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 2025-12-18.

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	12% 6% 2 6% 4 4 4 4 6% 7% 44%	126349
	Night	13% 6% 2 5% 4 4 4 3 5% 7% 47%	124825
Transparency	Day	37% 6% 10% 21% 19% 6%	129956
	Night	35% 5% 10% 20% 21% 9%	129295
Seeing	Day	13% 8% 20% 25% 23% 10%	16606
	Night	14% 6% 23% 32% 21% 3	26374

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% 9% 3 6% 4 3 3 2 4 5% 45%	4077
	11th to 20th	Day	16% 6% 2 4 3 3 3 2 4 7% 52%	4080
	21st to end	Day	22% 11% 3 5% 3 2 2 2 3 4 43%	4488
February	1st to 10th	Day	20% 8% 3 6% 3 4 3 3 4 5% 40%	1836
	11th to 20th	Day	22% 9% 2 6% 4 4 4 2 3 5% 40%	1948
	21st to end	Day	19% 10% 3 7% 4 4 3 4 3 5% 38%	1716
March	1st to 10th	Day	20% 10% 3 9% 4 4 4 3 4 5% 34%	4936
	11th to 20th	Day	12% 7% 3 5% 3 4 3 3 6% 6% 48%	4980
	21st to end	Day	14% 8% 3 8% 5% 4 4 3 4 5% 41%	5475
April	1st to 10th	Day	12% 7% 2 6% 5% 5% 4 4 5% 7% 43%	2400
	11th to 20th	Day	16% 7% 2 6% 4 4 4 4 5% 8% 42%	2374
	21st to end	Day	10% 6% 2 7% 5% 4 4 4 5% 8% 44%	2400
May	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 4 6% 8% 36%	5405
	11th to 20th	Day	11% 6% 3 8% 5% 5% 5% 4 6% 8% 39%	5404
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	6433
June	1st to 10th	Day	8% 4 2 5% 5% 5% 6% 5% 9% 10% 41%	2600
	11th to 20th	Day	5% 4 2 5% 5% 6% 6% 5% 8% 9% 45%	2600
	21st to end	Day	4 4 2 6% 5% 6% 6% 6% 9% 10% 42%	2600
July	1st to 10th	Day	5% 5% 2 8% 7% 7% 6% 6% 8% 12% 32%	5900
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 5% 8% 10% 44%	5900
	21st to end	Day	11% 7% 2 6% 4 5% 5% 5% 7% 10% 37%	6422
August	1st to 10th	Day	3 2 1 3 4 3 3 3 5% 8% 65%	4074
	11th to 20th	Day	5% 3 2 4 4 4 4 5% 8% 13% 49%	3849
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	4312
September	1st to 10th	Day	7% 4 2 6% 5% 6% 6% 5% 6% 9% 44%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 9% 43%	2400
	21st to end	Day	9% 5% 2 4 3 3 4 3 5% 7% 54%	2107
October	1st to 10th	Day	6% 3 1 5% 4 4 3 3 5% 6% 60%	2000
	11th to 20th	Day	10% 4 2 5% 3 2 2 3 4 6% 60%	2000
	21st to end	Day	13% 6% 2 5% 3 3 3 3 4 5% 54%	2200
November	1st to 10th	Day	11% 7% 2 5% 3 3 3 3 4 5% 54%	2058
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 5% 5% 54%	2100
	21st to end	Day	16% 6% 3 5% 4 4 4 3 5% 5% 44%	2027
December	1st to 10th	Day	18% 8% 2 6% 4 3 4 3 3 4 45%	2906
	11th to 20th	Day	15% 10% 3 8% 4 3 4 3 4 5% 41%	3454
	21st to end	Day	16% 7% 2 5% 4 3 3 3 4 6% 47%	4488
January	1st to 10th	Night	17% 5% 2 4 2 3 3 3 4 4 53%	5888
	11th to 20th	Night	15% 7% 2 6% 4 3 3 2 4 5% 49%	5900
	21st to end	Night	25% 7% 2 5% 4 3 3 2 3 4 40%	6490
February	1st to 10th	Night	16% 8% 3 5% 3 3 4 3 4 6% 44%	2560
	11th to 20th	Night	20% 8% 2 7% 3 3 4 3 4 5% 41%	2338
	21st to end	Night	20% 9% 2 5% 4 3 3 3 4 5% 42%	1930
March	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 4 5% 40%	4919
