000
	11th to 20th	Night	44% 5% 9% 22% 16% 4	1975
	21st to end	Night	45% 7% 12% 21% 11% 3	1935
May	1st to 10th	Night	48% 8% 11% 17% 14% 4	4060
	11th to 20th	Night	37% 8% 13% 26% 12% 4	3731
	21st to end	Night	41% 8% 11% 22% 15% 3	3950
June	1st to 10th	Night	32% 7% 12% 26% 19% 4	1600
	11th to 20th	Night	33% 7% 13% 24% 21% 3	1600
	21st to end	Night	35% 8% 16% 22% 15% 4	1600
July	1st to 10th	Night	36% 7% 13% 27% 14% 3	3580
	11th to 20th	Night	30% 8% 14% 25% 20% 2	3572
	21st to end	Night	37% 9% 15% 21% 15% 3	3832
August	1st to 10th	Night	26% 9% 18% 28% 17% 1	2761
	11th to 20th	Night	29% 8% 16% 27% 19% 1	3230
	21st to end	Night	27% 7% 12% 32% 19% 3	3586
September	1st to 10th	Night	29% 5% 11% 27% 23% 4	2000
	11th to 20th	Night	27% 6% 9% 28% 26% 4	2090
	21st to end	Night	35% 6% 12% 24% 20% 3	2200
October	1st to 10th	Night	21% 4 7% 33% 33% 3	3716
	11th to 20th	Night	30% 4 8% 23% 33% 3	3899
	21st to end	Night	38% 4 8% 25% 21% 4	4573
November	1st to 10th	Night	37% 5% 10% 27% 18% 4	2563
	11th to 20th	Night	46% 5% 12% 21% 14% 2	2600
	21st to end	Night	49% 4 11% 23% 12% 1	2659
December	1st to 10th	Night	41% 4 14% 29% 11% 1	4580
	11th to 20th	Night	55% 4 12% 18% 11% 1	5201
	21st to end	Night	72% 5% 8% 10% 5%	6996

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	20% 12% 36% 22% 8% 1	300
	11th to 20th	Day	21% 18% 41% 14% 5% 1	300
	21st to end	Day	20% 19% 32% 23% 6%	330
February	1st to 10th	Day	22% 14% 39% 18% 6%	300
	11th to 20th	Day	22% 16% 38% 20% 5%	300
	21st to end	Day	23% 16% 43% 13% 4	249
March	1st to 10th	Day	23% 20% 35% 19% 2	300
	11th to 20th	Day	23% 19% 33% 20% 5%	305
	21st to end	Day	28% 15% 35% 15% 6% 1	550
April	1st to 10th	Day	23% 14% 33% 22% 7% 1	500
	11th to 20th	Day	20% 18% 30% 20% 11% 2	492
	21st to end	Day	23% 12% 31% 25% 8% 2	500
May	1st to 10th	Day	21% 14% 27% 24% 12% 2	503
	11th to 20th	Day	20% 9% 27% 25% 14% 4	659
	21st to end	Day	15% 8% 31% 22% 16% 7%	789
June	1st to 10th	Day	9% 8% 28% 30% 20% 5%	730
	11th to 20th	Day	12% 5% 27% 31% 22% 4	730
	21st to end	Day	10% 9% 31% 30% 15% 5%	730
July	1st to 10th	Day	10% 3 18% 29% 25% 16%	721
	11th to 20th	Day	9% 4 20% 32% 23% 12%	718
	21st to end	Day	8% 3 18% 36% 27% 7%	794
August	1st to 10th	Day	5% 3 16% 37% 26% 12%	676
	11th to 20th	Day	8% 5% 18% 27% 28% 14%	519
	21st to end	Day	7% 2 17% 31% 30% 14%	583
September	1st to 10th	Day	12% 5% 18% 28% 27% 9%	530
	11th to 20th	Day	10% 2 13% 29% 30% 16%	530
	21st to end	Day	11% 9% 26% 24% 21% 9%	530
October	1st to 10th	Day	14% 6% 26% 30% 19% 6%	453
	11th to 20th	Day	14% 20% 31% 23% 11% 1	330
	21st to end	Day	28% 14% 31% 21% 6% 1	363
November	1st to 10th	Day	16% 10% 37% 23% 10% 4	306
	11th to 20th	Day	20% 18% 35% 18% 8% 1	300
	21st to end	Day	24% 11% 35% 24% 7%	300
December	1st to 10th	Day	17% 17% 39% 19% 7% 2	300
	11th to 20th	Day	17% 18% 34% 25% 5%	300
	21st to end	Day	25% 19% 36% 17% 3	330
January	1st to 10th	Night	19% 15% 38% 22% 6%	1000
	11th to 20th	Night	21% 16% 37% 20% 5% 1	1000
	21st to end	Night	21% 14% 36% 26% 4	1100
February	1st to 10th	Night	23% 12% 39% 22% 4	964
	11th to 20th	Night	20% 15% 35% 27% 4	783
	21st to end	Night	22% 14% 40% 21% 4	660
March	1st to 10th	Night	21% 15% 35% 25% 4	800
	11th to 20th	Night	17% 11% 37% 28% 5% 1	748
	21st to end	Night	24% 10% 38% 22% 6% 1	660
April	1st to 10th	Night	18% 13% 38% 25% 6%	600
	11th to 20th	Night	22% 13% 33% 26% 6%	593
	21st to end	Night	21% 11% 33% 29% 6%	600
May	1st to 10th	Night	18% 10% 34% 31% 8%	600
	11th to 20th	Night	17% 6% 31% 34% 12% 1	591
	21st to end	Night	12% 6% 29% 35% 17% 1	650
June	1st to 10th	Night	11% 3 27% 44% 14%	600
	11th to 20th	Night	12% 4 25% 43% 15% 1	600
	21st to end	Night	10% 4 26% 42% 17% 2	600
July	1st to 10th	Night	10% 2 15% 38% 31% 4	585
	11th to 20th	Night	7% 2 19% 43% 26% 3	582
	21st to end	Night	5% 1 15% 48% 29% 2	657
August	1st to 10th	Night	7% 1 13% 46% 29% 3	597
	11th to 20th	Night	7% 3 11% 44% 32% 3	594
	21st to end	Night	6% 2 16% 41% 33% 2	660
September	1st to 10th	Night	12% 4 18% 36% 29% 2	600
	11th to 20th	Night	9% 3 15% 39% 30% 4	690
	21st to end	Night	11% 6% 23% 34% 24% 2	800
October	1st to 10th	Night	12% 5% 24% 38% 19% 1	800
	11th to 20th	Night	18% 13% 30% 29% 10%	800
	21st to end	Night	22% 13% 34% 23% 8%	880
November	1st to 10th	Night	16% 11% 38% 25% 9% 1	789
	11th to 20th	Night	19% 14% 35% 25% 6%	800
	21st to end	Night	20% 12% 37% 24% 6%	859
December	1st to 10th	Night	21% 11% 39% 23% 5%	1000
	11th to 20th	Night	21% 13% 35% 26% 5%	1000
	21st to end	Night	27% 15% 33% 22% 3	1100

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