Monroe
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monroe clear sky chart from 2005-11-06 to 2025-10-19.

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% 9% 3 8% 5% 5% 5% 4 6% 8% 34%	125950
	Night	14% 10% 4 8% 5% 4 4 4 5% 7% 35%	123836
Transparency	Day	45% 5% 13% 22% 13% 1	129536
	Night	48% 5% 11% 21% 13% 1	128320
Seeing	Day	15% 4 17% 31% 24% 8%	16743
	Night	19% 5% 24% 32% 17% 3	26669

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% 14% 5% 16% 7% 5% 5% 4 4 6% 22%	3617
	11th to 20th	Day	13% 14% 5% 14% 8% 6% 7% 5% 6% 6% 16%	3662
	21st to end	Day	22% 16% 6% 13% 6% 4 4 4 5% 5% 16%	4466
February	1st to 10th	Day	14% 15% 4 11% 7% 6% 4 3 5% 5% 25%	1800
	11th to 20th	Day	14% 10% 4 13% 7% 5% 6% 4 5% 6% 26%	1905
	21st to end	Day	14% 12% 4 10% 5% 5% 3 4 7% 7% 28%	1650
March	1st to 10th	Day	16% 11% 5% 10% 6% 5% 4 4 5% 5% 30%	4607
	11th to 20th	Day	10% 9% 3 8% 6% 5% 6% 4 5% 7% 37%	4980
	21st to end	Day	16% 11% 4 10% 6% 6% 5% 4 5% 6% 27%	5465
April	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 4 6% 7% 31%	2315
	11th to 20th	Day	16% 7% 3 8% 6% 5% 5% 4 5% 7% 34%	2527
	21st to end	Day	17% 9% 3 7% 4 4 4 3 5% 8% 36%	2600
May	1st to 10th	Day	19% 10% 3 7% 5% 4 4 3 5% 6% 33%	5862
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 5% 7% 9% 33%	5861
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	6433
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	2735
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 9% 42%	2800
	21st to end	Day	8% 6% 2 7% 5% 4 6% 5% 8% 10% 40%	2800
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 7% 9% 44%	6360
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 7% 11% 44%	6360
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 4 7% 10% 43%	6429
August	1st to 10th	Day	10% 5% 2 5% 4 5% 4 4 7% 9% 46%	4234
	11th to 20th	Day	7% 5% 2 7% 5% 5% 7% 5% 8% 11% 38%	4174
	21st to end	Day	6% 5% 3 6% 5% 5% 6% 5% 7% 10% 41%	4609
September	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 3 6% 8% 47%	2254
	11th to 20th	Day	7% 4 2 5% 5% 4 5% 5% 6% 8% 49%	2200
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 6% 7% 41%	2200
October	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 6% 7% 46%	2150
	11th to 20th	Day	17% 7% 2 7% 4 5% 5% 4 5% 6% 37%	1980
	21st to end	Day	18% 8% 3 6% 6% 5% 5% 4 6% 7% 32%	1951
November	1st to 10th	Day	10% 8% 3 7% 5% 4 4 4 6% 7% 41%	1762
	11th to 20th	Day	15% 11% 3 9% 5% 5% 5% 3 4 6% 32%	1800
	21st to end	Day	18% 12% 4 9% 5% 4 4 4 6% 7% 28%	1781
December	1st to 10th	Day	13% 13% 5% 12% 7% 6% 6% 5% 5% 7% 22%	2600
	11th to 20th	Day	19% 17% 5% 10% 6% 5% 5% 4 5% 6% 18%	3039
	21st to end	Day	24% 18% 7% 13% 6% 4 3 3 3 5% 14%	3982
January	1st to 10th	Night	13% 14% 6% 13% 6% 5% 5% 3 5% 5% 25%	6348
	11th to 20th	Night	12% 17% 7% 12% 7% 5% 5% 4 7% 7% 17%	6299
	21st to end	Night	20% 14% 7% 10% 5% 4 4 3 4 4 25%	6490