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 7% 48%	4980
	21st to end	Night	16% 7% 3 6% 4 4 4 3 5% 5% 43%	5451
April	1st to 10th	Night	12% 6% 2 4 3 3 4 3 6% 8% 49%	2000
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 6% 6% 48%	1975
	21st to end	Night	10% 6% 3 5% 4 4 4 3 5% 5% 51%	2000
May	1st to 10th	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 38%	4490
	11th to 20th	Night	15% 6% 2 7% 5% 5% 5% 4 7% 9% 36%	4474
	21st to end	Night	10% 5% 2 6% 5% 4 5% 4 7% 9% 43%	4443
June	1st to 10th	Night	7% 4 1 5% 4 5% 4 5% 8% 9% 48%	1800
	11th to 20th	Night	5% 4 2 4 3 4 5% 4 6% 10% 54%	1800
	21st to end	Night	5% 4 2 4 4 4 5% 4 8% 9% 52%	1800
July	1st to 10th	Night	4 5% 2 7% 6% 6% 8% 6% 8% 12% 37%	4078
	11th to 20th	Night	5% 3 1 5% 4 5% 6% 5% 8% 12% 45%	4077
	21st to end	Night	9% 6% 2 6% 4 4 4 4 7% 12% 41%	4449
August	1st to 10th	Night	2 2 1 2 2 3 4 3 5% 8% 68%	3077
	11th to 20th	Night	3 3 1 4 3 5% 5% 5% 9% 14% 49%	3200
	21st to end	Night	6% 4 2 6% 4 4 4 4 6% 8% 50%	3586
September	1st to 10th	Night	6% 4 2 6% 5% 4 5% 4 7% 8% 50%	2000
	11th to 20th	Night	9% 5% 2 6% 5% 5% 4 3 6% 7% 48%	2000
	21st to end	Night	8% 4 1 4 3 3 3 3 5% 6% 59%	2266
October	1st to 10th	Night	6% 4 2 4 3 3 3 2 5% 6% 62%	2400
	11th to 20th	Night	9% 4 1 5% 4 3 3 2 4 5% 60%	2400
	21st to end	Night	12% 4 2 4 3 3 3 2 4 5% 58%	2640
November	1st to 10th	Night	12% 5% 1 4 3 3 4 3 4 5% 56%	2460
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 3 6% 57%	2520
	21st to end	Night	14% 6% 2 5% 4 4 3 3 5% 5% 49%	2577
December	1st to 10th	Night	20% 7% 3 5% 3 3 3 3 4 4 45%	4459
	11th to 20th	Night	16% 7% 2 7% 4 4 4 3 4 5% 45%	4908
	21st to end	Night	15% 8% 2 6% 3 3 3 2 4 4 49%	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	42% 3 6% 25% 20% 3	4078
	11th to 20th	Day	35% 3 5% 23% 25% 9%	4080
	21st to end	Day	48% 2 4 12% 22% 12%	4488
February	1st to 10th	Day	48% 3 6% 16% 18% 10%	1836
	11th to 20th	Day	49% 3 5% 17% 18% 7%	1958
	21st to end	Day	50% 4 6% 12% 19% 9%	1716
March	1st to 10th	Day	52% 4 5% 14% 16% 9%	4936
	11th to 20th	Day	36% 4 5% 18% 21% 15%	4980
	21st to end	Day	45% 5% 8% 19% 18% 5%	5477
April	1st to 10th	Day	41% 5% 8% 22% 16% 8%	2400
	11th to 20th	Day	42% 5% 9% 16% 20% 8%	2374
	21st to end	Day	38% 6% 9% 23% 22% 3	2400
May	1st to 10th	Day	45% 6% 10% 24% 12% 2	5440
	11th to 20th	Day	41% 7% 14% 18% 18% 1	5408
	21st to end	Day	36% 8% 14% 26% 15% 1	6446
June	1st to 10th	Day	34% 11% 16% 23% 16% 1	2600
	11th to 20th	Day	31% 9% 15% 26% 17% 2	2600
	21st to end	Day	31% 9% 18% 24% 16% 3	2600
July	1st to 10th	Day	38% 11% 21% 21% 8%	5836
	11th to 20th	Day	31% 9% 21% 31% 7% 1	5831
	21st to end	Day	39% 9% 16% 27% 9%	6240
August	1st to 10th	Day	18% 6% 12% 32% 29% 3	4060
	11th to 20th	Day	24% 8% 20% 34% 13% 1	3885
	21st to end	Day	37% 7% 13% 21% 20% 2	4311
