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 2024-04-25.

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% 8% 4 7% 6% 4 5% 5% 6% 7% 34%	83116
	Night	16% 10% 4 7% 6% 3 5% 5% 5% 7% 34%	85994
Transparency	Day	47% 6% 13% 21% 11% 1	82829
	Night	50% 5% 11% 20% 12% 1	85802
Seeing	Day	16% 4 18% 31% 24% 8%	14634
	Night	19% 5% 24% 32% 16% 3	24755

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% 15% 6% 10% 8% 4 6% 5% 4 6% 20%	2527
	11th to 20th	Day	15% 15% 6% 12% 9% 5% 7% 7% 6% 5% 12%	2559
	21st to end	Day	27% 17% 8% 10% 7% 2 3 4 3 4 13%	3124
February	1st to 10th	Day	14% 14% 4 10% 9% 5% 5% 4 5% 5% 25%	1710
	11th to 20th	Day	14% 9% 5% 10% 9% 4 6% 5% 6% 6% 26%	1807
	21st to end	Day	15% 11% 4 8% 7% 3 4 5% 7% 7% 28%	1570
March	1st to 10th	Day	18% 11% 5% 8% 7% 3 4 5% 5% 6% 27%	3205
	11th to 20th	Day	12% 9% 4 7% 7% 3 6% 5% 5% 7% 34%	3480
	21st to end	Day	19% 9% 4 8% 7% 4 5% 5% 5% 6% 27%	3815
April	1st to 10th	Day	14% 8% 4 7% 7% 4 5% 6% 6% 7% 32%	2199
	11th to 20th	Day	17% 6% 3 7% 7% 4 6% 4 5% 7% 35%	2399
	21st to end	Day	17% 9% 4 6% 5% 3 4 4 5% 8% 35%	2394
May	1st to 10th	Day	14% 8% 4 7% 6% 3 5% 5% 6% 7% 34%	2340
	11th to 20th	Day	17% 7% 4 6% 5% 4 5% 4 5% 8% 34%	2301
	21st to end	Day	9% 5% 3 5% 6% 3 6% 6% 7% 9% 41%	2531
June	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 6% 6% 9% 42%	2461
	11th to 20th	Day	9% 5% 2 6% 5% 4 6% 6% 7% 9% 42%	2520
	21st to end	Day	8% 5% 2 6% 6% 3 6% 6% 8% 10% 40%	2520
July	1st to 10th	Day	7% 5% 2 4 5% 4 5% 5% 7% 8% 48%	2520
	11th to 20th	Day	8% 4 2 4 5% 3 6% 5% 7% 11% 46%	2520
	21st to end	Day	7% 5% 2 6% 6% 3 5% 6% 7% 9% 44%	2552
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 6% 7% 9% 46%	2327
	11th to 20th	Day	8% 5% 2 6% 6% 4 6% 6% 7% 10% 41%	2303
	21st to end	Day	8% 5% 3 4 5% 3 5% 6% 7% 9% 44%	2538
September	1st to 10th	Day	11% 6% 2 5% 6% 3 5% 4 6% 8% 44%	2030
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 6% 6% 9% 46%	1980
	21st to end	Day	14% 5% 2 5% 4 3 5% 5% 7% 7% 42%	1980
October	1st to 10th	Day	12% 6% 2 7% 5% 3 4 5% 5% 7% 44%	1936
	11th to 20th	Day	18% 7% 3 6% 5% 3 6% 5% 5% 6% 36%	1800
	21st to end	Day	19% 8% 3 5% 7% 4 5% 6% 6% 7% 31%	1849
November	1st to 10th	Day	10% 7% 3 6% 6% 3 4 5% 7% 8% 41%	1672
	11th to 20th	Day	15% 10% 4 8% 6% 3 5% 5% 4 6% 33%	1710
	21st to end	Day	18% 10% 4 7% 6% 4 4 6% 6% 7% 29%	1692
December	1st to 10th	Day	16% 13% 7% 10% 8% 3 5% 5% 4 7% 21%	1520
	11th to 20th	Day	15% 12% 6% 9% 6% 4 5% 6% 6% 7% 24%	1942
	21st to end	Day	22% 17% 8% 12% 8% 3 4 4 4 5% 13%	2783
January	1st to 10th	Night	16% 15% 7% 9% 7% 4 4 4 5% 5% 24%	4428
	11th to 20th	Night	14% 18% 7% 10% 7% 3 6% 5% 7% 7% 14%	4407
	21st to end	Night	27% 16% 8% 10% 6% 3 4 4 3 4 16%	4532
February	1st to 10th	Night	17% 13% 5% 9% 8% 4 5% 4 4 6% 25%	2470
	11th to 20th	Night	14% 12% 6% 7% 6% 4 5% 5% 5% 7% 28%	2256