February	1st to 10th	Night	17% 14% 4 10% 7% 5% 5% 3 5% 5% 25%	2600
	11th to 20th	Night	14% 13% 5% 8% 6% 5% 5% 4 5% 6% 28%	2378
	21st to end	Night	19% 10% 4 9% 5% 5% 4 4 5% 5% 30%	1980
March	1st to 10th	Night	15% 11% 4 8% 4 4 4 3 5% 6% 37%	5245
	11th to 20th	Night	10% 6% 2 7% 4 4 4 4 6% 7% 44%	4980
	21st to end	Night	16% 9% 4 8% 5% 4 4 3 4 6% 36%	5467
April	1st to 10th	Night	16% 10% 3 7% 4 5% 4 4 6% 5% 36%	2100
	11th to 20th	Night	17% 7% 2 6% 5% 5% 5% 4 5% 7% 37%	1821
	21st to end	Night	17% 8% 2 6% 4 5% 4 4 5% 7% 38%	1800
May	1st to 10th	Night	20% 9% 3 9% 5% 5% 4 3 5% 5% 31%	4033
	11th to 20th	Night	17% 9% 3 8% 4 4 4 3 5% 7% 38%	4032
	21st to end	Night	14% 5% 2 6% 5% 4 5% 4 5% 8% 44%	4421
June	1st to 10th	Night	10% 5% 2 5% 5% 5% 4 4 7% 8% 45%	1660
	11th to 20th	Night	11% 5% 2 6% 4 5% 3 5% 7% 9% 43%	1600
	21st to end	Night	10% 5% 2 4 4 5% 5% 5% 6% 11% 45%	1600
July	1st to 10th	Night	8% 4 1 5% 4 4 4 4 7% 10% 47%	3618
	11th to 20th	Night	8% 4 2 6% 4 4 5% 4 7% 9% 46%	3617
	21st to end	Night	8% 5% 2 6% 4 4 4 5% 7% 9% 47%	4417
August	1st to 10th	Night	11% 6% 2 6% 3 4 4 4 6% 8% 45%	2915
	11th to 20th	Night	7% 5% 2 5% 3 4 5% 4 7% 8% 48%	2875
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 6% 9% 47%	3284
September	1st to 10th	Night	9% 5% 2 6% 5% 5% 4 4 5% 6% 49%	2125
	11th to 20th	Night	8% 5% 2 5% 3 3 3 4 5% 7% 55%	2200
	21st to end	Night	14% 6% 2 7% 5% 5% 3 4 6% 6% 42%	2200
October	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 6% 8% 47%	2250
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 4 5% 6% 38%	2377
	21st to end	Night	20% 8% 3 7% 4 3 4 4 5% 7% 36%	2646
November	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 6% 6% 43%	2536
	11th to 20th	Night	16% 10% 3 8% 6% 5% 4 4 6% 7% 33%	2600
	21st to end	Night	19% 13% 5% 8% 5% 5% 4 3 5% 6% 28%	2610
December	1st to 10th	Night	12% 13% 6% 11% 7% 6% 5% 3 5% 6% 26%	4580
	11th to 20th	Night	16% 17% 5% 11% 6% 5% 5% 3 5% 6% 22%	5136
	21st to end	Night	26% 19% 6% 9% 5% 4 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	62% 5% 11% 15% 6%	3618
	11th to 20th	Day	66% 8% 10% 7% 9% 1	3662
	21st to end	Day	69% 4 10% 10% 6%	4466
February	1st to 10th	Day	59% 5% 12% 16% 7%	1800
	11th to 20th	Day	59% 5% 10% 18% 8% 1	1915
	21st to end	Day	52% 5% 15% 18% 8% 2	1650
March	1st to 10th	Day	55% 3 14% 19% 8% 1	4607
	11th to 20th	Day	44% 5% 16% 24% 9% 2	4980
	21st to end	Day	54% 4 13% 18% 10% 1	5465
April	1st to 10th	Day	49% 5% 14% 19% 13%	2315
	11th to 20th	Day	46% 5% 13% 22% 12% 2	2527
	21st to end	Day	45% 4 13% 23% 12% 2	2600
May	1st to 10th	Day	49% 6% 10% 19% 14% 2	5897
	11th to 20th	Day	44% 8% 14% 21% 12% 2	5865
	21st to end	Day	39% 5% 11% 23% 17% 5%	6447
June	1st to 10th	Day	36% 7% 13% 27% 14% 3	2735
	11th to 20th	Day	34% 7% 16% 23% 17% 2	2800
	21st to end	Day	34% 8% 15% 23% 16% 3	2800
July	1st to 10th	Day	34% 5% 13% 29% 18% 1	6291
	11th to 20th	Day	30% 7% 15% 29% 18% 1	6285