September	1st to 10th	Day	34% 9% 13% 19% 17% 7%	2400
	11th to 20th	Day	37% 8% 10% 20% 20% 5%	2400
	21st to end	Day	29% 5% 10% 22% 23% 10%	2107
October	1st to 10th	Day	16% 3 5% 14% 26% 36%	3260
	11th to 20th	Day	17% 2 3 16% 33% 28%	3240
	21st to end	Day	26% 3 4 17% 37% 13%	3538
November	1st to 10th	Day	33% 4 8% 17% 28% 10%	2058
	11th to 20th	Day	31% 4 7% 18% 27% 13%	2100
	21st to end	Day	41% 5% 6% 18% 23% 7%	2027
December	1st to 10th	Day	44% 4 6% 20% 22% 5%	2906
	11th to 20th	Day	45% 4 5% 18% 19% 8%	3452
	21st to end	Day	40% 3 6% 20% 29% 3	4488
January	1st to 10th	Night	36% 3 6% 24% 26% 5%	5888
	11th to 20th	Night	39% 4 4 19% 26% 9%	5900
	21st to end	Night	49% 3 6% 14% 18% 10%	6490
February	1st to 10th	Night	41% 4 6% 19% 21% 9%	2560
	11th to 20th	Night	46% 3 5% 17% 20% 8%	2339
	21st to end	Night	46% 5% 6% 13% 16% 14%	1930
March	1st to 10th	Night	46% 5% 6% 12% 22% 10%	4919
	11th to 20th	Night	35% 5% 8% 15% 19% 18%	4980
	21st to end	Night	43% 5% 8% 17% 22% 6%	5451
April	1st to 10th	Night	33% 5% 11% 21% 19% 11%	2000
	11th to 20th	Night	36% 5% 9% 17% 22% 11%	1975
	21st to end	Night	34% 6% 7% 23% 25% 5%	2000
May	1st to 10th	Night	41% 8% 11% 21% 15% 3	4520
	11th to 20th	Night	42% 8% 13% 22% 14% 1	4475
	21st to end	Night	35% 8% 15% 23% 15% 3	4452
June	1st to 10th	Night	29% 9% 18% 25% 18% 1	1800
	11th to 20th	Night	25% 7% 19% 28% 18% 4	1800
	21st to end	Night	26% 9% 17% 27% 19% 4	1800
July	1st to 10th	Night	34% 12% 22% 22% 9% 1	4035
	11th to 20th	Night	27% 10% 29% 25% 9% 1	4026
	21st to end	Night	34% 8% 18% 27% 12% 1	4320
August	1st to 10th	Night	13% 6% 16% 31% 30% 4	3067
	11th to 20th	Night	22% 9% 20% 34% 13% 2	3230
	21st to end	Night	31% 7% 13% 22% 24% 4	3586
September	1st to 10th	Night	30% 9% 14% 22% 16% 9%	2000
	11th to 20th	Night	35% 7% 11% 18% 21% 9%	2000
	21st to end	Night	26% 5% 9% 23% 24% 13%	2266
October	1st to 10th	Night	16% 3 6% 15% 21% 37%	3920
	11th to 20th	Night	18% 3 4 15% 30% 31%	3899
	21st to end	Night	21% 3 6% 15% 38% 17%	4252
November	1st to 10th	Night	31% 4 8% 18% 25% 14%	2460
	11th to 20th	Night	30% 4 8% 17% 28% 13%	2520
	21st to end	Night	38% 3 7% 18% 24% 10%	2577
December	1st to 10th	Night	43% 4 6% 18% 25% 4	4459
	11th to 20th	Night	43% 4 7% 16% 23% 8%	4909
	21st to end	Night	40% 4 7% 20% 26% 4	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	24% 17% 40% 16% 3 1	300
	11th to 20th	Day	23% 19% 35% 16% 4 2	300
	21st to end	Day	27% 20% 29% 22% 2	330
February	1st to 10th	Day	26% 15% 34% 19% 5% 1	300
	11th to 20th	Day	33% 17% 36% 12% 1	300
	21st to end	Day	29% 27% 27% 12% 4	249
March	1st to 10th	Day	26% 15% 32% 22% 5%	300
	11th to 20th	Day	18% 24% 38% 18% 1 1	300
	21st to end	Day	18% 19% 39% 17% 6%	331
April	1st to 10th	Day	19% 15% 34% 23% 8%	500
	11th to 20th	Day	23% 16% 25% 24% 10% 1	492
	21st to end	Day	15% 13% 27% 28% 14% 3	500