	21st to end	Night	19% 10% 4 8% 7% 4 6% 4 5% 5% 30%	1884
March	1st to 10th	Night	17% 11% 5% 7% 6% 3 4 4 4 5% 36%	3647
	11th to 20th	Night	11% 6% 3 6% 5% 3 4 5% 6% 7% 44%	3480
	21st to end	Night	17% 7% 4 7% 6% 3 5% 4 5% 7% 36%	3817
April	1st to 10th	Night	15% 9% 4 6% 5% 4 4 5% 5% 6% 36%	1995
	11th to 20th	Night	18% 7% 2 5% 5% 4 5% 6% 4 7% 37%	1729
	21st to end	Night	18% 7% 2 5% 5% 3 5% 5% 5% 7% 39%	1665
May	1st to 10th	Night	18% 6% 4 7% 7% 4 5% 5% 6% 6% 32%	1620
	11th to 20th	Night	19% 6% 4 6% 4 3 4 4 5% 7% 39%	1592
	21st to end	Night	9% 5% 2 6% 5% 3 5% 6% 6% 9% 45%	1744
June	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 5% 7% 8% 44%	1494
	11th to 20th	Night	11% 5% 2 6% 4 3 4 5% 6% 9% 44%	1440
	21st to end	Night	10% 4 2 3 5% 3 5% 6% 6% 10% 45%	1440
July	1st to 10th	Night	8% 4 1 5% 5% 3 5% 4 5% 9% 52%	1440
	11th to 20th	Night	8% 4 2 4 4 2 4 4 7% 8% 53%	1440
	21st to end	Night	6% 4 2 3 4 3 4 6% 7% 9% 51%	1761
August	1st to 10th	Night	7% 3 2 4 5% 3 5% 5% 6% 9% 51%	1611
	11th to 20th	Night	8% 5% 2 4 5% 3 5% 5% 7% 9% 48%	1598
	21st to end	Night	9% 4 2 5% 6% 3 5% 4 5% 9% 49%	1813
September	1st to 10th	Night	9% 5% 3 5% 5% 4 5% 5% 5% 7% 47%	1912
	11th to 20th	Night	10% 5% 3 5% 4 2 3 5% 5% 7% 51%	1980
	21st to end	Night	13% 5% 2 5% 6% 4 4 4 6% 6% 44%	1980
October	1st to 10th	Night	14% 5% 2 4 5% 3 4 4 6% 8% 44%	2024
	11th to 20th	Night	17% 8% 3 6% 6% 4 5% 5% 5% 6% 37%	2160
	21st to end	Night	21% 8% 3 6% 5% 3 4 5% 5% 7% 35%	2506
November	1st to 10th	Night	13% 7% 3 5% 5% 3 4 5% 6% 6% 43%	2406
	11th to 20th	Night	16% 9% 3 7% 6% 4 5% 5% 6% 7% 33%	2470
	21st to end	Night	19% 12% 5% 7% 6% 3 4 4 4 7% 29%	2479
December	1st to 10th	Night	17% 13% 7% 9% 8% 4 5% 4 5% 6% 24%	2660
	11th to 20th	Night	16% 13% 5% 8% 6% 3 5% 4 5% 6% 27%	3230
	21st to end	Night	27% 18% 6% 9% 7% 3 4 4 4 5% 12%	4884

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	65% 5% 11% 12% 5%	2528
	11th to 20th	Day	71% 10% 8% 8% 3	2559
	21st to end	Day	75% 5% 8% 8% 4 1	3124
February	1st to 10th	Day	59% 5% 12% 16% 7%	1710
	11th to 20th	Day	58% 5% 10% 18% 8% 1	1817
	21st to end	Day	52% 5% 15% 19% 7% 2	1570
March	1st to 10th	Day	57% 4 14% 20% 5%	3205
	11th to 20th	Day	47% 5% 16% 22% 9% 1	3480
	21st to end	Day	54% 4 14% 19% 8% 1	3815
April	1st to 10th	Day	48% 5% 14% 19% 13%	2199
	11th to 20th	Day	47% 5% 12% 22% 12% 2	2399
	21st to end	Day	46% 5% 13% 22% 11% 3	2394
May	1st to 10th	Day	46% 5% 13% 21% 12% 2	2340
	11th to 20th	Day	47% 6% 12% 19% 15% 2	2305
	21st to end	Day	37% 6% 15% 26% 14% 2	2531
June	1st to 10th	Day	36% 7% 14% 27% 13% 2	2461
	11th to 20th	Day	34% 7% 17% 23% 18% 2	2520
	21st to end	Day	34% 8% 15% 23% 16% 3	2520
July	1st to 10th	Day	31% 6% 14% 26% 20% 3	2451
	11th to 20th	Day	30% 5% 15% 29% 18% 2	2445
	21st to end	Day	32% 7% 14% 27% 19% 2	2410
August	1st to 10th	Day	30% 6% 16% 33% 14% 1	2314