	21st to end	Day	34% 6% 15% 23% 21% 2	6245
August	1st to 10th	Day	32% 6% 16% 30% 15% 1	4221
	11th to 20th	Day	35% 7% 14% 31% 12% 1	4213
	21st to end	Day	33% 6% 15% 31% 13% 1	4608
September	1st to 10th	Day	35% 6% 15% 25% 17% 2	2254
	11th to 20th	Day	32% 6% 12% 33% 17% 1	2200
	21st to end	Day	39% 6% 13% 25% 16%	2200
October	1st to 10th	Day	28% 4 14% 32% 22% 1	3501
	11th to 20th	Day	39% 4 10% 27% 19%	3220
	21st to end	Day	42% 4 14% 25% 14% 1	3188
November	1st to 10th	Day	41% 6% 12% 26% 14% 1	1762
	11th to 20th	Day	53% 5% 12% 19% 10% 1	1800
	21st to end	Day	54% 6% 14% 19% 8%	1781
December	1st to 10th	Day	62% 7% 16% 11% 4	2600
	11th to 20th	Day	67% 4 11% 13% 4	3036
	21st to end	Day	74% 4 8% 9% 5%	3982
January	1st to 10th	Night	60% 5% 9% 17% 8% 1	6348
	11th to 20th	Night	66% 7% 9% 9% 7% 1	6299
	21st to end	Night	63% 3 13% 11% 10%	6490
February	1st to 10th	Night	61% 5% 11% 15% 7% 1	2600
	11th to 20th	Night	57% 5% 10% 20% 8% 1	2379
	21st to end	Night	56% 4 11% 18% 9% 1	1980
March	1st to 10th	Night	49% 4 13% 23% 11% 1	5245
	11th to 20th	Night	38% 5% 13% 27% 16% 1	4980
	21st to end	Night	49% 4 10% 21% 15% 2	5467
April	1st to 10th	Night	49% 5% 10% 20% 14% 2	2100
	11th to 20th	Night	46% 5% 9% 20% 18% 2	1821
	21st to end	Night	44% 4 11% 21% 17% 3	1800
May	1st to 10th	Night	55% 5% 7% 15% 14% 2	4060
	11th to 20th	Night	46% 5% 11% 25% 11% 2	4033
	21st to end	Night	39% 4 11% 24% 18% 3	4429
June	1st to 10th	Night	36% 5% 10% 28% 18% 3	1660
	11th to 20th	Night	35% 6% 13% 27% 16% 3	1600
	21st to end	Night	33% 6% 13% 27% 21% 1	1600
July	1st to 10th	Night	31% 6% 14% 28% 17% 5%	3580
	11th to 20th	Night	33% 8% 15% 27% 16% 1	3572
	21st to end	Night	31% 7% 14% 22% 24% 2	4288
August	1st to 10th	Night	35% 6% 13% 27% 16% 2	2904
	11th to 20th	Night	32% 6% 12% 33% 15% 2	2902
	21st to end	Night	34% 6% 11% 31% 16% 1	3284
September	1st to 10th	Night	35% 6% 12% 29% 16% 3	2125
	11th to 20th	Night	30% 5% 10% 31% 22% 2	2200
	21st to end	Night	41% 5% 12% 25% 16% 1	2200
October	1st to 10th	Night	26% 4 8% 32% 28% 1	3679
	11th to 20th	Night	39% 4 10% 26% 20% 1	3876
	21st to end	Night	38% 3 9% 32% 16% 1	4359
November	1st to 10th	Night	42% 5% 12% 24% 16% 1	2536
	11th to 20th	Night	52% 5% 11% 20% 11% 1	2600
	21st to end	Night	59% 3 12% 19% 6%	2610
December	1st to 10th	Night	61% 5% 14% 16% 4	4580
	11th to 20th	Night	62% 6% 13% 12% 6% 1	5138
	21st to end	Night	72% 4 10% 8% 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	18% 9% 30% 31% 10% 1	300
	11th to 20th	Day	20% 5% 39% 28% 5% 3	300
	21st to end	Day	28% 5% 26% 29% 11% 1	330
February	1st to 10th	Day	23% 5% 26% 37% 8% 1	300
	11th to 20th	Day	21% 5% 36% 26% 11%	300
	21st to end	Day	19% 6% 35% 33% 7%	249
March	1st to 10th	Day	18% 6% 25% 38% 12%	349
	11th to 20th	Day	17% 5% 25% 37% 15% 1	500
	21st to end	Day	23% 5% 30% 31% 11% 1	550
April	1st to 10th	Day	18% 6% 24% 36% 15% 2	500