May	1st to 10th	Day	15% 10% 31% 27% 14% 2	503
	11th to 20th	Day	15% 5% 26% 28% 19% 7%	527
	21st to end	Day	9% 5% 22% 33% 23% 8%	788
June	1st to 10th	Day	10% 4 12% 31% 30% 14%	730
	11th to 20th	Day	6% 3 12% 36% 35% 9%	730
	21st to end	Day	7% 1 12% 27% 35% 19%	730
July	1st to 10th	Day	5% 3 8% 24% 39% 21%	721
	11th to 20th	Day	5% 2 5% 23% 41% 24%	718
	21st to end	Day	7% 2 4 25% 42% 20%	794
August	1st to 10th	Day	4 2 5% 22% 48% 20%	631
	11th to 20th	Day	8% 1 3 21% 44% 23%	519
	21st to end	Day	14% 1 6% 21% 34% 24%	583
September	1st to 10th	Day	8% 1 10% 28% 37% 17%	530
	11th to 20th	Day	11% 2 9% 20% 37% 21%	530
	21st to end	Day	11% 5% 13% 28% 30% 13%	376
October	1st to 10th	Day	6% 2 19% 38% 26% 9%	330
	11th to 20th	Day	7% 5% 29% 33% 19% 7%	330
	21st to end	Day	20% 8% 26% 23% 17% 5%	363
November	1st to 10th	Day	19% 11% 25% 27% 14% 4	330
	11th to 20th	Day	11% 13% 31% 32% 10% 2	330
	21st to end	Day	15% 17% 32% 25% 9% 2	330
December	1st to 10th	Day	22% 10% 40% 21% 6% 1	330
	11th to 20th	Day	21% 12% 36% 21% 9% 1	321
	21st to end	Day	20% 17% 36% 19% 5% 2	330
January	1st to 10th	Night	21% 10% 33% 30% 6%	1000
	11th to 20th	Night	21% 12% 33% 27% 8%	1000
	21st to end	Night	24% 9% 34% 29% 4	1100
February	1st to 10th	Night	20% 11% 33% 30% 5%	960
	11th to 20th	Night	24% 13% 33% 26% 4	783
	21st to end	Night	24% 15% 32% 26% 3	610
March	1st to 10th	Night	18% 10% 33% 32% 7%	600
	11th to 20th	Night	17% 10% 36% 30% 7% 1	600
	21st to end	Night	15% 10% 34% 30% 10%	660
April	1st to 10th	Night	15% 10% 37% 30% 8%	600
	11th to 20th	Night	16% 10% 33% 29% 11% 1	593
	21st to end	Night	12% 9% 31% 35% 13% 1	600
May	1st to 10th	Night	9% 6% 28% 42% 14% 1	600
	11th to 20th	Night	12% 5% 26% 36% 20% 2	591
	21st to end	Night	7% 3 19% 36% 30% 4	650
June	1st to 10th	Night	8% 3 9% 40% 34% 6%	600
	11th to 20th	Night	5% 2 12% 36% 42% 4	600
	21st to end	Night	6% 1 7% 31% 44% 11%	600
July	1st to 10th	Night	5% 1 5% 29% 48% 12%	585
	11th to 20th	Night	6% 2 5% 25% 51% 12%	582
	21st to end	Night	6% 5% 30% 47% 12%	657
August	1st to 10th	Night	2 1 5% 26% 50% 15%	597
	11th to 20th	Night	8% 3 28% 50% 10%	594
	21st to end	Night	10% 1 8% 25% 43% 13%	660
September	1st to 10th	Night	7% 2 7% 37% 40% 8%	600
	11th to 20th	Night	11% 2 8% 32% 40% 8%	600
	21st to end	Night	9% 2 11% 37% 37% 4	717
October	1st to 10th	Night	8% 2 16% 37% 32% 5%	800
	11th to 20th	Night	11% 4 23% 36% 24% 3	800
	21st to end	Night	14% 6% 24% 34% 19% 3	880
November	1st to 10th	Night	15% 4 21% 37% 21% 3	820
	11th to 20th	Night	13% 6% 26% 39% 15%	840
	21st to end	Night	16% 8% 30% 32% 13% 1	840
December	1st to 10th	Night	22% 7% 29% 34% 8%	919
	11th to 20th	Night	22% 8% 29% 31% 9%	1036
	21st to end	Night	22% 11% 28% 30% 7%	1100

Page generated at 2025-12-15 00:13:55. Version ac07

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