	11th to 20th	Day	35% 6% 18% 26% 13% 2	2303
	21st to end	Day	32% 6% 14% 26% 20% 2	2538
September	1st to 10th	Day	37% 6% 16% 23% 16% 2	2030
	11th to 20th	Day	34% 7% 12% 32% 15% 1	1980
	21st to end	Day	38% 7% 13% 27% 15%	1980
October	1st to 10th	Day	39% 5% 13% 26% 15% 2	1936
	11th to 20th	Day	47% 5% 12% 22% 13%	1800
	21st to end	Day	52% 6% 12% 21% 10% 1	1849
November	1st to 10th	Day	41% 6% 12% 26% 15% 1	1672
	11th to 20th	Day	52% 5% 13% 19% 10% 1	1710
	21st to end	Day	53% 6% 14% 19% 8%	1692
December	1st to 10th	Day	65% 5% 11% 14% 5%	1520
	11th to 20th	Day	60% 5% 13% 17% 5%	1939
	21st to end	Day	75% 4 9% 7% 3	2783
January	1st to 10th	Night	62% 5% 10% 16% 6% 1	4428
	11th to 20th	Night	69% 9% 9% 9% 4	4407
	21st to end	Night	73% 3 10% 10% 3	4532
February	1st to 10th	Night	60% 5% 12% 15% 7% 1	2470
	11th to 20th	Night	57% 5% 9% 20% 8% 1	2257
	21st to end	Night	57% 4 10% 18% 9% 2	1884
March	1st to 10th	Night	51% 4 11% 24% 9%	3647
	11th to 20th	Night	38% 6% 14% 22% 18% 1	3480
	21st to end	Night	49% 5% 11% 24% 10% 1	3817
April	1st to 10th	Night	48% 4 10% 21% 14% 2	1995
	11th to 20th	Night	46% 5% 9% 21% 18% 2	1729
	21st to end	Night	45% 4 11% 21% 17% 3	1665
May	1st to 10th	Night	52% 5% 10% 18% 11% 3	1620
	11th to 20th	Night	46% 4 9% 21% 18% 2	1593
	21st to end	Night	36% 5% 13% 27% 16% 2	1745
June	1st to 10th	Night	37% 5% 10% 28% 17% 3	1494
	11th to 20th	Night	35% 6% 13% 26% 16% 3	1440
	21st to end	Night	33% 6% 13% 27% 21% 1	1440
July	1st to 10th	Night	31% 5% 12% 28% 21% 3	1400
	11th to 20th	Night	29% 6% 12% 30% 20% 2	1392
	21st to end	Night	26% 7% 17% 25% 21% 4	1663
August	1st to 10th	Night	29% 5% 16% 32% 17% 2	1600
	11th to 20th	Night	31% 6% 15% 30% 14% 3	1598
	21st to end	Night	33% 5% 13% 25% 21% 2	1813
September	1st to 10th	Night	36% 6% 12% 26% 16% 4	1912
	11th to 20th	Night	33% 6% 10% 30% 21% 1	1980
	21st to end	Night	39% 5% 13% 26% 15% 1	1980
October	1st to 10th	Night	40% 6% 10% 24% 20% 1	2024
	11th to 20th	Night	48% 6% 11% 20% 15% 1	2160
	21st to end	Night	51% 5% 10% 22% 10% 1	2506
November	1st to 10th	Night	42% 5% 12% 24% 16% 1	2406
	11th to 20th	Night	52% 5% 11% 21% 10% 1	2470
	21st to end	Night	58% 3 12% 20% 7%	2479
December	1st to 10th	Night	64% 4 11% 15% 6%	2660
	11th to 20th	Night	58% 6% 14% 14% 7% 1	3232
	21st to end	Night	74% 5% 11% 8% 3	4884

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	19% 9% 30% 31% 9% 1	270
	11th to 20th	Day	20% 5% 39% 27% 6% 3	270
	21st to end	Day	29% 5% 24% 29% 12% 1	297
February	1st to 10th	Day	23% 5% 27% 36% 9% 1	270
	11th to 20th	Day	22% 4 37% 26% 11%	270
	21st to end	Day	20% 5% 35% 33% 7%	225
March	1st to 10th	Day	19% 6% 25% 37% 13%	316
	11th to 20th	Day	18% 5% 25% 37% 15% 1	460
	21st to end	Day	24% 4 29% 32% 10% 2	506
April	1st to 10th	Day	17% 6% 23% 37% 15% 2	460
	11th to 20th	Day	21% 4 24% 32% 14% 4	452