	11th to 20th	Day	20% 5% 24% 32% 15% 4	492
	21st to end	Day	20% 2 24% 34% 18% 2	500
May	1st to 10th	Day	23% 2 19% 32% 20% 4	503
	11th to 20th	Day	17% 4 15% 31% 26% 7%	527
	21st to end	Day	13% 2 10% 31% 32% 12%	573
June	1st to 10th	Day	12% 2 13% 35% 32% 7%	665
	11th to 20th	Day	11% 2 11% 39% 29% 8%	730
	21st to end	Day	11% 3 10% 35% 33% 8%	730
July	1st to 10th	Day	9% 2 6% 30% 38% 16%	721
	11th to 20th	Day	9% 2 8% 31% 39% 12%	718
	21st to end	Day	8% 2 6% 28% 41% 14%	581
August	1st to 10th	Day	9% 2 5% 27% 39% 18%	526
	11th to 20th	Day	13% 2 6% 28% 40% 12%	519
	21st to end	Day	9% 3 5% 28% 37% 17%	583
September	1st to 10th	Day	11% 3 11% 26% 30% 18%	530
	11th to 20th	Day	9% 2 6% 23% 37% 23%	530
	21st to end	Day	19% 5% 13% 22% 27% 13%	530
October	1st to 10th	Day	11% 3 16% 30% 28% 13%	530
	11th to 20th	Day	17% 8% 21% 30% 19% 4	522
	21st to end	Day	24% 5% 25% 30% 15% 3	400
November	1st to 10th	Day	14% 5% 23% 34% 20% 5%	300
	11th to 20th	Day	21% 11% 26% 29% 12% 2	300
	21st to end	Day	22% 7% 28% 36% 7%	290
December	1st to 10th	Day	20% 8% 33% 29% 10% 1	200
	11th to 20th	Day	20% 9% 37% 27% 7% 1	235
	21st to end	Day	25% 6% 30% 32% 6% 1	330
January	1st to 10th	Night	23% 9% 33% 25% 8% 1	1000
	11th to 20th	Night	26% 9% 31% 27% 6%	978
	21st to end	Night	23% 4 32% 34% 7% 1	880
February	1st to 10th	Night	23% 4 34% 34% 6% 1	800
	11th to 20th	Night	21% 6% 33% 34% 6%	783
	21st to end	Night	24% 5% 34% 31% 5%	660
March	1st to 10th	Night	19% 5% 31% 34% 10% 1	800
	11th to 20th	Night	18% 6% 32% 33% 10% 2	800
	21st to end	Night	23% 4 26% 33% 12% 1	880
April	1st to 10th	Night	22% 6% 30% 32% 9% 1	700
	11th to 20th	Night	20% 4 28% 32% 13% 2	593
	21st to end	Night	22% 2 25% 35% 14% 1	600
May	1st to 10th	Night	21% 3 24% 33% 16% 3	600
	11th to 20th	Night	21% 3 19% 31% 23% 3	591
	21st to end	Night	12% 2 15% 36% 28% 8%	650
June	1st to 10th	Night	13% 2 17% 40% 25% 3	600
	11th to 20th	Night	13% 3 11% 41% 28% 4	600
	21st to end	Night	11% 1 17% 37% 29% 5%	600
July	1st to 10th	Night	10% 2 8% 34% 37% 9%	585
	11th to 20th	Night	9% 3 11% 38% 31% 8%	582
	21st to end	Night	9% 2 9% 40% 34% 6%	657
August	1st to 10th	Night	8% 2 11% 38% 31% 10%	597
	11th to 20th	Night	11% 2 9% 32% 37% 8%	594
	21st to end	Night	9% 3 11% 34% 35% 8%	660
September	1st to 10th	Night	11% 3 15% 28% 33% 10%	725
	11th to 20th	Night	10% 4 10% 27% 38% 11%	800
	21st to end	Night	17% 4 15% 32% 25% 8%	800
October	1st to 10th	Night	16% 5% 19% 32% 22% 7%	800
	11th to 20th	Night	22% 7% 26% 30% 13% 3	793
	21st to end	Night	23% 8% 28% 31% 10% 1	836
November	1st to 10th	Night	17% 9% 28% 29% 14% 2	780
	11th to 20th	Night	22% 11% 32% 25% 9% 2	800
	21st to end	Night	28% 7% 33% 26% 7% 1	800
December	1st to 10th	Night	24% 11% 34% 25% 7% 1	800
	11th to 20th	Night	24% 7% 36% 27% 5%	845
	21st to end	Night	28% 7% 30% 29% 5%	1100

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