	21st to end	Day	21% 3 23% 33% 16% 3	437
May	1st to 10th	Day	22% 2 21% 31% 20% 4	423
	11th to 20th	Day	18% 4 15% 31% 25% 6%	447
	21st to end	Day	12% 1 9% 30% 34% 14%	485
June	1st to 10th	Day	11% 2 12% 36% 32% 7%	571
	11th to 20th	Day	11% 2 11% 39% 29% 8%	630
	21st to end	Day	11% 4 10% 36% 31% 8%	630
July	1st to 10th	Day	8% 3 5% 28% 39% 17%	621
	11th to 20th	Day	9% 1 7% 32% 39% 12%	618
	21st to end	Day	9% 3 6% 29% 40% 14%	493
August	1st to 10th	Day	9% 2 4 28% 38% 19%	446
	11th to 20th	Day	13% 2 7% 29% 38% 12%	439
	21st to end	Day	10% 3 6% 29% 36% 16%	495
September	1st to 10th	Day	12% 3 11% 27% 30% 17%	450
	11th to 20th	Day	10% 2 8% 25% 36% 20%	450
	21st to end	Day	17% 5% 15% 24% 28% 12%	450
October	1st to 10th	Day	12% 3 17% 30% 26% 13%	450
	11th to 20th	Day	19% 9% 22% 30% 17% 3	450
	21st to end	Day	26% 5% 26% 30% 12% 2	364
November	1st to 10th	Day	14% 5% 23% 32% 21% 5%	270
	11th to 20th	Day	21% 11% 25% 29% 12% 2	270
	21st to end	Day	22% 6% 27% 38% 7%	261
December	1st to 10th	Day	21% 9% 32% 28% 8% 1	180
	11th to 20th	Day	19% 8% 38% 25% 8% 1	211
	21st to end	Day	24% 6% 32% 32% 6% 1	297
January	1st to 10th	Night	24% 9% 33% 25% 8% 1	950
	11th to 20th	Night	26% 9% 31% 27% 7%	930
	21st to end	Night	23% 4 31% 35% 7% 1	836
February	1st to 10th	Night	23% 4 33% 34% 6% 1	760
	11th to 20th	Night	20% 6% 33% 34% 6%	743
	21st to end	Night	24% 5% 34% 31% 5%	628
March	1st to 10th	Night	19% 4 31% 34% 11% 1	760
	11th to 20th	Night	18% 6% 31% 33% 10% 2	760
	21st to end	Night	24% 4 25% 33% 12% 1	836
April	1st to 10th	Night	20% 5% 30% 33% 9% 2	665
	11th to 20th	Night	21% 4 28% 32% 12% 2	563
	21st to end	Night	23% 3 25% 34% 15% 1	555
May	1st to 10th	Night	21% 3 24% 34% 15% 3	540
	11th to 20th	Night	21% 4 18% 32% 22% 3	531
	21st to end	Night	11% 1 14% 34% 30% 9%	584
June	1st to 10th	Night	13% 1 16% 41% 26% 3	540
	11th to 20th	Night	14% 2 11% 41% 28% 4	540
	21st to end	Night	11% 1 17% 37% 28% 5%	540
July	1st to 10th	Night	11% 2 7% 32% 38% 10%	525
	11th to 20th	Night	9% 2 11% 39% 30% 8%	522
	21st to end	Night	8% 2 9% 41% 33% 6%	591
August	1st to 10th	Night	8% 2 10% 39% 30% 11%	537
	11th to 20th	Night	10% 2 10% 32% 37% 9%	534
	21st to end	Night	10% 3 11% 33% 34% 9%	594
September	1st to 10th	Night	12% 3 14% 29% 32% 10%	652
	11th to 20th	Night	11% 4 11% 29% 36% 9%	720
	21st to end	Night	16% 4 15% 32% 25% 8%	720
October	1st to 10th	Night	18% 4 19% 32% 21% 7%	720
	11th to 20th	Night	23% 8% 27% 28% 12% 2	720
	21st to end	Night	24% 8% 28% 30% 8% 1	792
November	1st to 10th	Night	17% 9% 28% 29% 15% 2	740
	11th to 20th	Night	22% 11% 32% 25% 9% 2	760
	21st to end	Night	28% 6% 32% 26% 8% 1	760
December	1st to 10th	Night	24% 11% 34% 24% 6% 1	760
	11th to 20th	Night	24% 7% 36% 27% 5%	802
	21st to end	Night	28% 8% 30% 28% 5%	1045

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